Insulating solid walls

[GMM]

Hello folks.

I know this topic has been covered before but I can't seem to find the details I have been pondering about and I hope someone might know the answers. I have never done this before because my current place has insulated cavity walls but am now moving into a Victorian house with solid brick.

First of all, yes I know it's covered by building regs but I have no intention of bothering a BCO with such matters as the final U-values required are so impractical in terms of depth of insulation that it would never happen if I went down that route. Somehow I doubt the insulation police are going to knock on my door to check it out. Oh, and there's no way I can insulate on the outside, even though that might well be better.

From a whole range of sources I can see the standard approach (variants on wall - kingspan/celotex - membrane - plasterboard). Clearly, the kingspan sits between tanalised studwork that is protected from damp from the wall by a strip of dpc and/or spacers. All well and good. (I would look at insulation-backed plasterboard but this is in a kitchen and the studwork can be arranged to carry wall units etc).

So, the questions that arise are mostly born of a paranoia about damp from the wall in the longer term:

Should the plaster be removed from the wall? It adds some insulating properties but without ventilation could wind up as a big mess behind the whole thing - crumbling plaster behind the studding could destabilise the whole thing. On the other hand, removing the plaster would be a lengthy and dirty process.

How do you space the kingspan from the wall? It clearly shouldn't be against the brick, should it? I know it will sit snugly between the timbers if cut properly, but it could become displaced for a number of reasons. I was thinking of using 50mm kingspan between 68 mm studding, so there should be an 18mm (or thereabouts) air gap.

Is it bad for the wall in the long term? It seems to me that a conventional wall should dry (after rain etc) partly because of the heat from inside driving the water out. With an effective insulation layer, this effect must surely be reduced, although for all I know this contribution could be insignificant.

Any information gratefully received as usual!

[stuart noble]

I have been pondering the possibilities of skimming quite thin layers of closed cell foam so that the existing dimensions of the rooms can be maintained. Camping mats appear to be highly efficient, despite the

6-7mm thickness. Is it worth hacking off just to incorporate that much foam? Can you plaster directly on to it? Dunno, but I might do a trial this winter

[The Natural Philosopher]

No need. Its foil backed.

It clearly shouldn't be

Why leave an air gap? You have removed the moisture from the brick surface FROM the kitchen..so no need to 'dry the brickwork out - that will happen naturally as its porous. You don't even need a DPM except to protect the studwork from rot. BUT the overall wall humidity will be low anyway. Most moisture will be fom inside the house if the guttering is good and the wall is not exposed to massive driving rain for long periods.

You WILL need an extractor fan though to remove moisture explicitly.

The wall will dry out because the air outside is generally not saturated with moisture. And in any case slightly damp brickwork is no big deal - only if its so full of water that when and if it freezes it spallates, is there an issue.

And that can be solved by a waterproof coating on the outside..render or a paint on sealer. IF its necessary. But mostly it is not.

One hint that may be useful. If you are totally plating a wall with units etc, consider MDF not plasterboard. It paints well, tiles well and is strong enough to screw to. Only downside is it moves..and will crack at any butt joints. But it comes in 8ft lengths, which is often enough to span a whole wall, and horizontal joints can be covered in e.g. units. It also removes the cost and issues of skimming.

Use decorators caulk on the corners to cope with cracking there.

Also, this is a great opportunity to lay surface height sockets for kettles and microwaves, by simply tacking cables to the wall before insulating..

I'd simply tape some plastic or foil strips to the wall, whack up some

2x1 or 2x2 studs. infill with 1" or 2" celotex and TAPE OVER COMPLETLY and then cover in MDF.

caulk that, paint it ,fit electrical socket back plates (these can be screwed to the brickwork FIRST if the spacing works out OK) and fit the kitchen around it.

[RobertL]

On Sep 14, 10:34=A0am, GMM wrote: ...

There are exeptions in the regs that allow you to insulate less than the full requirement if that would impact the use of the room too much. We did this in our house in some places and applied 35mm of celotex-backed plasterboard instead of the 110mm (IIRC) that was actually required.

The celotex (or whatever) went direcetly onto the old plaster with no airgap. See here:

[Roger Chapman]

On an earlier occasion I raised the possibility of a product called 'hempcrete' (IIRC). A mixture of chopped hemp and lime mortar which apparently has insulating properties. Unfortunately no one rose to the bait and I don't currently have a link to my original information which included a video of a man (wearing rubber gloves) slapping the mixture onto an old wall before smoothing it off. The sort of rough diy that I could probably manage.

[Martin Bonner]

Well, anything's better than nothing. You'll be looking at a U value of about 2 atm, and regs call for something like 0.25 (off the top of my head) for new build.

No. The kingspan sit BEHIND the studwork. The design is wall- kingspan-battens-plasterboard.

See

have to sign up for the download annoyingly).

The problem with insulation *between* studwork is that heat flows through the studwork.

A system with 9" brick, 70mm PIR foam, 25mm battens, and 12mm plasterboard/MDF/plywood should get you to current regs.

Nearly all the damp in a wall comes from the *inside*. This seems counter-intuitive (it's dry inside and wet outside), but the point is that "warm and fairly dry" air contains more water that "cool and damp" air. When your steamy kitchen air passes through the insulation, the steam will condense and cause damp.

The solution is to be careful about the vapour control layer. The insulation will have a foil layer (which should be on the inside), you carefully seal this with tape ... and all should be well.

[stuart noble]

> Robert

I see Gyproc do a 27mm board. I reckon I'd have room for 20mm without upsetting the levels round doors and windows. Don't know what the u values would be but my gut instinct is that even 7.5 mm of foam would have a big impact on typical 9" walls.

