Optimal rafter pitch. Calculation of the distance between the rafters

The shed truss system came to us from the USA and Europe. Residents using it noted reliability and cheapness, so the popularity of this type spread very quickly. Despite the fact that a small amount of wood was required for the construction of one slope, few people dared to build such a construction. The fact is that most developers considered such a system too simple for residential buildings, while the other part simply did not know how to build it to prove the opposite. In this article I will try to explain to you how to easily and quickly create such systems and correctly select the pitch of the rafters of a pitched roof.

Basis of calculation

Despite its simplicity, one slope must meet all the installation rules. After all, if serious mistakes are made at the same time, then the roofing will deform, which will inevitably entail not only leaks, but also the collapse of the entire roof.

To achieve maximum stability of the roofing system, it is necessary to pay attention to four components:

1. Reliability of fastening of the rafter legs to the support beam and ridge;
2. Proper selection of auxiliary parts for the truss system;
3. Durable lumber and auxiliary elements;
4. Rafter step.

Do not think that by observing only four points you will achieve the most stable design. To do this, you will have to use all known methods and technologies.

Calculation values

You can’t perform calculations without knowing certain indicators, right? Therefore, before starting, you need to make sure that you have four basic values.

In addition to all these indicators, the main task of any project is to calculate the maximum allowable load on the roof. It includes quite a lot of values, and here is a list of elements whose mass is especially important in the calculation:

• rafter legs
• crate
• roofing cake

If you are far from the construction industry, then you will have to remember that the calculation of the maximum roof load consists of two parts. The first one takes into account all the materials used, and the second one contains the snow load of your region. Its meaning is written in a special reference book, which you can easily find on the net.

But even on this, the indicators will not be accurate, because you forgot about the wind load and the weight of the worker himself, who will carry out installation work and subsequent maintenance (repair, cleaning).

When developing a project by a construction organization, they use complex formulas of strength of materials, so if you don’t want to bother with this, you can use the recommendations of experienced people.

How to calculate the required distance between the rafters

The distance between the rafters of a shed roof largely depends on the previously calculated maximum possible step. To determine this value, you will need to have a total load value, roof parameters and data on the wood of the rafter legs.

You can calculate the optimal step of the rafter leg using the following method:

1. First of all, you need to find the total length of the roof. This value must include any ends and overhangs;
2. The resulting value is divided by the maximum allowable distance between the rafters;
3. The answer is rounded up. This number will indicate the number of spans;
4. Next, we take the value of the length of the roof and divide it into spans. So you will find the optimal step;
5. And to find the number of rafter legs, you need to add one to the spans.

This rule works for the vast majority of roofs, but there are those that cannot be calculated in this way. If you have just such a case, then you will have to acquire an additional rafter on one of the ends.

Rafter system depending on the roofing

It's no secret that the greater the mass of the roofing, the greater the number of rafter legs must be installed. Most manufacturers of this material in the instructions for their product indicate the optimal number of rafters and their dimensions.

You should not blindly trust these instructions, only if you do not live in the central strip of Russia, because they were written specifically for this territory. Before developing a drawing, it is necessary to carefully study the prevailing winds and draw a kind of rose, which will be a guide for future construction.

It is worth noting that in regions of the country where a large amount of precipitation in the form of snow falls, it is best to create steep roofs with a slope of 35-45 degrees. This will provide fast natural gathering snow cover from the surface.

In most cases, the truss system of private houses is created from logs with a diameter of 12 to 22 centimeters, timber or boards with thicknesses from 40 to 100 and widths from 150 to 220 millimeters.

Rafter system for corrugated board

Roofing corrugated board is a fairly light material and at the same time has good strength characteristics. Therefore, as rafter legs, you can use lumber of a small section, but with a frequent step: 0.6 - 1.2 meters. The roof slope should be at a slope of 12 to 45 degrees.

The required section can be selected based on the span distance between the supports. If the distance is about 3 meters, then the section can be taken 40x150 millimeters, at 4 meters this value increases to 50x180 millimeters, and at 6 meters it is necessary to use lumber whose section is 60x200 millimeters.

