Most cost effective wall insulation?

Has anyone any experience?

I drywall insulated a few rooms in a detached house using 50mm Celotex. I certainly cannot complain about the functionality, but it was pricey.

Wickes do a foam backed plasterboard, and my current project is a terraced house in the UK, so it isn't quite so exposed as the first job.

Is it a worthwhile proposition to clad the walls with, would it provide a significant improvement over the plastered brick walls ? I dont want to spend a great deal of cash in order to save a pound or so each month

Is the stuff "safe"? I wouldn't think there is any marked increase in fire risk, but it is something that has been brought to the fore, recently.

Regards

AB

Reply to
Archibald Tarquin Blenkinsopp
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First the most cost effective is the cheapest crap you can get, bulky and flammable. 2nd foam lined PB is always polystyrene, which is very flammable, and more expensive per amount than separate layers. So I don't really see the upside to it.

You choose how much flammability you want to live with. PB is a fire barrier, but once it burns through the polystyrene is nasty. Thick toxic smoke and rapid spread. I wouldn't use it, some do.

Any insulation is going to be a good bit better than none and can halve your heating costs. Also:

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NT

Reply to
tabbypurr

Many (if not most) of the insulated boards I've seen lately were PIR (or the more expensive phenolic). The risks of them in fires are patently being reviewed but they ain't all polystyrene (or PUR).

Reply to
Robin

nope, I don't think it can

full insulation up to modern standards might

but one random wall with 1980s standard insulation is going to see savings of 15 quid a year.

tim

Reply to
tim...

Branded celotex can be more pricey than some of the other makes of basically the same stuff - you can quite often find a 2 to 3x difference in price between brands. For example you can pay £35 or more for a 8x4 sheet of 50mm celotex from the sheds, but quite often get similar from some of the bulk distributors for £14/sheet. (especially if you don't mind "seconds" that may have a few dings in them etc). Prices usually improve for multi sheet purchases. Buying separate sheets and normal plasterboard is probably cheaper than buying foam backed PB, but the later is probably easier to use.

Its probably a similar PIR style foam - so going to be similar in performance.

Do you know if the current wall is cavity or solid?

Going from 9" solid wall to one with 50mm of PIR foam would reduce heat loss through the wall to a quarter of its current value. You could make a rough guess at say 30% of your heating bill being heat lost through the walls. So your monthly saving would be around 22% (i.e. 75% of 30%) of your total bill.

It would be worth doing a more accurate heat loss calc for the place to see what difference you can expect. There is a worked through example here that might help:

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PIR foam will not sustain a fire in its own right, although will burn if heated hard enough and long enough by a fire in something else (and like most PU foams, give off cyanide gas in the process). In a domestic situation its not so much of an issue since you will get out of the place asap anyway, and there are plenty of other things about that will pose a dangerous smoke risk before the insulation gets to be the main problem.

You probably get better fire performance from Rockwool or glass fibre, but then you will need at least twice the thickness for the same level of insulation - which can be a problem when dry lining rooms and losing space from the interior dimensions.

Reply to
John Rumm

Are you trolling?

NT

Reply to
tabbypurr

22 sheets of Ecotherm eco-liner 2400x1200 37.5mm came at ?22.50 + VAT. ea. I think that was 25mm PIR 12.5 p. board.

Comes with a built in foil moisture barrier.

I was pleased to discover that it can be easily cut with a jig saw:-)

Reply to
Tim Lamb

nope

adding insulation to one part of your 1960s home is not going to see a halving of your heating bill

simples

tim

Reply to
tim...

No, but reducing losses through the roof and walls to a quarter of their original losses is not that difficult if you are starting with and uninsulated place. That alone would have potential to halve the overall bill.

Reply to
John Rumm

Ie yes you're trolling.

NT

Reply to
tabbypurr

Although in practice what seems to happen is that the house ends up being maintained at a warmer winter temperature. But you are right that good loft insulation is a major energy saver - especially in a bungalow.

Reply to
Martin Brown

that is a very very ambitious target for after market insulation

I suspect it is unachievable

no it won't

because you will still be losing the same 70% through the bits that you didn't update

tim

Reply to
tim...

Which is also arguably a perfectly acceptable outcome - keeping costs much the same but enjoying being warm for the first time!

Reply to
John Rumm

Not especially... still its not difficult to do some basic sums to get a feel for the savings available.

A solid wall has a U value of around 2.2

If you add say 50mm of PIR foam to that (internally or externally), then you will reduce it to around 0.4 - that's more than a 5 times reduction.

Draft proof the windows to reduce air change losses, fit decent curtains with a thermal lining, and you will be well on your way to a 75% reduction of total losses through the wall - even without double glazing.

Sorry, not following the logic? Are you suggesting that if you stop it getting out one place it will just go find somewhere else to escape at the same rate?

I would suggest its not worth going overboard super insulating just one aspect, if you are not also addressing others since you quickly reach a point of diminishing returns.

Reply to
John Rumm

Many thanks John, very informative and clarifying once again that there is no real short cut to DIY.

I'll go for the separate plasterboard and cellotex equiv. 50mm may be a bit dfficult, but I'll do the sums for a thinner version.

Bloody obvious, I know, but the loft isn't insulated. I never actually thought of that. I recollect that loft insulation was almost given away some years back, I expect it's a bit more pricey now.

Anyway, thanks for the info.

AB

Reply to
Archibald Tarquin Blenkinsopp

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