Support for rafters sliding: photo, dimensions, application

The basis of the wooden roof of the house is the frame, which retains the roof covering. It contains a large number of elements, each of which is necessary and intended for a particular function. One of them is the support for rafters sliding, which serves to prevent deformation of the roof when shrinking the wooden house, when its geometry changes.

Shrinkage of a wooden house

For one year, the frame can be lower by 15%. The average shrinkage is 8%. In this case, it can occur unevenly, which negatively affects the condition of the rafter system. The change in the size of the wooden structure occurs all year round. In the rainy summer season, the wood swells, and in the winter the material dries up. In addition, the walls gain and lose moisture in different ways, depending on the light exposure and rose winds. In the presence of support on the central load-bearing wall, the deformations in it and the outer walls differ significantly, which also affects the uneven changes in the geometric dimensions of the house. During the heating period, the walls, especially the central one, decrease in size from desiccation.

In the absence of a central wall, even greater problems may arise. If the truss system is not assembled as a truss, its rigidity is much lower. As a result, not only the vertical but also the horizontal load acts on the walls. Under pressure, they can bend outward, and the house in plan will become a barrel shape. At the same time the roof is deformed and will sag in the ridge. "Pyatistenka" allows you to get rid of this problem or significantly reduce it.

Application of screw jacks

To compensate for sediment processes and seasonal movements of the house, screw jacks can be installed. They should be located on all vertical supports in the house. Turning jacks with the help of wrenches compensates the movements of the log structures.

Purpose of using sliding supports

It is not always expedient to rigidly fasten the rafter legs to the mauerlate or to the beams of the ceiling with nails, staples, etc. If the house box can shrink, it is necessary to create the possibility of the rafters to shift relative to the supports. Previously, this was done with the help of forged wire, which created a connection with a certain degree of freedom of parts of the structure.

Since then, the technology has changed, and began to use more advanced devices, such as the support for rafters sliding. It is attached to the walls as follows:

• To the upper crown of the log;
• To the upper frame of the frame structure;
• To the beams of the floor;
• To the Mauerlat.

Why do the supports become sliding?

Sliding support makes it possible to compensate for skewed skeleton of the roof during its operation. When the wood shrinks, the geometric dimensions of the structures change. The width of the house is thus reduced, but due to slipping along the girder, the sagging or ripping of the roof, leading to subsequent leaks, does not occur. The reason for precipitation to enter may be different, but under no circumstances should the effects of deformation from shrinkage be underestimated.

Advantages of sliding supports

• Create a reliable base connection with the roof.
• Ensuring the mutual movement of wooden structures while shrinking the base, which retains the strength and tightness of the roof.
• Simplicity of the device, reliability and durability.
• Low cost and the possibility of making their own hands from improvised materials. In this case, the steel plates must be at least 2 mm thick and protected from above with an anti-corrosion coating.

Design features of rafters

A pair of rafters of a gable roof is made by one sample. The connection in the ridge is done by butt, with a gap or overlap. Between the rafters are connected by a metal plate with bolts and nuts. The main feature of the construction is the creation of sliding fasteners in the lower supports. The rafters are placed on the mauerlate on top or with a cut-in to fix the structure in a vertical plane.

The support for rafters sliding, which serves as a fastening element, is made of two parts:

• A bar fixed to the rafter;
• A corner with a loop attached to the supporting bar (mauerlat or support beam).

There is an even simpler version of how a sliding support for rafters can be made (photo below). For this, a corner with a slot is used. It is attached to the rafters along its axis, and in the slot with a gap is the head of the bolt screwed into the body of the Mauerlat.

This support for rafters (sliding - Kucis 120h40h40) costs only about 25 rubles apiece and is easier than others in the installation.

The devices are made of galvanized steel plates. They are attached to one or both sides of the rafters. Two-sided option is preferable for roofs with high wind and snow loads and low weight of the roof structure. Fasteners are applied with a coating against corrosion, so as not to spoil the wood. The stroke length depends on the expected displacements and is from 6 to 16 cm.

Open and closed supports

Sliding supports for rafters ("skoljchki") open type, consisting of two parts, you can make by yourself, but you should use a template. All parts must be fit in size. The open joint consists of a curved plate (fastening strip) and a corner with holes for fastening (at least five).