[GMM]

Thanks for that. I had clearly been thinking about it the wrong way around, imagining water from outside to be the bigger problem!

The MDF suggestion is interesting: I had been thinking of organising things so that hardly any of the plasterboard joints were on show, but hadn't thought of MDF as I have normally found that PB makes a pretty good finish when just painted. The wall in question has a window taking up the centre third and the space each side will be covered by base units, tiles or something (incorporating sockets as you say), then wall units, so it's only the edges of the windows and the wall above the wall units that will show.

[js.b1]

Insulation need not meet regs...

a) 5% rule - where you would lose more than 5% of the floor area, not difficult in a tiny box room which even victorian houses may have

and

b) Reasonably Practical - where a door hinges against the outer wall leaving you perhaps 25-30mm of space for insulation & plaster, you are not expected to demolish the house to force 50mm insulation in - nor spend ridiculous sums on the special insulations.

There are many ways of fixing. Studwork is a lot of hassle and people tend to just hammer-fix insulated-plasterboard directly to the wall with special oversized washers and skim over. I believe that is most popular with Celotex Technical at the moment, along with fixing battens OVER celotex which is foil-taped, then insulation between those slim battens, then plasterboard over the top. This has the benefit of creating a more air tight surface at the solid brick wall. Solid brick means some do not recommend dot-n-dab adhesion methods, but it comes down to exactly how dry - triple engineering brick with paper wide mortar is pretty dry unless you have a guttering leak.

So rule #1 is fix the guttering before you stick insulation up, ie, fix the damp now rather than try to make it go away. Then rule #2 is buy/hire a cheap waterproof video camera and stuff it up all your drains to check none dropped, cracked, full of tree roots. Then rule #3 is have a nosey around for any leaking water main, ie, newly forming cracks or boggy areas.

Insulation is everything, it pays back every year.

Mess... did someone mention mess... do the main living area first and as well as you can, ie, where you will get the biggest payback re likely temperature. For example a living room may be 22oC, but a unused box room may be 12oC. Celotex etc are not cheap and you can always leave space to add more later if need be. "Seconds" are your friend, and DO foil tape the joints as necessary.

[The Natural Philosopher]

your gut is correct.

even 3mm of foam makes huge difference

[The Natural Philosopher]

(you have to sign up for the download annoyingly).

yes, but its less width overall.

[The Natural Philosopher]

+1

I improved condensation on a solid brick kitchen with 3mm CORK TILES.

That's how little you need to make a difference.

celotex is 50 times better an insulator than brick.

So you can halve U values with just 1/50th the depth of the brick wall. If that's 9", that's about 5mm or less

[Robin]

I've been contemplating the same job and have noted that Kingspan and Celotex both advise an airgap but in different places. As in that link Celotex have:

wall+insulation+battens-with-airgap-plasterboard

But Kingspan seem to favour:

wall+battens-with-airgap+insulation+plasterboard

I've not got the faintest idea why (but being cynical I wondered if Kingspan are trying to push their combined insulation-and-plasterboard products.)

[GMM]

I had seen that Celotex diagram before and couldn't see any reason for the battens: Why not stick the PB to the celotex and save the depth of the battens? Whatever the reason, it's hardly practical in a kitchen where dirty great heavy wall cabinets full of stuff need to be hung. Screwing a cabinet through PB into studding that's well fixed to a wall would be fine, whereas screwing through PB, batten, celotex and then (a bit) into a wall would seem to be a recipe for trouble and not a problem I'd want in a new kitchen. That would be even worse if the aim was to meet the regs and use 75 or 100 mm celotex. Clearly timber studs will provide a bit of cold bridging but the aim here is to make things better within the limits of practicality rather than doing a perfect job at one level only to generate a whole range of other problems.

It seems that sealing the whole thing is the key however and I'll make sure that's done well.

Cheers

[GMM]

Well, drains are top of my agenda (having had a pro- camera survey), pretty much before anything else, but that won't be DIY or it would never be finished. Unfortunately, there's no way I can do anything in the living room: I wouldn't lose appreciable floor space, but there's no way I'd ruin original Victorian cornices by adding anything to the thickness of the wall, so we'll just have to live with the heat loss there, after dealing with the floor, windows etc.

[GMM]

Is there a ready source of U-values anywhere? I was trying to look it up and although I could find the celotex calculator, that models the wall according to their formulae. It would be useful to know the influence of any given material.

[fred]

In article , GMM writes

You may be able to something in the lounge too.

Older plaster will likely be an inch or so thick so if you remove this you can fit 25mm insulation backed plasterboard, screwed though into the brick to gain a bit of insulation.

To avoid damage to the cornice you can isolate it completely by cutting a groove just under it all the way down to the brick.

There's often a plain step out at the first part of the cornice so if you are prepared to lose a bit of that feature then you can fit a thicker insulation board.

Is your plaster straight onto external wall? Here it is straight onto internal brick walls but is gapped lath and plaster on external walls so there is more thickness to play with.

[The Natural Philosopher]

brickwork has a K value of about 1, so a thickness of 100mm (4") is about ten in terms of U value.

Celotex is about 0.02 k value.So 100mm of that is about 0.2 U value.

It's in my building regs bookiewookie.

a typical outside hardwood door is about 3-5 so better than 4" of brick..

[GMM]

I shall have to investigate that a bit once I actually move and I'm free to poke about with the place. It would be good if I could do something with the walls at each end (both ends are outside walls) and I have to do quite a lot of work in that room anyway so a bit more mess won't matter, if I can fit things.

[stuart noble]

I lined my son's bedroom in cork 30 years ago. Nice big noticeboard

Hmm, that is very interesting.