Construction of mansard roof rafters. Calculation, fastening and installation of the mansard roof truss system. Erection of the structure and laying the "pie"

Choosing this or that form of a roof for the future house, the owner actually determines the type of its truss system. From right choice, competent calculation and installation, the effective functioning of the entire roof structure depends, and as a result, the longevity of the house and the comfort of its inhabitants.

The concept of a mansard roof

Houses with a mansard roof (mansard) are different from other types of residential buildings, although they are often confused with two-story or attic buildings.

Mansard roofs in their design are very different from ordinary ones.

The attic, like a full-fledged floor, is a residential superstructure. It is included in the registration certificate of the house and has communications - heating, plumbing, lighting. The main difference lies in design features buildings:

floor - a tier with the same walls around the entire perimeter, on which the rafters rest;
attic - under-roof space, the height of which varies under the slopes.

Thus, the mansard roof is the walls of the upper floor and at the same time the roof of the house, which is clearly visible in the exterior of the building.

A house with a mansard roof looks interesting and stylish, but a full-fledged multi-storey a private house- respectable and more reminiscent of urban objects

The height of the attic is regulated by standards - at least 1.5 m - which distinguishes it from the attic roof. In reality, the height of the attic room is chosen by the developer, taking into account:

strength of the foundation and walls;
wind and snow loads on the roof;
the purpose of the attic;
architectural style of the house;
the comfort of staying in the attic room.

All these nuances are discussed at the design stage of the house and, according to the result, the roof truss system is selected.

Video: truss systems, what determines the price and complexity of manufacturing

Varieties of truss systems for a mansard roof

Mansard roofs today are presented in different formats and, accordingly, have a different design of the truss system.

Modern building technologies allow you to equip an attic under any roof, but you need to understand that the efficiency of using the under-roof space will be different for them.

There are the following types of mansard roofing systems:

Shed mansard roofs - simple designs, which are most often erected on small houses, since the arrangement of a large ramp will require reinforcement roof frame and increased costs for roofing materials.
Attic in a house with pitched roof it is necessary to plan in advance in order to raise the lower point of the slope at least 1 m above the ceiling during the construction phase
Gable - the most popular among all types, as they are economical and easy to install. The load-bearing frame consists of straight parallel rafters connecting the walls and the ridge run. However, their slope limits the usable area of the attic, which in some cases makes it difficult to use. Although recently, designers have been using the asymmetry of gable roofs, which partially solves the problem.
Roofs consisting of two slopes with triangular gables are the most popular option for all types of buildings, both with and without attics
Broken roofs - variety gable systems with different slopes of slopes, thanks to which you can create a spacious and comfortable area under the roof. The basis is made up of rafters divided into several parts, which, when connected, form a concave or convex broken line, which is used by designers to style the exterior. Broken attics have the greatest height, and rooms without sloping walls are no different from the usual rooms.
The broken structure is the most effective and simple, it was these roofs that were originally called attics
Hip, semi-hip and vaulted - a kind of mansard roofs with a large number pitched breaks, which allows you to create spacious rooms with acceptable high ceilings. Such structures look unusual and very attractive, but they have a complex rafter system, the construction of which will require experience, knowledge and large financial costs.
A mansard hip roof of complex configuration requires accurate calculations of all loads on the foundation and walls of the building
Hipped attics - have 4 or more identical slopes and are suitable for square-shaped houses. Under such structures, it is easy to equip a living room, in which the largest height will fall in the middle, and the edge space will be limited in use due to low ceilings.
Hipped mansard roofs give buildings an extraordinary appeal
Multi-gable and combined structures - usually such roofs are erected on houses with complex architecture. They have several pediments, are surprisingly beautiful, drain rainfall well and are distinguished by excellent resistance to mechanical stress. The multi-gable truss system is very peculiar. It can be made from both hanging and layered rafters (if there is a capital internal partition). In addition, it consists of several departments, thanks to which the house looks unusual and presentable. In most cases, several attic rooms are equipped under such roofs, where the size of each depends on the particular rafter department.
Intricate multi-gable roofs resemble an origami flower, which is why architects love to use these structures, although they are much more difficult to manufacture and maintain than other types.

The main difficulty in choosing an attic is the variety of its geometric shapes and placement possibilities.

Broken and triangular, occupying the entire area of \u200b\u200bthe house or only part of it, facing both sides or one, symmetrical and asymmetric attics differ in their location relative to the outer walls of the building, which directly affects the complexity of the truss system, its manufacture and installation. They can be of a corridor type, sectional or mixed, located both inside and outside the walls with a small extension of the lower floor or significant, requiring the formation of additional supports in the form of walls, hangers, columns.

Any attic looks aesthetically pleasing and gives the building completeness

Be that as it may, the creation of attics comes down to three types:

Video: broken truss system for a mansard roof

https://youtube.com/watch?v=nENtDpL0m5E

Features of the attic truss system

The supporting frame is the basis on which reliability depends mansard roof. It consists of:

The strength of the truss frame depends on the correct design, quality materials, precisely calculated technical parameters and reliability of the connection of roofing units using screws, welding, bolts and the tongue and groove method. To create a carrier system, hanging, layered or mixed rafters are used, which in a certain way affects the capacity of the attic:

Hanging rafters. They rest on the outer walls and are joined together on a ridge run. Rafters of this design do not need a Mauerlat - for horizontal alignment of the walls, it is enough to lay a board on top of the roofing material. This provides significant savings on lumber. In addition, there is no need to arrange intermediate supports with a span of up to 6 m, which allows you to get free studio space. The spacer load is neutralized by puffs laid at the very base or higher (raised). Lifting the puff must comply with building codes, since the strength of the structure depends on it. For larger spans, the frame is reinforced with headstocks, crossbars and struts.
If there are no main internal walls in the building, then hanging truss systems are used.
Overhead rafters. This is a more reliable design, used mainly for large-span buildings. The rafters rest on the ridge run (above), the side runs, and also on the walls. Reinforced with puffs and struts. But with this design of the truss base, the attic space is limited by the size and location of the racks - in the center, symmetrically along the edges or with a shift to one side. Although it is the racks that make it possible, if desired, to stylishly zone the room.
The layered construction is more profitable and not as heavy as with hanging rafters, which is why less materials are required for its arrangement.
Mixed rafters. As a rule, they are used in broken structures. The lower part is mounted according to the scheme of layered rafters and is crowned with a triangle of hanging rafter legs, where the puff simultaneously serves as an attic floor beam.
The mixed construction of the truss frame is mainly used in the construction of broken mansard roofs.

The differences between the attic truss system are:

Intervention in the design of the supporting frame and any changes for the sake of personal preferences and design imagination require a thorough calculation.

Calculation of the supporting structure for a mansard roof

Video: truss frame design in SolidWorks and ArchiCad

We will consider how to calculate the rafter system on our own, which will allow any developer, having elementary concepts of the calculation process, to control the design and construction progress. We will do the calculation according to a simplified method so as not to touch on aerodynamics and strength of materials.

We draw a sketch of the house on paper and display on it the parameters necessary for the calculation:

The house is being built in Kazan ( private sector within the city). We have taken all the initial data arbitrarily to show the calculation procedure using an example.

variables - wind, snow and provided during maintenance of the roof;
constant - the weight of the roofing filling (pie) and the equipment planned for installation;
fatal - earthquakes, floods, etc., which are rare, so it makes no sense to calculate them, it is enough to add 5–10% to the total loads.

