Insulating a non-cavity wall
James - 11/9/20 at 11:44 AM
Greetings,
Hope you're all well and avoiding Corona!
DIY question for you if I may... unfortunately photo archive not allowing me to put up shots to make this explanation easier.
Recently extended our spare room with a timber tile-hung dormer into the 'loft space' above the garage. Being short of cash I paid the
builder just to build the basic structure of the dormer, fit a window, tile hang it etc. and I said I would do the internals.
It's getting there now and I'm looking at the internal insulation as it's freezing cold. Apart from air leaks one of the big issues is
that half of 1 original wall is only single skin. (rest of the house is cavity wall).
It's a triangular shaped section ceiling height at one end and tapers to nothing, about 8-10 foot long.
Its this tile-hung wall (tiles have been sorted since this v.old photo)
I have a couple of options I can think of:
1) build a 4" stud wall with a 40mm cavity between it and the 'cold' wall- and celotex and plasterboard it.
2) glue 50mm foam-backed plasterboard to it
3) something amazing the collective suggest...
I guess I also need some sort of vapour barrier/DPM between them whichever option I go with?
Thank you!
James
P.s. sorry for no pictures to make this clearer.
[Edited on 11/9/20 by James]
pigeondave - 11/9/20 at 12:20 PM
Isn't there a robust detail from https://www.british-gypsum.com which would sort you out?
cliftyhanger - 11/9/20 at 12:39 PM
OK, this is on 9" solid walls (are yours 4"?) but I had plasterers use plasterboard adhesive and stick insulated plasterboard on the
external walls to help with insulation.
The insulation was 40mm from memory.
Plasterboard adhesive is good stuff, mix it like plaster, blobs on the wall and just stick it up. Use a length of 4x2 to slap it level. Then tape
joints and use easyfil to skim the joints, job done.
ianhurley20 - 11/9/20 at 01:29 PM
I used the dot and dab method to insulate a 1920's bungalow - 50mm insulation with 12.5mm plasterboard, used the same 4 x 2 to get everything in
line and taped the seams. Made a world of difference to the bungalow. Got all the insulation from secondsandco.co.uk at a really good price. I used
them since on an extension where I bought sheets of 100mm foil backed insulation that was seconded because it had been made at 105mm, they were only
£9/ sheet!
Mr Whippy - 11/9/20 at 04:09 PM
I think I would just use Kingspan Insulated Plasterboard, yeah it's not cheap but neither is heating a house...
Sam_68 - 11/9/20 at 07:11 PM
As Mr Whippy's response, insulated plasterboard is the routine solution.
But there are issues you need to be aware of. For example: at some point you've got to deal with the fact that the insulation layer on your
extension is on the inside face of the wall, whereas on the 'normal' (cavity) walls it's the cavity down the middle. Where it jumps
from one to the other, you've got a cold bridge and potential condensation risk.
This work should have been subject to a Building Regulations application, and this information agreed with the Building Control Officer.
SteveWalker - 11/9/20 at 07:11 PM
I too would suggest insulated plasterboard. However, another option for fixing, rather than the adhesive that you mix as you go, is polyurethane
plasterboard adhesive - basically a low expansion polyurethane foam. Its fast setting, so you can be filling the joints very soon after fixing and its
waterproof - handy if your single-skin brickwork ever gets any moisture through it, as it won't travel through the adhesive to the board.
chillis - 11/9/20 at 07:43 PM
I would strongly suggest talking to building control first as any alterations of this nature would need to be either certified by them through the
inspection rocess or carried out by someone registered under the competent person scheme. You will also be required to meet certain requirements for
thermal insulation which may involve more than just insulating the walls with some foam backed plasterboard. (other insulation such as loft and double
glazing may be needed to raise your saps calc. It may prove more cost effective not to insulate the walls 
ianhurley20 - 11/9/20 at 09:04 PM
quote:
Originally posted by Mr Whippy
I think I would just use Kingspan Insulated Plasterboard, yeah it's not cheap but neither is heating a house...
Perhaps I should add that secondsandco are the official outlet for Kingspan products and that is what I purchased
SteveWalker - 11/9/20 at 10:36 PM
quote:
Originally posted by chillis
I would strongly suggest talking to building control first as any alterations of this nature would need to be either certified by them through the
inspection rocess or carried out by someone registered under the competent person scheme. You will also be required to meet certain requirements for
thermal insulation which may involve more than just insulating the walls with some foam backed plasterboard. (other insulation such as loft and double
glazing may be needed to raise your saps calc. It may prove more cost effective not to insulate the walls
If the building inspector is still to inspect the work, then there is no choice but to to what they want.
If however the work is already signed off and it is just insulating the wall that is to be done as separate work, I'd just do it - on the basis
that you are making it better than it already is and that adding double glazing, etc. is too much extra cost and disruption for such minor work. Who
is going to know anyway? After a period of time (2 years?) building control can't serve an enforcement notice or take legal action either.
