What is the distance between the rafters. Through what distance do the rafters for a gable and shed roof are placed - calculation for different types of roofing: corrugated board, metal tiles, ondulin, etc.

The distance between the rafters under the metal tile without fail takes into account the efforts made up of the wind, snow load, own weight of structures, roofing. In addition, the following factors affect the pitch of the rafters under the metal tile:

the location of the pipes wooden elements roofs should be 25-35 cm from the chimney, should not interfere with direct trajectories ventilation ducts, fan pipes;
roof configuration - must have rafter leg at the junction of the ridge of a gabled, hipped roof.

All wooden elements truss system are made from coniferous trees, the humidity of which does not exceed 20%.

The step of the rafter legs is calculated at the design stage for budgeting. This will significantly reduce the amount of waste, cuttings of sawn timber.

What you need to know when choosing the optimal distance between the rafters?

The scheme of the roof with hanging rafters.

Having collected the loads present during the strength calculation, the designer evenly distributes them on the load-bearing walls. The principle of calculation is the same for layered, hanging rafters, only the schemes for fastening the elements in the ridge, on the Mauerlat, differ.

The minimum, maximum step of wooden rafters under the metal tile is regulated by 0.7 m, 1.2 m, respectively.

When choosing a step of 60 - 100 cm, the length of the rafters cannot exceed 6 m, with its decrease, a run-up of up to 1.2 m is allowed. If you put your feet more often than 60 cm, this will unnecessarily make the roof heavier and increase the construction budget. If you increase the step more than 1.2 m, the bearing capacity and the resource of the structure will sharply decrease.

A solid crate of wood-containing boards adds strength and rigidity to the truss system. In this case, it is allowed to increase the step by 0.3 - 0.2 m compared to a periodic crate made of a bar or edged board. However, to save the construction budget, a continuous crate for metal tiles is used extremely rarely. The material has sufficient strength and rigidity due to additional transverse profile ribs.

A step of more than 1.2 m is not used even when using rolled metal rafters, despite a sufficient margin of safety of the material. This is due to the possible deflection of the roof sheets during heavy snowfalls, hurricane winds.

The cross section of the beam from which the rafter legs are made also affects the step of the rafters, since the area of \u200b\u200bsupport of the crate and the weight of the roof change. The best option a beam of 150 x 50 mm is considered with a discharged crate with a step of 4 - 7 cm, depending on the step of the transverse wave.

Calculation example for a gable roof

During the implementation of the project, specialists at the initial stage know the roofing material. In order to find out the recommended pitch of the rafters, you can use the SNiP tables, and then adjust the value in accordance with the operating conditions. An example table is shown below:

Leg section (cm)	Rafter pitch (cm) depending on their length (m)
Leg section (cm)	5	4	3
board 20 x 2	70	120	–
board 18 x 2	–	100	–
board 16 x 2	–	70	130
timber 22 x 6	–	120	–
timber 20 x 5	–	110	–
timber 18 x 5	–	90	150
log 180	90	150	–
log 150	–	90	150
log 140	–	70	140
log 130	–	–	110

Table values correspond to the rafters of simple single gable roofs. First, the section of the leg, the length of the element, the distance between the centers of the log, the beam is obtained automatically. At the next stage, the length of the slope in the ridge is divided by the pitch of the rafters with the addition of one. Thus, the number of legs is counted, rounding the number up. Then it remains to adjust the distance between the wooden rafters in fact. For example, with a ridge length of 7.5 m, a rafter leg with a section of 16 x 2 cm (board) 4 m long, you get:

7.5 / 0.7 \u003d 10.7 + 1 \u003d 11.7 pcs. round up to 12 rafters.

The specification of the size allows you to calculate the center-to-center distance for mounting after installing the outer legs:

7.5/12 = 62.5 cm.

Dormer windows are located between adjacent rafters, in the places where pipes and chimneys pass, the legs are displaced by the distance specified in SNiP. All other elements of the system remain in place, the area of adjacency to the pipes, if necessary, is enhanced:

a bed is cut into two adjacent legs;
a short rafter cuts into it at one end, the second adjoins the element of the opposite slope in the ridge;
offset legs at the top rest on ridge run, fixed to two roof trusses at least.

