What size rafters to use for the roof. Correct calculation of the roof truss system. Rafter pitch depending on material

The house is the final stage of construction. This is a responsible event on which both the longevity of the building and the safety of the people living here depend. This matter cannot be accomplished without correct calculations.

An obligatory element of the entire system is the rafter leg. It will bear permanent and temporary loads. Therefore, before producing it yourself, you need to familiarize yourself with all the details of this process. There are certain norms and rules that govern the arrangement rafter system.

general characteristics

The rafter is the main supporting structure. It bears the main load. To ensure the reliability of the system, each rafter leg is rigidly attached. This allows the roof to withstand gusts of wind, snow drifts and other impacts.

The material for such structural elements is most often wood. It is easier to adjust, and the cost of work is significantly reduced. Should be given Special attention special antiseptic and fireproof impregnations.

Tilt angle rafter elements equal to the slope of the roof slopes. The bottom rests on the mauerlat. This allows the load to be evenly distributed. The top of these elements rests on a beam under the ridge or intermediate supports.

Rafter legs are sometimes also called diagonal or slanted legs, or simply rafters.

Load

The rafter leg is subjected to various loads. These are permanent and temporary varieties. The first group includes the total weight of the rafter system, as well as other roofing materials (vapor barrier, waterproofing, roofing felt, slate). This also includes elements interior decoration rooms or attics.

Live loads can arise due to the most various reasons. They can only be calculated approximately. In this case, the maximum possible amount of precipitation that can be observed in this climatic zone is taken into account. Gusts of wind can also affect the roof. If in this area they are long lasting and have great strength, this feature should be taken into account when calculating.

It is necessary to take into account the weight of the people who will perform construction or maintenance of the roof in the future, as well as the total size of their tools. Take into account the load that will be exerted optional equipment(chimney, antenna, aerator, ventilation, etc.). If additional structures are installed on the roof, their weight is also taken into account.

Calculation rules

To perform a calculation rafter leg, after assessing the load, you should decide on the type of material, as well as the type of roofing system. It can be suspended or layered. In the first case, the rafters have two points, but where the outer supports stand. This creates a horizontal bursting force. perform compression and bending work. To reduce this force, they are connected using stretching.

The layered type of construction is applicable in buildings with an average load-bearing wall or intermediate supports, the ends of which are adjacent to the external walls. In this case, the rafter leg performs only a bending function. At the same time, overall material costs are reduced. But such a system is suitable only for those buildings in which the supports are spaced no further than 6.5 m from each other.

When performing calculations, the angle of inclination of the roof is also taken into account. At this stage, they also think through everything additional elements systems.

Length

The length of the rafter leg is also calculated in accordance with all existing operating conditions of the roof. Initially, you should determine the size of the building itself. In this case, all projections, verandas, and attics that the building plan contains are taken into account.

Next, the shape and slope of the roof are thought out. Next, based on the data obtained, choose the length of the rafter leg. Usually this figure does not exceed 6 m. This is due to the standardization of lumber that goes on sale. To purchase longer varieties of products, you will have to shell out a decent amount of money.

If necessary, these structural elements are increased. The need for long rafter legs sometimes arises when arranging hip, half-hip or diagonal rafters.

Section

After calculating the length, it is necessary to determine the cross-section of the rafter leg. Its type is influenced by several factors. All operating conditions specific to the roof will play a role in this process. The level of loads, the slope of the roof, and the type of roof must be taken into account when choosing a section. An important factor is total area buildings, its configuration. The more factors that influence the operation of the building, the wider the cross-section of the rafters should be chosen.

Also, do not forget to take into account the features climate zone. It is important to immediately plan what material is used during the construction of the rafters. Most often this is wood. She must be good quality. for rafters should be 20-22%.

Today there are many special programs, which allow you to calculate the cross-section of the rafter leg. To avoid mistakes, you should use them. But it is better to entrust this work to a professional. The most popular section size is 50 by 150 mm.

Laying step

The rafter leg, the dimensions of which were calculated in accordance with building regulations, requires correct installation. To do this, you will need to calculate the laying step of these structural elements.

In this matter, an important role is played by the load that the factors listed above exert on the roof. By correctly choosing the parameters of the rafters using special tables, you can calculate the laying step. At standard size section (50 by 150 mm) and a length of 3 m, the distance between the rafters will be 1 m.

