Re: studwall butting up to external wall - insulate or not?

[IMM]

I have been lurking here for many months while I do a fairly

> comprehensive destruction job on my wee cottage (back to stone walls, > no internal walls, foot of earth dug out of floor, new services etc). > > Anyhow, new floor was poured last week, and I am starting to dry-line > and rebuild internal walls. My question is this: stud walls > traditionally butt up directly to the existing walls. As I am > drylining, with celotex and battens, will the stud wall form a > bridging point for cold to enter, or can I continue the celotex > unbroken, and butt the stud up to that, with longer fixings to get a > good purchase on the wall behind? Any thoughts anybody?

You can do that and it is advisable. If the Cellotex is 25mm thick, you can make 25mm spacers from copper pipe, then the wall will be well fixed and the insulation not squashed. But the wall must be well fixed. Fixing it well to the ceiling and floor should be enough. The wall may be so well fixed top and bottom, that only long screws is all you need to stop lateral movement.

[Dave Liquorice]

Anthing that is in direct contact with the real external wall and not insulated will form a cold bridge.

I'd fully line all external walls forming a "warm box", not sure what you do about any joists though... Your architect/engineer/BCO will have something to say surely?

I'd build the drylining frame work with provision for the fixing of the stud wall ends to that.

[Tom Dixon]

Good advice, thanks, I thought this the common-sense approach, but sometimes you just need some reassurance!

[IMM]

I have seen this method. The outside wall had a partition stud wall not touching the outside wall totally eliminating cold bridging. Insulation was in the void. Fermacell prefinished drylining was used. This is similar to MDF in makeup and is very stiff, so much you can hang cupboards on it.

Where the partition wall that is to be 90 degrees to the outside wall was to but onto the outer wall inner stud frame a stud was fixed. The new partition wall had a stud that was fixed to the outside wall stud doubling up the thickness, using heavy coach type bolts. This stud then was the end stud of a partition wall that was at 90 degrees to the outer wall, with plasterboard pinned to it.

The outside walls to not have to touch the inner stud frame walls. The partition walls at 90 degrees to the outside walls, do not have to be secured to the outside wall, the inner stud frame is enough.

Then total elimination of cold bridging. Watch out for cold bridging at the reveals of doors and windows. People ignore these. One method devised in windows was to make a box out of plywood and slide this into the opening. The frame then slid inside the box.

[John Rumm]

The complete cover idea is best. However, if you do need to bridge the insulation and you are filling the stud voids with 100mm urethane/PIR foam, then you will still meet the required u values even with the cold bridge.

[IMM]

Required U values? he wants to eliminate cold bridging. Building reg U values mean nothing. They are so poor anyway.

[Tom Dixon]

Thanks for all contributions to my original post. The plan is to insulate all external wall surface with Celotex (40mm), and all reveals with 20mm Celotex - the floor gets 70 mm and the loft loads!. The joists and the internal window ledges will be the only bridge points (although I might see if it is practical, because I have removed the existing rotten ledges, to insulate beneath the replacement ledges...) Because I am placing Celotex directly against a rubble wall I am using studwork, secured top and bottom, to secure insulation and to provide a cavity for electrics, plumbing, more insulation etc and to mount plasterboard / hang cupboards on. This ensures that the vapour barrier / insulation isn't breached in any way, and the thought of securing battens or whatever to the rubble wall didn't appeal at all! I haven't settled on a spec for the studwork, I was wondering if I could get away with 3 x 2 but used "flat" against the wall - I really don't want to sacrifice any more floor space than I have to, this being a small cottage.

This meets the required u levels, the building inspector is happy, now all I have to do is check budget - the first timber arrives tomorrow!

Tom

[J]

If it is possible Tom, would you be able to put up a couple of pics of the details as you complete them? We are shortly to undertake a similar project and it would be useful to actually see how it is done. Regards John.