Housing - Renovation: IWI - is a 9" solid brick wall good enough?

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- CommentAuthorkristeva
- CommentTimeDec 13th 2020
Hi all

I was just wondering what people opinions were of this article I found on the Heritage House website?

https://www.heritage-house.org/stuff-about-old-buildings/insulation/internal-insulation-to-old-house-walls.html

It argues a solid brick or stone wall alone is good insulator provided its dry. If you internally insulate an old house you lose the benefits of heated walls, particularly external walls, that provide an overall thermal mass with gentle constant heating. Its an interesting idea.

I've been making plans to insulate some of my internal walls with Steico wood fibre boards, probably no more than 40 - 60mm so I'd be interested in what people think.

Cheers

P
- CommentAuthorbhommels
- CommentTimeDec 13th 2020
The heritage house pages come across as very orthodox to me. It is all anecdotal without any numbers on U values, heat loss figures, or even wall thickness to back up their arguments, which I find very unconvincing.
Perhaps their aggressive, conservative attitude is necessary when dealing with people (outside this forum) wanting to "improve" historic properties?

Anyway. The core of their argument is well known around here: IWI should not be overdone so that there still is some deliberate heat loss through the solid walls to keep them dry, and warm enough to avoid interstitial condensation and freezing of saturated masonry. There are calculators for this, and although there are better ones you could try to have a go here:
https://www.ubakus.com/en/r-value-calculator/
- CommentAuthorkristeva
- CommentTimeDec 13th 2020
Posted By: bhommelsThe heritage house pages come across as very orthodox to me. It is all anecdotal without any numbers on U values, heat loss figures, or even wall thickness to back up their arguments, which I find very unconvincing.
Perhaps their aggressive, conservative attitude is necessary when dealing with people (outside this forum) wanting to "improve" historic properties?

Anyway. The core of their argument is well known around here: IWI should not be overdone so that there still is some deliberate heat loss through the solid walls to keep them dry, and warm enough to avoid interstitial condensation and freezing of saturated masonry. There are calculators for this, and although there are better ones you could try to have a go here:
https://www.ubakus.com/en/r-value-calculator/

Thanks for your comments. Yes, I would tend to agree with you here, and this is one of the reasons I wasn't planning to go above 60mm with a breathable system.
- CommentAuthorPeter_in_Hungary
- CommentTimeDec 13th 2020
Posted By: kristevaI've been making plans to insulate some of my internal walls with Steico wood fibre boards, probably no more than 40 - 60mm so I'd be interested in what people think.

As you will probably have read here - EWI is better than IWI for several reasons, however why are you planning to insulate some of your internal walls ??
- CommentAuthorbxman
- CommentTimeDec 13th 2020
I have only so far read the first page

And I think the writer fail to proof read with care ;

It follows that if you insulate the external walls of your house, you are stopping heat from getting to the outer walls. This means that the thermal mass of the entire outside envelope of the house is lost - the walls cool down in winter and stay cold. So the only barrier between you and the outside world is effectively the insulated stud wall that you put inside the wall. So - you are ending up, not with a thick, warm wall, but with a very thin wall - mostly freezing cold, with a veneer of insulation which is your only protection from the elements. Why bother insulating - just use the nice thick wall and keep it dry!

I think he intended to say
It follows that if you insulate the internal walls of your house ........................

In this case I agree with every word.

Having EWI fitted 5 years ago it was the best investment I have ever made ,
- CommentAuthordjh
- CommentTimeDec 13th 2020
Posted By: kristevaI've been making plans to insulate some of my internal walls with Steico wood fibre boards

You mean the insides of your external walls, I hope? There's no point in (thermally) insulating internal walls.

My opinion, which I think is fairly mainstream around here, is that EWI is better than IWI where it is possible. It keeps the thermal mass available to the interior, keeps the structure dry, and is often easier to detail.

Water vapour and (interstitial) condensation is the chief bugbear of IWI, followed by the risks of damage to newly cold structure (e.g. spalling of brick or stonework) plus the complexity of detailing around junctions. But sometimes it's the only choice.
- CommentAuthorkristeva
- CommentTimeDec 13th 2020
Posted By: Peter_in_Hungary
Posted By: kristevaI've been making plans to insulate some of my internal walls with Steico wood fibre boards, probably no more than 40 - 60mm so I'd be interested in what people think.