If the load level is high, it is better to reduce this indicator. This is especially true for slate roofing. If rafters with a standard cross-section but 4-4.5 m long are used, the pitch between structural elements is reduced to 60 cm.

The slope of the roof is also important in the calculations. For example, with a slope of 45 degrees, the pitch of the rafters can reach 120-140 cm. But in the event of a fall in this area large quantity precipitation, this figure is reduced to 60-80 cm.

Installation Basics

The rafter leg assembly consists of several elements. These include crossbars, racks and struts. Their participation in a system of small width is especially important. If this is not done, over time the rafter structure may sag. Therefore, in such cases, a special grill is installed.

The legs of the rafters, as you know, rest on the mauerlat. It is placed across the entire width of the building or placed only under the bottom of the structural elements. If the rafter system is wooden, the mauerlat is made of logs or timber. This is the top of the log house. But in brick buildings the Mauerlat is installed flush with the inner surface of the walls. A layer of waterproofing is laid between them.

Installation of a conventional roof

The rafter leg and the mauerlat protrude very important elements the entire structure. The quality of the roof depends on the correct installation. They can be attached in two ways. Installation can be rigid or sliding. The right variety selected according to the type of rafter system (sloping, hanging).

The rigid type of fastening ensures the immobility of the structure. At the same time, cuts are made on the rafters. Structural elements are secured with metal brackets, angles, wire or long nails.

A sliding joint is also called a hinge joint. If it is necessary to ensure freedom of settlement wooden elements for a log house, this type of installation is preferable. A notch is made on the rafter leg and secured to the mauerlat with two nails. They are driven in at an angle. Another nail is driven in from above.

Hip roof installation

When settling in hip roof The rafter leg is often longer than 6 m. This requires extension. Two rafter boards are paired. In this case, they need to be strengthened. This procedure involves arranging struts. These are vertical racks, of which no more than 2 pieces are installed in the structure.

These reinforcements rest on a wood backing. It is mounted on the ceiling or on a tie. Diagonal rafter elements are always longer than ordinary ones. They are subjected to a load that is 1.5 times greater than normal. Therefore, the amplification procedure in this case is simply irreplaceable.

Having become familiar with such an element as the rafter leg, every novice builder will be able to delve deeper into the process of constructing a roof. By complying with all building codes and regulations, high quality construction can be achieved.

The construction of any house ends with the construction of a roof, for which it is necessary to make a rafter system. Its design includes: Mauerlat, rafter legs, struts, tightening, sprigs, racks, trusses, sheathing and other elements that provide rigidity and strength.

Rafter leg in different designs roofs can be called slanted (diagonal) or ordinary rafters. The dimensions of the rafter leg are selected based on the constant and variable loads that will subsequently affect the roof. This is necessary to ensure that the rafters are strong enough to withstand the impact.

• coating weight;
• mass of other elements truss structure;
• weight of hydro and vapor barrier materials;
• a lot of ceiling finishing if there is an attic room.

Characteristics of rafter legs

Based on the calculation of loads, they choose - the dimensions must be such that they can withstand the planned impact. In this case, pay attention to the type roofing, view of the roof. Rafters can be layered or hanging; complex roofing systems consist of both types.

IN hip roofs In addition to the rafter legs, they also use shortened rafters - sprigs, which also have to be calculated. It is necessary to calculate the dimensions of additional elements of the rafter system - tie rods, racks, struts, crossbars, since part of the load from the rafters is transferred to them.

The length of the rafter leg is determined based on the parameters of the building and the roof slope, which depends on the selected type of roof. The size of roof rafters usually does not exceed 6 meters in length, since lumber of longer lengths is not commercially available. But it happens that the dimensions of the house require the use of elements of greater length - in this situation they are increased (read: ""). Long rafter legs are most often found in diagonal parts, during the construction of half-hip or hip roofs.

The selection of the rafter leg section is influenced by various factors:

• slope of slopes;
• type of coating material;
• house dimensions;
• roof type;
• climatic features of the region;
• the quality of the material from which they were made.

To create a rafter system, they usually use conifers wood When choosing, you need to pay attention to the fact that there is no blue stain or a large number of knots on the beams or boards.