Thus, the system receives the necessary rigidity without losing bearing capacity fire safety requirements are met wooden parts roofs.

Rafter leg material

The material of the rafters is often a beam of 25 x 10 cm - 15 x 4 cm, which allows to reduce the construction budget.

When choosing lumber natural humidity the developer is guaranteed to shrink the structure in the first year and a half by 5-7 cm in height. By increasing the cost estimate for the arrangement of the truss system by 70%, you can purchase glued laminated timber, significantly reducing structural loads, and doubling the roof resource.

The distance between the rafters will remain unchanged, however, instead of a planed beam of 17.5 x 5 cm, recommended building codes for five-meter legs spaced every 0.6 m, you can get by with a glued beam of a smaller section of 15 x 4 cm. Transportation costs will be reduced, work at height will be facilitated, cutting the material.

Prefabricated rafters from boards are used with the truss fastening scheme of the same name hip roof. The upper slopes are made of single boards, the lower ones are made of three boards sewn with self-tapping screws with an offset in the rows.

The choice of metal rafters is justified with a complex configuration of the roof, an abundance ventilation pipes, chimneys, which cannot be bypassed in compliance with the requirements of SNiP, fire safety. In this case, the step between the rafters is maximized, since rolled metal is much stronger than lumber.

If the rafters are attached at the bottom to the Mauerlat, the step of the legs is not critical, the elements can, if necessary, move to the desired distance in any direction. If the support scheme is used on puffs, which are floor beams, shift individual elements much more difficult. In this case, the amount of cutting waste increases when sheathing the draft ceiling, the floor of the attic or attic space.

Before installing the truss system, the question arises with what step to put the floor beams. Correctly calculating the distance between the rafters means preventing later deformation or even destruction of the roof frame. After reading the article to the end, readers will find out what should be the distance between the rafters for different kind roofing and how to calculate correctly.

Even at the stage of designing a house made of wood, you need to make all load calculations. This also applies to the truss system. This is especially important in wooden housing construction, since the upper link is often used instead of the Mauerlat. Correcting errors in such a design is subsequently difficult. For the correct calculation of the distance between the beams, there is a technique.

The span of the roof frame for the construction of a house from a bar standardly exceeds 1 m, and the smallest allowable value is 60 cm, such indicators are indicated in GOSTs (see figure). Correctly calculate the length of the rafters, their step can be the following option:

Using a tape measure, the length of the roof slope is measured, the result is divided by the step size of the roof frame. For example, if the distance between the rafters is 1 m, then you need to divide by 1, if 70 cm, then by 0.7. The resulting figure is summed from 1 and rounded up to the nearest more. So you can determine the number of beams for one roof slope.

By the result you need to divide the length of the future slope. The result is the distance between each rafter.

For example, consider a roof whose slope is 25.5 m and a step of 0.6 m. You need to calculate the following indicators: 25.5: 0.6 \u003d 42.5, to 42.5 + 1 \u003d 43.5. We round this figure to the nearest larger integer, we get 44. This is the number of rafters per 1 slope of the future roof.

Now we calculate the span between the rafters: 25.5:44 \u003d 0.58 m. It turns out that you need to put the legs of the frame after 58 cm. So you can easily calculate the step of any roof frame, shed or complex, without taking into account the roof. But professionals recommend their calculations for a certain type of roof.

Rafter leg step depending on the material

Since each forging material has its own characteristics and features. Among the most common are:

Decking. It has a different thickness and shape of a tropezoidal bend. It costs from 120 rubles.
Ceramic tiles. Expensive material from 670 rubles. Has 12 color options.
Metal tile. It's over cheap material unlike ceramic and costs from 320 rubles.
Ondulin. Soft roofing insulates the house from rain, hail, etc. It costs from 340 rubles.
Slate. The most economical option from 90 rubles.