As you will probably have read here - EWI is better than IWI for several reasons, however why are you planning to insulate some of your internal walls ??

Hello again Peter, yes I was already aware of the benefits of EWI over IWI before I joined this forum. The first factor for me is the extra cost i I don't think I can afford it. I'm also not sure I'd want to alter the appearance of my house. And timing is an issue as a large proportion of the front of the house was previously repointed with cement which I want to remove next summer. And The back of the house was previously painted with a lead based paint which is now deteriorating and needs to also be removed.

With regard to insulating 'some of my walls' I'm currently only renovating the ground floor first, and there is a downstairs cupboard which separates my kitchen/diner from the back of house external wall. This is a small awkward space that acts as a void with central heating pipes running through it and the electric consumer unit. The downstairs loo is also a very small space where the external wall has a window and therefore very little space to actually insulate.
- CommentAuthorkristeva
- CommentTimeDec 13th 2020
Posted By: bxmanI have only so far read the first page

And I think the writer fail to proof read with care ;

It follows that if you insulate the external walls of your house, you are stopping heat from getting to the outer walls. This means that the thermal mass of the entire outside envelope of the house is lost - the walls cool down in winter and stay cold. So the only barrier between you and the outside world is effectively the insulated stud wall that you put inside the wall. So - you are ending up, not with a thick, warm wall, but with a very thin wall - mostly freezing cold, with a veneer of insulation which is your only protection from the elements. Why bother insulating - just use the nice thick wall and keep it dry!

I think he intended to say
It follows that if you insulate the internal walls of your house ........................

In this case I agree with every word.

Having EWI fitted 5 years ago it was the best investment I have ever made ,

Yes, I noticed this too. It's slightly confusing because you think he's talking about EWI.
- CommentAuthorkristeva
- CommentTimeDec 13th 2020
Posted By: djh
Posted By: kristevaI've been making plans to insulate some of my internal walls with Steico wood fibre boards

You mean the insides of your external walls, I hope? There's no point in (thermally) insulating internal walls.

My opinion, which I think is fairly mainstream around here, is that EWI is better than IWI where it is possible. It keeps the thermal mass available to the interior, keeps the structure dry, and is often easier to detail.

Water vapour and (interstitial) condensation is the chief bugbear of IWI, followed by the risks of damage to newly cold structure (e.g. spalling of brick or stonework) plus the complexity of detailing around junctions. But sometimes it's the only choice.

Yes indeed, I'm not planning to insulate internal walls.
- CommentAuthorjfb
- CommentTimeDec 14th 2020
I went with 60mm woodfibre steico, 20mm on reveals - works very well.

I think the anti IWI argument from such sources is a load of sh...e!

Clearly EWI is better and there is a danger of overdoing IWI leading to condensation risk.

How flat are the walls? Brick/stone? Original Lime render in place?
Having to add a flattening layer of render (also the airtight layer) adds to the effort but was needed for my stone walls.
- CommentAuthorlineweight
- CommentTimeDec 14th 2020
Posted By: bxmanI have only so far read the first page

And I think the writer fail to proof read with care ;

It follows that if you insulate the external walls of your house, you are stopping heat from getting to the outer walls. This means that the thermal mass of the entire outside envelope of the house is lost - the walls cool down in winter and stay cold. So the only barrier between you and the outside world is effectively the insulated stud wall that you put inside the wall. So - you are ending up, not with a thick, warm wall, but with a very thin wall - mostly freezing cold, with a veneer of insulation which is your only protection from the elements. Why bother insulating - just use the nice thick wall and keep it dry!

I think he intended to say
It follows that if you insulate the internal walls of your house ........................

In this case I agree with every word.