By the way, the crate in this matter also plays an important role. In the case when the rafter step is a decent value, you will have to use wider boards. For example, for a step of 0.6 meters, elements with a section of 25x100 millimeters will be needed, and for 1.2 meters - 40x100.

The crate for corrugated board is arranged discharged method, and the step of its elements should be 50-80 centimeters. However, these values ​​\u200b\u200bmay go beyond due to the characteristics of the roofing itself. You can also find tips on how to arrange these parts in the instructions that came with the purchased material.

Rafter system for ceramic tiles

Ceramic tiles are a unique roofing material. It is made of clay, which makes this material very heavy. The designed truss systems must necessarily follow the following requirements:

In the roofing sphere, there are only 3 types of crates. One of them can be arranged at an angle of 12-60 degrees, and the other two at an angle of 20-45 degrees. As elements of the crate for clay tiles, you can most often see a beam with a section of 50x50 millimeters.

Rafters for metal tiles

Due to the fact that metal sheets have a much smaller thickness, you do not have to arrange a serious truss system. Therefore, you can safely follow the advice and recommendations of roofing material manufacturers.

It is worth saying a few words about the only nuance that will allow you to save some lumber. So, it lies in the fact that the minimum step of the crate can be increased to 1 meter. This is due to the dimensions of the sheet material. When a metal tile is tripled, then, as a rule, it is supported by a crate in only a few places, and with a rafter pitch of 0.6 meters, it is impossible to create an “economical” crate, so you have to change it along with the rafter system.

Rafter structure for ondulin

To date, ondulin has given way to more modern coatings, but despite this, developers whose roofs were laid with asbestos slate began to look at this material as a profitable alternative. It is made on the basis of bitumen and fiberglass, has a low weight and high quality.

The truss system for ondulin must comply with the following parameters:

• The slope of the slope should be in the range from 5 to 45 degrees;
• With a small slope, the step of the rafter legs should be minimal: 0.6 meters, and with a steeper roof, this distance increases to 0.9 meters;
• With a sloping roof, say up to 10 degrees, it is necessary to arrange a continuous crate. To do this, it is best to use moisture-resistant plywood, OSB boards or edged boards with a section of 30x100 or a beam of 40x50 millimeters.

As for the section of the rafter legs themselves, it is selected according to the same rules as for corrugated board.

Rafter system for corrugated asbestos-cement sheets (slate)

Surprisingly, everyone knows the roofing material called "slate", because the vast majority of private houses are covered with this particular product. Due to its rigidity and components, this material has a fairly solid weight, so it is necessary to follow the recommendations for the construction of the truss system so that it does not collapse even before the start of operation.

• The low tightness of the finished plane does not allow the use of slate with a slope of less than 22 degrees, this will lead to leaks. If you cannot find any recommendations for the installation of asbestos-cement sheets (which is unlikely), then you can always use the instructions that came with ondulin;
• The maximum possible slope of the rafters with a slate roof is less than 60 degrees;
• The optimal step of the rafter legs lies in the range from 0.8 to 1.5 meters. Here everything will depend on the load and cross-section of lumber;
• As a rule, a wooden system for slate requires a slightly larger section of the legs than with a light roof. An example is the situation when the pitch of the rafters is 1.2 meters. For the rafters, you will have to take a bar with a section of 75x150 or 100x200;
• As for the crate, its elements will also differ from the step of the rafter legs. If it is up to 1.2 meters, then a bar of 50x50 millimeters will do, and with a larger step - 60x60 millimeters;
• The step of the crate beam should be selected so that one sheet is supported by 3 elements. The slate should extend beyond the edges by 15 centimeters on both sides. For example, if we consider the standard dimensions of an asbestos-cement sheet (175 centimeters), then we can use a crate step of 80 centimeters.

It is probably worth remembering that asbestos is harmful substance, therefore, when working with a material that contains its particles, safety precautions must be observed. Which states that the worker must wear personal protective equipment.

