The Case Against Twin Skin Log Cabins

The term ‘Twin Skin’ log cabin refers to a design of log cabin wall that is made up of two logs with a gap between them to fill with insulation. The pairs of logs interlock at 90 degrees with other pairs of logs at traditional corner joints.

From an engineering view point, we would not entertain such a poor design, as it defies the critical rules in log cabin technology to design with respect to the natural timber movements that are well known to occur in log cabins.

The philosophy of a log cabin is that by design it allows the logs to individually swell and contract and in doing so there will be a significant accumulative growth or shrinkage in the overall height of the cabin. Features such as doors and windows are designed to accommodate such movements and dimensional changes.

It follows therefore, that when you build a cavity wall cabin it is important to keep the outer wall and inner wall totally independent of each other. This allows the outer wall to grow in height due to moist atmosphere and the inner wall may reduce in height due to dry heated atmosphere. The result is two opposing changes in dimension of the two walls.

If the two walls are rigidly fixed together, as in the ‘Twin Skin’ design, and such changes take place, then the result is almost certainly a curved wall, or if the wall does have areas that remain straight then gaps will appear in the inner wall.

It is also possible that in different conditions, that the outer wall may be drying out and shrinking greater than the inner wall. In such circumstances the gaps would then form in the outer wall and if so would allow any subsequent moisture to enter the insulation cavity but unknown to the owner because it is degrading out of sight behind the inner wall.

If you would like your log cabin walls to be insulated, we recommend our Keops extremely efficient wall insulation system. This properly designed cavity wall insulation system also incorporates a damp proof membrane, a vapour control barrier and an air gap.

Have you read our information on roof and floor insulation for log cabins?