Settlement and shrinkage of logs is probably the single most important detail concerning the construction of a log house. If a log company or builder tells you there is no settlement - move on - you are in deep trouble if you continue with them.

Timber shrinks significantly in width not in length. This is why there is a huge difference between log buildings and timber frame. In timber frame the length is mostly vertical so there is no significant settlement. In log buildings the length is horizontal so each log shrinks horizontally by a small amount. Care must be taken when mixing log construction with timber frame or block work as in chimneys. Anything that is fixed to log walls or is free standing inside a log house must be accommodated. This includes wardrobes, walls presses & counter tops. Wall tiling & mirrors. Electrical & plumbing- as in ducts, pipe work, sinks & toilets. The chimney stack should be free standing and rafters should never be fixed to the chimney. The Log House Company has designed a special flashing that accommodates movement.

Log construction is a beautiful natural building material and when you work with and understand the character of wood it is very satisfying. The Log House Company has researched this area thoroughly from the beginning. The good news is that the settlement stops after about 2 years.

If the house is a dormer with a timber frame and timber clad gable and standard roof trusses then you can exclude the upper floor from the settlement equation. It is when you mix logs, timber frame and roof trusses that you can run into trouble.

OK let’s look at how much settlement. Take a log size of 180mm high by 120mm wide. We are not concerned with the width of the log for the moment though this shrinkage affects the thickness of the log wall and can open corner joints a fraction. We are concerned with how many horizontal logs there are and by how much they shrink. Also we are dealing with two types of pine logs. Standard with a moisture content of 20% aprox and laminated with a moisture content of 16% aprox.

We have measured that each standard log settles by 4mm from 180mm to 176mm aprox. The standard ceiling height is 2400mm so the ceiling will come down by 53mm and a 6 metre ridge with log gable will come down by 133mm aprox. Also because of the logs in the gable the rafters will splay and move out from the side wallplate by about 30mm depending on roof pitch. The laminated log settles by 3mm from 180mm to 177mm.

There is nothing wrong with standard logs but The Log House Company now use laminated logs where possible. Because the lamination makes the logs more stable the timber can be dried to a lower moisture level. This means less settlement, less twisting and the corner joints don’t open.

Please Note: The Log House Company takes no responsibility for use of the above information. They are general guidelines and suggestions. Each project should be individually assessed.

Regards
Eamon Murray

Filed under: Log House construction in Ireland on October 2nd, 2007