The foil film must be laid end to end.

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General rules for installing vapor barriers for the walls of a wooden house
For the vapor barrier to work effectively, it is necessary to adhere to several simple rules, such as:

The film must be laid with an overlap. Adhesive tapes are used to connect sheets of film.
When using film, fiberglass and roofing felt, it is necessary to fusion data the strips of the material used with an overlap. To connect the foil material, it is necessary to use tape with a metallized coating.
It is better not to use construction tape, as it tends to peel off after some time.
Conclusion
Despite the fact that houses built of wood are, by definition, warm, in some areas of our country the thermal insulation properties of wood may not be enough to ensure that the house has an optimal, comfortable temperature for living. And therefore, many homeowners are forced to take measures for additional insulation of walls, floors, roofs and vapor barrier is an important component of this system. Moisture retention extends the life of the insulation material and the entire system as a whole.

Vapor barrier for walls – how to make a wooden house warm and cozy?
In all residential buildings, vapor barriers are always installed in the walls. This also applies to wooden houses. In them, measures to protect against accumulated moisture can be carried out both from the inside and from the outside.

Is vapor barrier necessary for a wooden house?
Nowadays, private wooden houses are very rarely built with single-layer walls. Every person wants their home to be as warm as possible. Therefore, wooden houses are now built with multi-layer walls. In addition to the interior decoration and the wall itself, they also have an additional insulating layer. This led to the fact that the residential building began to "react" completely differently to the evaporation of moisture formed in the rooms.