Rafter system of one and two slopes

Recently, the shed roof is gaining more and more sympathy. It is understandable, because materials are only getting more expensive, and you want to save money. Due to the simple design, this can be done. The rafter system of one slope is quite primitive. To do this, you just need to put the beams on the crown and secure. Of course, do not forget about the insulating material.

The maximum slope of a shed roof can be 30 degrees, and the span is 6 meters (this rule applies to lumber). The most optimal slope is 15-20 degrees. At this angle, the wind load will not cause much harm, but the snow cover will cause some inconvenience. The solution to this problem can be to place your building "downwind", which will allow it to remove the snow mass from the roof in a natural way.

An alternative option for a single-pitched roof is a double-pitched one. It is a number of rectangles connected together with a Mauerlat and a ridge. It is worth noting one interesting fact. When the shape of a triangle approaches an isosceles one, its rigidity increases. In this regard, with a roof slope of up to 60 degrees, it is possible to expand the step between the rafter legs.

But do not flirt with calculations, because this can lead to an increase in windage and lumber consumption. The most optimal slope of the slopes for a gable system is 45 degrees.

If you decide to build a roof yourself, then you will certainly need some tips that will not only make your work easier, but also increase the operational period of your roof as a whole.

• Calculating the structure correctly is not an easy task, but even if it is done correctly, it can be broken if it is incorrectly fastened. Therefore, mounting the rafter legs in their places, do the work with all responsibility. To improve your skills, you can read information on the network, or invite a knowledgeable person to the facility;
• The step of the rafter legs should not affect the thermal insulation in any way. It is worth remembering that the plates can vary slightly in size. Take advantage of this and push them as tightly as possible. In a hardware store, there are standard sizes of insulation boards of 60, 80, 100 and 120 centimeters;
• For most roofs with a slope of less than 45 degrees, it is necessary to include the weight of the worker in the calculation. As for sharper roofs, this is not necessary, therefore, it is possible to reduce the pitch of the rafter legs by 20%;
• Take advantage of modern technology and calculate your roof with online calculators. All you need is to enter the exact parameters;
• Regulatory documents regarding wind and snow load you can find on the net or from the craftsmen at the construction site;
• Any wood used for construction purposes should be dried as much as possible. This will avoid its deformation in the future.

The roof of a building is one of the most important elements of the entire building. If you start saving on a roofing pie, then soon you will face costly repairs that will affect not only this area, but the entire building as a whole. Therefore, if you want to get the maximum operating period from your comfort, then you should not use low-quality materials.

The roof structure is one of the main enclosing elements of the building, the quality characteristics of 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.

From above, the elements are equipped with a polymer coating, 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 roof frame structure, 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

The constituent elements of the truss roof, 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 the load-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 crawl 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. It consists of boards, bars or plywood sheets (in the case of subsequent laying of bituminous tiles), which are located at a right angle relative to the rafter legs, while being an additional rigid element.
• . The junction of two roof slopes.
• Overhang. A roofing element protruding from the 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:

1. Practicality. The gable roof has a significant angle of inclination, thanks to which rainwater does not accumulate on its surface, and snow and wind loads are distributed most optimally.
2. 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.
3. Aesthetics. A roof with a gable structure is organically written into the surrounding infrastructure.
4. Reliability(if done correctly).
5. 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 low specific gravity, the rafters will experience less constant load.

This allows you to reduce the value of 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 bearing elements, which limits the use of hanging rafters only for buildings with a span of no more than 6 m.

They can be made of wood or metal, as well as installed at the bottom (acting as a supporting 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 ensure the quality of the tightening, care must be taken on the reliability of fastening with load-bearing rafter legs.

Combined variant

Used to create an 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?

To carry out the correct selection of parts of the roof frame, it is necessary 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 documents ( 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);

c - 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 the rafter elements is determined 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 pitch

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:

One of the important stages of any construction is the construction of the roof of the building, the basis of which is the installation of a truss system. The uniform distribution of the weight of the roof on the frame, the reliability of the roof and the duration of its operation as a whole will completely depend on how correctly the pitch of the rafters is chosen, that is, the distance between them. With any slight calculation error, damage and collapse of the entire roof can occur.

