Calculating the rafters with your own hands

The rafter system is the "skeleton" of any roofing structure. The reliability, quality and durability of the roof depend on the correctness of its manufacture and installation. If desired, you can handle the truss system independently. Do you want to know how? Read the following instructions!

Kinds of the trussing systems

There are layer and hanging rafter systems. According to statistics, the designs of the nylon type are most often used. With the arrangement of such a system, the rafters abut the Mauerlat. The function of the central part is performed by a simple ridge run. To increase the strength of the system, support beams are mounted.

In the case of suspended rafters, the system design is complemented by additional racks that help to optimize load distribution throughout the roofing area.

Manufacture and installation of rafters of both varieties is carried out in the same sequence, but with the above features and differences.

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rafter system

rafter system construction Any rafter system consists of such basic components:

• rafters. Mounted in parallel with respect to the slopes. Prevent the deflection of the roof structure;
• run. It is a transverse beam, installed longitudinally from above;
• is more durable and racks - supports truss rails;
• struts - components of the trussed truss, which provide additional stability rafters.
  

  Scheme of rafters

Where to make rafters?

Most often the rafters are made of coniferous wood. This is a relatively inexpensive, sufficiently strong and easy-to-handle material

. In the case of self-made rafters, it is best to use a bar with a cross-section of 10x10 or 15x15 cm.

Also, when choosing wood, you need to pay attention to its moisture content. The maximum permissible value is 20%.At higher values, the material will shrink, which will lead to a disruption in the configuration of the entire roofing system.

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Preliminary calculations

We calculate the optimum length of rafters. The standard length of the products of factory production is 450 or 600 cm. If necessary, the length of the rafters can be changed.

To determine the optimal cross-section of the timber, you need to know the following:

• the length of the rafters;
• step of assembling the elements;
• calculated indicators of future loads.

The required information is given in the following table.

Table 1. Selecting the step for installing rafters depending on their length and section

Length of rafters, m	Distance between rafters, cm	Section size of rafters, cm
Up to 3	120	8x10
Up to 3	180	9x10
Up to 4	100	8x16
4	140	8x18
Up to 4	180	9x18
Up to 6	100	8x20
Up to 6	140	10x20

The remaining elements of the roofing system must have the following sections:

• Mauerlat - 10x10 or 15x15 cm. It is also permissible to mount the Mauerlate from a bar section of 10x15 cm;
• diagonal rafter legs and valleys - 10x20 cm;
• tightening - 5x15 cm;
• runs - 10x10, 10x20 cm;
• struts - 10x10 or 15x15 cm;
• filing boards - 2,5х10 cm;
• crossbars - 10x15 or 10x20 cm.
  

  Load calculation for rafters

Knowing the length and section of the rafters, as well as the step of their installation, you can easily calculate the required number of elements, focusing on the length of the wall of the structure.

In addition, the calculation of the rafters for deflection must be performed. That is, you need to know how much the rafters can bend, until they break. For example, in the design of a roof dormer, the calculation of the farm should be made so that the deflection is no more than 1/250 of the length of the section that is subjected to pressure. Based on the above, if the length of the rafters is 500 cm, the maximum allowable deflection value will be 0.2 cm. The figure seems unimportant, but if it exceeds the deflection of the roof, it will be visually perceptible, and this will not be reflected in the design reliabilityway.

Video - Calculating the rafters

Turning the wooden beam intorafters

We make a template, with the help of which further work will be carried out. The rafters are of the same design, so the template will allow you to save energy and time.

pattern. We join two boards along one edge with a nail. As a result, you should get a design that resembles a pair of scissors.

We put free edges of the "scissors" on the supports at the points of future placement of the rafters. This will determine the slope of the roof slope.

Take an extra pair of nails and fix the angle between the boards. On this template is ready. Additionally, fix it with a crossbeam. That the established angle of the slope of the roof slope did not change under the influence of loads, fix the crossbar with screws.

Be extremely careful when creating a template. Even because of the slightest deviations, the entire structure can deteriorate.

Next, we make a new template for the preparation of mounting cuts on the elements of the system. Use a plywood thickness of 0.5 cm. To strengthen, use a 2.5-cm board. The dimensions of cuts should be selected taking into account the section of the rafters used.

With the help of ready-made templates, we make slashes and begin to collect the farm.

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Order of assembling the farm

The construction includes support legs and connecting components. The farm is like a triangle. Do the work in this order, and the finished design will be able to adequately carry all incoming loads.

The farm can be made on the ground with a further rise upwards or directly on the roof. The first option is more simple and convenient to perform.

We assemble the rafters in the following order. First cut the harvested material to the desired size, join the bars with the upper edges and fasten with screws. To prevent the appearance of cracks in the bonding points, we first drill holes in the bars with a diameter slightly smaller than the size of the fastening elements.

We also use bolt for connecting rafter legs. Fixing is performed half a meter below the upper fastening point of the elements. Rigels will help to increase the rigidity of the structure and eliminate the risk of deflection. Fastening of crossbar is performed in the grooves, pre-arranged in rafters by cutting.

If necessary, the rafters are cut at an angle, if required by the features of the roof structure to be fitted.

Installation of trussed truss

Installation of trusses we perform in the following sequence:

• mount the edge trusses;
• fix the central truss.

When installing end farms, we adhere to the following important rules:

• the base of the triangle is installed on the Mauerlat or the upper frame in case of arrangement of the roof of the wooden structure;
• preliminary make several holes in the base for its subsequent bonding with the log;
• is sure to control the straightness of the truss installation. To do this, use the plumb bob fixed on the crossbar;
• the foundation of the truss is fixed only after confirming the smoothness of its installation;
• to ensure additional stability of the farm we fix the jibs from the frame to the rafter leg. The length is chosen according to the situation, it does not matter in principle;
• before tightening the jib with screws, we are again convinced of the straightness of its placement.
  

  Roof truss

  

  Roof truss shroud

  

  Assembling trussed truss

  

  Assembling trussed truss

  

  Trussed trusses installed in the design position

After completing the installation of the outermost trusses, we turn to the fixation of the central and subsequent structures, if their location is stipulated by the design. The optimal step for the installation of the truss is 100 cm.

To fix the central truss triangle, we use temporary jibs. After the visor is installed, the jibs can be removed. Recommendations for securing the central and other farms are the same as in the case of extreme structures.

After installation of all elements of the structure we proceed to fixing the crate and further arrangement of the roofing system: moisture, heat and vapor insulation, and also installation of the chosen finish coating.

Good work!

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