The humidity of the raw materials should be no more than 20-22%, since an overly wet tree will change in size during drying, and this can cause a violation of the roof’s tightness and other adverse consequences.

It is advisable to entrust all calculations related to the rafter system, including, to a specialist - currently there are enough enterprises that provide this service. You can also find ready-made programs on the Internet that allow you to calculate rafter legs - their length and dimensions. You only need to enter the data necessary for the calculation into the program, and the program will calculate what the section, length and should be.

When constructing roofs of private houses, boards are often used. The size of the rafter boards is such that the cross-section is 50x150 millimeters - they are suitable for roofs various designs. The pitch of the rafter legs is approximately one meter - this distance depends on the type roofing material, roof slope and amount of snow in winter.

If the roof slope exceeds 45 degrees, then the rafter pitch can be 1.2 - 1.4 meters. If the region is characterized by winters with a lot of snow, then the pitch between the rafters will be 0.6 - 0.8 meters.

Much attention should be paid to the type of roofing material. The most severe is natural tiles. The greater the length of the legs of the rafters and the step between them, the larger the cross-section will be. The dimensions of the timber for rafters are usually 150x150 millimeters.

Installation of rafter legs

It is very important to correctly attach the rafter legs to the mauerlat. The strength and reliability of the roof depends on how it is done with the Mauerlat. There are two mounting options - rigid and sliding. Each of them fits certain rafters - hanging or layered.

Rigid fastening makes any turns, movements or bends of the rafters impossible. To do this, make cuts on the rafters and secure the leg with the Mauerlat using wire, metal staples or long nails. You can also use metal corners.

A sliding joint (also called a hinged joint) can have two degrees of freedom. It is usually used when constructing roofs over wooden house, since it allows the roof to settle over time on the frame, which shrinks over the first few years. In this case, the connection of the rafters to the ridge is not made rigid. With this method, the rafter leg is joined to the mauerlat by sawing and strengthening on both sides with two nails driven diagonally or opposite each other. It is also possible to hammer one nail into the rafter leg from top to bottom, penetrating into the mauerlat (read also: "

To strengthen them, they make struts in the form of vertical posts. More than two racks are rarely installed. To strengthen the slanted rafters, a strut or stand is also installed, which should rest on a wooden lining located directly on the ceiling (in the case of a reinforced concrete slab) or on a tie, which is also ceiling beam. The struts are supported on a bench and placed at an angle of 45 to 50 degrees. Their main purpose is the ability to take on the maximum load from the rafters.

In order to calculate the roof truss system, a person who is not familiar with all the nuances of complex design calculations in accordance with SNIP and other standards can use our roof construction calculators.

As initial parameters, it is necessary to enter the data of some elements of the rafter system:

• indicate the pitch of the rafters (the distance between them - the step regulates the load on the rafter system),
• rafter dimensions - the so-called section = thickness x width of the board or beam

It’s worth saying here that the board is more affordable option for installing a roofing system, since it can withstand loads, and, importantly, costs several times less.

In the two tables below we have collected Dimensions of rafter legs and sheathing often used in construction broken down by type of roofing. Minimum angle The optimal slope of the roof is also given depending on its type, in some places the minimum angle is indicated, but everything is in accordance with SNIP.

The main most commonly used parameters of the elements of the rafter system are the pitch and cross-section of the rafters, the angle of inclination of the roof depending on the type of roofing material:

Calculate the rafters gable roof V automatic mode The rafter calculator on our website will help you.

The following table contains data on lathing, counter-lattice and according to the roofing material:

In order to independently determine the dimensions of the entire rafter system, it is necessary to calculate the main influence of wind, snow masses, as well as the weight of roofing materials and structural load-bearing elements roofs in total.

Again, we remind you that the calculation is presented for reference in a significantly simplified format, since for an accurate calculation it is necessary to take into account the vertical and horizontal loads on the rafter legs, additionally calculate the resistance of the rafters to bending, compression and tension, and check the structures for their ability to withstand chipping and crushing.

If you do not have a complex architectural structure, you can easily build a roof yourself, based on optimal sizes timber or boards, to standardized roof design parameters.

The figure and table below indicate standard sections of elements truss structure:

Let us repeat once again that in a simplified format, everyone is capable of calculating the ability of a roofing system to withstand loads.