The step size for the most common types of coverage will be discussed below.

The step of the rafter beams under the corrugated board

Envy the distance between the roof beams on the size of the sheet that the corrugated board has. The step of the roof frame beams under the corrugated board is taken as a standard not less than 60 cm and not more than 90 cm.

If this distance is greater, then boards with a large section are attached between the rafters. The cross section of the rafter legs for corrugated board is selected 50x100 or 150 mm.

The most important thing to consider when planning to fix corrugated board is the crate. They make it from a board with a section of 30x100mm, you need to mount it with a span of 50 cm or more. It depends on the brand and thickness that the corrugated board and the slope of the roof have.

So the roof at 15º grade C 10 is mounted on solid crate, corrugated board C 21 is mounted on a crate with a span of 30 cm. The largest corrugated board C 44 is mounted on a crate in increments of 50 cm to 1 m. ventilation hood etc.

Step of rafter beams under ceramic tiles

The specifics of the installation of the truss system for laying ceramic tiles related to the weight of this roof. Ceramic tiles are made from clay, and this roof has a weight greater than that of a metal tile by 9-10 times. The calculation of the load on the roof system for ceramic tiles is 40-60 kg / m 2.

Beams are made for the roof truss system under ceramic tiles only from dried material. The cross section is suitable for 50x150 or 60x180 mm. The standard distance between the rafter legs when roofing tiles is 80-120 cm. The span depends on what kind of slope the roof has. At an angle of 15º, the span between the rafters is 80 cm, at 750 after 1 m 30 cm.

When calculating the step, you need to take into account the length of the beam. Taking maximum length the distance between the rafters is minimal. And, on the contrary, with a minimum length of rafters, the step is maximum.

When laying ceramic tiles, it is important to consider that you will need to move along the roof. The maximum safe step of the rafter legs for such a movement is 80 cm.

When laying ceramic tiles, it is important to calculate the span of the crate. This distance is directly related to the size of the roofing material. standard sheet tiles have a length of 40 cm. Laying occurs with an overlap of 50 to 90 mm. When calculating the step of the crate, the size of the overlap is subtracted from the length of the tiles. The result is a step of 305-345 mm.

For shed roof for the construction of a house from a profiled beam, it is not difficult to make a calculation. If the roof is of a complex multi-pitched shape, then each distance between the rafters is calculated separately for the step of the crate. By fixing the cord on the opposite side of the roof slope, you can easily mark the rows.

Features of the roof frame under the metal tile

Metal tiles are used more often than ceramic or corrugated board. Externally, the roof resembles ceramic tiles, but unlike it, it is easier to install and lighter.

The metal tile weighs from 35 kg / m 2 of the roof. This makes it possible to lighten the design of the rafters and use beams of a smaller section. In this case, the step between the rafter legs of the roof frame increases and is equal to 60 to 90 cm. A beam is used with a section of 50x150 mm.

To create a ventilated space in the beams under the roof, holes are drilled with a diameter of 12-13 mm.

The design of the roof frame for metal tiles is not much different from corrugated board or ceramic tiles. But there is a small peculiarity: the support from above is attached to the ridge run from above, and not from the side, as in other cases. So a ventilated gap will appear under the metal tiles, which will eliminate the accumulation of condensate.

Features of rafter legs for ondulin

Ondulin is soft roof used for the construction of a house from glued laminated timber or from other material. Ondulin is produced in the form of sheets, it looks like painted slate, but light. This material is great for wooden houses both small and large.

Rafter beams under ondulin are placed with a distance of at least 60 cm, maximum 90 cm. For the rafter system, a beam of coniferous wood with a section of 50x150 or 50x200 mm is used. A smaller section will not provide sufficient strength to the rafters.

The crate on the rafters is placed from a material with a section of 40x50 mm in increments of 60 cm. This is quite enough for fastening sheets of ondulin with an overlap of 30 cm. Ondulin is fastened with special nails that are sold in the kit.

