The roof structure of any house must be extremely reliable and durable, otherwise the entire building will be endangered. That is why experts recommend to pay close attention to the roof truss system, to carry out a preliminary calculation. It includes the choice of the type of truss system, the accounting of all loads, the selection of suitable crates for roofing. From this will depend on the strength, durability, reliability of the entire structure.
Diagram of the truss system of a sloping roof.
Elements of the truss system
- mauerlat, which allows you to properly distribute all loads, for this purpose a wooden bar with a cross section of 150 * 150 mm is used;
- truss legs that serve as a solid frame;
- ridge - board that connects the roof slopes;
- the fillies are a continuation of the rafter legs;
- roof overhangs are a continuation of the slopes;
- racks, struts, tightening - elements of strengthening the truss system;
- the crate serves as a framework for laying roofing material.
What is taken into account when building a truss system?
When calculating the truss system of the roof, it is taken into account which material will be used, which architectural features and loads will be observed.
Schematic of hanging trusses.
During the calculation, such moments are taken into account:
- The design of the gable roof should have a slope of 5 degrees, in some cases it is up to 90 degrees.
- If the house is being built in an area where there is heavy rainfall, then the angle should be 35-40 degrees. This will allow precipitation not to linger on the roof, as a result, the design is obtained as protected as possible. With such an angle of inclination to do the used attic or mansard room is no longer possible. In this case, a broken roof is designed.
- With strong wind loads, flat roofs should be made, the slope can be up to 15-20 degrees. Then the design will be as protected as possible.
- During the calculation, it is taken into account that a roof that is too steep has a greater sail area, and this can be dangerous.
Installation of truss legs
After the calculation of the pitch and cross section of the truss system has been made, the installation can be started. For a gable roof, it is best to use rafters with a cross section of 50 * 150 * 6000 mm . The width of one board should be 180 mm, since a large length reduces the strength of the board. The installation of roof rafters is carried out as follows:
Options for attaching rafter legs.
- First, a template is cut out, according to which all truss legs will be made.
- It is necessary to cut rafters from the prepared material, to perform lower gouges.
- When installing roof rafters, it must be remembered that they are installed in pairs. This allows you to immediately reduce the load on the horse.
- For long slopes boards have to be increased. To determine the overall size requires careful calculation, which will show how long the boards will be, at what point they will be mounted. According to the rules, the extension is carried out for boards with a length of 1.5-2 m, the joint is always at the bottom, a special stand is installed under it.
- Rafter legs are fastened with nails, it is important not to forget about supports.
- If the construction of a mansard roof is necessary, then intermediate racks should be used, which are also the basis for the construction of the side walls.
- The pitch of all beams must be determined at the design stage. This calculation is performed using special programs. If there is no confidence in the correctness of their use, it is better to contact the experts.
Stiffness of truss
Any truss structure must be sufficiently rigid to withstand a variety of loads. To make a gain, you must perform the following steps:
- If the roof system is made for a small structure, for example, for a country house, bath, any household building, then the reinforcement is performed by puffs connecting each separate pair of truss legs. On top of the legs are connected bolts.
- For larger homes, construction should be more durable. The calculation includes the use of not too massive roof, which will rely directly on the walls. With a building width of 6-8 m, the structure is tightened even more. In the middle it is already necessary to mount the supports, which are also called attendants. They are placed near each truss pair.
- If the truss system has spans up to 10 m, it is necessary to use special reinforcing beams. They should be in the middle of the truss foot or as close as possible to the ridge board. Grandmas fasten the lower end to the rafters.
- For a long roof, the calculation is not complete without taking into account reinforcing braces.The upper end of the brace should rest against the corner of the gable, and the lower end should be mounted on the ceiling beam. To fix the entire structure, it is necessary to use a bar with a large cross section.
- For the construction of the roof in areas with strong wind loads, it is necessary to use diagonal connections, mounted from one edge of the rafter to the other.
When deciding how to strengthen the truss structure, it is necessary to single out the correct calculation of fastener elements.
Nails cannot be used in this case, even if their length seems sufficient.
They will not be able to provide the necessary fasteners. Only special parts are used, such as spikes, galvanized screws and so on.
How to make a batten?
A batten is the last, final stage of the construction of the roof structure before you start laying the selected roofing. The batten can be a solid slab of OSB or plywood, fiberboard, or it can be constructed in the form of wooden slats of the required size.
The calculation and choice of the batten depends largely on which coating will be used. For example, a continuous crate in the form of slabs is used for bitumen shingles, but a system of wooden slats is suitable for metal tiles.
Mounting scheme for roof lathing.
Installation procedure for the lathing of the roofing system:
- First you need to choose the right beam for the manufacture of the lathing, if it will be made in the form of rails with a certain step. The tree must be dried, not have knots, cracks and other defects. Starting to nail all the bars is necessary only from the bottom, and near the ridge of the roof to arrange the flooring of 2 boards, so that there is no gap. It is important to make the crate in such a way that it can withstand all the loads perfectly, the crate system should not have any deflections. That is why, before starting the installation, it is necessary to calculate the cross-section of the beam, its pitch.
- If a truss system is to be installed for soft roofing, then a completely different type of crate should be used. We'll have to make part of the design discharged, and the second layer - solid. The construction itself is performed a little differently. First, parallel to the ridge, you must put boards with a thickness of 25 mm and with a width of up to 140 mm. The gap between the roof boards is allowed no more than 10 mm. After that, a continuous layer of plywood is laid on the boards on top, which will act as a batten under a flexible roof. It is important that when fastening the heads of nails and screws do not protrude above the surface.
- If metal roofing is used as the roofing material, then a timber will be suitable, the cross section of which is 50 * 60 mm. The step between the bar will be 10-50 cm, it all depends on the type of roofing and what is the construction of the roof itself. All caps screws and nails must be embedded in the surface of the wood so that they do not cause damage to the roof covering.
The rafter system of the house requires utmost attention. This applies not only to the choice of system, but also to crates for the selected roofing. Only in this case, the roof will be strong and durable.