Internal insulation of single leaf external walls: is it safe?

This is technical so apologies in advance.

I'm encountering a significant issue with a house I intend to insulate. The house is from the 1960s. The external walls are not cavity walls. They are, as I understand it, ‘single leaf’ masonry constructions. Plasterboard was put on the external wall and it was never plastered (instead, wallpaper was just put directly on to that plasterboard). There is no existing insulation. I had intended to internally insulate all of these external walls as it was substantially cheaper than external insulation/rendering. According to the BER, "Internal insulation involves a layer of insulation being fixed to the inside surface of external walls, and a suitable fire resistant finish being incorporated or applied." This is what I was hoping to do.

However, I've been advised that there is a high risk of mould growing if I do the internal insulation on these types of walls. Most worringly, there is also an increased risk of asthma and other health problems for residents. I was very surprised at this as SEAI has no issues with it, and the government actually offer a grant to do it. Nevertheless, this person was firmly of the belief that this will be a scandal of the future.

For the scientific evidence against drylining/internally insulating such external walls, I was advised to read the following two articles.

Joseph Little, 'Breaking the Mould 1-A study of condensation in single-leaf concrete wall upgrades'
(March 2009, Construct Ireland)

Joseph Little, 'An analysis of single-leaf insulation upgrades' (May - June 2009, Construct Ireland)

This seems to put a very strong case against this type of drylining internal insulation being used. However, before I decide to spend considerably more money on external insulation, would other people in architecture etc be able to put a defence of this internal insulation to put my mind at ease - or is the scientific evidence generally against this type of internal insulation despite the SEAI etc supporting it? As there'll be a very young family in the house I wouldn't want to make the wrong decision on this, but I also don't want to spend money on external insulation if internal would suffice. Thanks.

PS: I found this article and this article very clear and helpful in understanding the issues here.

listermint

For my money I would externally insulate.

There is a reason folks on the continent laugh at us living in drafty damp and cold houses warming ourselves by a fire.

You'll get more bang for your buck externally insulating by avoiding many of the thermal bridging issues that come with internal slabs.

tradesman

As far as I know there is a sizeable grant available for external insulation. Would make it more appealing and IMO the better way to insulate

BryanF

Hi OP

This has been covered to death on this forum. Most of the regulars are jaded from explaining this so often

Internal insulation is cheap. it's not a good solution as poorly installed it leads to interstitial condensation followed by mould. An interstitial calc should really be carried out to determine dry-lining insulation thickness. External insulation is a better solution.

I have done the same course as the report writers above, and I'd eco their comments.

Rabbo

If you can effectively install a vapour barrrier, interstitial condensation will not be an issue. This is very difficult to do with insulated plasterboard as it would involve cutting back plasterboard slabs at the perimeters and taping the foil.

It more easily achieved by installing a stud system that you can insulate between and then fitting a full vapour barrier over before installing the plasterboard. The Isover Optima is one such system. The downside to this is it takes up a greater thickness and you get much less insulation than a PIR insulated plasterboard. You also have to be very particular about taping joints, junctions, etc.

I would opt for the external insulation if feasible. The SEAI grant for external drylining a detached house is €4500 so it can go a long way particularly if the house is small.

Mellor

Worrying about interstitial condensation is a waste of time imo. The volume of water condensing within the wall is tiny compared to the amount of rainfall the wall will take in.

mp31

The thing I found about Joseph Little's articles is that his work is based on software simulation (using a package called 'WUFI') rather than real life examples where internal dry lined walls have been taken apart to see the amount of interstitial condensation and subsequent mould growth after a period of time. Does anyone have links to such data?

lor2ie

I recently purchased an older house with solid walls. I was going to do internal insulation on the 3 bedrooms and the hall as the house has a brick finish outside, but first of all I got a quote of €12,000 and no grant for internal insulation. Apparently that included changing internal doors etc but still out of my pocket and doors are fine. Then i noticed on an extended section of the house that did get dry wall already that there was mould busting through the drywall and yet the bedrooms and living area was dry and mould free. So outside of the cost i am reluctant in getting the internal insulation. I asked was it a breathable insulation but I did not get a satisfying answer. So now i have come to the stage that I want to do with out the insulation but the bedroom walls and hallway have a rough texture which I would like to skim. Then I came across this stuff called wallrock, its a 4mm breathable insulation wallpaper that also covers texture walls and can be painted over. So I want to know has anyone heard of it, its expensive to purchase but at least its breathable and not costing me a small fortune. http://www.erfurtmav.com/index.php/erfurt-mav-wallpaper-products/wallrock/wallrock-thermal-liner Sorry in advance if in the wrong place...

antiskeptic

lor2ie wrote: »

I recently purchased an older house with solid walls. I was going to do internal insulation on the 3 bedrooms and the hall as the house has a brick finish outside, but first of all I got a quote of €12,000 and no grant for internal insulation. Apparently that included changing internal doors etc but still out of my pocket and doors are fine. Then i noticed on an extended section of the house that did get dry wall already that there was mould busting through the drywall and yet the bedrooms and living area was dry and mould free. So outside of the cost i am reluctant in getting the internal insulation. I asked was it a breathable insulation but I did not get a satisfying answer. So now i have come to the stage that I want to do with out the insulation but the bedroom walls and hallway have a rough texture which I would like to skim. Then I came across this stuff called wallrock, its a 4mm breathable insulation wallpaper that also covers texture walls and can be painted over. So I want to know has anyone heard of it, its expensive to purchase but at least its breathable and not costing me a small fortune. http://www.erfurtmav.com/index.php/erfurt-mav-wallpaper-products/wallrock/wallrock-thermal-liner Sorry in advance if in the wrong place...

Current build regs (if I have them right) look for 100mm PIR insulation on external walls. It strikes me as highly unlikely that 4mm of anything, however space age, is going to do anything worth the trouble.

Lumen

antiskeptic wrote: »

Current build regs (if I have them right) look for 100mm PIR insulation on external walls. It strikes me as highly unlikely that 4mm of anything, however space age, is going to do anything worth the trouble.

4mm of perfect vacuum might do it, and is quite space age. Might work if sufficient air-tightness. Bah-dum-tish!

Mellor

antiskeptic wrote: »

Current build regs (if I have them right) look for 100mm PIR insulation on external walls. It strikes me as highly unlikely that 4mm of anything, however space age, is going to do anything worth the trouble.

It's wallpaper, not insulation.
He's suggesting it for its breathability and the fact it won't require a skin coat, not thermal properties (I hope).