Log construction is a traditional method of timber construction in which the loadbearing walls are built of logs. In Finland, the logs are usually arranged horizontally and joined together with special corner joints. Logs can also be arranged vertically; the advantage of this is that they will not settle or sink (painua) as wood does not settle when placed in a vertical mode.
Log is a thick building material made of solid wood and shaped by hand, by planing, or by turning on a lathe. It is used principally for wall construction. A log may have a round or rectangular cross section, and may be made from one piece of wood or from two or more pieces glued together. The logs are usually made from spruce or pine, but occasionally from other woods such as aspen.
Hirsikerta means one course or layer of logs. A log joint is called a ‘salvos’, and may be long or short.
Varaus means a lateral groove cut into the underside of the log. It is formed in order to make it easier to seal the joints between the logs and to control shakes and splits so that they occur in the same direction as the wall. The top of the lowest log is formed in such a way that water cannot enter the joint or, if it does, it can flow out easily. A ‘varaus’ can be either an ‘avovaraus’ (open fit) or an ‘umpivaraus’ (closed fit). A ‘kynsivaraus’ is a combination of the two.
In an Avovaraus the edges of the groove are open and the upper and lower logs touch only at the mid-point of the groove. The open sides are sealed or caulked as necessary. In an Umpivaraus, the edges of the groove are closed and the upper and lower logs touch on both edges of the groove. The open space in the middle is then sealed or caulked as necessary.
There is a Seal between upper and lower logs. Its main functions are to keep out the weather and prevent draughts.
Vaarnaus (dowelling) prevents the logs from moving sideways by joining together two or more courses of logs. A ‘vaarna’ is a wood or metal dowel used in dowelling a log wall. Screws can also be used instead of dowels. Through bolts are used when a log wall or log beam has to be joined to form a single unit.
Kierrejalka (Screw-jacks) are used to support ‘non-sink’ structures such as columns. Allowance can also be made for ‘sink’ by inserting wedges which can be removed as the ‘sink’ takes place.
Hirsipalkki is a log beam made of two or more logs joined together. Log beams are used in loadbearing construction e.g. to support a roof or to trim an opening, etc.
Karapuu (buck) is a vertical timber fixed in a groove cut in the ends of the logs in the reveal to an opening in a log wall. Its function is to prevent the logs from moving sideways in relation to each other. Sink or settlement in the wall must be considered where a ‘buck’ is used. Non-sink structures in openings, such as door and window frames, are always fixed to a ‘buck’.
Följäri (follower) is a vertical timber support used to prevent a wall from buckling. They are used to support long walls and the reveals of openings, either on one side or both sides of the wall. They are fixed directly to the logs, or fixed to each other through the logs.
Painuma means the sink or settlement of a log wall caused by shrinkage resulting from drying out of the wood, or by loading due to the weight of the building and compression of the wall joints.