Features of the truss system for slate

Slate is rarely used for roofing. modern houses. But in summer cottage construction and households. buildings, this material is indispensable. It is low cost and easy to install.

Rafter under slate

Rafter legs for slate are used with a section of 50x100 or 50x150 mm. The fastening step between the rafters is not less than 60 cm and not more than 80 cm.

The crate for slate is made of bars 50x50 mm or a wide board 30x100 mm. The crate is laid from the steps, depending on the slope of the roof. For a steep shed roof, it is 45 cm. The consumption is 4 bars per 1 sheet of slate. For a flat shed or gable roof 63-65 cm, so the consumption is reduced to 4 bars per sheet.

The step of the rafter system under the slate roof structure differs. For the host buildings are often mounted shed.

A feature of the size between the rafters of a shed and gable roof

Whether a safety margin is needed during installation depends on what shape the roof is. And the distance between the beams of the rafters directly depends on this.

single truss system

Shed roofing is more durable and easier to assemble. The thickness of the rafters is selected depending on the type of wood, its strength and the specifics that this or that design has. The step between them can be 60-140 cm. The distance also takes into account whether the structure will be insulated. If yes, then the step should correspond to the width of the insulation.

The thickness of the rafters must be calculated depending on the slope of the roof. For a slight slope of 15-20º, you can use a material with a section of 50x100 mm. For a steep slope of 45º, stronger ones with a section of 50x150 mm are needed.

Gable truss system

If the calculation of the foot step of the frame of a shed or other type of roof is not correct, then the roof can be taken away, and the beams will sag and bend due to the severity of the structure. In this case simple repairs can not do, you have to redo the entire structure. Therefore, it is so important to correctly calculate the distance between the legs of the rafters, depending on the roofing material used: corrugated board, ceramic or metal tiles, ondulin or slate, etc.

The roof structure is one of the main enclosing elements of the building. quality characteristics which are subject to rather stringent requirements.

One of the most common roof sheathing materials is metal shingles, which are made from thin sheets of steel, aluminum, or copper.

Top elements are equipped polymer coated, which protects metal from aggressive external influences.

Externally, the metal tile is similar to ceramic, but it is more durable. This material is used to cover pitched roofs, the slope of which must be at least 14 degrees.

This is the national team frame structure roofs, consisting of many wooden or metal parts. She is rests on load-bearing walls, which are a reliable basis for all overlying elements. The rafter system serves as a kind of skeleton, on the basis of which it is made, - and the roof, as well as laying the roofing finish roofing layer.

truss system

Elements roof truss, and their main characteristics:

Mauerlat. A softwood beam, which is a connecting element between the rafters and the underlying structures. It has a square cross section with a side of 100 or 150 mm. Mauerlat is laid along bearing wall along its entire length. With the help of the Mauerlat, the loads from the roof are evenly distributed throughout the building.
Sill. A beam having a square section similar to a Mauerlat. It is laid transversely to the bearing walls, as it serves to redistribute the load from the roof racks.
Rafter leg. From these elements, the main triangular roof structure is created, which experiences the full severity of external atmospheric influences (rain, wind, snow, hail, etc.).
Rack. Vertical connecting elements that distribute compressive loads from the ridge assembly over the entire area of bearing walls. They are made of square bars, the length of the edge of which is determined by calculation.
Puff. It is the final horizontal element of the triangle of rafter legs, which does not allow them to creep under the pressure of external loads and the own weight of the roof. It is used in systems with hanging rafters.
Struts. Perceive and redistribute bending loads from the ridge assembly.
Crate. Consists of boards, bars or plywood sheets (in case of subsequent laying shingles), which are located relative to the rafter legs at a right angle, while being an additional rigid element.
. The junction of two roof slopes.
Overhang. Roof element protruding beyond load-bearing wall structures at a distance of about 0.4 m. Its purpose is to limit the penetration of moisture to the walls.
Filly. These elements are attached to the ends of the rafters if they are not long enough to organize an overhang.

