Spacer lining rafters: description, schemes, device and features of the calculation

Rafters are the basic supporting element of the construction of any roof. There are many ways to install them. Very often roofs of houses are collected, for example, on layered spacer rafters. Their main feature is that they work during the operation of the roof and on bending, and on squeezing. That is, not only the vertical but also the horizontal force is transmitted to the walls.

Design Features

In fact, such rafters are a transitional option from the layerless to the hanging invisible. Vertical load they transmit through the ridge run and the racks. Spacious pressure such rafters render on walls because of that are fastened to mauerlatu or beams rigidly. With this method of fixation, a horizontal stress inevitably arises in the roof frame. Scheme of layered rafters spacer, presented below, demonstrates the principle of their work visually.

What to consider when drafting

Before installing the roof, of course, detailed schemes for the installation of all its elements, including rafters, should be developed. When drafting the roof structure, first of all, it is necessary to determine:

• With the angle of inclination of the layered rafters;
• Their cross-section;
• Type of used lumber;
• Installation step;
• Ways of fastening.

What should be the angle of inclination

The calculation of this parameter should be approached as responsibly as possible. The reliability and durability of a structure, such as a roof with nylon rafters, depends on how correctly the angle is chosen. It is best, of course, to arrange a roof over the building more abruptly. In this case, the house can be equipped with a residential loft or attic. In addition, and look like suburban buildings with such roofs are more solid. However, steep roofs are cheaper, of course, more expensive than flat.

In addition to the features of operation of the future roof and the architecture of the building, when choosing the angle of inclination of skates, it is necessary to take into account also such factors as:

• Total weight of the roofing material used;
• Possible snow load;
• Wind load.

For each specific roofing material, there is its own minimum allowable angle. So, for example, for a metal tile it is 12-14 degrees, for a slate - 22 degrees, etc. When designing a project, this, of course, needs to be taken into account.

Possible wind and snow load on the roof is determined by special tables compiled for each specific region. In most areas of Russia, the optimal angle of inclination of rays with these parameters is 30-45 degrees.

Which materials to choose

For obvious reasons, the most important part of the roof frame is the layered rafters. The design (and knots, and the legs themselves) of them, as the main support element in this case, should be as stable and strong as possible. Therefore, the choice of sawn timber for them should be approached as much as possible responsibly.

Most often for rafters of roofs of country houses a pine bar is used. In such wood contains a lot of tar, and therefore it is quite resistant to moisture. In addition, pine sawnwood has a fairly large margin of safety and is not too expensive.

How to make a calculation of layered rafters

The cross-section of the beam for the supporting elements of the roof frame is calculated taking into account the following factors:

• Total weight of the roofing pie;
• Step between rafters;
• Their length.

Mounted rafters can be installed in steps of 50 to 120 cm. In regions where there is a lot of snow in winter, the distance between these elements is usually reduced. The same applies to roofs, finished with heavy roofing material, for example clay tiles. If there is not too much precipitation in the region during the cold season, it is possible to save and install rafters with a large step. In the European part of Russia, when used to coat the roof of unduline or profiled sheet, rafters are usually mounted at a distance of approximately 80-100 cm from each other.

As for the necessary length of the legs, it is quite simple to define it. The construction of layered rafters, like any other, is such that in the frontal projection the roof of the house usually represents an isosceles triangle. Therefore, in order to calculate the length of the leg, you simply divide half the length of the span of the building into the cosine of the slope angle of the ramp. To the resulting figure should be added about 40 cm to overhangs.

Knowing the length of the rafter legs and determining the distance between them, it is easy to find out which section they should have. To do this, use special tables. Most often under the rafters take a bar cross-section of 150x150 cm. Under the Mauerlat, because it is in use during the operation, a heavy load is usually used, the material is thicker - 150x200 or 200x200 cm.

How to fix the bottom

Mauerlat to the concrete and brick walls is usually fixed to the anchor, previously immured in the masonry or mortar. There are several ways of fixing the actual rafters themselves:

• By cutting;
• Using galvanized corners and bolts;
• With the use of nails, clamps and wire.

