Thinking about a log cabin, insulation, twin wall...?

[DaMekon]

Been looking at log cabins for a short while, but cant quite find the answers I am looking for, so thought Id throw them in here...

My biggest concern is it being like a sauna in the summer, especially as we have a south facing garden which gets the sun all day. I assume to have a space that can be used all year round, I would need to look at an insulated cabin, but would I need to go as far as a twin wall (cavity) construction, as these do jump up in price a bit.

I then came across an article that basically said that twin skin cabins that used interlocking technique are poor design and can lead to structural defects:

http://www.logcabins.co.uk/twin_skin.asp

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.

This sort of makes sense to me, but would like to think the people who design these things would have taken this into account.

Is this a real concern? Or could simply getting a, say, 44mm log cabin suffice, if I then cladded internally with the likes of celotex or alternative? Or do things like having a roof overhang to shade the windows and wall, and painting alight colour, really make a difference?

 

[AronSearle]

I'd agree that twin skin log walls are risky on paper, internal heating or external wetting will cause them to swell differently, I'm not sure how much of a problem this actually ends up being though.

If you start lining the internal walls with insulation, then you might risk more moisture being held in the outer wall, or seeping through the logs and being held behind the insulation, a small risk but definatly there. Good overhangs, and well maintained breathable finishes on the outside will help mitigate this risk.

Personally I don't really get the point of "log" cabins that are to be insulated, They are not really "logs" but more typically 44mm machined timber, which will give an appalling U-value, you then cover these "logs" over.

May as well just build a stud wall, which you can then insulated better, make yourself (or buy for cheaper), clad it with "log" cladding, which you can provide a small cavity for and have a very robust, durable cheap building.

And who will know the difference when it is built?

 

[DaMekon]

Personally I don't really get the point of "log" cabins that are to be insulated, They are not really "logs" but more typically 44mm machined timber, which will give an appalling U-value, you then cover these "logs" over.

May as well just build a stud wall, which you can then insulated better, make yourself (or buy for cheaper), clad it with "log" cladding, which you can provide a small cavity for and have a very robust, durable cheap building.

Started off just looking for a simple shed, but then thought would be good if we could actually get some use out of the space, so I ended up looking at "log" cabins, which as you say, aren't really logs at all!

I couldn't really find any other alternatives to these sorts of buildings. They all seem to be plank based.

DIY aint really my thing, so actually building a structure myself from raw materials aint gonna happen! I would contemplate flat pack or a kit!

---Just stumbled on SIP's and kits.. looks interesting!