Varieties of pitched roofs

Depending on the number of inclined planes, roof structures can be divided into:

In private housing construction, the most commonly used option gable roof, since he has a number of advantages. These include:

Practicality. gable roof has a significant angle of inclination, due to which rainwater does not accumulate on its surface, and the snow and wind load are distributed most optimally.
Ease of device and operation. The assembly and joining of two pitched elements is much easier than with complex roof structures. In addition, the repair of such a roof will also be simple.
Aesthetics. A roof with a gable structure is organically written into the surrounding infrastructure.
Reliability(if done correctly).
Democratic price constituent materials.

Types of pitched roofs

Gable roof - truss system for metal tiles

Frame from rafters under a gable roof from a metal tile has no significant differences from structures with other covering roofing materials.

But, in view of the fact that metal thin sheets have a small specific gravity , the rafters will experience less constant load.

This makes it possible to reduce their cross section, due to which can save a lot on the purchase of wood materials.

Ideal for metal roofing the angle of inclination must be at least 14 degrees.

For a roof with two pitched elements, the following apply: frame options:

Laminated rafters under a metal tile.

In this case, 2 load-bearing rafter legs are fastened together using lying down(horizontally) and racks(vertically). The bed is laid parallel to the Mauerlat element, while taking on some of the force effects. The rafter system under the metal tile is taken over only bending loads, which significantly affects the selection of the calculated cross section. Such a system can be used for buildings with large and small spans.

Types of rafters

Hanging rafters.

Unlike layered systems, in this embodiment, two rafter legs fastened together only in the ridge knot. In this case, significant bursting forces arise on the supporting elements, which limits the use of hanging rafters only for buildings with a span of not more than 6 m.

They can be made of wood or metal, as well as installed below (they play the role carrier beam) or at the top of a triangular structure. It is worth considering that the higher the puff is located, the greater the effort it will take.

NOTE!

To provide quality work tightening needs to be taken care of on the reliability of fastening with load-bearing rafter legs.

Combined variant

Used to create original roof structure. Includes elements of both hanging and layered systems.

How to calculate the angle of inclination of the rafters?

To implement a gable roof, you need to know a few geometric values of the building, namely:

Half span - L;
The distance from the load-bearing wall to the roof ridge (or the height of the support post) - H.

Standard formula: α = arctg(L/H)

Where α is the desired angle of inclination of the roof.

Knowing this value, you can calculate the length of the supporting rafter leg:

l = H/sinα.

Where l is the length of the truss element.

Rafter Angle

How to calculate the load?

For implementation correct selection roof frame parts calculate live and permanent load values acting on its structural elements.

The constant load includes the weight of all elements, as well as the mass of the load-bearing elements themselves and the crate.

The composition of temporary loading options includes force effects from wind, snow cover, rain masses, as well as the weight of a person (to take into account options for subsequent repairs).

Dead Load Calculation

Roofing cake weight.

It is determined by adding the masses of all its elements, namely steam, hydro and thermal insulation, as well as roofing from metal tiles. In this case, the weight of one linear meter (can be found in the regulatory documentation) is multiplied by the value of its length.

The weight of the truss system.

It is determined by adding the weight values of the crate, rough flooring, as well as the supporting frame. The mass of each element is calculated by the formula:

M=V*p,

Where V is the volume of the element, calculated depending on the geometric characteristics of the cross section and the length of the element;

P - The density of the wood used (depending on the species).

Total permanent load \u003d weight of the rafter system + weight of the roofing pie.

Calculation of live loading

Conducted in accordance with regulatory documentation (SNiP 2.01.07-85 "Loads and impacts" or Eurocode "Actions on structures" part 1-4).

To determine the value of the wind effect, the roof structure is conventionally divided by height into several parts. For each of them, the value of the wind load is calculated. To obtain the total wind pressure, they must be summed.

Formula for calculation:

Wm=Wo×k×c,

Where Wm is the value of the wind load;

Wo is the normative value of wind pressure determined from zoning maps;

k - wind pressure coefficient (determined depending on the height according to the regulatory documentation);

With - aerodynamic coefficient(for a gable roof - 0.8).