Collection of the required calculated values ​​\u200b\u200bto establish the pitch of the rafters

The rafter system includes the following components:

• farms;
• ridge and side runs;
• Mauerlat;
• diagonal elements.

Farms consist of a crossbar, base, rafter legs, binding and fastening elements. The rafter legs are beams located along the slopes, the lower ends of which are connected to the Mauerlat, and the upper ends to the girders.

Rafter pitch is the exact distance between two rafter legs.

To get the exact indicated value, you must first find out the values ​​​​of some quantities important for this.

All calculations for the roof covering system should be correctly made at the design stage of the house. Such a responsible business can be carried out by yourself or entrusted to its specialists. The more accurate the calculations are, the stronger the base for the roof will be.

In order to correctly make all the required calculations, including the rafter pitch, you need to know:

• permanent and temporary loads;
• their size;
• slope angle;
• type of roofing;
• material for the manufacture of rafters;
• roof type.

One of the indicators that must be taken into account when calculating the pitch of the rafters are permanent and temporary loads. These include:

• the weight of the roofing and truss structure;
• weight of the interior roof finish;
• snow cover weight;
• the weight of the person carrying out the maintenance of the roof.

It should be noted that these data are taken in special tables developed by scientists, depending on climatic zones, for various territorial regions.

The angle of the slope can be determined by knowing the length of the wall of the house and the height of the roof. The steeper the roof, the more installed, since the load on such roofs will be transferred mainly to the load-bearing walls. After making further calculations, the length of the rafters is easily calculated. Most often they have standard sizes: 4 and 6 m.

Coniferous wood is well suited for the manufacture of a roofing system. Lumber must be of high quality, without knots, rot. Before work, all wooden elements must be treated with antiseptic special compounds.

The step of the rafters will also depend on the type of roof, that is, on the functional features and its shape. The size of a simple and complex roof will be different.

How the type of roofing will affect the pitch of the rafters should be considered in more detail.

General technology for calculating the distance between the rafters

Having made all the necessary measurements, it is possible to make a constructive calculation of the pitch of the rafters. Based on practice, this indicator is in the range from 0.6 to 1.0 m.

In order to correctly perform this calculation on your own, you must adhere to the following technology:

1. The total length of the roof slope is taken.
2. The optimal step of the truss truss is selected.
3. The length of the slope must be divided by the pitch of the rafters.
4. One is added to the resulting value.
5. To get a whole number, the result is rounded up.
6. This calculation is the number of trusses (rafter legs) located on one roof slope.
7. Now the entire length of the roof slope is divided by the resulting value, showing the number of trusses. This determines the pitch of the rafters.

It should be noted that this calculation is made in the center of future rafters. However, the calculations cannot be considered accurate and constant. In each case of the construction of the roof of a house, the angle of the roof slope, the features of the selected roofing material, and other indicators are taken into account. In this regard, it is necessary to consider the features of choosing a rafter pitch for the most common roofing materials: metal and ceramic tiles, corrugated board, slate and ondulin.

Features when choosing the distance between the rafters for metal and ceramic tiles

Metal tiles as roofing are extremely common in both urban and suburban construction. The very design of the roof truss system when using metal tiles will differ little from the general scheme. However, due to the fact that this building material is light in weight, rafters and other elements of the system can be taken with a smaller section, i.e. with a smaller margin of safety. The distance between the rafters when using metal tiles is 60-95 cm. All work on the installation of roofing from metal tiles is much easier than from other roofing materials. A feature of the lathing device of this material is that the board near the cornice should be about 1.5 cm thicker than the others. Usually, the cross section of metal rafters is 50x150 mm.

Ceramic tile is a roofing material that has a significant weight, which is 10 times the weight of a metal tile. In this regard, it is necessary to more thoroughly approach the calculation of the roof truss system. should be slightly increased - up to 60x180 mm. The average distance between the rafters for covering ceramic tiles is set in the range of 0.8-1.3 m. The angle of the slopes of the slopes is necessarily taken into account: the distance between the rafters is made larger, the higher the roof.