Having EWI fitted 5 years ago it was the best investment I have ever made ,

That just doesn't make any sense... "the only barrier between you and the outside world is effectively the insulated stud wall you put inside the wall"

Do they think the thick stone wall outside of it disappears, or stops doing anything? If the IWI is very effective then yes the stone wall will cease to contribute much to thermal insulation. If the IWI is very effective then you've got an effective barrier. If it's not very effective - then the stone wall will carry on doing some work like it did before. How do they come to the conclusion that adding some insulation to a buildup can make it less effective?
- CommentAuthorEd Davies
- CommentTimeDec 14th 2020
Posted By: lineweightThat just doesn't make any sense... "the only barrier between you and the outside world is effectively the insulated stud wall you put inside the wall"

Do they think the thick stone wall outside of it disappears, or stops doing anything?
Maybe they think the no-longer-heated wall will become wet and therefore not be such a good insulator. Dunno, it sort of makes some sense but it'd be difficult to say how much difference it'd make.
- CommentAuthorlineweight
- CommentTimeDec 14th 2020
Posted By: Ed Davies
Posted By: lineweightThat just doesn't make any sense... "the only barrier between you and the outside world is effectively the insulated stud wall you put inside the wall"

Do they think the thick stone wall outside of it disappears, or stops doing anything?
Maybe they think the no-longer-heated wall will become wet and therefore not be such a good insulator. Dunno, it sort of makes some sense but it'd be difficult to say how much difference it'd make.

But if it's no-longer-heated enough to get wet, then that means that hardly any heat is getting to it, which means the internal insulation is doing its job perfectly well, however "thin" it might be!
- CommentAuthorEd Davies
- CommentTimeDec 14th 2020
You'd probably need WUFI or the like to see how those arguments play out with any particular wall. I doubt it's simple. E.g., if there was just enough heat before to keep the wall dry then adding IWI might allow the outer bits to get wet which increases their conductivity enough that the next layer in cools enough to get wetâ€¦
- CommentAuthorPeter_in_Hungary
- CommentTimeDec 14th 2020 edited
One of the against reasons I have heard from the 'against IWI camp' is that without the heat the wall can get /stay wet as alluded to above and this will increase the risk of frost damage due to freeze/thaw cycles. Obviously this doesn't happen with EWI.
- CommentAuthorWillInAberdeen
- CommentTimeDec 14th 2020 edited
I heard that argument while living in a farmhouse with a barn attached. The walls of the house and the barn were built identically, except that the barn had never been heated in the 150+ years it had been standing there. I was therefore confident in IWIing the house, which caused no problems for the subsequent decade I stayed there.

A lot of scare stories about IWI started by misreading the influential 'Breaking the mould' series of articles, which were thoughtfully written about a specific set of walls in Dublin, but their conclusions have been misapplied to many other places. Well worth a read. The author was upfront that the WuFi predictions didn't seem to match real world observations, and had some thoughts about why not.

There are advantages and disadvantages to both IWI and EWI and the trick is to apply the right one to the right wall, but not be scared off and leave it poorly insulated!

Edit: re the question of the original post, 9" of brick is no longer enough insulation, as you can tell by touching it. 60mm of woodfibre would double its resistance but still not meet the legal minimum for upgrades in many countries. You only want to do this messy job once so I would want thicker insulation than that, or a higher performance type.
- CommentAuthorPeter_in_Hungary
- CommentTimeDec 15th 2020
Posted By: WillInAberdeenI heard that argument while living in a farmhouse with a barn attached. The walls of the house and the barn were built identically, except that the barn had never been heated in the 150+ years it had been standing there. I was therefore confident in IWIing the house, which caused no problems for the subsequent decade I stayed there.

I have seen a brick built barn with badly spalled brickwork on the lower courses - presumably due to frost damage to damp bricks, I also own a (now converted) stone / rubble built barn a couple of hundred years old that has no problems. I guess it depends upon the construction materials used as to the susceptibility of the problem.
- CommentAuthorkristeva
- CommentTimeDec 15th 2020
Posted By: jfbI went with 60mm woodfibre steico, 20mm on reveals - works very well.

I think the anti IWI argument from such sources is a load of sh...e!

Clearly EWI is better and there is a danger of overdoing IWI leading to condensation risk.

How flat are the walls? Brick/stone? Original Lime render in place?
Having to add a flattening layer of render (also the airtight layer) adds to the effort but was needed for my stone walls.

My walls are a bit of a mix tbh. When I first got the house I was a bit naive and removed all the lime plaster in readiness for an internal dpc, so they are back to brick and mostly not flat. Some of it had to come off because it was loose due to damp anyway but in retrospect I could have kept a bit of the original lime on other walls that weren't so badly affected.

