Solid wall insulation.

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Let me run my thoughts by you for my old solid wall insulation that forms part of the extension (cavity walled).

Solid brick wall > 50x50mm treated wooden battens > 50mm celotex between battens > VCL > plasterboard > skim

This OK? If not, what to do differently
 
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I used 25 x 50mm battens, 50mm celotex (foil both sides), 12.5mm plasterboard, then skim.
Why do you need such a big air gap?
With foil board, there is no need for VCL if you foil tape the joints.

I think 100mm is the recommended u value (could be wrong), but you could easily do 75mm if you used 25mm battens.

Only think to bear in mind, screw length for insulation and even longer for plasterboard.
I used 70mm for celotex and 80mm for plasterboard.
 
You'll potentially get pattern staining on the plasterboard from the battens, unless you insulate across them too before plasterboarding.
 
I used 25 x 50mm battens, 50mm celotex (foil both sides), 12.5mm plasterboard, then skim.
Why do you need such a big air gap?
With foil board, there is no need for VCL if you foil tape the joints.

I think 100mm is the recommended u value (could be wrong), but you could easily do 75mm if you used 25mm battens.

Only think to bear in mind, screw length for insulation and even longer for plasterboard.
I used 70mm for celotex and 80mm for plasterboard.
There was no plan for an air gap... should there be?
 
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You'll potentially get pattern staining on the plasterboard from the battens, unless you insulate across them too before plasterboarding.
I could "double insulate" but from my initial suggestion there would be the VCL separating the battens from the plasterboard...
 
That was my thought - maximising space. What purpose does that air gap serve? It's not vented anywhere?
 
Should there be any condensation, there is a gap to stop it being bridged into the room... apparently.

I've noticed no staining using this method... well so far.
 
I also used expanding foam to seal any gaps under the battens to the wall, it makes for a really solid job... but does take a bit of time.
Concrete screws hold the battens in place.
 
This is where my confusion lies.... I thought interstitial condensation comes from the warm room side. Warm moist kitchen air travels into the walls and condensates when it reaches the cool part - hence the VCL immediately behind the plasterboard...
 
This is where my confusion lies.... I thought interstitial condensation comes from the warm room side. Warm moist kitchen air travels into the walls and condensates when it reaches the cool part - hence the VCL immediately behind the plasterboard...
Yours, mine and everybody's.

If you search long enough, you'll find different methods to beat the condensation, some with gap, some without.
All I can say it what I've done seems to work, in theory only the batten is touching the external walls, yes this batten could get damp, but the foil on the celotex will stop it being transferred to the plasterboard, likewise, warm air from the room can't penetrate the foil layer either.
This in turn could be a problem, but with window opening, ventilation should be good.

I'm not an expert, but just giving my thoughts, after lots of reading.
I lost 25+50+12.5mm of room off all external walls.
 
I could "double insulate" but from my initial suggestion there would be the VCL separating the battens from the plasterboard...

A vcl does nothing to stop the thermal bridge caused by the uninsulated timber battens.

And you don't want any air gaps or cavity in this type of construction.
 
And you don't want any air gaps or cavity in this type of construction.

Not wishing to doubt, but when I called celotex the batten method was suggested by them, and reading their installation pdf this is one of three ways to apply to internal walls.
 
Not wishing to doubt, but when I called celotex the batten method was suggested by them, and reading their installation pdf this is one of three ways to apply to internal walls.

Yes the batten method is OK, but without any air gaps or cavities. Its not a no-no, but it then adds risk, and there is no need to do that.
 

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