The length of the rafter legs in this case will have a strong influence on the result. The distance between the rafters decreases with increasing their length.. With their long length, increased deflection loads may occur, which can be significantly reduced if an additional system of struts, supporting racks and other elements is installed.

Features when choosing a rafter pitch for slate, corrugated board and ondulin

The most common roofing material is slate. This is due to its low cost, ease of installation, and the possibility of replacement if individual elements of the roof are damaged.

The features of the crate for slate is its thinned type, consisting of any type of board or timber, but with a mandatory cross section of at least 30 mm. This is necessary for the correct and high-quality distribution of the weight of the slate on the crate.

The optimal distance between the rafters, when combined with the load from the weight of the slate sheets, should be 80 cm. It is worth constantly taking care of the margin of safety of the truss system, which may be due to various unforeseen circumstances. Otherwise, its installation under a slate roof does not differ from other options.

Now you should pay attention to some features when installing a truss system for roofing materials such as corrugated board and ondulin.

The weight of corrugated board and ondulin is much lighter than that of ceramic tiles or slate, so the technology for installing rafters for these materials is practically no different from installing metal tiles. The distance between the rafters for a corrugated roof is 60-90 cm, and from ondulin - 60-100 cm.

If it is necessary to increase the distance between the rafter legs, it is necessary to strengthen the structure of the system with transverse elements of the crate.

The sheathing device for corrugated board is very similar to the sheathing device made of metal tiles. It is important to remember that in this case, the last board should also be slightly thicker than all the others.

A feature of the installation of the crate for ondulin should be considered the need for its continuous type for high-quality resistance to various loads. In some cases, a thinned type crate can also be used, but then the step between the rafters should be no more than 30 cm.

Thus, being able to make all the necessary measurements, knowing the basics of installing a truss system for basic roofing materials (tiles, corrugated board, slate and ondulin), you can correctly calculate the distance between the rafters.

truss system, undoubtedly, is the most important structural element of any pitched roof. The consequence of its improper installation can be not only the deformation of the roof, requiring expensive repairs, but also the complete collapse of the roof on the head of an insolvent builder.

The following four main factors influence the stability of the truss system to various loads:

1. fastening strength rafters to the ridge and Mauerlat;
2. correct calculation of the supporting structure for rafters, depending on the length of the span;
3. choice roofing material;
4. step between the rafters.

The topic of this article is the choice of material and pitch between the rafters, taking into account the intended type of roof.

What are the calculations based on?

When making calculations, four main indicators are taken into account:

The most important is the calculation of the maximum roof load, consisting of:

• rafter weights,
• crate weight,
• weight of roofing material and insulation,
• snow load (reference information unique to each region),
• wind load (also reference information),
• person's weight (if repair or cleaning is necessary, 175 kg/sq.m).

To carry out accurate calculations, experts use special formulas from sopromat, but when building a private one, you can use approximate recommendations.

Method for calculating the distance between the rafters

Accurate Distance Calculation between rafters is based on the results of a preliminary calculation of the maximum allowable step. To make this calculation, the total load, the roof structure and the material used on the rafter legs are taken into account.

Method for calculating the step of the roof frame:

1. Measure the length of the roof from end to end.
2. Received distance divided by the maximum step size.
3. The resulting value is rounded up to a larger integer.. This is the number of inter-rafter spans.
4. Divide the total length of the roof by the number of spans. This is the required rafter step size.
5. Add one to the number of spans.This is the required number of rafters.

For some types of roofing material it is desirable to use fixed distances between the rafters, in which case an additional rafter with a non-standard pitch is installed on one of the ends of the roof.

Rafter leg step depending on the material

Can be increased as the strength of the material from which they are made increases. Most often, for each roofing material, the step of the rafters required for it and the permissible sections of the rafter legs, taking into account the load, are indicated.

These recommendations are regional character and are applicable to the central strip of Russia and more southern regions. Before developing a drawing, you should definitely check the level of wind pressure and snow cover in your region, and adjust the pitch and / or cross section of the rafters.

