Diy rafter roof system - device and installation

Properly constructed and assembled according to the technology, the roof serves as a barrier to prevent cold air and moisture from entering the house. From the outside, with the naked eye, we see only a small part of the structure - the roof covering. But the roof frame, which is the most important component, performs the basic support functions and takes on the effects of wind and snow loads.

So that it does not deform as a result of operation, it is necessary to correctly calculate the size of the cross section of its elements and determine the distance between them, taking into account the weight of the roofing material, slope and climatic conditions. In this article we will tell you what the rafter system of a gable roof of a house is, what it consists of, how it is designed and assembled with your own hands.

What is a truss system?

The rafter system for a gable roof of a house is a system of interconnected supporting elements, which together form the framework of the structure. It is made of wood or metal in accordance with the calculation of the loads that will affect them during operation. The roof frame of the roof performs the following functions:

1. It gives roof slopes the necessary slope. The traditional form in the form of an equilateral rectangle of a sloping roof is attached by the rafter frame, which forms the slope between the base of the roof and its ridge. The angled surface allows snow and water to slide freely from the ramp.
2. Distributes the load on the weight of the roofing pie. The weight of the roofing pie, taking into account the snow load, can reach up to 500 kg / m2, therefore the double-slope roof is subjected to intensive load, especially in the winter period. The rafters of the gable roof evenly distribute the weight that lies on them, and then transfer the load to the supporting walls and the foundation of the house.
3. It serves as a basis for fixing thermal insulation and roofing material. The roof frame of the roof serves as a kind of skeleton of the structure around which its “body” is built. Thermal insulation should be installed between the rafter legs, and a roof covering that protects against moisture penetration is fixed on the batten.

Please note that the design of the truss roof system of a sloping roof is rather complicated for design and assembly, especially if the master lacks experience. After all, in order to be able to withstand intense loads, it is necessary to correctly calculate the section of the rafters and the step of the rafters, taking into account the slope and length of the slopes, the used roofing material, and also to make a drawing on which the assembly will be performed.

Kinds

Rafter systems differ in many factors, their composition depends on the layout of a wooden or brick house, the total weight of the roofing pie, the material from which the frame is made, and the type of roof covering. An important characteristic of the design is their bearing capacity, which determines how much weight they can sustain without deformation. The characteristic features distinguish the following types of roof systems:

• Наклонная. The rafter frame of the nylon type is called the frame, the rafters of which have 2 points of support. The upper end of the foot rests on the ridge girder mounted on vertical pillars fixed to the inner wall. And the lower end of it is installed on the mauerlat. Assembling a truss system of a slant roof type on a sloping roof is possible only if there is at least 1 carrier partition or capital column inside the house. Rafter legs of the hull type experience only bending, which can be eliminated by various struts. The suspended rafter system allows to block houses up to 14 meters wide.
• Hanging. A hanging truss system is distinguished by the fact that its rafters are supported only by the lower end of the power rail mounted on the external load-bearing walls. The upper end of the truss legs of this design does not rely on anything, but hangs in the air, as it were, because of which there are 2 types of load: bending and bending. The bursting load of such a layout of the elements on the outer walls is so great that it has to be compensated with the help of numerous bolts and ties, due to which the rafter pairs are tied together. . It is believed that the complexity of the hanging rafters mounting scheme is much higher. The truss system of a dual-slope roof is assembled with its own hands without difficulty, if you correctly calculate the step of the rafters, that is, the distance between the rafters and the size of their section.

Important! Sliding roof frame is another type of frame, which is distinguished by the fact that truss legs are mounted on the power plate not using a rigid attachment, but using a movable support. Sliding fastening allows the roof to change the dimensions in the course of shrinkage of a wooden house within the power reserve range.

Composition

The structure of the roof system of a dual-slope roof of any of the listed types is a combination of auxiliary and supporting elements. They evenly distribute the weight of the roofing pie, and also compensate for the bursting and bending loads that occur between them.