So I'll need to apply a flattening render as you say before fixing the boards.

Did you do the work yourself?
- CommentAuthorkristeva
- CommentTimeDec 15th 2020
Posted By: Ed Davies
Posted By: lineweightThat just doesn't make any sense... "the only barrier between you and the outside world is effectively the insulated stud wall you put inside the wall"

Do they think the thick stone wall outside of it disappears, or stops doing anything?
Maybe they think the no-longer-heated wall will become wet and therefore not be such a good insulator. Dunno, it sort of makes some sense but it'd be difficult to say how much difference it'd make.

I think the idea is that you loose the insulation effect of the porous red brick in favour of the wood board so you're just replacing one with the other rather than getting benefit from both. So he's asking the question, what's the point.
- CommentAuthorkristeva
- CommentTimeDec 15th 2020
Posted By: WillInAberdeenI heard that argument while living in a farmhouse with a barn attached. The walls of the house and the barn were built identically, except that the barn had never been heated in the 150+ years it had been standing there. I was therefore confident in IWIing the house, which caused no problems for the subsequent decade I stayed there.

A lot of scare stories about IWI started by misreading the influential 'Breaking the mould' series of articles, which were thoughtfully written about a specific set of walls in Dublin, but their conclusions have been misapplied to many other places. Well worth a read. The author was upfront that the WuFi predictions didn't seem to match real world observations, and had some thoughts about why not.

There are advantages and disadvantages to both IWI and EWI and the trick is to apply the right one to the right wall, but not be scared off and leave it poorly insulated!

Edit: re the question of the original post, 9" of brick is no longer enough insulation, as you can tell by touching it. 60mm of woodfibre would double its resistance but still not meet the legal minimum for upgrades in many countries. You only want to do this messy job once so I would want thicker insulation than that, or a higher performance type.

Yes, solid brick walls are often cold to the touch in winter. I always thought they acted a bit like a fridge. I once rented a flat in a converted period property and I'm sure the walls were damp and always cold to touch.

I think what the article is saying is that with dry walls and keeping the house at a constant temperature with the fireplaces going the walls/bricks gradually heat up and provide a barrier to the outside weather.
- CommentAuthorkristeva
- CommentTimeDec 15th 2020
Posted By: Peter_in_Hungary
Posted By: WillInAberdeenI heard that argument while living in a farmhouse with a barn attached. The walls of the house and the barn were built identically, except that the barn had never been heated in the 150+ years it had been standing there. I was therefore confident in IWIing the house, which caused no problems for the subsequent decade I stayed there.

I have seen a brick built barn with badly spalled brickwork on the lower courses - presumably due to frost damage to damp bricks, I also own a (now converted) stone / rubble built barn a couple of hundred years old that has no problems. I guess it depends upon the construction materials used as to the susceptibility of the problem.

I've got some spalled bricks on the lower parts of my external walls which must have bene due to the high external ground level allowing water to penetrate above the dpc. I'm hoping my ground works will solve that

Also, a fair bit of the wall was re-pointed with cement.
- CommentAuthorkristeva
- CommentTimeDec 15th 2020
Posted By: WillInAberdeenI heard that argument while living in a farmhouse with a barn attached. The walls of the house and the barn were built identically, except that the barn had never been heated in the 150+ years it had been standing there. I was therefore confident in IWIing the house, which caused no problems for the subsequent decade I stayed there.

A lot of scare stories about IWI started by misreading the influential 'Breaking the mould' series of articles, which were thoughtfully written about a specific set of walls in Dublin, but their conclusions have been misapplied to many other places. Well worth a read. The author was upfront that the WuFi predictions didn't seem to match real world observations, and had some thoughts about why not.

There are advantages and disadvantages to both IWI and EWI and the trick is to apply the right one to the right wall, but not be scared off and leave it poorly insulated!

Edit: re the question of the original post, 9" of brick is no longer enough insulation, as you can tell by touching it. 60mm of woodfibre would double its resistance but still not meet the legal minimum for upgrades in many countries. You only want to do this messy job once so I would want thicker insulation than that, or a higher performance type.