In those regions where the snow load significantly exceeds the wind load, the use of roofs with a slope is recommended. 35 – 45 degrees.

truss system in private houses, it is most often made of logs with a diameter 12 - 22 cm, beam/board thickness 40 – 100 mm and width 150 - 220 mm. When calculating, it is possible to allow the use instead of logs of a certain diameter of bars of the same width, thickness 100 mm.

Rafter structure for corrugated board

Roof structure for ceramic tiles

Ceramic tiles has significant differences from other types of roofing materials, which must be taken into account when designing a truss systems for it:

• 5 to 10 times the weight resulting in doubling the weight of the entire roof. This leads to the need to use the frequent step ( 0.6-0.8 meters) and increased by 25% cross-sectional area of ​​the rafters.
• Fine-grained nature of the material. Increases the requirements for the accuracy of the installation of the transverse battens. The step of the sheathing beam, the permissible sections and installation angles are always indicated in the instructions for each specific tile model.

There are models of tiles designed for installation at an angle. 12 - 60 degrees, ordinary models are recommended to be mounted at an angle 20 - 45 degrees. For crates most often use timber 50x50 mm.

Roof structure for metal roofing

metal tile in fact, it is a less rigid and lighter decorative version of corrugated board, therefore the requirements for the rafter system, in particular for the recommended sections of the rafter legs, are largely the same.

A feature of the truss structure under the metal tile can be called a significant reduction in the pitch of the crate, which should be equal to the length of the longitudinal wave (30 cm for most species). This leads to the need to reduce the distance between the rafters. up to 0.6 - 1 m, to reduce the cost of lumber for the crate. The angle of the roof slope is selected from 22 to 45 degrees.

Rafter structure for ondulin

Ondulin- slate based on fiberglass and bitumen, produced by only one manufacturer and has unified technological installation standards:

• permissible mounting angle - 5 - 45 degrees;
• distance between rafters - 60 cm at a slope angle of up to 15 degrees, up to 90 cm - at an angle of more than 15 degrees;
• crate - solid plywood on a slope up to 10 degrees, board 30x100 mm step by step 45 cm on the slope 10 - 15 degrees, beam 40x50 mm step by step 60 cm on the slope above 15 degrees.

Given the low weight of the material, the cross section of the rafter legs is selected based on the same recommendations as for corrugated board.

Rafter construction under a covering from slate

Slate- traditional, rather rigid and heavy roofing material, fragile, but resistant to constant loads. Such properties change the recommendations for the optimal design of the truss system towards the use of more durable elements and increasing the step between them:

• Due to low tightness, it is undesirable to use slate roofs with a slope angle of less than 22 degrees. If it is necessary to install such a roof, you can use the recommendations for installing an ondulin as an instruction, adjusted for the universal batten pitch - 55 cm.
• Permissible angle for installing rafters under slate - up to 60 degrees.
• The installation step is selected from 0.8 to 1.5 m, depending on the section of the rafter leg, the load and the presence of the crate material.
• The material for the rafters is selected with a slightly larger section than for light roofs. For the most popular move 1.2 m a bar is taken with a section from 75x150 to 100x200 mm, depending on the length of the span between the supports.
• Material for the crate selected in accordance with the distance between the rafters - timber 50x50 mm up to 1.2 m, beam 60x60 mm - 1.2 m and more.
• Lathing step is selected in such a way that each sheet lies on three bars, and has an overlap on 15 cm with neighboring. Considering the standard sheet length 1.75 m, step is used 80 cm.

Rafters for single-pitched and double-pitched roofs

What is the distance of the rafters for a pitched roof? shed roof does not require a complex truss structure. The rafters are laid from wall to wall, most often without the use of a Mauerlat, directly on the crown.

No extra ribs stiffness sets the maximum slope angle - 30 degrees and allowable span length - less than 6 m(for wooden rafters). The optimal angle 15 - 20 degrees.

Such roofs usually not subject to wind loads, but require protection from precipitation. In regions where wind pressure is comparable to snow load, the correct installation of a shed roof “downwind” can lead to self-cleaning of the roof.

gable roof is a system of parallel triangles interconnected by a Mauerlat and a ridge. There are many elements for firmly fastening the sides of the triangle to each other and transferring loads from the rafter legs to the walls - racks, ties, jibs, support beams, and so on.