We carry out the calculation, guided by the collection of rules under the number 17.13330.2011 and 20.13330.2011 with the regional load distribution maps embedded in it, as well as the standards 2.01.07–85.

wind load

We calculate the wind pressure on the map, the corresponding tables, and also by the formula W m \u003d W o x k x c, where:

Table: k indicator according to SNiP 2.01.07–85 for various types of terrain

Building height Z, m	k coefficient for terrain types
Building height Z, m	A	IN	WITH
≤ 5	0,75	0,5	0,4
10	1,0	0,65	0,4
20	1,25	0,85	0,55
40	1,5	1,1	0,8
60	1,7	1,3	1,0
80	1,85	1,45	1,15
100	2,0	1,6	1,25
150	2,25	1,9	1,55
200	2,45	2,1	1,8
250	2,65	2,3	2,0
300	2,75	2,5	2,2
350	2,75	2,75	2,35
≥480	2,75	2,75	2,75
Note: "A" - open coasts of the seas, lakes and reservoirs, as well as deserts, steppes, forest-steppes, tundra; "B" - urban areas, forests and other areas evenly covered with obstacles more than 10 m high; "C" - urban areas with buildings over 25 m high.

Since the force of the wind sometimes reaches an impressive value, when erecting a roof, especially a mansard one, due attention should be paid to the reliable fastening of the rafters to the base.

We substitute the data into the formula W m \u003d W o x k x c, given that Kazan belongs to the I region (according to the map), the height of the building is 6514 mm, construction is carried out within the city, but in the private sector without the presence of high-rise buildings nearby. So, 24 x 0.65 x 0.8 (if the slope of the slopes is ≥ 30 °, then the wind is pressing on the roof, then according to the standards 2.01.07–85, clause 6.6, the highest aerodynamic index is taken into account) ≈ 13 kg / m².

There is little antenna-mast equipment on the roofs of private buildings, and modern covering materials are distinguished by high thermal and frost resistance, which is why, as a rule, climatic and ice loads are not calculated for them.

Snow load

On the snow load distribution map, we find the value for Kazan (240 kg / m²) and substitute it into the calculation formula S \u003d µ x S g, where:

There is a small nuance here - if it is impossible to measure the slope of the slopes (for example, the house is being built from scratch, and there is no load-bearing frame yet), then the angles should be determined from the table, based on the span width (L) and the planned height of the building from the floor to the ridge (H ).

According to the basics of trigonometry, the tangent of the angle of inclination (tg α) is calculated as the ratio of height to half the length of the span or to the full length for a shed roof

Table: the ratio of the size of the house and the slope of the slopes

Determining the slope of a roof
H value:½ L (tg α)	Angle α°
0,27	15
0,36	20
0,47	25
0,58	30
0,7	35
0,84	40
1	45
1,2	50
1,4	55
1,73	60
2,14	65

Let's move on to our parameters: 3514: ½ 6600 = 1.06, which means that the lower slope angle will be approximately 47 °, and (3514 - 2200) : ½ 4050 = 0.649, i.e. the value of the upper slope angle will be approximately 32 °.

The correction value depends on the slope of the roof:

if the slope angle (α) ≤ 30°, then µ = 1;
if the angle α ≥ 60°, then µ = 0 - the snow load is not calculated, since snow does not linger on steep slopes;
if 30°< α < 60°, то µ высчитывают по формуле → µ = 0,033 х (60 - α).

Therefore, the correction factor for the slope of the slopes of 47 ° is calculated by the formula 0.033 x (60–47) = 0.429. Thus, the snow load is 0.429 x 240 ≈ 103 kg/m².

roof load

The attic structure has a typical roofing pie:

Its layers in one way or another put pressure on the supporting frame. Usually, in a simplified calculation, all layers of the roofing filling are taken into account, which leads to strengthening of the supporting structure, but also to its rise in price. However, all layers exert pressure only when the attic is equipped with decorative exposed rafters and all roofing materials are laid on top of them.

One of the ways to arrange the attic is that the wooden elements of the truss system remain open and serve as an interior decoration.

With standard device roofing cake insulation, vapor barrier, retaining counters and sheathing can not be taken into account in the calculation of the roof load, since they are placed between the rafters and under them. However, to calculate the Mauerlat, they must also be taken into account. This division is relevant for the calculation of large roofs, where the difference in cost will be significant.

Having decided in advance on the covering material, it is easy to calculate the weight of the roof, focusing on the technical parameters declared by the suppliers.

Table: average weight of roofing materials:

Material name	Weight, kg/m²
Ondulin	4–6
bituminous tiles	8–12
Slate	10–15
Ceramic tiles	35–50
Decking	4–5
Cement-sand tiles	25–45
metal tile	4–5
Slate	45–60
Draft flooring	18–20
Laminated wooden rafters and girders	15–20
Hanging rafters under a cold roof	10–15
Wooden crate	8–12
Bitumen	1–3
Polymer-bitumen waterproofing	3–5
Ruberoid	0,5–1,7
Insulating films	0,1–0,3
Plasterboard sheets	10–12

Let's return again to the example and calculate the load from the roof, given that we will cover the roof with metal tiles and leave the rafters open. The weight of the layers of the roofing pie without insulation = 5 (metal tile) + 5 (polymer-bitumen insulation) +12 (sheathing) + 12 (drywall) + 0.3 + 0.3 (hydro and vapor barrier films) ≈ 35 kg / m².

To calculate the thickness of the insulation, there is a formula T \u003d R × λ, where:

As a heater, we choose Isover plates " pitched roof". Then T \u003d R × λ \u003d 4.95 x 0.04 \u003d 0.198 m. Multiplying the thickness by the density of the material indicated in the technical specifications, we get it specific gravity→ 0.198 m x 15 kg/m³ ≈ 3 kg/m². Therefore, the total load from the roof = 35 + 3 = 38 kg/m².

Summing up all loads → wind + snow + roofing = 13 + 103 + 38 = 154 kg/m² + 10% margin of safety ≈ 170 kg/m².

The total load on the roof must be at least 200 kg/m².

In our example, the total load is less. In this scenario, for further calculations, the minimum allowable value, that is, 200 kg / m², should be taken as a basis.

To determine the pressure on the Mauerlat, it is necessary to add the weight of the rafters (≈ 20 kg / m²) to the total loads, which will be 220 kg / m².

Calculation of the section of lumber and the length of the rafters

After determining the total load, we select the required section of wood, for which the first step is to calculate the length of the rafter legs. Let's go to the sketch. The rafters of a sloping roof consist of two parts - before and after the break. We calculate both parts separately, using the Pythagorean theorem in both cases:

Table: the relationship between the load and the thickness of the beam

After calculations, we select the width of the board according to the specification of the lumber produced, focusing on the bottom plate.

Table: softwood lumber (section according to GOST 24454–80)

Board thickness, mm	Board width, mm
16	75	100	125	150	-	-	-	-	-
19	75	100	125	150	175	-	-	-	-
22	75	100	125	150	175	200	225	-	-
25	75	100	125	150	175	200	225	250	275
32	75	100	125	150	175	200	225	250	275
40	75	100	125	150	175	200	225	250	275
44	75	100	125	150	175	200	225	250	275
50	75	100	125	150	175	200	225	250	275
60	75	100	125	150	175	200	225	250	275
75	75	100	125	150	175	200	225	250	275
100	-	100	125	150	175	200	225	250	275
125	-	-	125	150	175	200	225	250	-
150	-	-	-	150	175	200	225	250	-
175	-	-	-	-	175	200	225	250	-
200	-	-	-	-	-	200	225	250	-
250	-	-	-	-	-	-	-	250	-

As you can see, for a board with a thickness of 40 mm there is a wide range of choice. In order not to overpay too much, but at the same time to provide the rafters with sufficient strength, there are formulas in which, with a known thickness of the timber, it is necessary to substitute in turn the corresponding width of the board, starting from a smaller value:

α < 30° - H ≥ 8,6 х L max х √Q r: (B х R изг);
α > 30° - H ≥ 9.5 x L max x √Q r: (B x R izg).