Thanks. Useful to know regarding your barn. I'm not totally convinced that not heating a wall can cause damp. You just have to make sure that the dpc isn't breached and pointing / guttering is in good condition.
- CommentAuthordjh
- CommentTimeDec 15th 2020
Posted By: kristevaI think what the article is saying is that with dry walls and keeping the house at a constant temperature with the fireplaces going the walls/bricks gradually heat up and provide a barrier to the outside weather.

They warm up on the inside and make the inside of the house more comfortable. They lose a lot more heat as a result of the greater temeperature difference and it makes little difference to their ability to keep wind and rain out. So no change to the barrier.
- CommentAuthorPeter_in_Hungary
- CommentTimeDec 15th 2020
Posted By: kristevaMy walls are a bit of a mix tbh.

So I'll need to apply a flattening render as you say before fixing the boards.

Did you do the work yourself?

when I applied EWI to my uneven stone walls I put a thick line of adhesive top and bottom and then about 6 dollops on the middle then pressed it to the wall. Any mis-matching was rectified with a course sandpaper block made for the purpose. This uses more adhesive but quicker and cheaper than a render coat first.

I did the work my self.

I didn't get a flat wall but then the wall had lots of 'character' to start with and for the size of the wall (36m long, 3m high) getting it flat would have cost a fortune.

Posted By: kristevaI think the idea is that you loose the insulation effect of the porous red brick in favour of the wood board so you're just replacing one with the other rather than getting benefit from both. So he's asking the question, what's the point.

When you add insulation you get the benefit of the insulation and the original wall added together.

Posted By: kristevaYes, solid brick walls are often cold to the touch in winter.

Because they are cold and they conduct heat easily so when you put your hand on them the heat is drawn out so cold is felt. Insulation doesn't conduct heat so well so it is warm to the touch.

Posted By: kristevaI'm not totally convinced that not heating a wall can cause damp.

It doesn't, damp gets there for other reasons - but not heating a wall will mean that any damp already there will not be dried out

I did a quick calculation using ubskus with the 60mm wood fibre as IWI and then as EWI. Both had the same U value (0.498) but with IWI condensation was shown on the inner surface of the brick but with EWI no condensation risk was shown. There was no VCL in either calculation. 9" brick with internal plaster gave a U of 1.726 so your 60mm of wood fibre will make a big difference, so if you IWI make sure you have a good VCL inboard of the woodfibre board.
- CommentAuthorMike1
- CommentTimeDec 15th 2020
Posted By: Peter_in_HungaryI did a quick calculation using ubskus with the 60mm wood fibre as IWI and then as EWI. Both had the same U value (0.498) but with IWI condensation was shown on the inner surface of the brick but with EWI no condensation risk was shown. There was no VCL in either calculation. 9" brick with internal plaster gave a U of 1.726 so your 60mm of wood fibre will make a big difference, so if you IWI make sure you have a good VCL inboard of the woodfibre board.

AFAIK, ubskus if fine for u-Value calculations, but for moisture only does Glaser calculations, which don't reflect the conditions in hygroscopic materials. WUFI is preferred for that.

The importance of VCLs was stressed when I was at college, but it's now recognised that they can be problematic, particularly when hygroscopic materials are involved. They impede the drying of the wall back into the room as well as impeding moisture take-up by the wall, and only do the latter if very well sealed. Various other threads on the topic.
- CommentAuthordjh
- CommentTimeDec 15th 2020
Posted By: Mike1AFAIK, ubskus if fine for u-Value calculations, but for moisture only does Glaser calculations

If both of you are talking about ubakus, it seems to do more than Glaser as described in the links in the Quick Start Guide

"Moisture protection in wood structures is particularly important. For this reason, in addition to (LINK) moisture protection according to DIN 4108-3 (in German), (LINK) a drying reserve in accordance with DIN 68800-2 (in German) is required, which should also allow harmless drying of unintentionally penetrated moisture."

Variable permeability membranes (of which the best known is Intello) solve most problems with VCLs. I don't know if there are any equivalents for the VCL paints that are now available?
- CommentAuthorRick_M
- CommentTimeDec 17th 2020
Perhaps the author was referring to the method of insulating by building internal stud walls inboard of external walls and then adding ventilation (eg air bricks) between the two. Therefore "the only barrier between you and the outside world is effectively the insulated stud wall you put inside the wall".

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