Determined by the formula:

S = µ×So;

Where So is the normative value of the snow load, determined from the zoning map.

µ is a coefficient that is determined depending on the angle of the roof:

For α≤30 deg. — µ=1
For α≥60deg. -µ=0
For 30≤α≤60 deg. – µ=0.033×(60-α)

Snow load areas

How to choose a beam and calculate the pitch of the rafters under the metal tile?

Determining the value of the cross section of the beam of the truss element is carried out in several stages.

Calculation of the load distributed on each linear meter of the structure:

Qр = L×Q;

L - Step of the rafters.

The L value is calculated as follows:

The length of the roof slope is divided by the estimated step of the structures (for convenience, it is most often taken equal to 1). Then 1 is added to the resulting value. The resulting value reflects the number of rafters that need to be installed on one pitched roof surface. At the last stage, the value of the axial distance between truss elements, by dividing the length of the roof slope by the number of rafters.

The distance between the rafters under the metal tile - the standard step is 0.6-0.95 m.

Rafter step

Then we determine the maximum working area of \u200b\u200bthe rafter leg (Lmax). We proceed to the calculation of the cross section. To do this, we find its height using the formula:

H ≥ 8.6*lmax * sqrt(Qp/(b*r)), with roof slope α<30 град;

H ≥ 9.5*lmax * sqrt(Qp/(b*r)), with a roof slope α≥30 degrees;

Where b is the width of the cross section,

r - the value of the normative resistance of wood to bending loads (determined according to regulatory documentation, depending on the type of wood).

To simplify the calculations, you need to use the standardization table for truss elements (GOST 24454-80 “Softwood lumber. dimensions").

If the inequality is not observed, it is necessary to increase the value of the geometric characteristics of the section and repeat the calculation.

What is the difference between the truss system for cold and warm roofs?

The main difference between these two roofs is the support system of the truss elements. In the case of a warm attic, the main supporting element is the Mauerlat, as well as the supporting beam system. In a cold roof, rafters are installed directly on load-bearing walls.

Installation of rafters under the metal tile

All installation work on the installation of the roof is carried out at a sufficiently high height. To minimize the risk of falls, as well as greatly simplify work at height, you can assemble the frame of the supporting truss system on the ground.

To do this, you need to create a template from the boards, according to which further assembly will be carried out.

It is made in several stages:

The boards are raised above the walls of the building, leveled, and then fasten together with the help of a nail.
Align the angle of the boards in accordance with the project, by lowering and raising them. The elements are fixed.
The result should be a structure that resembles in shape the future truss system, made in accordance with the estimated geometric dimensions of the roof.
The template is lowered to the ground, in accordance with it, the finishing elements are fixed to each other. More details in the video below.

Then you should take care of installing the support element - Mauerlat. As mentioned earlier, it is laid on load-bearing walls in the longitudinal direction. Fastening is carried out using studs (on an armored belt or masonry) or using a wire rod (for buildings with a small roof height).

CAREFULLY!

When using a hairpin connection, connecting elements do not need to be tightly sealed into the wall. They should protrude from the wall by 30-40 mm, as the nut will be screwed onto the studs.

The next step is to create ridge run, serving as a supporting part for the entire structure of a gable roof. It is made from timber or hewn logs. If the span of the building is not more than 6 m, it can be supported without additional supporting elements. Otherwise, construction trusses must be used for installation.

Mounting. Part 1

After installing these elements, it is possible to carry out the lifting and installation of the main truss element, assembled according to the template. Fastening with a Mauerlat can be carried out in 2 ways:

Rigid connection. It is carried out with the help of corners and beams. Less often, fastening is used by means of washing down on rafter legs, followed by fixation with nails or staples.

Features: in addition to the main connection, it is necessary to tie the rafters to the wall using anchors or a wire structure.

Sliding. It is based on the creation of a swivel joint. It is made by joining elements using cuts. The elements are connected with a metal embedded part with holes for bolts, or with 2 nails that need to be hammered in at an angle.

