Garage conversion insulation how to attach to walls

[Ivor Windybottom]

Sigh. All points missed. Do you know what a vapour membrane is? Let's start with the basics.

 

[Ivor Windybottom]

It's an impermeable membrane that should be between the room and the insulation.

If there isn't one you'll get damp within the insulation.

Yes there's a cavity even in this case, it's between the plasterboard and wall and happens to be full of celotex but it still performs the same function as a cavity.

 

[Ivor Windybottom]

There's a transition of temperatures across the cavity - from room temperature on the inside, to outside temperature on the outside.

If you let that warm damp air from the room get into the insulation then it's likely to condense at some point, which will cause damp, rot and smells.

 

[Ivor Windybottom]

Plasterboard and ply are not impermeable.

 

[noseall]

It's an impermeable membrane that should be between the room and the insulation.

Eh?

Are you confusing vapour control with a DPM? It sounds like you are.

Vapour should not migrate from the warm side to the cold side - VCL - fitted behind the plasterboards via sealed PIR foil coated boards with foil tape etc.

Damp/rain/water should not permeate into the internal structure - DPM (impermeable membrane or visqueen)

 

[noseall]

There's a transition of temperatures across the cavity - from room temperature on the inside, to outside temperature on the outside.

If you let that warm damp air from the room get into the insulation then it's likely to condense at some point, which will cause damp, rot and smells.

Warm damp air can get to the internal face of the insulation, but not beyond it to the cold side.

 

[freddiemercurystwin]

Eh?

Are you confusing vapour control with a DPM? It sounds like you are.

Vapour should not migrate from the warm side to the cold side - VCL - fitted behind the plasterboards via sealed PIR foil coated boards with foil tape etc.

Damp/rain/water should not permeate into the internal structure - DPM (impermeable membrane or visqueen)

No he's not, a VCL is a not a vapour barrier they are not the same things. You fit a Vapour Barrier behind plasterboard, that is an impermeable membrane not a Vapour Control Layer which typically is not airtight. If you wanted you could swap a VB for a DPM fitted imediatly behind the PB in a wall situation they would achieve the same thing.

 

[noseall]

Does it need a vapour barrier under the plasterboard, to stop moisture migrating from the room condensing within the wood?

The wood is at room temp, due to the continuous layer of insulation, separating the wood and the garage wall.

 

[noseall]

No he's not, a VCL is a not a vapour barrier they are not the same things. You fit a Vapour Barrier behind plasterboard, that is an impermeable membrane not a Vapour Control Layer which typically is not airtight. If you wanted you could swap a VB for a DPM fitted imediatly behind the PB in a wall situation they would achieve the same thing.

With regards to my image I posted, the black polythene is acting as a DPM. The foil tape is dealing with the vapour etc. I'm a bit lost on Windy's explanations and terminology in respect to that.

 

[robinbanks]

If there isn't one you'll get damp within the insulation.

Not inside a sheet of aluminised kingspan you won't. WUFI can claim the dewpoint is in the middle of a big block of PIR all it wants; you aren't going to see water dripping out the bottom of it

a cavity .. happens to be full

No. Go and look up the definition of "cavity" in a decent dictionary