Green Building Forum - Internal wall insulation on brick house Tue, 19 Dec 2023 07:07:50 +0000 http://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302449#Comment_302449 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302449#Comment_302449 Fri, 14 Jul 2023 02:14:20 +0100 alexeix
We’re extending our 1953-ish semi and the majority of the external walls will be new.
The existing walls are 260mm thick and supposedly cavity wall, however, the cavity must be tiny.
We’ll check that when the build commences.

In terms of the finished building, 3/4 of the front of the building will be the original walls, but the rest of the external walls in this be house will be new.

We’re building new cavity walls and all the external walls (new and old), will also have internal wall insulation panels fitted (37mm).
The panels will include a damp proof membrane and will be taped, and we plan to fit an MVHR system, to take care of moisture in the air inside the house.

Our concern is what will happen to the external brickwork during the winter?
If it gets particularly water logged and then we have a spell of subzero temperatures, the brickwork may get damaged.

Is there anything we can do to prevent this or should we not be concerned?

We’re in the south of England.
Thanks in advance!]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302450#Comment_302450 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302450#Comment_302450 Fri, 14 Jul 2023 07:10:34 +0100 Peter_in_Hungary
Do you have planning constraints that will prevent EWI ?

EWI is better than IWI. What is the reason to use cavity wall on the new build ? Cavity walls are unknown over here, the typical build is single block with EWI to get whatever u value you need.

I recently put up an extension with 250 mm Porotherm blocks (sufficiently load bearing for roof etc.) and 200 mm EPS EWI which gives a u value of about 0.11. Quicker and cheaper than cavity wall and easy to see the insulation going on so no issues with the quality of workmanship putting in the cavity insulation.

And to answer your question about external brickwork issues in the winter - it depends on the type of bricks (porosity and hardness) but EWI doesn't have any of these problems]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302454#Comment_302454 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302454#Comment_302454 Fri, 14 Jul 2023 09:29:26 +0100 alexeix
As for planning constraints, I’m pretty certain we would need to obtain permission to use EWI, since all other houses in our road have brick facades, so we’d be changing the character.
Plus our attached neighbour is brick, so it would look odd.
Also, it’s more expensive than EWI.
I did consider it initially and I can see how it would be a good option in the right circumstances.

No particular reason to use a cavity build other than the existing house is cavity (?!) wall and nobody has suggested anything else up to now - and our building regs stuff has all been done and submitted already.

We are hoping to start building in September, so to change now would mean going back to the builder for a requote, going back to the structural engineer and architect, planning, et al.
So we’d be looking at a considerable delay.

I’ll look into your comments about her porosity of the bricks, since that makes sense and I should ensure our builder doesn’t ‘cheap out’.

Where is “here” for you?]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302457#Comment_302457 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302457#Comment_302457 Fri, 14 Jul 2023 11:18:08 +0100 djh Posted By: alexeixWe’re building new cavity walls and all the external walls (new and old), will also have internal wall insulation panels fitted (37mm).Why on earth would you put IWI on a new cavity wall? You could either build a single-skin wall with EWI as PiH suggests (his nickname gives a clue where he is BTW) or you could build a wide-cavity wall and cavity fill. Either would be better than IWI.

Our concern is what will happen to the external brickwork during the winter?
What has happened to the brickwork of all the houses around you over the past 70 years? Why would yours be any worse?

As for planning constraints, I’m pretty certain we would need to obtain permission to use EWI, since all other houses in our road have brick facades, so we’d be changing the character.
You could use EWI on everywhere except the front facade without an issue, and you haven't said you're in a conservation area so you could most likely use it on the front facade as well without any problems.

We are hoping to start building in September, so to change now would mean going back to the builder for a requote, going back to the structural engineer and architect, planning, et al.
So we’d be looking at a considerable delay.
You'll only be doing this work once, so it's worth doing it right. Forget your timetable and take the time to learn more about what will produce a result you'll be happy with.]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302461#Comment_302461 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302461#Comment_302461 Fri, 14 Jul 2023 12:03:17 +0100 WillInAberdeen
The new walls will need new linings anyway, so no harm in using this stuff rather than regular plasterboard, though the main thickness of insulation will need to go into the new cavities and there needs to be positively no air infiltration between the walls and the insulated plasterboard.

IWI and EWI each have pros and cons. For retrofitting unfilled cavity walls while avoiding cold bridges in a semi, IWI is possibly a good choice, if thick enough.]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302471#Comment_302471 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302471#Comment_302471 Fri, 14 Jul 2023 16:53:46 +0100 alexeix
We want to insulate as much as possible and our architect suggested the IWI, as EWI is not an option we want to pursue.
I've also not come across UK builders building single skin walls with IWI, so didn't know that it was an option.

<blockquote>Our concern is what will happen to the external brickwork during the winter?</blockquote>What has happened to the brickwork of all the houses around you over the past 70 years? Why would yours be any worse?

Doing my research, I noted that this was a concern when using IWI on older buildings. I'm guessing that my neighbours homes don't have the same level of insulation, so there would be some heat transfer through the walls.

<blockquote>As for planning constraints, I’m pretty certain we would need to obtain permission to use EWI, since all other houses in our road have brick facades, so we’d be changing the character.</blockquote>You could use EWI on everywhere except the front facade without an issue, and you haven't said you're in a conservation area so you could most likely use it on the front facade as well without any problems.

