Insulating single skin wall - garage conversion

[0Floz0]

Hi,

Just ordered most of the wood for my conversion. Thanks for all the help so far on that.

I've got one wall that's slightly tricky. Its single skin so will be insulated using PIR sat within a timber frame. I've just ordered some tyvek house wrap to use as the breather membrane. However, there are piers on the wall I've got to go round. The plan is to layer it (without tape), so top layer hangs in front of the bottom layer (as its 1.4m width roll).

What's the best way of attaching the membrane to the wall? I've got 2 piers to get round. The timber frames were going to go either side and in between the piers and then overlaid with 30mm of PIR. I'm wary of piercing the membrane but need to ensure its fully covering the piers and I've not got any gaps. Any tips?

There seems to be some damp in the bottom corners, I've attached a picture if that helps. I'm going to put some DPM down over the slab anyway as the DPM under the slab doesn't seem to be working at the edges. Whats the best way to tie the dpm into the vapour membrane?

TLDR:
How would you attach the tyvek to the wall/piers
How do you attach the tyvek to the DPM i'm going to put down.

It'll be a floating floor so there won't be any joists to screw into at the bottom. Unless I run that wall first and then screw into the concrete. Could that cause damp issues as the DPM would be pierced.

Thanks

 

[motorbiking]

Rather than infilling between the timber studs with celotex and boarding over. Have you though about using plasterboard foam adhesive directly on to the wall? No need for DPM if the celotex/PIR is foil backed and the result will have a better U value as the PIR will be butted up to each other. You really don't need to stud this job out. The other benefit is its much easier to get the wall straight.

This stuff plus some screws in to rawplugs with board washers will hold it in place during drying / fire.

Soudal Genius Gun Plasterboard Adhesive Foam

Soudal Plasterboard Adhesive Foam is a fast curing replacement for traditional mortar adhesives. Use it to fill cavities and for bonding plasterboard to walls. You'll find that this foam is suitable for use on all common materials such as concrete, stone, plaster and wood.The adhesive comes...

www.toolstation.com

For the piers you just clad them in PIR like a chimney in a house.

 

[0Floz0]

Rather than infilling between the timber studs with celotex and boarding over. Have you though about using plasterboard foam adhesive directly on to the wall? No need for DPM if the celotex/PIR is foil backed and the result will have a better U value as the PIR will be butted up to each other. You really don't need to stud this job out. The other benefit is its much easier to get the wall straight.

This stuff plus some screws in to rawplugs with board washers will hold it in place during drying / fire.

Soudal Genius Gun Plasterboard Adhesive Foam

Soudal Plasterboard Adhesive Foam is a fast curing replacement for traditional mortar adhesives. Use it to fill cavities and for bonding plasterboard to walls. You'll find that this foam is suitable for use on all common materials such as concrete, stone, plaster and wood.The adhesive comes...

www.toolstation.com

Building regs said I need a fair bit of PIR and some overlay across the piers as well. What would I be attaching the plasterboard to? Straight onto the PIR?

 

[motorbiking]

Yes. Using the same bonding foam and then add some screws for convenience/fire safety.

 

[^woody^]

Rather than infilling between the timber studs with celotex and boarding over. Have you though about using plasterboard foam adhesive directly on to the wall? No need for DPM if the celotex/PIR is foil backed and the result will have a better U value as the PIR will be butted up to each other. You really don't need to stud this job out. The other benefit is its much easier to get the wall straight.

This stuff plus some screws in to rawplugs with board washers will hold it in place during drying / fire.

Soudal Genius Gun Plasterboard Adhesive Foam

Soudal Plasterboard Adhesive Foam is a fast curing replacement for traditional mortar adhesives. Use it to fill cavities and for bonding plasterboard to walls. You'll find that this foam is suitable for use on all common materials such as concrete, stone, plaster and wood.The adhesive comes...

www.toolstation.com

For the piers you just clad them in PIR like a chimney in a house.

You can't adhere to a wall that might get damp.

Also, what would be preventing damp, or evaporating moisture from getting into the room or structure, or running down and into the floor?

 

[^woody^]

What's the best way of attaching the membrane to the wall?

Fix at top above those timbers (on top edge) and just drape it down the wall.

Allow for overlap at the floor and tape/lap with the floor DPM

 

[0Floz0]

Fix at top above those timbers (on top edge) and just drape it down the wall.

Allow for overlap at the floor and tape/lap with the floor DPM

Thanks. Will do that. What tape would you use? Or could you get away with none as long as it goes far enough behind the dpm?

How would you fix the battens on top? Was thinking of going into the ceiling joists and into the floor so it’s not connected to the single skin wall. Is that wise or is there a better way? Wary of piercing the dpm on the floor.

 

[^woody^]

What does the top and bottom look like?

How are you forming the floor?

 

[Mr Chibs]

Why not put some insulation 'wedi' washers and screw the boards to the wall? Either insulated plasterboard or separate boards.

Staple the membrane to the wall plate, drape down, just sandwich it the wall with the above washers.

 

[0Floz0]

What does the top and bottom look like?

How are you forming the floor?

Floor is floating floor. So it’s a concrete slab, will have pir which I’ll put aluminium foil tape on joints. Then chipboard. I’m tempted to use polystyrene as I’ve got 220mm to fill but it’s only 8m2 so it’s probably a £180 saving for full poly over pir. Worried poly could sag though after a while.

Top is ceiling joists for the pitched roof.

Is it almost better to have lots of vertical strips hanging down rather than 2 horizontal strips as it’s only a 1.4m wide roll.

 

[^woody^]

Here's the principle.

You would use polythene vertically and across the floor, and lap and tape the joint as shown. You are making a floating floor, so ignore the joists, and just butt up to the frame.

I'm confused that you mention using a breather membrane. Was that to be used instead of polythene? If so you will need to construct the frame first and then staple the membrane to the back then fix the frame. Awkward. And strictly, if using membrane you would need a minimum 25mm vented cavity for it to work. I suppose you could have the membrane tight up the back of the wall, but it's a bit non standard, and you'll need to be careful with the detailing. You'll also need to fit a strip of polythene to the frame first, which will lap the floor DPM after the frame is fitted, and then the membrane over the top of the polythene.

 

[motorbiking]

You can't adhere to a wall that might get damp.

Also, what would be preventing damp, or evaporating moisture from getting into the room or structure, or running down and into the floor?

They both have a vapour barrier and the plasterboard foam is suitable for gluing to a damp surface. I'd still put a DPC in the floor, but with two vapour barriers on the board there is no need to do it on the walls. I'm just repeating what celotex and kingspan say.

 

[Mr Chibs]

They both have a vapour barrier and the plasterboard foam is suitable for gluing to a damp surface. I'd still put a DPC in the floor, but with two vapour barriers on the board there is no need to do it on the walls. I'm just repeating what celotex and kingspan say.

I thought celotex's stance was battens and PIR attached to this, leaving a 25mm gap if damp is present?

Or is this for solid 9"?

 

[motorbiking]

The guide shows dot and dab for solid walls and the factsheet says it provides a vapour control layer when combined with foil tape.

I don't understand why a vapour sheet is needed against another vapour sheet.

I've done it both ways on a 9" wall and I got way better results with the direct bonding method. Its much easier to get a tight seal. But I bow to woody's superior knowledge. I'm just a DIYer

 

[^woody^]

I don't understand why a vapour sheet is needed against another vapour sheet.

A DPM is required to deal with damp that will conve through a single skin wall.

A DPM is not VCL.