Shrinkage is mechanical and natural. Mechanical is caused by the pressure that the upper logs exert on the lower ones. In other words, the house sags under its own weight. And natural shrinkage is called a change in the size of wood due to its drying out. If the “mechanics” can be dealt with with the help of special devices, then it is more difficult to deal with the nature of the tree. There is GOST 6782.1-75, which regulates the shrinkage of wood from conifers, but most often it is not used, because the amount of shrinkage depends on the type of material – for example, it will be different for rounded logs and glued beams. The size of the logs and beams, their length and width are of great importance. Humidity, type of wood, and the time of year when the house was assembled also play a role. Wooden buildings settle unevenly: faster on the south side, slower on the north. The ridge and pediment walls sit faster and stronger than the side walls, and the internal partitions “walk” after the installation of the openings and turning on the heating. It is impossible to defeat natural shrinkage: hardly anyone will argue with the laws of physics. However, we will not give up and try to minimize problems.
Modern methods help a wooden house to withstand at the time of shrinkage, but no one canceled the old-fashioned methods – they are still successfully used. For example, each crown can be upset with a special mallet – this allows you to dock the bars more tightly without damaging them. Also, a heater (jute) is laid between the crowns, which softens the pressure.
For a more uniform shrinkage, bars are mounted in door and window openings. This is called casing or swarms, salary or bobbing. Logs not only dry out, but also change shape: they are twisted and oppressed, therefore, since ancient times, builders have used a jig: it strengthens the walls weakened by openings. To reduce the pressure on the opening, a gap is left when installing the window – the upper logs will have a place to “sit down”. In addition, a spike or groove is cut at the ends of the logs, along which the logs slide during shrinkage. Most often, shedding in wooden houses is made from an array of conifers.
Also, in window and door openings, builders use technological gaps (about 2 cm wide), which are made on top of windows and doors. They are invisible to the eye, since platbands are put on the openings.
The type of timber used can also affect the amount of shrinkage. So, profiled beams adhere more tightly to each other. Thanks to the “Norwegian castles”, the carriage has a good bow.
For “easy landing” during the construction of a wooden house, a dowel is used. This is a wooden dowel that prevents the logs from rolling around its axis. Incorrect use of dowels or their absence leads to distortions, sagging or dumping of logs. The pins are staggered relative to each other, the holes for them must be strictly vertical, in the center of the log. The depth of the hole usually exceeds the diameter of the dowel by 3-4 cm, so that there is room for its movement during shrinkage – otherwise, the upper log will hang on the dowel, and we will get a gap. The best material for the dowel is birch.
The structure shrinks not only due to the pressure of the beams against each other, but also, as already mentioned, due to a change in the natural size of the wood. No matter how tightly the beams or logs come together, the house will change in size in any case – therefore, we need shrinkage compensators.
The shrinkage compensator is a device also called a screw jack, lift, or adjusting screw. The device consists of an adjusting anchor, a nut and two plates – support and counter. The anti-shrink kit is attached to the structure with
self-tapping screws. Compensators are installed on each vertical post from the top or bottom. For this, a hole is drilled in the post, corresponding to the size of the compensator itself. When the house sits down, the nut on the compensator is tightened, so that the beams resting on the post do not hang. In the first month, it is necessary to monitor the compensator daily and, if necessary, tighten it. In the future, control will no longer be so frequent.
An innovation in wooden housing construction was the use of sliding supports for truss systems. The ridge part of the wall is higher and heavier, therefore, sits faster. Because of this, the rafter system sags in the ridge more strongly, and the rafters themselves bend and go out on the side walls – as a result, the angle of inclination of the roof changes. Sliding supports allow you to compensate for the shrinkage of the log house.