The section, length and step of the rafters are determined using engineering calculation, taking into account the weight of the roofing pie, the climatic conditions in the construction region, as well as the slope of the structure. The structure of the rafter frame of a dual-pitch roof usually consists of the following elements:

1. Reward. Mauerlatny timber set on the outer walls of the house, on which the roofing ramps. It serves to soften the pressure on the supports and to evenly distribute the load on the weight of the roofing pie. It is made of durable timber with a section of 150x150 mm or 200x200 mm and is attached to the upper belt of the walls using anchor bolts or long metal studs.
2. Sill. This is an analogue of the mauerlat, only it is installed on the internal load-bearing walls, and on it it is necessary to expose a vertical resistant for mounting a ridge purlin.
3. Rafter legs. This term refers to the elements of the frame, which are made of boards with a cross section of 150-40 mm and set at an angle to the base of the roof, forming the angle of inclination of the slope. How to make the distance between the rafters, their length and thickness is determined by means of calculation, taking into account the cumulative loads to which they are subjected during operation.
4. Tightening. Tightening is called beams, which are placed horizontally and connect the legs of one truss pair to each other in order to reduce the shearing load on the external walls of the structure. The bolt is a puff set under the very ridge of the structure.
5. Racks. The rack is called a vertical bar, set on a log to support the ridge girder. Determining what distance should be between the posts is simple, because it repeats the rafter step.
6. Подкосы. Diagonally arranged props supporting the rafter legs in the middle or in the lower part, preventing them from bending, are called braces.

Please note that to determine how to properly arrange the elements of the truss system can only calculate the temporary and permanent loads to which they will be subjected during operation. The calculation of the total weight of the roofing pie helps to determine the correct distance between the rafters, to calculate their length and the required thickness.

Payment

The calculation of the roof system of a dual-slope roof is based on the fact that in the frontal dimension it has the shape of an equilateral triangle, the sides of which can easily be calculated using simple trigonometric formulas. These simple calculations help determine the optimal distance between the rafters, their thickness and length. The design calculation is performed in the following sequence:

• Determine the design and slope of the roof. There are various ways to choose the type and deviation of the roof structure. This parameter depends on the climatic conditions and operational characteristics of the selected roofing material.
• Determine the total load on the structure. To do this, add constant loads (the weight of the roof covering, its weight of the frame, thermal insulation and floors) with temporary loads (snow load, wind load), multiply by a correction factor taking into account the slopes of the slopes, and then add to this figure 10-15% to the frame had some margin of safety.
• Calculate the length of truss feet. To do this, use the Pythagorean theorem, because the roof truss is an equilateral triangle. It turns out that the square of the length of the truss foot is equal to the sum of the squares of the height of the blood and half the length of the foundation. Knowing how to calculate the length of the rafters, you can calculate the height of the ridge.
• Determine the cross section of the elements. The optimal cross-section of elements is chosen according to the tables in accordance with the length of the rafter legs and the distance between them. The more these indicators are, the thicker the rafter should be.

Remember that before you calculate rafters on the roof, you need to decide on the basic design parameters. In particular, it is necessary to know exactly the height of the ridge and the slope of the roof, as well as the dimensions of the room to be covered. The result of the calculation of the elements of the roof should be a detailed diagram of the truss system, reflecting their dimensions and the angles between them.

Assembly technology

Before you install the roof frame, you must calculate the parameters of its elements, based on the calculation of the total load on the structure, and create a detailed drawing that reflects its results.

Having in front of a skeleton scheme, it is much easier to install a truss roof system in a high-quality manner. The technology of assembling a structure implies the following sequence:

1. First, on the upper belt of the outer walls, on which the slopes will be supported, lay the mauerlat, and on the internal partitions, if the system is nylon, they mount the deck. These elements must be firmly fixed with anchor bolts or studs.
2. Then perform the mounting rafters. They are fixed with the help of nails to the mauerlat, and also connected to each other with the help of a metal lining. It is worth recalling that in the rafters they made drunk under a power-iron beam, and not vice versa. First, the rafters are installed that are located on the edge in order to set the level along which the remaining pairs will be aligned.
3. After installing the rafters, you should put auxiliary support elements that will support them - struts, fasteners, fights. To more reliably fix the bolt, its end is made with a protrusion in half the thickness of the beam and hem it to the rafter, fixing it with nails in several places.
4. On top of the rafter legs pin the crate, which is fixed roofing material. The material and the pitch of the batten are chosen in accordance with the characteristics of the roofing material and the slope of the roof.

Remember that a well-designed and well-assembled truss system is a guarantee of durability, reliability and durability of a dual-slope roof. Therefore, do not neglect the help of professional roofers and designers in creating a project of a roof structure for your home.

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