Wherein:

Video: what to consider when choosing lumber

We carry out the calculation and check for strength:

Determine the width of the lower rafters. Since the lower slope angle is 47 °, we will use the second formula, substituting the tabular and calculated parameters into it → H ≥ 9.5 x L max x √Q r: (B x R izg) = 9.5 x 2.543 x √160: ( 4 x 140) \u003d 12.8 cm, that is, H ≥ 12.8 cm \u003d 15 cm (the nearest larger value in the table).
We check the correctness of the calculations, for which the inequality must be observed [(3.125 x Qr x Lmax³) : (B x H³)] ≤ 1 = [(3.125 x 160 x 2.543³) : (4 x 15³)] ≤ 1 = 0.61 ≤ 1, that is, the inequality is maintained and the section 40x150 mm for the lower rafters is chosen correctly.
Similarly, we determine the width of the upper rafters using the same formula, since the angle of the break is 32 ° → 9.5 x 2.414 x √160: (4 x 140) ≥ 12.15 cm = 12.5 cm (closest values).
We check by substituting the result → [(3.125 x 160 x 2.414³) : (4 x 12.5³)] ≤ 1 = 0.9 ≤ 1.
To summarize - for the lower rafters with a good margin of safety, a board of 40x150 mm is suitable, and for the upper ones with a small margin of 40x125 mm.

The basic rule of construction is to make all roundings up in any calculations. The same applies to tabular and normative values.

Mauerlat calculation

There are no requirements for the cross section of the beam for floors and Mauerlat in the standards, therefore you should navigate according to the table, adjusting its values for the calculated load.

Table: the ratio of the thickness and length of the timber for Mauerlat and ceilings

The load on the Mauerlat according to our calculated values \u200b\u200bis equal to 220 kg / m², therefore, 220/400 \u003d 0.55. This index is multiplied by a tabular value close to the pitch of the rafters and the length of our span - 150x250 mm - 0.55 x 150 and 0.55 x 250 = 82.5x137.5 = 100x150 mm.

Video: choosing wood, how to win on a section

Calculation of the step and the number of rafter legs

The step of the rafters must be calculated, and not taken at random, since this indicator affects the construction of the roofing pie, contributes to savings during construction, and also ensures the durability and reliability of the entire roofing system:

We calculate the number of rafter legs → wall length: recommended step +1 = 8.8 / 0.8 + 1 = 12 pieces on one side.
We calculate the step → length of the house: number of rafters = 8.8 / 12 = 0.73 ≈ 0.8 m. This step was adopted by us initially, so there is no need to adjust it.

Video: rafter pitch under various roofs

We summarize the calculations - for the construction of a supporting frame for a broken mansard roof, according to our example, you will need:

62 linear m board Ø40X150 mm (24 lower rafters 2543 mm long);
60 rm. m board Ø40X125 mm (24 upper rafters 2414 mm long);
29th line m timber Ø100X150 mm for Mauerlat, laid around the perimeter;
80 line m of timber Ø100X150 mm for floor beams installed in 0.8 m increments - when calculating, take into account that the interfloor ceiling must withstand a load of up to 400 kg / m², taking into account the weight of the beams themselves, besides, try to lay the beams rationally - the shorter they are, the smaller the cross section required;
27th line m timber Ø100X150 mm for vertical racks;
49th line m of timber Ø100X150 mm for the upper floor beams - permissible load for the upper (attic) floor - 200 kg / m².

For each position, 5–10% should be added, which will be used to equip puffs, attendants, lengthen the rafters if necessary, or to replace defective wood.

The calculation of the mansard roof truss system is simple, just voluminous, but it is desirable to understand it, especially since it is presented consistently and as fully as possible.

Video: a version of the simplified calculation of the truss system

Installation of a broken truss system

Installation of the supporting structure begins with preparation for the construction of the roof, which includes the following work:

purchase of lumber according to the calculations, their sorting and treatment with antiseptics;
checking the availability and serviceability of all working tools;
clearing working area from excess garbage;
installation scaffolding, bridges and ladders;
checking the geometry of the base by measuring the box diagonally (a deviation of no more than 20 mm is permissible), as well as the height of the walls around the entire perimeter of the house relative to the ground;
preparation of girders, crossbars, struts and a template for creating roof trusses.

Video: installation of a gable roof truss system, part 1

Installation is carried out in the following order:

Mauerlat installation. To increase the rigidity of the structure, professionals advise equipping an armo-belt under the Mauerlat, into which anchors or studs are poured in increments of no more than 2 m. Two layers of roofing felt or roofing material are laid, which will serve as waterproofing, protect the Mauerlat from getting wet and rotting. A beam is laid on top of the roofing and fixed with anchors, studs or staples (for brick or block walls). In wooden or frame buildings, the last crown or beam serves as the Mauerlat.
The longevity and operational efficiency of any roof largely depends on the quality of installation and the strength of the Mauerlat fastening.
Installation of floor beams. They are laid on top of the Mauerlat or in pre-arranged wall pockets with a step chosen for the rafters. With a large rafter pitch, floor beams can be installed more often (optimally every 60 cm in order to later lay tile insulation without trimming), although this will entail an increase in lumber.
Before you do wooden floor, it is necessary to make a full calculation of the expected loads, purchase necessary material and tool
Mounting the subframe. Vertical racks are installed on the laid beams of the floor floor, forming an attic. On top of them, attic floor beams are laid and the racks are connected by longitudinal runs. Headstocks are mounted in the center of the racks and a ridge run is laid. For alignment, use a level or a bright cord stretched between the extreme racks.
Installation of rafters. Start with the installation of layered rafters. First of all, according to the estimated dimensions, a template is made from a rejected board. Apply it to the Mauerlat and the run, mark the shape of the gash and cut it out. According to the finished stencil, all lower truss pairs are made. They are leveled and, if necessary, strengthened with struts. Similarly, a stencil is made for the upper rafters, applying it to the girders and cutting out the edges according to measurements. Hanging rafters are fastened together on a ridge beam end-to-end or overlapped with metal plates, wooden linings, bolts, etc.
The frame of the future attic can be made and installed independently, observing the technological features of roofs of different configurations

Video: installation of a gable roof truss system, part 2

Installation of the main components

The main nodes of the attic structure are:

ridge knot;
node "rack-strut-rafter";
node "beam-rack-struts";
and others, depending on the type of the chosen structure and the presence of crossbars, puffs, etc. in it.

The installation of roofing units, methods of fastening, the possibility of horizontal shift, etc. is a separate big topic, therefore, within the framework of this article, as an example, we will consider the formation of some.

ridge knot

To ensure greater structural strength, especially with a small slope of the slopes, a strong ridge run is mounted so that it can take on part of the loads exerted on the rafters. Then proceed as follows:

Fastening rafters to Mauerlat

In order for the fastening of the rafters to the supporting base (Mauerlat, floor beams or to the wall) to be reliable, static and dynamic loads, as well as the coefficient of linear expansion, must be taken into account. Previously, the rafters were fastened by cutting, which formed a strong knot, but increased the consumption of wood. Cuttings are still used today on wooden structures large section.

But more often, in order not to weaken the structure, the rafters are fixed to the support by washing down or “thorn-groove”, striping a thrust beam or cutting grooves in the Mauerlat. Galvanized corners, nails, staples, dowels are used as fasteners. Such mounts are rigid and not always appropriate.

