Single Skin Garage Conversion

[Lectrician]

My attached garage is to become a dining room.

So far I have french doors intalled where the window was, and have put an opening from the lounge to the garage.

I am getting conflicting recommendations with regards the wall.

One builder is saying to rubberoid the walls, fix 2x2 battens, celotex between, plasterboard and skim.

The other builder says no need to rubberoid as celotex is foil backed and repels moisture, and use foil backed plasterboard.

Both builders have said I "could" also put in a vapour barrier before the plasterboard if I want.

Both builders are family friends.

Which way to go?




Also, the floor.

The floor is going to be raised by building a few dwarf walls, and creating a timber suspended floor. This is about an inch below the DPC of the single skin wall, but I have been told this makes no odds due to the construction of the walls, and the floor is not going to touch the outer wall as such.



What would you constuct first? The walls or floor? I am looking for something to do this weekend!

Cheers!

 

[^woody^]

The concept is - an outer weathering face (ie bricks), then a waterproof barrier, then insulation, then a vapour check barrier (depends on the construction detail though) then an internal finish (plasterboard)

Foil backed insulation and plasterboard are not waterproof membranes - they are vapour checks to stop moisture from the internal room air getting into the wall and condensing and rotting timber.

Insulation between timber will lead to a thermal bridge of the timber batten and either pattern staining or worse condensation in lines where the timber is. You really need an layer of insulation across any timber battens

If the wall construction is to have no air voids, then you can use Rubberoid/Sealocrete etc or just use polythene as the waterproof membrane. If you are constructing a timber frame and there are air voids in the wall, then you should use a breathable membrane on the inside of the bricks, and also a vapour check layer immediately behind the plasterboard - which can be either foil-backed board or continuous celotex etc with all the joints taped and sealed with foil tape

Remember to pay attention to how the waterproof membrane joins to the existing DPC - to avoid penetrating rain running down into the base of the new internal wall and floor

Whether you do the floor or wall first will depend in the detail at the wall base.

But why can't you just span the joists off hangers and not bother with sleeper walls?

 

[Lectrician]

Thanks.

I think it hugely depends on the area of the country you are to what way things get done.

I was told the floor should be independent of the walls? You would need to attach a piece of wood for the hangers on one or the other wall which is single skin.

 

[^woody^]

No, the building regs and construction methods generally, are national.

I would decide what you are doing with regards to the outside wall and then fit your battens or frame etc, and then fix a horizontal timber off which hangers are fixed for the floor.

The important things are to sort out the junctions of the existing DPC, the new wall membrane and the new floor DPM or ventilation. Then how the wall and floor fit together is just down to the most economical way to get it done

There is no need for the floor to be independent of the walls - think about your floor upstairs?

 

[Lectrician]

Yea, it was because the wall is of an odd construction that I was told the floor should be independant.

The FFL will be an inch below the actual DPC of the old garage. I was told this is fine as the wall is to have a DP anyway in some form or an another.

The garage is brick for 6 courses, and then rendered blockwork. Single skin on the two walls that form this new room.

The BCO dealt with a conversion down the road from me, and he was told he could just put battons on the wall, then celotex, then a vapour barrier and foil backed plasterboard.

It really is doing my head in currently, as everyone has a different approach as to what is required.

I think I am going to wait for the BCO on this now.