The step between the rafters of a gable roof is made taking into account the size of the heat insulator that is laid between them. Approximate step between rafter legs 1-1.2 meters

Rigid Triangle Strength increases as its shape approaches isosceles, therefore, with an increase in the slope angle up to 60 degrees you can expand the step between the rafters.

However, this will also lead to an increase in material consumption and to a multiple increase in the windage of the roof. The optimal slope angle for snowy regions is 45 degrees, for windy - 20 degrees.

Distance between rafters roofs attic type determines how much of the load falls on each element. When designing hip roofing step rafters should be between 60 cm and 1 m.

• The correct fastening of the rafters is no less important than the correct calculation of the structure. Before installing the roof yourself, you should take a lesson from an experienced carpenter and read educational literature.
• When choosing a rafter pitch, do not forget about thermal insulation. All types of insulation can shrink a little, so you can buy them by approximate size. The most commonly produced sizes are 60, 80, 100, 120 cm.
• For roofs with a slope of 45 degrees or more, the weight of a person on the roof can be ignored. This removes 175 kilograms of design load per square meter and allows you to put rafters on average 20% less often.
• Snow and wind load in Russian regions can be found by regulatory documents - maps in the application F to .
• There are many online roof calculators on the web., capable of, if not correctly calculating all the nuances, then at least advise on the selection of the correct section for the rafters.

The roof frame must be reliable and durable. But without well-conducted calculations, this is difficult to achieve. In the process of carrying out the calculations, it is determined at what distance to put the rafters on the roof.

What can lead to an incorrect or inaccurate calculation of the loads that the truss structure will undergo? To the most negative consequences, ranging from deformation of the rafter legs and damage to the roof covering and ending with the collapse of the base of the roof frame. Therefore, when designing buildings, the list of mandatory calculations contains data on what should be the distance between the roof rafters. There is a certain technique that allows you to calculate this value.

Method for calculating the distance between the rafters

The distance between the rafters on the roof is called the pitch of the rafters. As a rule, the step of the rafter legs in the roof structure usually exceeds one meter, and the minimum gap varies within 60 centimeters.

The calculation of the required number of rafters for a roof of a certain length and the pitch of the rafters is carried out as follows:

Roof structure for metal roofing

During the construction of suburban private real estate, metal roofing can be found most often. This roofing material is similar to the flooring made of clay tiles, but in comparison with it has a number of advantages. Sheet metal tiles are easy to install, so you can build a roof in a shorter time, the rafter system for metal tiles is also not difficult.

Metal tiles are lighter than ceramic products, the difference in weight sometimes reaches 35 kilograms per square meter, depending on the thickness of the products (read also: ""). Due to a significant reduction in the weight of the roofing, it becomes possible to reduce the thickness of the elements of the truss structure and the cross-sectional dimensions of the lathing bars, and increase the installation step of the rafters.

Under the metal-tiled coating, the rafter legs are mounted with a distance of 600 to 950 millimeters, while the cross section of the construction material is 150 by 50 millimeters. According to experts, in this case, if a heater 150 millimeters thick is placed between the rafters, then such thermal insulation will create comfortable conditions for staying in the attic room. At the same time, for greater reliability, it is advisable to choose a 200 mm insulation.

When installing rafters, to ensure ventilation of the space that is filled with insulation, holes with a diameter of 10-12 millimeters are drilled in the rafters near the upper roof.

The technology for creating a truss system for metal tiles does not differ significantly from structures for other types of roofing materials. The only feature is that at the rafters, the upper support is mounted on the ridge run from above, and not on the side of the ridge beam. The presence of a free zone between the rafters ensures air circulation under the roofing, and this, due to the use of metal material, reduces the risk of condensation.

Shed roof truss system, main advantages and characteristics ").

The distance between the rafters of a gable roof is made taking into account the size of the heat insulator that is laid between them. An approximate step between the rafter legs is 1-1.2 meters (read: ""). Rafters regulate the size of the roof overhang.