Rigid fastening of the rafters on the Mauerlat guarantees the absence of any displacement of all key elements

In some cases, the rafters must be able to move horizontally (mainly in wooden houses, since the wood is subject to temperature and humidity deformations, and this can cause the walls to skew), which is achieved using sliding supports. Such supports consist of a guide bar fixed to the rafter and a corner with a support platform fixed to the Mauerlat or the upper crown of the log house.

The choice of sliding rafters is justified only when a ridge beam is provided, against which they could abut with their upper part

Video: fastening the rafters to the supporting base

https://youtube.com/watch?v=WKsOgTaVVQY

Fastening rafters to the floor beam

In this node, it is important to avoid slipping of the rafters in order to prevent the destruction of the roof, for which the following connections are used:

emphasis on the end of the beam;
spiked tooth;
pointed tooth.

All elements are connected with screws, bolts, corners, nails, triangular overlays, spikes.

The rafters are connected to the floor beams only when they know for sure that they will withstand the pressure exerted.

Video: how to install the rafters evenly and in the same plane

The attic can have an unusual shape, a beautiful coating, and is made of the most modern materials, but if the supporting frame is not made correctly, then all the attractiveness of the attic will be reduced to zero. And with it, the reliability and durability of the roof structure, which will undoubtedly affect the comfort and coziness in the house. Therefore, to know the principles of the construction of the mansard roof truss system and correctly calculate its main elements is the primary task of the developer. Good luck to you.

Today we will talk about popular solutions for mansard roofs, their capabilities. After reviewing the illustrations, diagrams of the truss system, you will get a clear idea of their device. And having studied the basics of calculation, you can optimize the cost of lumber. Get information about important points space layouts. Find out in what sequence the mansard roof truss system is mounted.

The mansard roof is a complex structure and requires careful calculations.

Drawings of the truss system

Any mention of an attic is associated with a voluminous "pentagonal" roof in which you can live, but there are other options.

Shed

Extremely simple, reliable shed mansard roof. Thanks to the rectilinear forms, it looks modest, but elegant. Special respectability is added by large panoramic windows"to the floor", because such a design not only allows, but provokes their installation.

House with a shed roof, with windows almost on the entire wall

truss system very simple: the straight rafters of a single slope rest on the Mauerlat of opposite walls of different heights, and if necessary on intermediate supports. The proportions of the walls are selected for a slope of 35-45 degrees, which guarantees stability to wind loads and normal snowfall.

The volume is used effectively - if desired, this is an additional full-fledged floor, since the usable area is equal to the area of the previous floor.

gable

Relatively simple widespread roof. It looks unpretentious, but inspires confidence, as it maintains the traditions characteristic of the Russian style. As a result, it is rarely designed specifically for the attic, more often it is adapted in finished form.

The gable roof is traditional, and most often the choice falls on it.

Structurally simple - specifications and truss system as usual gable roof. Straight rafters rest on the Mauerlat, angled into a ridge. Gables are triangular in shape, straight, sheer, almost always glazed, often with access to a balcony.

Most often, a similar scheme is used for arranging an attic in small house with gable roof

It is problematic to fully use the volume, but it is possible, even necessary. The useful area is relatively small, the ceiling is usually "broken". However, the skillful arrangement of furniture, bold design solutions disadvantages can be turned into advantages.

broken line

The most popular option is a sloping roof with an attic. Which is not at all surprising - despite the complexity, it is the most convenient and practical. Overall forms and broken lines symbolize solidity and professionalism. Appearance of this roof "by default" is associated with the "mansard". This is quite natural - it is purposefully designed for living quarters.

To add space on the attic floor, preference is given to a sloping roof.

The rafter system is quite complicated, but its advantages are worth the money and effort spent. Characteristic pentagonal gables, with the functionality of a gable roof - the same opportunity to insert windows, arrange an exit to the balcony.

The circuit is more complex, but gives more space

Spacious attic roof of a private house. The volume is used to the maximum - at full height, the useful area of \u200b\u200bthe room is equal to or slightly less than that of the previous floor.

Calculation basics

The purpose of the calculations is to find a compromise between aesthetics, reliability and cost.

aesthetic side. To begin with, a general sketch of the roof is being designed. The proportions are determined, compared with the size of the house.

The difference between a sloping roof and a gable roof is significant

After that, a constructive calculation is carried out, where factors are taken into account:

Own weight structural elements of the roof. The load from it acts on each element of the truss system.

Wind loads. They are variables and affect all elements.

Weight people, interior elements and furniture. Loads only the floor.

Factors are processed, summarized. Based on the results, conclusions are drawn about the dimensions of the structural elements. For guaranteed strength, they are rounded up. But technological assembly is hampered by the individual width and thickness of each structural element of the truss system, and their customization is unprofitable. Therefore, the elements are combined into groups of standard lumber sizes. And standard solutions significantly reduce the cost of the project - after all, custom-made is always more expensive.

If the project is individual and non-standard, it is better to order accurate calculations. Taking into account the number of factors, their specific impact on the truss system, the conclusion suggests itself - an accurate calculation is the business of specialists. It makes no sense to do calculations on your own - there is a high probability of error. For standard and standard solutions you can adapt the finished existing project.

In addition to the main points, a few practical recommendations will come in handy:

Rafter pitch corresponds to the dimensions of the heater.

Rafter width corresponds to the thickness of the insulation.

layout

Ladder - key moment. Its position must be linked with future floor beams. If the pitch of the rafters allows, we simply orient it between the beams. Otherwise, we design a reliable convenient entrance to the attic.

At the planning stage, it is useful to think over the interior. At this stage, decisions are made about partitions and additional natural light – skylights. Of course, it's too early to think about decorating, but the engineering part should become clear - what functionality will be implemented.

In the attic you can equip an office with a corner for music lessons

After all, the features of such premises: broken-inclined ceilings, their reduced height, unusual walls and custom lighting.

Therefore, a specific layout of the premises is necessary, and in them, the distribution is correct - space zoning:

For the main life activity, are allocated bright and well ventilated premises.

Uncomfortable areas are equipped under the storage.

"Unusual conditions" to give away at the disposal of children.

Interior design and ultimate comfort are created by the skillful use of potential finishing materials, furniture and accessories.

Assembly

In most cases, the construction of a mansard roof begins with a Mauerlat device. A strictly horizontal position, parallel, reliable fastening of its bars is important.

Mansard roof truss structure

For the installation of the rafter system, two options are practiced: the elements of the truss system on the ground are assembled into trusses, lifted and installed ready-made. Or everything is collected separately at the top - "in place", observing procedure:

Roof beams are laid. This takes into account the step of the truss system and the possibility for arranging stairs.

Straightaway laying a rough ceiling, or temporary flooring for safe work.

Racks are mounted. Temporary braces are arranged to keep them in vertical position. Runs are laid on the racks.

Over runs stacked puffs.

Mounted lower rafters.

Temporary braces change to permanent wind connections in the longitudinal position.

Installed top rafters.

exhibited pediment frame, taking into account the design, openings are organized for: windows, balconies, other options are provided.

Further down the rafters roofing membrane is laid, and is pressed against them with a counter-lattice - bars with a section of 50x50 mm. To organize the ventilation gap. These are preparatory measures for warming. They need to be carried out at this stage. Missing is a huge omission.

On the counter-lattice crate stuffed, with a step corresponding to the roofing.

mounted roofing, its additional elements: wind boards, ridge.

The same house can look different and have different usable area.

Video description

About the features of the calculation of the mansard roof in the video:

Exactly according to the same principle, an attic floor with a gable roof is mounted. Moreover, its device is even simpler - all the rafters are solid.

The next step is to insulate the roof. Of course, it can be done from the outside, before the installation of the membrane, battens and roofing. But it is safer from the inside - there will be no threat of precipitation and work will be carried out more carefully, because successful operation depends on it.