It is necessary to carry out the installation of wooden trusses in a certain sequence. First, extreme trusses are installed, located at the ends of the building. Then a cord or rope is pulled between them, with the help of which the verticality of their installation is checked. Further, under the cord, further installation of truss structures is carried out in accordance with the specified design step.

Mounting. Part 2

Creating a roof from a metal tile is a rather laborious process that requires certain skills and a full hand. Therefore, for proper installation, you must at least work under the supervision of a competent specialist.

Useful video

Video instruction for self-installation of rafter legs:

It is pointless to argue about the importance of the roof for any building. It is not for nothing that over a dozen different types of roofs have been invented in the history of mankind, from simple to quite complex in design and construction. An important element in planning the construction of a roof is the step between the rafters - strong bars that are the basis of the structure. This will be discussed in this article.

The distance between the base of the roof slopes is not a constant value and depends on the following components:

type of roof;
slope angle;
the type of roofing material to be installed;
rafter section dimensions.

Before proceeding with the process of erecting the upper structure of the house, a calculation should be performed by determining the optimal distance between the rafters.

Gable roof rafter pitch

The most widespread in our country are gable roofs. They are a structure that has two parallel planes, with an angle of inclination relative to the horizon from 20 to 50 degrees.

With an insufficient slope of the gable roof in snowy areas, there is a danger of accumulation of large snow masses, which can lead to the destruction of the structure. An increase in the slope angle in regions with a predominance of strong winds is also fraught with a high load and the risk of breaking not only the roof, but the entire structure as a whole.

Mansard roof truss system

Most private houses have an exploited under-roof space called an attic. This design is characterized by an increased height of the slope, which is caused by the need to create a living space of a comfortable height. As a rule, the slopes of the mansard roof are broken, having a varying angle of slope. For their installation, a double truss system is used.

The steepness of the lower slopes of the mansard roof significantly exceeds the slope of their upper extensions. The plane load perceived by them is not great. Thanks to this, the rafters in the lower part can be installed with a maximum pitch. The upper ridge slopes are recommended to be mounted with a reduced gap from each other.

Rafters in a shed roof

For outbuildings and some private houses, roofs with one slope are used. Due to the limited angle of inclination, high pressure is exerted on them. Experts recommend using lumber of increased cross-section for the rafters of a single-pitched roof, with the installation of a minimum step from each other.

When calculating the distances at which roof beams are installed, special attention should be paid to the amount of snow load in a particular area. With a small slope, this characteristic is of great importance. Roofing material for such roofs is best chosen with a minimum dead weight, which will reduce the bending load.

Hip roof truss system

The hip roof truss system is considered the most difficult in construction. This type is called four-pitched, since the roof is formed not only by side, but also by additional end slopes, where the installation of rafters is carried out not on the ridge, but on the corner bowstrings. This places special demands on the organization of the roof frame.

Under the hip roof, the attic is not often arranged. This is due to the small angle of inclination of the rafters and the roof as a whole. In the case of an increase in the angle of the slopes to the horizon, the distance between the rafters is increased, with a decrease, vice versa. An additional aspect of the calculation is the roofing material used.

The dependence of the pitch of the rafters on the roofing material

In addition to variable snow and wind loads, a constant (static) one also acts on the roof, the force of which depends on the roofing material used. It is no secret that different types of roofs have their own weight, which can differ by 10 or more times.

The right choice of material affects not only the top, but also all other parts of the structure of a residential building and other buildings. Not without reason, when designing the foundation, it is necessary to decide in advance on the choice of the roof.

Roofing from profiled sheet

Currently, one of the most common roofing materials is a profiled sheet, which is produced galvanized or followed by a polymer coating. The distinguishing features of the profiled sheet include the following parameters:

High corrosion resistance;
As a result, a long (more than 15 years) service life;
Easy installation even without the necessary qualification;
Small sheet weight (weight 1 m 2 is 4-5 kg).