ABOUT online roof calculators will help you calculate the amount of timber, roofing and sub-roofing materials for the construction of the roof and rafter system, as well as the parameters of the roof, sheathing and rafter legs.

This way you can roughly estimate how much building materials you need to purchase how and in what quantity the sheathing and rafters will be placed.

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The rafter system is a structure that provides the strength of the roof and serves as the basis for laying roofing material. It is shown in the photo.

The roof is a load-bearing structure that performs following functions:

• makes the building beautiful appearance;
• takes on external loads;
• protects the attic from the outside world;
• transfers the load from the sheathing and the material on it to the building walls and internal supports.

The main elements of the roof include sheathing, rafters and mauerlat. also in load-bearing structure includes additional fastening elements - crossbars, racks, rafter struts, spacers, etc. The reliability and strength of the roof is most influenced by the rafter system. Rafters are the main load-bearing part of the roof. The rafter system bears the weight of not only the roof covering, but also the snow cover and wind pressure. It must withstand all these impacts, so the calculation is made taking into account the type of roofing material and climatic features region.

Rafter system design

Connecting the rafters to each other gives rigidity roof frame, and the result is a strong rafter structure. The load on the rafters can be quite significant, for example, during strong wind, so the frame is tightly connected to the building frame.

In the construction of private houses and cottages, wooden rafter systems are usually used, which are easy to manufacture and install. If mistakes were made during the construction of the walls, these products can be easily processed: shortened, extended, hemmed, etc.

During installation, fasteners of the rafter system are used: bolts, screws, clamps, nails, staples. They are also used to strengthen the load-bearing roof structure. The interconnected elements of the roof create a truss, which is based on triangles, which are the most rigid geometric figure.

When choosing a material for the manufacture of a rafter system, it is necessary to take into account the structural and architectural nuances of the project. Do not forget about antiseptic and fire impregnation for them, since this affects the durability of the roof.

The system consists of rafter legs. The rafters are installed at the slope angle of the roof slopes. The lower sections of the rafter legs rest on external walls with the help of a Mauerlat, which promotes uniform distribution loads. The upper ends of the rafters rest on a beam under the ridge or on intermediate supports. Using a system of racks, the load is transferred to load-bearing internal walls.

Types of rafters

The design transmits a significant horizontal bursting force to the walls. In order to reduce the load, a stretcher is used to connect the rafter legs. It is done either at the base of the rafters or at a greater height. The brace at the base of the rafters is also a floor beam - this is important when creating mansard roofs. When increasing the height of the brace, it is necessary to increase its power and ensure that it is securely attached to the rafters.

Part layered rafters includes: rafter leg, mauerlat, headstock, strut, tightening. This type of rafters is installed in buildings that have a middle load-bearing wall or intermediate supports in the form of pillars. Elements of this design work only in bending, performing the function of headstocks. The weight of the layered rafter system is less, and less materials are also required, so it is cheaper than a suspended system.

Installation of a layered system is done if the supports are no more than 6.5 meters apart from each other. If there is an additional support, the rafters sometimes cover a width of 12 meters, and if there are two supports, up to 15 meters.

Rafter legs most often rest not on the walls of the building, but on a special beam - a mauerlat. This element can be located along the entire length of the house or placed only under the rafters. If the structures are wooden, for the mauerlat they take a log or timber, which is the upper crown of the log house.

At brickwork wall mauerlat is installed flush with inner surface walls are timber fenced from the outside with a masonry projection. A layer of waterproofing is laid between this element and the brick - for example, you can put roofing felt in two layers.

If the width of the rafters is small, they may sag over time. To prevent this from happening, use a grid consisting of a rack, a crossbar and struts. At the top of the structure, a purlin is laid that connects the rafters or trusses. This is done regardless of the type of roof. Subsequently, the roof ridge is made on this run. In places where there is no load-bearing walls, the heels of the rafters rest against the side purlins - longitudinal beams of considerable power. The dimensions of these parts depend on the expected load.

When building private houses, rafters made of logs are used - they are lighter. To create roofs on multi-storey residential buildings and industrial buildings metal rafters are used.

Installation of rafter systems

The slope angles of the slopes are selected based on the type of building and the purpose of the attic space. The amount of slope is also influenced by the material chosen to create the roofing.

