Shrinkage of a wooden house: what is it and how does it go

Shrinkage of a wooden house: what is it and how does it go

09.07.2021 Construction technology

Shrinkage of a timber house is a reduction in the volume of wood caused by moisture loss. It is contained in the raw material, and after sawing or cutting, the workpiece begins to dry out. A beam or log becomes thinner, which entails a decrease in the height of the walls.

What is a shrinkage blockhouse?

The customer receives the complete set on the foundation, with a permanent or temporary roof. The construction object is connected to utilities. A rough finish is being carried out in the house, if necessary, internal frame partitions are carried out. Door and window openings are protected from precipitation into the room. After shrinkage, the rest of the work is carried out to put the building into operation.

How long does a wooden house shrink?

The duration of natural drying of wood depends on the type of lumber and the time of assembly of the log house. A house built in summer takes up to 1 year on average. When building an object in winter, the process takes no more than 6-8 months. In the cold season, the material dries more slowly, so the volume of the wood changes more evenly. Drying peaks in the first 3 months after installing the wall kit, after which the dynamics decreases.

The shrinkage table for timber and logs will give you an idea of ​​how dry the materials are:

Type of lumber Shrinkage (in centimeters)
Chopped log 10-11
Rounded log 7-10
Shrinkage of a house made of profiled timber of natural moisture 6-8
Kiln drying bar 2.5-3
Not dried timber 4-5
Glued timber Up to 2
Double bar 2-3

When does a wooden house begin to shrink?

The shrinkage time of a wooden house also depends on the type of building material:

  • The shrinkage of the log home begins after the installation of the wall kit and blood. On average, it lasts 1 year and is up to 4% of the height of the walls. In the case of high humidity, the wood will take longer. The second stage of shrinkage of a log building occurs after finishing work and starting the heating system. Subsequent shrinkage lasts up to 4 years, but does not exceed 4%;
  • Shrinkage of a house made of chamber-dried profiled timber and rounded logs occurs at the end of finishing work and after turning on the heating devices. This stage lasts 3-4 years, the material shrinks by 3-4%;
  • Shrinkage of laminated veneer lumber is within 1-2% of the height of the walls, and in time it takes up to three years.

As you can see, the degree of drying depends not only on the material, but also on the method of its manufacture (processing). Natural moisture materials take longer to dry in the first stage, so they take longer. When calculating the shrinkage of the timber, the indicators will be lower, since the sawn timber is dried in advance.

Features of the shrinkage of log houses

Chopped logs shrink by 10% of their original size during the year, round logs - by 7%. This process practically does not affect the length of the building material. When erecting a residential building or a bath from a log for shrinkage, it is necessary to take into account the possible formation of cracks in the walls. This is due to the different drying rates of the wood outside and inside. The outer part dries almost immediately, while the inner part takes time.

We hasten to reassure you: the appearance of cracks does not affect the service life of the building and its reliability. But deformations with a width of more than 5 mm must be repaired with putty, sealant or caulk. The owner's inaction is dangerous because a large accumulation of moisture in the crack provokes the process of decay of the lumber and violates the aesthetic properties of the structure.

To prevent strong cracks during shrinkage of the log, use only dry lumber impregnated with protective compounds. They should be stored in a dry room or outdoors if the place is protected from ultraviolet radiation.

Timber house for shrinkage: the subtleties of shrinkage

Percentage shrinkage of timber is significantly lower than that of log material. To minimize shrinkage, it is best to use dry lumber that has been condensed dry. This type of processing is carried out at low temperatures and takes less time than drying in natural conditions. In addition, the shrinkage of a house made of dry timber does not have negative consequences, which cannot be said about the building material obtained after chamber drying.

Glued timber dries even less. This is due to its gluing from several lumber, which minimizes longitudinal torsion. Although the shrinkage of laminated veneer lumber is faster, this type of wood is not as popular as profiled. In addition, an adhesive composition is used to connect the boards, which, when exposed to the sun, releases toxic substances and thus has a bad effect on the comfort of living. The shrinkage of the profiled bar lasts longer, regardless of the drying method. But at the same time, sawn timber is completely natural and environmentally friendly.

How to compensate for log shrinkage?

We are often asked how to accelerate the shrinkage of a wooden house and are offered to do it with heating. This is absolutely impossible to do! When heated early, the lumber will crack. But there are several techniques that will help compensate for the shrinkage of the structure and eliminate adverse consequences:

  • Use of expansion joints. The technology involves the installation of a vertical support. It is installed between the lumber and the load-bearing floor, which is located under the roof of the building. Longitudinal and transverse shrinkage occurs in different ways, so the material dries disproportionately. To adjust the shrinkage of the log house, an expansion joint is used (most often - a screw jack). In the process of drying a bar or log material, the expansion joints must be twisted in order to achieve uniform shrinkage of the wall kit;
  • Laying insulation. Jute or flax fiber is most often used as an insulating element. The first is more in demand due to its greater density and durability. In addition, in a log house, lumber must be tightly fitted to each other for shrinkage. This set of actions will avoid the formation of cracks;
  • The device of the window. It is a structure made of wood that relieves the load from the openings. The planting is carried out in the form of a solid wooden box, consisting of massive bars. The design does not prevent the vertical displacement of the rims, but prevents them from horizontal displacement and frame distortion. A gap must be left between the casing and the crowns of the wooden structure to ensure natural drying. This space is filled only with insulation; it is forbidden to resort to using polyurethane foam;
  • Elimination of skewing of openings. When erecting a house from a bar for shrinkage, a dressing is made from a log in windows and doors. It protects the structure from distortion during natural drying. Before the installation of the casing and the installation of door and window structures, the dressing is cut out. This trick allows you to eliminate skewing of the frame, unscrewing the crowns and the formation of gaps along the edges of the lumber. As a result, nothing prevents the craftsmen from making accurate installation of the openings;
  • Solid base. The lower rims of the log house should be made of a more durable type of wood. The shrinkage of a larch and oak house will be the most successful;
  • Creation of a temporary roof. For the period of drying of lumber, you need to make a temporary roof from roofing material or hydraulic film. This technique will allow the rafter system to settle with the log house and protect the building from external influences. A permanent roof is installed at the end of the drying out of the house.

To reduce the shrinkage of timber baths or wooden houses, dried materials are usually used. Indoor humidity should be in the range of 40-70%. The ends of the lumber are impregnated with a special agent that prevents moisture removal. It is better to cover all horizontal and vertical parts where rainwater and snow can theoretically accumulate.