Log cabin floor insulation question.

Mr_Reeman

Im looking to build a log cabin\summer house (i.e. fancy shed!) that will be used all year round.

I have laid a large concrete base, which I plan to put a damp proof membrane down. This will then have 70 mm pressure treated bearers laid on it and then the cabin goes on these. The floor of the cabin is solid wood floorboards which are nailed to the bearers. If I put 25mm polystyrene insulation sheets between the bearers resting on the damp proof membrane, will this cause any issues? Should the insulation be supported closer to the base of the floor boards with a gap between the bottom of the insulation and the damp proof membrane, to allow some airflow between joists?

Thanks for any help.

Kiran

25mm of standard jablite style insulation? That wont be that effective unfortunately. If you go for a full fill cavity wall insulation and lap your dpm up the sides of the base you could have the full 70mm providing you with an effective insulated floor.

HTH

Mr_Reeman

Excellent reply thanks. I saw the jabalite stuff and thought it looked cheap and waterproof!

If I wrap the sub floor in the dpm and fill the voids between joist and floor with insulation, would I need to worry about damp or condensation at all do you think?

My main concerns are the floor rotting over time due to it being damp and having no air circulating to dry it out. Amy I being overly concerned?

Kiran

As this is a log cabin/summer house I would consider one of the following.

Do away with the timber bearers and have an insulated slab then build of of that although as you have already laid your slab possibly not ideal for you

Alternatively go with the full fill solution but either use pressure treated boards for the floor or treat the floor boards. Full fill timber frame is common as by its definition full fill won't have a path for air/ moisture to travel. If you wanted to be extra sure, and in my opinion this is serious overkill for a log cabin, you can have a sprayed insulation which is both full fill so efective but also breathable.

Kiran

There's no issue with building on engineering/staff blues but at the same time there is no issue with laying on pressure treated timber. If the top of the concrete base is level or above ground level then you will have sufficient air flow below the underside of the suspended floor to prevent rising damp issues.