If roll products are to be laid, the angle of inclination should be 8-18 degrees. For tiles required angle equal to 30-60 degrees, for roofing steel or asbestos cement sheets - 14-60 degrees.

The installation of the rafter system begins after the construction of the load-bearing walls of the house (more details: ""). The design of the rafters of a log house differs significantly from systems for houses made of foam aerated concrete, brick, frame wooden or panel houses. The differences are significant even with the same shape, type and type of roof. As for how to treat the rafter system, it is necessary to use antiseptic and fire fighting equipment so that the roof lasts for a long time.

The main elements of the supporting structure are the sheathing. The roof is outer part roof, which is laid on a supporting structure consisting of sheathing and rafters.

To produce rafters, material of a certain size is taken. Thus, the thickness of the rafters (section) is most often 150x50 and 200x50 millimeters. For lathing, beams and boards measuring 50x50 and 150x25 millimeters are usually used. The distance between the rafter legs is on average 90 centimeters. If the roof slope is more than 45 degrees, this step is increased to 100-130 centimeters, and if a huge amount of snow falls in the region, then it is reduced to 60-80 centimeters.

To make more accurate calculations regarding the gap between the building legs, you need to take into account their cross-section, the step between the supports (struts, ridge run, uprights), and the type of roofing material.

The floating rafter system is attached using special brackets, allowing the rafters to “sit down” along with the shrinkage of the gables and not hang over the ridge log.

In mountainous areas, the chalet rafter system is popular (more details: ""). A feature of this design is the significant protrusion of the roof beyond the load-bearing walls. Sometimes such a protrusion reaches two to three meters, and the angle of the roof slope is small. Snow does not linger on such a roof, so it lasts a long time. But the best option is a roof overhang of 1-1.5 meters (read also: “Characteristics and design of roofs: rafter systems”).

The installation of the rafter system must be carried out in strict compliance with all requirements. If you have no experience in construction, it is better to entrust the construction of the roof to specialists, since this is not an easy task, and the slightest mistakes can lead to its collapse.

Acquisition the right material– one of the most important aspects of any construction. When constructing a rafter system, you need to understand that it has a lot of responsibility, so to create such a structure you should use only reliable, high-quality raw materials. You can buy ready-made roof trusses, or you can make the necessary parts from logs or other material yourself. The dimensions of the rafters, methods of their installation, fastening elements and other nuances should be chosen individually for each building and rafter system.

There are three standard options for purchasing rafter boards; it is worth considering the pros and cons of each of them:

• Cubic meters of lumber. Buying wood in cubic meters is a completely acceptable way; to do this, you just need to order the required number of cubic meters of timber or boards from a specialized company. Next, they will still need to be cut and processed, only after that can construction begin. In this case, it is worth taking into account waste when processing wood, so it is better to take about 10 percent more than calculated according to the construction plan.
• Custom cut boards. The next option is to purchase ready-made rafters after cutting. Now many companies are engaged in cutting wood to order according to given parameters; builders will only have to assemble the rafter system on the roof. There will be practically no waste here, and the process of constructing the structure will go wherever faster.
• Ready-made roof trusses. This option easier than the first ones two. Such structures are easier to install on walls directly on the roof, which will reduce the time of assembling the entire structure to one or several days. This truss only needs to be installed and connected at the ridge. The amount of waste is minimal, but the price of this option is noticeably higher.

For self-made rafters, it is enough to know their necessary parameters, such as angle of inclination, distance, cross-section, fastening method, and so on. In order to calculate right size rafters, use carpentry tools. Modern special construction calculators carry out these calculations extremely quickly.

Requirements for lumber

When calculating a rafter structure that involves the production of rafter legs from boards, in addition to all dimensions, it is also extremely important to take into account the quality of the lumber used. First you need to decide which wood is best suited for rafters. Here the answer is clear - this is deciduous and coniferous lumber that meets the requirements of GOST 2695-83 and GOST 8486-86. Based on these standards, a board for making rafters may have:

• Non-through cracks not exceeding half the board in length;
• No more than three knots per linear meter material, while the maximum permissible knot diameter is 30 mm;
• Humidity no more than 18% (according to moisture meter readings).

