What is a Twinskin?
INSULATION – WHY THE TWINSKIN LOG CABIN IS THE BEST SOLUTION
In our opinion, there is only one economic way to ensure that a log cabin can be used throughout the year, regardless of the season.
The key lies in the insulation of the log cabin. A Twinskin construction has insulation in the walls as well as in the roof and floor, which is achieved by building a cavity into the wall that can then be filled with various types of insulation.
The insulated walls can perform at the equivalent thermal value of a solid wall which is 5 times thicker, thus saving both space, materials and most importantly, cost.
It is worth reviewing how a log cabin is constructed before looking at the various options:
- Log cabins are built without the use of a vertical framework which would hold the walls at a set height. They are composed of horizontal logs which lie on top of each other and are taller during the Autumn/Winter.
- The walls are usually 17 logs high and each log can absorb enough atmospheric moisture during the Autumn/ Winter that they can each swell by 1mm, so the log cabin could be 17mm higher during the Autumn/Winter.
Log cabins are normally insulated in one of 3 ways:
1. Dry lined over studwork - a standard log cabin with a single thickness of log wall is lined out with framing and plasterboard or similar material.
This method requires that an expansion gap must be left all around the top of the inner wall to allow for movement of the logs without fouling the roof boards using sliding brackets. This means that the roof boards can be lifted off of the supporting side wall or gaps can appear between the wall logs if it has been incorrectly installed.
The expansion gap cannot be defined exactly because the cabin will ‘settle down for the first few weeks after installation whilst the corners joints and logs fully interlock ; and
The season in which the log cabin is installed will affect the building. If the cabin is built in the Winter, in addition to the first few weeks of settlement there will also be the 16mm average seasonal movement.
In addition to the expansion gap issues, this method causes some considerable problems with the finish of the internal linings around the windows and doors because the windows and doors will rise and fall with the cabin walls, but the internal lining doesn't move so it cannot be fixed to the windows and doors for a clean and neat finish. As admitted by advocates of this type of insulating method - "Any window reveals and door reveals should not create a rigid link from the inner wall to the outer wall. They must allow the two walls to move independently of each other." In other words, it's not a very satisfactory way of doing it!
2. The dual walled method
This method is where an individual cabin is built inside another individual cabin, but the internal cabin is not interlocked (connected) to the external cabin. The gap between the two cabins is then insulated.
We believe that this method substantially increases the likelihood of gaps between the logs and the consequent malfunctions of the doors and windows.
The internal cabin will dry, shrink and settle down whereas the external cabin will move with the seasons.
In the Winter, when the external cabin is at its maximum height, the tops of the openings for the windows and doors (reveals) will not be at the same height as each other.
In addition to these problems, there is no additional strength in the corners of the log cabin, which render it a weaker overall building.
3. The "Twinskin" - a log cabin method is to build a second, fully interlocking cabin inside.
The inner logs are fully interlocked with the outer logs, so they will rise and fall in unison. You can see this easily because there are 2 logs that protrude on each corner where the inner logs are also visible.
This eliminates the expansion issues because expansion gaps are not required at roof height or around the windows and doors. The Twinskin cabin is very rigid because of the box section that is formed at each corner.
Special metal straps and timbers are used where the ends of the inner and outer logs are not directly connected around the window and door reveals to maintain their alignment.
The photo above show how a typical 45mm Twinskin cabin is constructed. Log cabins constructed with 35mm or less walls do not have corner bolts as the timber is too thin to drill large enough bolt holes into without compromising the log strength, therefore conventional timber wind braces are used.
Twinskins of 60mm or thicker logs have a 90mm insulation cavity for an even better thermal value.
We offer the following Twinskin options:
1. 28mm inner and outer log with 50mm insulation cavity
2. 35mm inner and outer log with 50mm insulation cavity
3. 45mm inner and outer log with 50mm insulation cavity
4. 45mm inner and outer log with 90mm insulation cavity (complies with Part L Building Regulations for habitation)
5. 60mm inner and outer log with 90mm insulation cavity (complies with Part L Building Regulations for habitation)
6. 70mm inner and outer log with 90mm insulation cavity (complies with Part L Building Regulations for habitation)