Insulated Stud Wall Ventilation

[scruffmeister]

Hi all, looking for some advice please. I have a single skin brick garage. The brick walls are sound but are only single skin so can’t be consider “watertight”.

I have built stud walls on the internal face leaving a cavity gap of approx 50mm to the wall (i.e. they are attached wall and ceiling only).

The plan is to put foil-back Cellotex or similar in between the studs, then a vapour control layer before finishing in 18mm ply.

My question is around ventilation between the back of the insulation and the brick wall. I have the cavity but no cavity tray/weep holes. I don’t think I can fit a cavity tray here and without that weep holes seem a bit useless as any water is unlikely to find them.

I could however add some air bricks behind each was section. Would think be a good plan it does it actually increase the risk of getting water into the cavity to start with?

Thank you in advance for your thoughts and any other advice that may be in any way relevant to this build, this is very much a new experience for me! Photo of the current state below.

 

[Spectric]

I assume you used a DPM under the wood attached to the floor. The problem is warm air contacting a cold surface like the brick wall where any moisture in the air will condense out so using PIR board between the studs and using aluminium foil tape to completely seal the face will prevent this happening. You will need to ventilate the space behind to allow any moisture through the bricks to escape.

 

[Doug71]

Bit late now but when I did similar on my house we put a breathable membrane (Tyvek) on the outside face of the stud wall.

 

[Fitzroy]

Looks great, construction approach of skin, air gap, insulation, vapour barrier, internal board is sound. Ventilation to the air gap is sensible in case you do have any moisture penetration or condensation, air bricks top and bottom would be ideal.

 

[scruffmeister]

Thank you all for your feedback. I like the idea of Tyvek on the outside but not an option now. Similarly I confess that I overlooked putting a DPM under wood, but the wood is treated timber and the floor has historically been dry and I suspect has a DPC under the slab so hopefully will be OK.

I am a bit unsure how to secure the vapour barrier to the brick piers that exist next to some “end sections”. E.g in the photo below to the right of the door I would need to fix the vapour barrier around the door where there is brickwork. I could fix to wood frame edge but this will leave an unprotected gap between the wood frame and brick pier. I had thought maybe fill this gap with expanding foam, and run the vapour barrier onto the brickwork, but I don’t really know how to affix/seal it once I get there. Any advice?

 

[TomGW]

Ventilate the space by cutting out a few bricks top and bottom (staggered, not directly above each other) and replacing with vents or ventilated bricks. I would also paint the outside of the brickwork with two coats of Thompson's Waterseal.

 

[Adam W.]

Create a warm wall.

50 mm glass fibre insulation up against the brickwork then stuff your celotex or whatever into the studwork.

Staple your tyvek on and board it all off.

This is assuming that you are not going to convert it afterwards and make it part of your living space or rent it out as a home.

 

[Lard]

I'm in the middle of doing something similar to you. What I'm doing differently is that I'm also adding a raised (battened) floor where the battens line up with the wall studs. This means that I have continuous air spaces from wall-wall or floor-ceiling. I have this because I have not fitted a top wall plate or base plate to the wall studs and so the top of the walls are open to the soffit vents around the perimeter of the roof, hence (hopefully) continuous air movement behind my vapour barrier (which is multifoil).

 

[Fitzroy]

Thank you all for your feedback. I like the idea of Tyvek on the outside but not an option now. Similarly I confess that I overlooked putting a DPM under wood, but the wood is treated timber and the floor has historically been dry and I suspect has a DPC under the slab so hopefully will be OK.

I am a bit unsure how to secure the vapour barrier to the brick piers that exist next to some “end sections”. E.g in the photo below to the right of the door I would need to fix the vapour barrier around the door where there is brickwork. I could fix to wood frame edge but this will leave an unprotected gap between the wood frame and brick pier. I had thought maybe fill this gap with expanding foam, and run the vapour barrier onto the brickwork, but I don’t really know how to affix/seal it once I get there. Any advice?

You need a frame somewhere to ‘finish’ the wall on. I’d frame out the door with 15mm reveal where you can run the plywood/plaster into.

The membrane is stapled to the frame, the gap between frame and brickwork filled with a building mastic, board over frame scribed to wall and edge between board and brick filled with decorators caulk.

You could also do the same at the edge of your current frame if you wanted to leave some exposed brick around the door.

Fitz

 

[scruffmeister]

You need a frame somewhere to ‘finish’ the wall on. I’d frame out the door with 15mm reveal where you can run the plywood/plaster into.

The membrane is stapled to the frame, the gap between frame and brickwork filled with a building mastic, board over frame scribed to wall and edge between board and brick filled with decorators caulk.

You could also do the same at the edge of your current frame if you wanted to leave some exposed brick around the door.

Fitz

Thank you Fitz, that is great advice and really detailed. I think I will give something along those line a try.