According to the requirements of SNiP, when purchasing lumber for the production of rafters and other components of the roof frame, it is imperative to check the documents informing about the quality of the purchased products. They should indicate:

• Product name and standard number;
• Manufacturer's name with basic information about him;
• Type of wood, size of lumber, degree of humidity;
• Date of release of the product batch;
• Number of units per package.

Wood is natural material, so it is quite susceptible to biological destruction. To reduce the risk of damage to the structure assembled from this lumber, it must be prepared before installation. Preparation involves carrying out various constructive and protective measures.

The protective ones include:

• Impregnation of wood with special fire retardants to prevent the possibility of fire;
• Treating wood with antiseptic compounds to prevent premature decay;
• Treating rafters and other wooden elements with pest protection products.

Constructive measures include:

• Formation of waterproofing under the roof and vapor barrier on the side of the room;
• Installation of waterproofing gaskets at junction points wooden structures to brick;
• Roof pie ventilation equipment.

Rafters made from boards, subject to all prescribed roof construction technologies, will last a long time without any repairs.

Rafter dimensions

The choice of cross-section and length of rafter elements is extremely important. All rafter legs must be of the same length and thickness, which depend on the pitch of the rafters and the expected load on them. The materials for rafters are logs, beams or boards. The disadvantages of log rafters include their considerable weight and the need to make complex cuts for fastenings, which significantly weakens load-bearing capacity designs. Timber is more suitable for making rafters, but it costs more than boards.

Important! For rafters most the best option is a timber that has been aged for some time: it does not change shape after the construction of the roof, which ensures the stability of the structure. A beam 10–15 cm wide is used, and its thickness should be about 5 cm.

Rafter legs made of boards - best choice, this material very popular and actively used to create side rafter legs. It is also convenient to make elongated side rafters and strong slanted rafter legs from the board.

The thickness of the board significantly affects its characteristics. Regular board, suitable for making rafters, has a thickness of 40-60 mm.

Important! It is worth noting that when constructing roofs on outbuildings, it is better to take 40 mm thick boards, this will help reduce costs. When constructing the roof of a residential building, this parameter should not be lower than 50 mm.

The width of the rafter board is selected depending on the length of the opening to be covered - the longer the rafter leg is, the wider the board is needed for its production. When the length of the rafters does not exceed 6 meters, for their manufacture you can take a board 150 mm wide - that is minimum size The cross section of the rafters for the roof of a residential building is 50x150 mm. If the rafter leg is more than 6 meters, then the width of the board should be at least 180 mm. The elongated leg is made from cohesive boards, the width of which is 150 mm.

Another important parameter is the cross-section of the rafters. It depends on the loads on the roof: both from external weather conditions and from the severity of the rafter system itself. The calculation of the section is also influenced by the angle of inclination of the slope, the width of the building and the length of the opening to be covered. For calculations, special formulas and tables are used; there are many corresponding computer programs. Having determined the cross-sectional value of the rafter legs, it is worth paying attention to the installation features of this structure.

Features of installation of rafter legs

After selection optimal material for the rafter system, adjusting the dimensions of the rafters, going through all stages of their processing, it is also necessary to correctly install the rafter legs on the mauerlat. The strength and reliability of the entire structure largely depends on this connection. There are two mounting options - sliding and rigid. Each of them is applicable to a specific type of rafters, and its choice depends on many factors.

Rigid fastening eliminates the possibility of any turns or bends of the rafters. For it, cuts are created and the rafter legs are secured to the Mauerlat using various fasteners.

A sliding joint, also often called a hinge joint, has a couple of degrees of freedom. It is usually used when constructing a roof over a wooden house, since it allows the roof to settle on the frame over time, which gives a certain shrinkage in the first few years. In this case, the connection between the ridge and the rafters is not made so rigid. The rafter leg is fixed to the mauerlat by sawing and strengthened with nails on both sides.

When constructing a hip roof, the slanted rafters can be more than 6 meters in size. Because of this, the rafters are increased in length. To strengthen the rafter legs, struts are made for them from vertical posts. More than two racks are rarely installed in this case.

Many people have the following questions: how to make rafters with your own hands, how to install rafters correctly, what is the best material to choose for them, and so on. Now you can find a lot of information on this subject in various sources and do the work yourself. If any questions arise and you cannot cope on your own, then it is better to turn to the services of professionals, whose reliability there is no doubt.