Log cabin floor ventilation

[opps]

Hi all, I am currently helping a friend to build a 5m*4m log cabin (on a new concrete base).

The supplier insists that the tanalised 3x2" floor bearers should run all around the perimeter of the cabin. The other log cabins that I have built had the cabin sitting on floor bearers (spanning the width of the cabin) that are parallel with each other, the T&G floorboards are then tacked to those.

We didn't realise that the client hadn't noticed that floor is an optional extra (it costs about another £500). We phoned the supplier who told us that they will supply uncut boards that we need to nail to floor bearers and that it will end up being a floating floor. When we asked about floor ventilation, they insisted that it wasn't necessary, adding that we could put some dpm down if we wanted. They also insisted that parallel floor bearers won't be able to support the building.

The building was supplied with 8 floor bearers. Unless advised otherwise, we are planning to stick with the parallel bearer option, buy more and space them at 12" apart, is that sufficient for 18mm T&G floor boards?. I find it hard to believe that a cabin on a new concrete base does not need ventilation- am I wrong? The cabin is L shaped, the concrete base is rectangular and slightly larger than the cabin foot print.

 

[r896neo]

To be honest it's hard to work out what your on about. The word bearers is so many times it make it confusing, to me at least

" They insist paralell bearers won't be able to support the building"

It's hard to know what this refers to?

Perhaps you could do a quick sketch or a photo?

Having no ventilation is a poor idea unless you have a very watertight setup and could use a floating floor over dpm and perhaps inspuation board.

Normally you would want the slab to be fractionally smaller than the building to allow cladding to extend past and prevent rain getting under.

 

[r896neo]

I've re-read and I think you were expecting the building to have a floor like a shed of say 3x2 joists and 18mm boards on top. But actually what you've got is simply walls and a roof with no floor but just timber sole plates under each wall?

Is that right?

 

[opps]

Sorry if i wasn't clear.

AFAIK most log cabins sit on top of loads of parallel 3x2 joists.

This firm says that the 3x2 should only sit under the perimeter of the building, rather than running parallel like a shed.

The firm says that you can put a DPM under the "floating floor" but if using the parameter method, doesn't that mean that the 3x2 will only be able to dry out on the outward face.

I appreciate your point about concrete bases larger than the floor plan leading to an increased risk of wter running under the structure.

 

[r896neo]

Yep the floor type you describe is the norm for sheds and summer houses but larger and more expensive garden rooms and cabins are often done as you would a proper timber frame building.

This seems to be what you have where the walls are attached to a sole plates (the perimeter 3x2).

The oversized base is your problem as it will tend to drag water in. I would consider using a dpm and screed.