The insulation from the inside of the room is protected by a vapor barrier film. And between it and the interior trim, a mandatory ventilation gap device - interior decoration not mounted directly on the rafters. For her, specially, as well as outside for the crate, a counter-rail is stuffed, or a frame is arranged.

On our website you can find contacts construction companies who offer a turnkey roof calculation and repair service. You can directly communicate with representatives by visiting the exhibition of houses "Low-Rise Country".

Conclusion

Mansard roof is perfect solution, allowing you to increase the usable area of \u200b\u200bthe house without a significant increase in the cost of its construction. Erection Solutions attic floor there are quite a few - they can be both standard and designed for a particular home. But in any case, the installation of the attic requires specialized knowledge and this work should be done by professionals.

The attic is a great opportunity to increase the total and useful area of the house. It settles down in the attic and is quite habitable, provided that it is designed correctly. The mansard roof truss system, the drawings of which can be found in this material, is the basis of the entire structure. And it is she who needs to be given the closest attention when designing.

Mansard roof truss system - drawings

An attic is a room that is located directly under the roof. Its facade is partially or completely formed by roof surfaces (according to SNiP 2.08.01-89).

SNiP 2.08.01-89. Residential buildings. Download file (click on the link to open the PDF file in a new window).

It is a full-fledged residential floor; there may be one or more rooms, depending on the design parameters.

On a note! The word "attic" comes from France. It was the French architect who in 1630 came up with the idea of usefully equipping attic spaces. And this man's name was Francois Mansart - hence the name of this type of superstructure appeared.

The peculiarity of mansard roofs is not only the special design of the truss system, but also the need for detailed consideration of other aspects - insulation, moisture and vapor barrier, etc. Since the load on the foundation and walls of the building itself usually increases due to the attic, then mainly all of it elements are built from lightweight materials. That is, to create a truss system, it is recommended to use wood; light material options are used as a heater.

The attic can be of impressive size and occupy the entire area of the building, but within its walls. Sometimes it settles down only on part of the ceiling, and then the back covers the usual roof.

Very often, the attic is used in individual construction, because it is an opportunity to increase the living space of the house, make it warmer (heat loss through the roof is reduced by an average of 7-9%). And the cost of arranging the attic will be much less than the construction of a full-fledged floor.

In general, building an attic is not very difficult and you can cope with the task yourself. The main thing is to correctly calculate the wind, snow and other types of load.

Bar prices

Types of attics

The design of the attic will directly depend on what form it is supposed to equip the roof. After all, part of the walls of this room will be formed just by the slopes of the roof. Depending on this, there are several types of mansard roofs.

Perhaps the easiest option for arranging the roof itself and the attic floor directly. This roof has only one slope, which rests on the multi-level walls of the building. Thus, the slope angle is formed. By the way, it should not go beyond strictly limited limits - 35-45 degrees (if the slope is less, then snow will constantly accumulate on the roof in winter time, which will significantly increase the load on the entire house and will cause the installation of additional supports in an already small attic). The truss system here is extremely simple.

On a note! The construction of the rafters will not need additional supports if the distance between two walls located opposite each other does not exceed 4.5 m.

Such mansard roofs look original, despite the simplicity of their design. Usually, a fairly large window is made from the side of the high wall of the attic, which allows you to get a well-lit room.

Mansard roof with two slopes

This option is also relatively simple in execution and due to this it is widely distributed as much as possible. The main thing is that the height of the roof itself allows you to equip a living space under it. The truss system of this roof looks like that of a conventional gable roof, it can be asymmetrical or symmetrical, depending on the location of the ridge.

Gables, as a rule, are simple and straight, and the room inside will have the shape of a trapezoid or a square (the latter option is possible only if the attic space is spacious enough). The height of the ceilings near the walls should not be more than 1.5 m, the sloping cone-shaped ceiling goes higher.

Main disadvantage gable roof in terms of arranging the attic, this is the loss of most of the free space. That is, the lion's share of the room is cut off by the roof slopes. Of course, this free space is usually used as a warehouse, but this aspect affects the size of the attic very significantly.

Broken mansard roofs

In fact, this is also a kind of gable roof, but its slopes have, as it were, two parts located at different angles relative to the ceilings. Due to this, you can get a fairly spacious attic floor, which in area will be equal to almost a full-fledged second floor (it will be less than the lower floor by only 15%). The height from ceiling to floor will be the same throughout the attic and will be about 2.2-2.3 m.

Broken mansard roof - drawing

However, this design implies the construction of a rather complex truss system. And not every novice master can cope with this task. However, despite this, the variant of a broken roof is quite common.

Roofs are four-pitched (hip) mansard

Such a roof involves the creation of the most complex type of rafter system, which requires the most accurate and painstaking calculations. The surface of the roof itself will have a fairly large area, because of which you will have to spend a lot of money on other materials - insulation, hydro and vapor barrier films, etc. But in general, the attic turns out to be quite spacious, although parts of the usable area are cut off from it .

But such a roof has maximum resistance to snow and wind loads. Overhangs can be large enough and will be ready to protect the walls of the building from the effects of precipitation. Such mansard roofs look very attractive.

Attention! When arranging a hipped roof, it is important to take care of the need to strengthen the layered rafters - it is they who experience the maximum load.

Roof truss system

When arranging a mansard roof, the truss system can be made of elements of a layered or hanging type. In the first version, the rafters are installed so that they form a triangle with even edges. In this case, the support is carried out on the Mauerlat, fixed along the perimeter of the walls, on additional supports installed under the rafters, and the junction of two boards in the ridge area also serves as a reference point.

When installing rafters of a hanging type, supports in the form of additional beams are not provided. They rely only on the walls of the house. Drawstrings may be used. The rafters themselves in this case work on bending and compression.

Hanging and layered rafters - an example of a drawing

Creating a rafter system during the construction of the attic is a paramount task. It is first important to correctly calculate it and take into account all the subtleties of its construction. To understand what will be discussed, you need to familiarize yourself with its main elements.

Table. The main details of the rafter system.

Element	Description
Mauerlat	This is a beam (or board), which is fixed on the upper end part of the bearing wall of the building. Rafter legs will be attached to it. It plays the role of a support and will transfer the entire load from the roof to the walls of the building.
Rack	Any vertically located beam that acts as a support for rafter legs.
Overlappings	This is a series of beams laid horizontally and forming the floor of the attic floor. They also play the role of the ceiling of the first floor of the building.
Rigel	These beams are located horizontally and are additional reinforcing and supporting elements for the rafters. They can also be called "puffs".
rafters	Also called "rafter legs". It is they who form the frame of the roof and give it shape. Moisture-proof materials, lathing and roofing will be attached to them from above.
crate	A lot of bars or sheets of plywood that are attached to the rafters. It is on them that the roofing material will be directly fixed.
Suspension	A board that helps distribute the load. It is installed under the crossbar or puff.
Filly	The board that forms the overhang of the roof is fixed at the bottom of the rafter leg.

Prices for building boards

Building boards

Required Calculations

In order to avoid mistakes when designing an attic, it is important to carry out a number of preliminary calculations. Depending on the chosen type of truss system and the type of roof, they may differ. The easiest way is to use some special program, but you can try to do all the calculations manually.

It is important to determine the area of \u200b\u200bthe final roof, the size of the attic, the width of the floors. The calculation is based on the following data:

length and width of the house;
precipitation volumes in winter and summer (this will help determine the required angle of the roof slope);
the width of the joints between the parts of the floors.

