Insulation in a confined space

[duncancallum]

Right, Basicly there is no cavity in the timber section of my upstairs front wall. Just the 3 inch space from the joists. I was planning on extending this and then using something like rock wool to pack it with.

But the O/h is concerned about loss of space as the rooms are not huge to start with.

Any suggestions and pointers grateflly recieved.

[Stegel]

I take it you're referring to a bay window or similar, with the timber framing clad externally with render on lath or tile hung? If you use a phenolic foam board, such as Kingspan K7, 75mm will give you a U value of 0.25, which is pretty good by itself. Line the inside with Duplex plasterboard (the board with the aluminised plastic on the rear) which will control water vapour passing into the insulation and add to the thermal performance. If there is a vented path within the inside of whatever is cladding the outside of the wall, in theory you should leave this clear with a 25mm gap on the outside of the insulation, but if this is a bay window, I doubt very much if such provision exists, so just fill it full depth.

EFS

Edited by Stegel on Wednesday 3rd November 14:05

[dickymint]

Rip out plasterboard, staple this on.............

http://www.wickes.co.uk/Thermal-Insulation-Foil-Ro...

Then re-board.

[GuinnessMK]

As Stegal has said, but I'd be tempted to use a composite plasterboard (normal plasterboard with a layer of foam bonded to the back). You can get various thicknesses of insulation to suit different U values / applications.

[Stegel]

Agreed - a plasterboard with attached foam insulation (thermal laminate) will also avoid any cold spots caused by the studs passing through the insulation inserted into the void.