Since this roofing material does not exert a high load on the rafter system, the distance between the elements is chosen as much as possible for a particular angle of inclination. In addition, the profiled sheet does not require high strength characteristics from the roof lathing. All this together allows minimizing the total load on the foundation and walls.

Roofing from a metal tile

The second common type of steel roofing materials is metal tiles. This type of profiled sheet, which successfully imitates natural clay material, but with a lower mass (10 or more). A feature of the rafters under the metal tile is the smaller section size.

When choosing at what distance to install the rafters, first of all, you should be guided by the dynamic load. Like a profiled sheet, a metal tile is not demanding on the size of the rafter legs and is well mounted on a crate made of an inch coniferous board. All this makes a metal roof low-cost.

Rafter system for ondulin

In the 21st century, corrugated sheet materials were replaced by a more durable and lightweight analogue - ondulin. Among others - the most lightweight material. The weight of the sheet does not exceed 6 kg.

The small thickness of ondulin sheets at slope angles of less than 15 ° requires the construction of a continuous crate of plywood sheets, for example, which will require an appropriate rafter pitch. This should be taken into account in the calculations.

slate roof

Not so long ago, a wavy material from an asbestos-cement mixture, called slate, was widespread. High mass and fragility are the main disadvantages, however, even today he finds his fans in the construction of various outbuildings.

A high mass, comparable to the weight of a clay tile, will not allow the use of the same truss system as under a metal tile. Building codes define a minimum angle of slope for a slate roof of 22 degrees or more. Otherwise, the load from the material itself and the truss system with the crate exceeds the permissible parameters. The step of the inclined bars, as well as their cross section, are selected individually in each case.

Polycarbonate roof

In recent years, more and more often on the roofs of verandas and gazebos, an artificial polymer material, polycarbonate, has been used. Produced in two versions - monolithic and honeycomb. The first in its properties is similar to ordinary quartz glass, but significantly exceeds it in strength. The second one has less mechanical properties, but high thermal insulation and light transmission.

Cellular polycarbonate is standardly much lighter than a monolithic counterpart. It is used as a roof without the use of lathing, provided that the step does not exceed ½ of the width of the sheet of material. The high strength of the monolithic analogue also makes it possible to avoid elements transverse to the rafters. Sufficient flexibility allows you to cover semi-circular roofs on a metal frame, the pitch of which does not exceed 0.9 meters.

Thematic material:

Rafters under a soft roof

The original pattern can be obtained through the use of soft roofing materials, which are spread with an adhesive layer. They are installed on a continuous crate made of plywood or OSB. The step of the rafters should allow you to fix the sheets, so it is chosen as a multiple of ½ of the width. Given the standard dimensions of plywood 1520x1520 mm, the center distance between the rafters will be: 1520: 3 = 506 mm.

Rafter step for insulation

The installation of residential under-roof spaces is often combined with the laying of insulation sheets in the rafter gap. The most common plates with dimensions of 600x1000mm. These parameters are used as starting points.

Rafter pitch calculation scheme

According to building codes, the pitch of the roof rafters is in the range of 0.6 - 1 meter. Its final calculation is performed according to a simple formula, depending on the total length of the roof. For the calculation, you must perform the following list of actions:

determine how much distance should be between the rafters for your specific building conditions. According to the reference book, the magnitude of wind and snow loads in the area is determined.
the length of the roof is divided by the desired distance by adding one. The result will be equal to the number of rafter legs that are installed on one roof slope. If the value is not an integer, it is rounded off.
the length of the roof is divided by the number of rafters calculated above, we get the final step in meters.

For example, with a slope of 30 degrees, the maximum distance between the rafters of a gable roof under a metal tile is 0.6 measure. The length is assumed to be 16 meters. Consequently:

16:0,6+1=27,66;
rounding the result, we get 28 rafters per slope;
16:28 \u003d 0.57 meters - the center gap of the rafter legs for these specific conditions.

As you can see, the calculation technology is not complicated, but this is just an approximate scheme. Taking into account many other parameters mentioned above can make certain adjustments.