It is a ridiculous situation that, for instance, my parents' house has solid brick walls and adding 50mm of insulation would make a huge
difference to comfort and heating costs, but adding more would reduce the size of the box room so a bed would not fit, the width of the stairs would
be affected, a bath, washbasin and toilet would not quite fit in the width of their bathroom, but 50 mm will not meet the requirements, so they have
no insulation at all! The alternative, is do it on the quiet. Any improvement is surely worth having, even if it is not enough of an improvement to
meet the regulations?
[Edited on 11/9/20 by SteveWalker]
Sam_68 - 11/9/20 at 10:54 PM
quote:
Originally posted by SteveWalker
It is a ridiculous situation that, for instance, my parents' house has solid brick walls and adding 50mm of insulation would make a huge
difference to comfort and heating costs, but adding more would reduce the size of the box room so a bed would not fit, the width of the stairs would
be affected, a bath, washbasin and toilet would not quite fit in the width of their bathroom, but 50 mm will not meet the requirements, so they have
no insulation at all!
The alternative, is do it on the quiet.
The alternative is to talk to someone who actually knows what they're talking about: someone who will then tell you that Approved Document
L1B to the Building Regulations says:
"If achievement of the relevant U-value... is not technically or functionally feasible or would not achieve a simple payback of 15 years or
less, the element should be upgraded to the best standard that is technically and functionally feasible..."
SteveWalker - 12/9/20 at 12:05 AM
Except that they would simply say that putting the bed the other way around and using a narrower washbasin would allow more insulation - despite the
upheaval of that and the fact that turning the bed around would prevent a computer desk also being in that room.
Sam_68 - 12/9/20 at 12:26 AM
quote:
Originally posted by SteveWalker
Except that they would simply say that putting the bed the other way around and using a narrower washbasin would allow more insulation - despite the
upheaval of that and the fact that turning the bed around would prevent a computer desk also being in that room.
You're now moving the goalposts to suit your argument, of course.
... But in my experience (into my 5th decade in the industry, and currently Director of an Chartered Architect's practice), you're quite
wrong. They are usually very pragmatic and helpful when approached with intelligent arguments.
NuZil - 12/9/20 at 01:34 PM
It's not difficult to achieve a U value that would be compliant with the technical standards wherever you are.
Insulated plasterboard on its own is highly unlikely to do that on its own unless the existing building fabric was pretty good, which it
wasn't.
It could, however, be used in tandem with a modern insulation material, like Kingspan rigid board insulation between the studs of a newly constructed
inner leaf.
This is a job you'll do once, and the reduced energy bills and increased comfort both make it worth doing once and doing properly.
In broad terms, and pending a calculation of the actual U value, that's the sort of solution I'd be looking at, after having consulted the
technical standards.
(I'm in Scotland, so won't make specific comment on England.)
Sam_68 - 12/9/20 at 05:43 PM
quote:
Originally posted by NuZil
It's not difficult to achieve a U value that would be compliant with the technical standards wherever you are.
As per my first post, above, though, you do need to exercise a certain amount of care not to create a thermal bridge and/or condensation problems.
quote:
Originally posted by NuZilInsulated plasterboard on its own is highly unlikely to do that on its own unless the existing building fabric
was pretty good.
You can, in fact, get insulated plasterboard with enough insulation thickness bonded to it to do the job on a single-skin brick wall (which is what
you tell us you've got, plus the tile hanging).
Basically, you're looking at a minimum U-value of 0.28 or 0.55, depending on whether it's 'extension' or 'refurbishment of an
existing thermal element'. Try to work to the former anyway.
72.5mm. Kingspan Kooltherm K118 insulated plasterboard on adhesive blobs will give you an acceptable U-value in most cases.
Some builders bellyache that it's a bit heavy to handle, and say they prefer to do it as a separate insulation layer plus plasterboard, but then
if I specify the latter (as an architect) they invariably grumble that that it's easier to do as one process with insulated plasterboard...
basically, builders whinge at architects: it's just a long-standing tradition. 
NuZil - 12/9/20 at 05:48 PM
I think the point we're both making here is that a good and compliant standard is perfectly possible.
(using slightly different solutions, but that's ok.)
I'm a Building Surveyor, so I guess in the eyes of the RICS, a jack of all trades ;-)
James - 17/9/20 at 01:39 PM
Hey Folks,
Thank you for the advice I took it and went with the insulated plasterboard in the end.
By luck more than judgement I actually managed to do it all with a single sheet of board (plus a 1" x 4" space filled with an off-cut of
celotex).
I even lucked in with the adhesive as Jewsons had a split bag they offered me for free! 
Now just got to attack the rest of the gaps with spray foam, plasterboard the vaulted ceiling and then let the plasterer do his worst!
Thanks again!
James
[Edited on 17/9/20 by James]