An example of calculating the pitch of the rafters in the program "Rafters 1.1"

Consider a calculation example: the length of the house is 12 m, the width is 3 m. The amount of precipitation in the area indicates that the required angle of inclination of the roof should be about 40 degrees. The calculation is made according to the formula Hk \u003d L x tgA, where Hk is the desired height, L is ½ the width of the structure, tgA is the tangent of the angle. Total: Nl \u003d 3/2 x tg40 \u003d 1.26. This means that the recommended roof height should be 1.26 m.

On a note! Most often, when constructing mansard roofs, owners opt for broken truss systems. The methodology for calculating the parameters in this case can be found in SNiP 2.08.01-89 and TCP 45-5.05-146-2009.

There are several options for roofs under which you can place a comfortable living space. In order to ensure the maximum volume of the under-roofing attic space, it is necessary to select optimal angle the slope of the slopes and do not forget about the snow and wind load on the roof. We will consider the most popular designs of the attic truss system in the middle lane.

Mansard roof truss system design

The mansard roof makes it possible to obtain additional usable space with a relatively small financial investment, so this architectural solution has gained great popularity. So what is an attic?

Attic (from French mansarde) - exploited attic space (both residential and non-residential premises) formed on last floor house, or the last floor of a part of the house, with a mansard roof.

Wikipedia
https://ru.wikipedia.org/wiki/Attic

The attic is located within the bearing walls of the building and rests on them through the Mauerlat, horizontal beams (puffs) and rafters. The larger the attic space, the greater its useful volume, which is achieved by increasing the angle of inclination of the slopes and is formed by a more complex truss system. The location of the mansard roof rafters depends on the design, which can be different types, namely:

Hipped or pyramidal design with a minimum amount of under-roof space.
The slopes of the tent structure rest on the side rafters and center pillar, so the amount of under-roof space is minimal here
Hip or semi-hip roof, in which the main living space is located under the trapezoidal slopes.
Hip roof rafters form two triangular and two trapezoidal slopes
Gable construction, which is a symmetrical gable roof with gables cut at a right angle, which provides a significant amount of attic space.
A multi-gable roof allows you to equip a full-fledged attic floor
A gable symmetrical roof with a mansard is a classic option that is easy to install and resistant to wind due to its rigid structure.
A gable roof requires the least amount of working time and a small consumption of building materials
The rafter system of the mansard sloping roof, providing the maximum amount of living space at a relatively low cost.
The sloping roof is optimal solution by the ratio of the cost of construction to the volume of usable attic space

The truss system must withstand constant loads, which consist of the weight of structural elements, insulation and roofing. In addition, there are variable loads that depend on the strength of the wind and the weight of snow on the roof. The choice of the section of the bearing elements and the method of their connection should be aimed at creating the most durable and rigid structure that evenly distributes the load on the walls of the building.

Depending on the width of the building, different types of attic truss systems are used, which are divided into hanging, layered and combined.

Hanging rafters are called, which rest on the walls of the building through the Mauerlat and puff, and form a ridge in the upper part. With this method of connection, there is no intermediate support, and the bursting pressure on the walls of the house is reduced with the help of crossbars, racks and struts. The hanging rafter system is usually used with a building width of no more than 6 m.
To compensate for bursting forces in hanging truss structures with a span of up to 6 m, puffs and crossbars are used
Rafters are called rafters with an intermediate support on inner wall Houses. They are used when the width of the building is from 6 to 16 m. The larger it is, the more elements are used to evenly distribute the load.
Rafter rafters have one or more supports inside the house
The combined type of truss system is used in mansard roofs with a variable angle of inclination of the slopes. The most typical example is a broken mansard roof, where the lower rafter legs are layered, supported by a rack and mauerlat, and the upper ones are mounted as hanging rafters, supported by a puff and headstock. When building mansard roofs, all types of truss systems are used, and their choice depends on the design in which they are used.
In the construction of a sloping roof, the upper rafters are hanging, and the lower ones are layered.

Scheme of the truss system of the mansard roof

To build a roof, you must have a project that indicates the list and size of structural elements, as well as the method of their connection. To understand the principle and sequence of installation, you need to know the purpose of the elements of the rafter group and the way the roof fits to the walls of the building. The mansard roof consists of the following elements:

the connecting element between the wall of the building and the rafter group is the mauerlat, which is attached to the walls of the house with studs, brackets or anchors;
puffs are attached to the Mauerlat parallel to the short wall of the building, and beds are installed along the long side;
vertical racks are mounted on the central bed;
the ridge run rests on the racks;
the upper part of the rafters rests on the ridge run, and the lower part is connected to the puff, forming a cornice overhang;
rafter legs in the upper part are connected by crossbars;
on hip roofs, diagonal rafters and shortened sprigs are used;
Sprengels serve as an additional support for the diagonal rafters;
racks and struts are used for intermediate fastening of rafters;
if necessary, the rafters are lengthened with fillies.

The main load-bearing elements of the mansard roof are rafter logs, beds and puffs, as well as vertical racks and a ridge run.

The diagram indicates the dimensions of the elements of the truss system, their location, angles of inclination and methods of tie-in at the connection nodes. Be sure to also provide information about the location of the double rafters, the presence of additional supports, the dimensions of the eaves and gable overhangs.

The scheme is the main document for assembling the rafter system, it reflects all the necessary parameters. However, before cutting the material, it is necessary to check the calculations again and create templates for the main parts. In the absence of a project, you need to carry out calculations and create a scheme yourself.

Mansard roof rafter step

Before starting work, you need to choose the pitch of the mansard roof rafters. The distance between the rafters and the joists (in the case of a hip roof) depends on several factors:

building size;
type of truss system;
constant and variable load on the roof;
sections of rafters, racks and slopes;
type of roofing;
type and step of the crate;
heater sizes.

For rafters, battens and counter battens, softwood material is selected in accordance with SNiP II-25, and the load on the rafters is calculated according to SNiP 2.01.07 and ST SEV 4868. Based on the above building codes and the rules, we can say that for rafters less than 9 m long, a beam section from 50X150 to 100X250 mm is applicable at a step of 60 to 100 cm. The size of the building affects the design of the farm and the presence of racks, struts and crossbars, the use of which increases the strength of the rafter legs and allows you to increase the step between the rafters up to 120 cm or more. Usually, reference tables are used to select a step, which contain recommendations, taking into account the length of the rafters and the cross section of the timber.

Table: dependence of the step between the rafters on the cross section of the beam and the length of the rafters

The type of roofing used also affects the choice of rafter spacing, because different materials have different weights:

tile, depending on the type, weighs from 16 to 65 kg / m 2, slate - 13 kg / m 2. Such heavy coatings imply a decrease in the pitch of the rafter legs to 60–80 cm;
the weight of metal coatings and ondulin does not exceed 5 kg / m 2, so the pitch of the rafters can be increased to 80–120 cm.

On hip roofs, in any case, the spacing of the sprigs is chosen to be 50–80 cm to make the slope more rigid.

In addition, the installation step of the rafters depends on:

The length of the rafters and lathing of the mansard roof

With independent calculations, the dimensions of some structural elements of the roof have to be calculated according to the existing dimensions of the building and the angle of inclination of the slopes. The length of the rafters sometimes needs to be adjusted to different types mansard roof, picking up optimal dimensions the entire structure as a whole.

Suppose that the main dimensions of the building are known and it is necessary to calculate the length of the rafter logs for several proposed options for the angle of inclination and the type of roof. Let half the width of the building L be 3 m, the size of the cornice slope be 50 cm.

Additional calculations show that an increase in the angle of inclination of the lower slope from 60 to 70 ° will increase the width of the attic by 10%.