In the closed connection, the fixing bar is inserted into the bracket holder with the possibility of moving, but not removed from it and is not folding. The assembled design allows for better installation. If there is an effort to tear off the rafters from the Mauerlat under the influence of wind loads, the loop can unbend, and the sliding support of the rafter closed has greater strength.

Important! The rafter system with the possibility of sliding relative to the base is expedient to be made only for a symmetrical gable roof. This is its advantage, as it increases reliability at low costs. Supports can be used for a single-pitched roof.

Sliding support for rafters: dimensions

The support includes two components - a guide plate and a corner. The size of the product depends on the permissible movement of the rafter.

The popular sliding support for Kucis rafters of open and closed type has a width of 40 mm plates, support height - 90 mm, length - up to 160 mm. The metal for the plates is taken to be 2-2.5 mm thick. They are profiled by cold stamping from low-carbon steel, which has good plasticity. Corrosion protection is a hot-dip zinc coating. Acquiring products without coating, they should be painted with paint, so that the material does not rust.

The corner is attached to the support beam. If its surface is round, a flat area is prepared for installation, stripping the wood on a log to the size of the L-shaped part of the part. The photo below shows a similar sliding support for the rafter closed (Paz). Both types of products are manufactured by stamping and are inexpensive.

The rails are attached to the rafters in the extreme position to ensure maximum movement. Since the angle of inclination with respect to the ridge varies with shrinkage of the roof, it is necessary to make a hinged bolt joint at the top of the rafters . Special plates with perforations can be used here.

Installation

The support for rafters sliding when installing the roof frame is applied as follows.

• Rafters are made of boards with a width of 150-200 mm and a thickness of 50 mm. With insufficient length, the rafter leg is lengthened, increasing lapping with a chaotic arrangement of the fastening elements to prevent cracking.
• On top of the installation run - a supporting beam, located horizontally and perpendicular to the sliding rafters.
• In the lower part, the rafter's feet are fixed on the cuts made in the Mauerlate. Do not jam them. But at the same time, blades should keep the boards from transverse distortions. The presence of the Mauerlat evenly distributes the load to the entire building. In its absence, the local pressure on the walls from the rafters becomes larger.
• Fixing parts of suitable dimensions are selected depending on the range of the rafters' displacement.

• A playground is prepared under the corner on the supporting log.
• The angle is fixed perpendicular to the log to ensure free movement of the plate.
• The guide is inserted into the loop of the corner and fastened to the rafters along its axis. Installation is made to the lowest position, as the wall from below will be compressed and reduced in size. At the same time, the rafter's leg will go down.
• The rafters are connected from above in a hinged way.

Conditions guaranteeing the strength, reliability and durability of the roof

• Observe the necessary mechanical properties and dimensions of sliding supports for rafters.
• The location of the guide rail is parallel to the axis of the rafters, and the corner is perpendicular to ensure reliable sliding.
• The cross-section of the boards under the rafters should not be less than 150x50 mm.
• The roof frame must be treated with an antiseptic and a fire-resistant compound.
• Observe the correct proportions of the roof frame.
• Making the whole rafter system by template.
• Creating a hinged ridge connection.
• The construction of rafter legs should be done alternately in the lower and upper parts.

Sliding support for rafters: application for other purposes

Compensation for shrinkage of wood is used not only on the skeletons of roofs. It is used wherever it is necessary to create the possibility of moving parts of wooden structures, for example, when erecting partitions in houses made of wood. If it is necessary to finish the wall in the bathroom with ceramic tiles, it is impossible to simply coat it with sheet material.

It is necessary to establish a "floating" frame, fixed from above on the sliding supports, and then fix the plasterboard to which the tiles will be glued. And the stitching is not done up to the ceiling. When the walls are deformed, the frame will remain stationary, and the lining will not collapse.

Conclusion

Sliding supports for rafters in wooden houses are necessary to prevent deformation of the roof when shrinking the house. It is especially active in the first years after construction (about 8%). Proper installation of the rafters will ensure a permanent tightness and strength of the roof.