The rafters are assembled during the assembly of the roof frame or directly on the Mauerlat, or on the exposed walls beyond the plane of the beam. In the latter case, the fastening can be performed in two ways:

1. On steep roofs (more than 35 degrees), the rafters are often cut into the beam by a single tooth. In this case, a thorn is cut out in the leg, and in the reciprocal part - a special stop. Actually, the fastening itself is done using a bolt.
2. On flat roofs to increase the reference area, the joint is made by cutting with a double tooth.

When fastening directly to the Mauerlat, only the landing socket is cut in the rafters. Hard fixation is most often done with special galvanized perforated corners. They are installed on the sides of the legs and bolted. To reduce the horizontal load on the walls from the roof, sometimes on the rafters from below also fill the bar (for the stop in the Mauerlat). Such a fastening unit is usually additionally fixed with wire-rod. It is embedded in the wall at the stage of masonry or pouring reinforcing belt.

Sometimes wooden layered rafters are fixed on the Mauerlate and on a bundle of three nails. This is also a fairly reliable method. In this case one nail is hammered in the middle of the rafters, and two others at a slight angle on both sides of it. With this method of fastening, it is also advisable to additionally use wire-rod. Sometimes special clamps are used instead of it, covering the rafter over the mauerlat.

How to attach from above

Above layered rafters can be fixed also in several ways. Sometimes they are attached directly to the ridge run by the method of cutting, but more often still pair in pairs over it. In the latter case, the farms can be assembled using the "half-way" method or using thick steel plates or bars.

Since the layered spacer rafters are transferred to the walls, including the horizontal load, on large spans, they, like hanging ones, are sometimes also connected in pairs in pairs by a crossbar under the ridge.

Mounting order

There is a collar system of rafters of this kind of house as follows:

• From the long board a pattern is cut out, along which the rafters are subsequently cut. Its use makes it possible to make absolutely identical elements, and, consequently, to assemble a neat roof.
• The extreme racks (on the gables) are installed.
• Between them the level is strictly horizontally stretched inelastic reference cord.
• To the beams of the ceiling are attached intermediate posts.
• They fix a ridge run. To fasten it to the racks, you can use the Folding method or the corners.
• The extreme rafter trusses are mounted.
• With the selected step, intermediate settings are established.

After the base of the roof frame has been assembled, proceed to install the insulation, waterproofing, roofing and roofing material.

Additional elements of layered rafters

Very often the frame of this variety is installed on large houses with wide runs. In this case, in order to avoid the need to use a thick bar, and hence unnecessary expenses, the roof structure usually includes additional elements - struts or trims. The first one is fixed at the junction of the rack and the foot, and the second, at an angle of 45 degrees, to the rafters themselves. As a result, an additional support is obtained, preventing the leg from flexing too much under severe loads. You need to cut the bobbin exactly at an angle of 45 degrees. The presence of gaps between him, the rack and the leg is not allowed.

The use of under-beams allows the collection of even more reliable roofs on houses with very wide spans. In this case, the ridge run is not installed. Instead, two scaffolds are first installed along the walls, onto which the racks are fastened. On them, and laid beams, reliably supporting layered rafters. The attachment points in this case are carried out in the same way as in the Mauerlate. That is, in the rafters first select the landing nest, and then it is attached to the beam with the help of corners.

What you need to know about

Use layered rafters spacer basically only on houses with brick, block or monolithic walls. This is primarily due to the fact that in this case the attachment to the Mauerlat is made rigidly. On wooden houses rafters of this variety are not installed, because such buildings after construction are able to give strong shrinkage. As a result, the roof fixed on the top crown can simply lead. At such houses the rafters are fixed to the Mauerlat on special elements - "sleds", providing their mobility.

Conclusion

As you can see, it is not so difficult to independently calculate and install layered spacer rafters. However, whichever method of fixing them to the Mauerlat, Beams and Runs has not been chosen, all work needs to be done carefully - using quality supplementary elements, without violating the technologies. Otherwise, the roof will be unreliable and will soon require repair or even reinstallation.