The length of the sheathing connecting the rafter legs is determined taking into account the gable overhangs that protect the walls of the facade from precipitation. The length of the gable overhang depends on the height of the building and is selected in the range from 40 to 60 cm. Therefore, the total length of the slope will be equal to the length of the house, increased by twice the length of the overhang.

Suppose that the length of the house is 10 m, and the gable overhang is 0.6 m. Then the dimensions of the crate must be calculated taking into account the length of the slope, equal to 10 + 0.6 ∙ 2 = 11.2 m.

The parameters of the lathing should be calculated taking into account the length of the gable and eaves overhangs

Any adjustment of the project requires a careful recalculation of the parameters of the truss system, taking into account the changes that have occurred.

Video: mansard roof calculation

The nodes of the truss system of the mansard roof

The nodes of the roof truss system are the junction of individual elements into a single structure, which allows you to evenly distribute the load on the walls of the building. The connection is made with nails, self-tapping screws or bolts using overhead wooden elements or metal squares and plates, as well as by connecting into a groove. For the construction of a gable roof, the following main components are used:

A ridge knot that connects the rafter legs to each other and to the ridge run.
Places where the crossbar connects the rafters to give greater strength and rigidity to the truss trusses.
Attachment points for struts and struts that give additional support to the rafters.
A cornice assembly in which rafters are attached to a puff or mauerlat, forming a cornice overhang.

The nodal connections of the truss system must be carried out in such a way as to ensure the most rigid fastening of the elements to each other.

For a gable sloping roof, the node is characteristic, where the upper and lower rafter logs, a vertical post, a crossbar and a run are connected. Such a complex connection requires the use of tie-ins, bolts, steel plates and building brackets.

In the most complex node of a broken mansard roof, five truss elements are connected

The most complex node of the hip mansard roof is the junction of the lateral or diagonal rafter legs with the Mauerlat. The side rafter in the lower part rests on the corner beam of the Mauerlat and on the embedded beam; in another version, a vertical stand or sprengel is placed between the embedded beam and the rafter leg. The upper part of the hip rafters is attached to the ridge run with bolts or nails.

The corner rafters of the hip roof carry the greatest load, so the knot of their connection with the Mauerlat must be thought out most carefully

The nodes described are most often used in the installation of truss systems. different designs and allow the installation of load-bearing elements on their own. For efficient and high-quality assembly, drawings and the manufacture of templates with verified angles of joints and tie-ins are necessary.

Video: nodes of the truss system

Calculation of the truss system of the mansard roof

The truss system is the basis of the roof, so it is important to choose the design that best suits the climatic conditions of the region and the existing requirements for the size of a residential attic. After choosing the design, the angle of inclination of the slopes and the height of the ridge are calculated for the required dimensions of the attic room. Calculations are made taking into account the size of the cornice according to the following formulas:

Meaning trigonometric functions can be found in the reference tables.

Table: values of trigonometric functions for various slope angles

The hardest part of designing mansard roofs is counting the lumber. Calculating the number of rafters needed and linking them to a standard length of 6 m can sometimes be quite difficult. Let's say that we have chosen the most difficult in the calculations hip roof size 10X13 m, taking into account the cornice overhangs 80 cm long and the angle of inclination of the slopes is 45 o. Then the side rafters will have a length of 5 / sin 45 o = 7.04 m. Therefore, the standard six-meter beam will have to be lengthened. Usually, for rafters a little more than 6 m long, a 100X200 mm beam or a 50X250 mm board is used.

If the building is large, then it requires longer rafters standard size 6 m, so the timber has to be lengthened

As for the horizontal floor beam, since the width of the building is 10 m, the puffs should consist of two parts, which either rest on the inner wall of the building, or are joined together by reinforcing elements and rely on the run. For puffs and runs, a beam with a cross section of at least 50X200 mm is used. A mauerlat runs along the perimeter of the building, for which a beam of 150X150 mm or 200X200 mm is used. According to the scheme we have chosen, the perimeter of the building is 39.6 m, so seven six-meter bars will be required to install the Mauerlat. The dimensions of all other elements of the truss system will not exceed 6 m.

The weight of the lumber of the truss system is calculated by summing up the lengths of all elements with a certain section and converting their number into cubic meters. This is necessary to determine the mass of the entire roof, and is also necessary when purchasing and transporting material. The calculation is made according to the table, and then the obtained values \u200b\u200bare multiplied by the weight of 1 m 3 of lumber.

Table: calculation of the amount of lumber in 1 m 3 and the volume of one unit of material

Pine lumber weighs 505 kg/m 3 at 12% humidity, and 540 kg/m 3 at 25% transport humidity. Here are some examples of calculations:

If 1 m 3 of material with a section of 50X200 mm contains 16.6 boards, then the weight of one board will be 540/16.6 = 32.5 kg.
If 25 m 3 of lumber is purchased, then it will weigh 25 ∙ 540 = 13,500 kg.
If 100 boards 25X200 are required, then you need to buy 100 / 33.3 = 3 m 3 of wood, which will weigh 3 * 540 = 1,620 kg.

It is important to note that it is advisable to purchase edged lumber with the lowest moisture content so that after installation it does not warp or crack, especially for large-section timber. For the construction of the truss system, the moisture content of the wood should not exceed 18%.

Installation of the attic truss system

Installation of a truss system with a residential under-roof space requires careful preparation. It is necessary to mount convenient scaffolding, decking and ladders, as well as provide workplaces with safety ropes. Workers must be provided with overalls, protective equipment and serviceable equipment. On the ground, you need to choose a flat place for pre-assembly of trusses, marking corners and making templates. All wooden elements must be treated with antiseptic and fire-fighting compounds.

After that, you can begin work, which takes place in the following sequence:

On walls with walled studs, a Mauerlat is mounted around the perimeter. If there is a load-bearing wall inside the building, we lay a bed or run of the same height with a Mauerlat on it.
If the house is being built from building blocks, then it is most convenient to lay the Mauerlat on threaded studs that are immured into the wall during its laying
Puffs with eaves extensions are attached to the Mauerlat parallel to the short wall.
On the puffs, vertical racks are set, limiting the attic room.
Racks are connected with a puff that serves as a ceiling attic space. The trusses installed in this way are interconnected by horizontal runs.
Vertical racks, top puffs and horizontal runs form the frame of the attic room
The lower and then the upper rafters are installed, which are attached to the ridge part.
To strengthen the lower and upper rafters, struts, grandmas and surfs are used.
The crate and frontal board are mounted on the cornice overhang.
After installing all the rafters, it remains to lay the crate and nail the frontal board

We examined the assembly of the truss system using the example of a broken mansard roof. The construction of other structures consists of similar operations and mainly consists in performing work according to the design installation diagram, which reflects the methods of connecting the elements of the truss system. In the presence of carefully calculated drawings, a team of four people is able to mount a roof with a truss system of any complexity.

Video: installation of a mansard roof

We examined the truss group of the mansard roof, its design, calculation, as well as the diagram and description of the main components. Offered an option step by step installation load-bearing structures of the attic, attached illustrations and videos that explain the assembly procedure for the structural elements of the attic roof. Now its successful erection depends only on the thoroughness of fulfilling the requirements of instructions and technologies and the availability of certain skills for performing construction works. We wish you success.

The construction of a semi-attic allows you to give the house an expressive, aesthetic appearance. But the rafter system of a semi-mansard roof requires a special design approach.

Benefits of a semi-attic

The issue of increasing the useful area of the house by arranging an additional upper floor is one of the most relevant in private construction. The construction of a full-fledged second (third and more) floor requires serious financial investments and significantly increases the total cost of construction work. The most popular solutions include the construction of a mansard roof - this allows you to equip additional living quarters directly under the roof. The walls and roof of the attic floor are roof slopes. If you wish to create vertical walls in the attic floor - partitions are installed.

A semi-attic is a fundamentally different approach to arranging an additional floor. A semi-attic is a living space, the side walls of which are formed by a vertical building structure and a roof slope.

Vertical part of the side outer wall semi-attic does not exceed 1.5 meters.

Unlike the attic, in the semi-attic, the side vertical walls are load-bearing. The advantages of this design include rational use interior space, the ability to perform practical vertical glazing.

Significant heat losses occur through the roof structures of the house, therefore, during the construction of the attic floor, special attention must be paid to the thermal insulation of the roof. It is much easier to insulate a semi-attic, since its walls are built from the same material as the entire box of the house. It should be noted that the final cost of building a semi-attic floor is higher than an attic one. In addition, it is necessary to take into account some features of the arrangement of the semi-mansard truss system.

Semi-attic roof design

When developing a half-attic roof frame project, it is important to choose the right angle of inclination of the roof. Due to the architectural features of such a building, the roof is rarely made high so as not to violate the proportions of the building. But at the same time, the roof must successfully cope with operational loads, including snow. The semi-attic is usually supplied with a shed or gable roof. It must be borne in mind that the rafter system must be non-thrust so as not to transfer the expansion load to the walls of the semi-attic.

The prepared scheme of the truss system should reflect not only the location of the structural elements, but also the principles of their fastening. To prevent the rafters from transmitting thrust to the walls, a roof frame with layered rafters is erected, and the rafter legs must be attached in a special way, with certain degrees of freedom. The thrustless system is commonly used in the construction of buildings made of stone, brick and other block materials.

The installation of a system with layered rafters requires the laying of a mauerlat and the installation of a ridge run, which must be supported by gables or special strictly vertical racks.

In order for the rafter to bend and not transmit thrust to the walls, one of its supports must be fixed, but be able to rotate freely. In this case, the second support is made movable and freely rotating.. Such installation of rafters can be performed in three different ways.

Installation of non-spacer layered rafters: method number 1

The lower part of the rafter leg can be hemmed with a support bar, or a cut can be made in it with a tooth to rest against the Mauerlat. At the same time, in the upper part of the rafter, it is necessary to make a horizontal cut with a bevel. The depth of this cut should not exceed A= 0.25h, and the support area in length should not be more than h- the height of the rafter section. The trimming bevel allows you to avoid the spacer load when the rafter is bending - washed down without a bevel will firmly rest against the run with the side cheek. The length of the beveled cut must be at least two A.

If it is not possible to trim the top of the rafter, it must be hemmed with a cut board of the same section as the rafter leg and secured on both sides with wooden ribs or mounting metal plates. The rafter legs with their upper ends are freely laid on the ridge beam. In a gable design, fastening to the run is carried out according to the principle of a sliding support, while the rafter legs are not fastened together. Thus, this version of a gable roof can be considered as a complex of two separate single-slope structures adjacent to each other.

Hemming with ribs of the upper part of the legs of the rafters or washed down are performed horizontally. The installation of rafters with a change in the scheme of supporting the rafter legs on the run leads to the occurrence of spacer loads.

Installation of non-expanding layered rafters: method No. 2 and method No. 3

Installing rafters in this way is the most common option for mounting a non-bracing structure in the construction of a gable roof. The lower part of the rafter leg is carried out on a slider, while the top needs to be fixed, for this purpose:

the rafters abut against the run or against each other and are connected with wooden surfboards or jagged metal plates;
the upper parts of the rafter legs are fastened with a bolt or nail connection.

Particular attention is paid to the principle of attaching the lower part of the rafters to the Mauerlat. It is necessary to fix the rafters in the design position, for which one nail is driven into the side surface at an angle on both sides. Either a single long nail can be driven in from above or a flexible steel plate can be installed. You can also use steel corners - in this case, the rafter is fixed on both sides with corners, and nails are not driven into it. Additionally, these elements of the truss structure are fastened with flexible wire twists - they prevent wind overturning of the roof, without interfering with the main mount to work as a slider.

If you use rigid fasteners with big amount nails or self-tapping screws, the attachment point of the lower part of the rafter will transfer the spacer load to the Mauerlat.

The features of the third mounting method are the rigid pinching of the ridge assembly, while in the lower part the rafters are fastened on a slider. It should be noted that such a design provokes the occurrence of a strong bending moment in the ridge assembly, which can cause its destruction. At the same time, the deflection of the rafters outside the ridge knot is minimal. There are certain difficulties with self-calculation of the maximum bending moment of such a ridge assembly, therefore it is recommended to apply calculation formulas for beams with two supports (single-span). The nodal connection device with rigid pinching of the rafter legs in the upper part allows you to perform the truss system with a certain margin of safety.

Features of the construction of a non-thrust truss system

All three installation options provide for special rafter attachment: one end of the rafter is on a sliding support that allows rotation, and the other end is attached using a swivel that allows only rotation. Modern fasteners (plates) are easy to use and allow you to successfully fix the rafter legs on the sliders and in the hinges of the system. Traditional fastener options can also be used using staples, nail fights, scraps of boards and bars. It is important to choose the right type of fastener so that it fully fulfills its task: it allows the rafter leg to slide in the support or prevents it.

The design scheme, which is used in the development of the truss system project, is based on the assumption of a uniformly distributed load on the roof, that is, it is considered that the same force acts on all points of the roof slope planes. In reality, loads on roof slopes are unevenly affected, depending on the wind rose, the orientation of the house relative to the cardinal points (on the south side, snowdrifts melt faster), etc.

Installation of rafters in all three ways provides the necessary static stability of the truss system, if the key condition is met: the ridge run must be rigidly fixed.

To provide the necessary rigidity for fixing the ridge run, it is inserted with its ends into the gables of the half-attic. This prevents it from moving horizontally. If you support the ridge run only on the racks, an uneven load on the slopes can lead to a displacement of the roof, in the case when the load on one of the slopes is close to the calculated one, and on the other it has decreased significantly.

Increasing the rigidity of the structure

To increase the stability of the rafter system, you can use a horizontal scrum, which should be fastened to the posts supporting the ridge run with a nail fight. In a non-thrust design, the scrum does not function in the absence of high snow loads, but in the pre emergency it works in tension. Such situations include deflection of the ridge run under increased load, uneven subsidence of the foundation. Contractions are usually mounted at a height of about 2 meters from the half-attic floor so that they do not interfere with the free movement of people around the room.

When installing a non-thrust rafter system according to the second and third options, it is possible to equip the slider (the rafter support unit on the Mauerlat) with the end of the rafter leg outside the wall. This design is more statically stable, including more successfully resists uneven loads.

In order to increase the stability of a non-thrust system with layered rafters, it is recommended that the bottom of the racks supporting the run be rigidly fixed by cutting into the bed and fastening to the ceiling in order to turn the hinged support of the bottom end of the rack into a rigid clamping structure. If we are talking about a semi-attic made of stone or brick, in which the ridge run is securely fixed in the gables, additional strengthening of the racks is not required, but it is desirable to install anti-accident bouts.

The installation of the fight has its own characteristics. When arranging nodes with the installation of bolts or studs, you need to carefully consider the manufacture of holes for fasteners. Their diameter must exactly match the diameter of the bolt or stud, or even be less than this value by 1 mm. In the event of an emergency, the wrestling starts to work only after choosing the gap between the bolt and the wall of the hole. During this period of time, the rafter legs in the lower part will “disperse” for a certain distance (its value depends on the height at which the fight is set), as a result of which the Mauerlat may be shifted or damaged. In difficult cases, the roof eaves may be damaged, and the rigidly fixed Mauerlat will force the light walls to move apart.