We're not in a conservation area, but understand from our planning department that changes such as rendering the front of the property would need permission.
Also, budget wise, we can't do it.

<blockquote>We are hoping to start building in September, so to change now would mean going back to the builder for a requote, going back to the structural engineer and architect, planning, et al.
So we’d be looking at a considerable delay.</blockquote>You'll only be doing this work once, so it's worth doing it right. Forget your timetable and take the time to learn more about what will produce a result you'll be happy with.</blockquote>

Forgetting the timetable is not something we can do.]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302473#Comment_302473 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302473#Comment_302473 Fri, 14 Jul 2023 17:07:18 +0100 alexeix I mean, we have to rewire and replace the heating system as well, so we'll have to move out at a certain point anyway.

I'll discuss the IWI thickness with the architect - thank you.

Retrofitting seems like a big experiment.

Maybe I'm worrying unnecessarily over the brickwork.]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302475#Comment_302475 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302475#Comment_302475 Fri, 14 Jul 2023 18:02:09 +0100 djh Posted By: alexeixForgetting the timetable is not something we can do.You're in for a disappointment then, because timetables on building projects always stretch. Still, your choice of how to spend money and live your life. You're clearly still learning about the possibilities so insisting on a fixed timetable is unwise IMHO.]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302478#Comment_302478 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302478#Comment_302478 Fri, 14 Jul 2023 22:27:39 +0100 Nick Parsons Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302480#Comment_302480 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302480#Comment_302480 Sat, 15 Jul 2023 10:06:42 +0100 alexeix Posted By: Nick ParsonsAs W in A points out 25mm is not going to excite anyone, not least Building Control. Who has drawn up the specification, and what reference is made to the Regs? 25mm PIR on a 225mm solid wall might give you around 0.85W/m2K, where the U value target is 0.3W/m2K.

None of the wall are/will be solid - existing structure has cavity walls, just not much of a cavity.
The majority of external walls will be new after the build is completed and will be cavity, as per building regs.
The IWI is in addition to that and we may go for thicker panels after the previous comments from W in A - I’ll be speaking with the architect.]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302589#Comment_302589 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302589#Comment_302589 Sat, 22 Jul 2023 23:05:09 +0100 wookey
The right thing to do is build the cavity wide enough to achieve the U-value you want. I built my extension (in 2014) with a 200mm cavity containing dritherm 32 (rockwool). Other insulations will work fine too. Also use basalt wall-ties to reduce thermal bridging. That gives a U-value of 0.15 which is generally considered 'good' and what I would recommend for any new wall construction (unless you have done more detailed sums).

Another thing to do is make sure that you remove thermal bridges where new extension walls meet existing house walls. i.e connect the insulation. If you just butt up the new wall against the old one then the outside brick layer will be a massive thermal bridge to the interior at the corner.

If you are currently planning 100mm cavity plus 25mm of internal insulation then you want at least a 125mm cavity. It essentially costs nothing to go wider so I'd do at least 150. 200 is good.

(the best thing to do is EWI as has also been pointed out - I have a brick building and it was no problem getting permission to turn it into an insulated and rendered one on the front facade, or you could have use brick slips to keep it looking like bricks, but it's too late for this info to be useful to you).

The other things to think about are making sure the thermal bridge at the foot of the wall is treated (i.e the inner leaf is not just sat on concrete footings in the ground without a quinn-lite block or foamglass block as a thermal break. And similarly the eaves detail to minimise thermal bridging there.

I see no reason to worry about the external bricks. External bricks outside insulated cavities are totally normal and I've not heard any instances of them blowing, even in construction with wide and well-insulated cavities.

IWI on the inside of a cavity wall is fine if you can't/won't do EWI. I have this too on part of my house. The thing you really need to worry most about is airtightness. The standard bonded plasterboard+insulation panels are impossible to air-seal properly, because you can't tape the membranes together. It is cheaper and better to put up separate insulation and plasterboard, taping the insulation before adding the plasterboard.

If your airtightness layer is somewhere other than the internal wall then this doesn't matter. So you _could_ parge or airtightness-paint the existing internal surface, and get your airtightness test done before adding the IWI and then the bonded stuff is fine. If your walls are currently plastered and it's in good nick (well attached, not too cracked) then that's a good airtightness layer. Doing this behind the IWI has the advantage that when you screw things to the walls later it may not make holes in the airtightness layer.

I have 100mm of PUR on my cavity walls, to add to the 65mm of fibreglass in the cavity, which gets a U-value of 0.15. You could go less than that but I really would do at least 60mm PUR which would get you U=0.2.

You will also need to pay attention to where the 1st-floor joists go into the wall and ensure they are properly sealed (with tape) . You do not want a lot of soggy internal air going out of holes there and condensing on the ends of the joists inside the wall.

Hope that's useful. There are a lot more details it sounds like your architect may not have advised you very well on.

Most fundamentally, what quality of building are you aiming for? i.e what annual space-heating load? 50kWh/m2.yr, 25? 100? No-one should be building new things or doing retrofits that don't achieve 50 or so these days, because it's just dumb. Both LETI and the AECB agree on this target. Just doing 'building regs minimum' is not sufficient, as they were set more than a decade ago, before there was a climate emergency (well, before most people noticed).]]> Internal wall insulation on brick house http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302670#Comment_302670 http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17901&Focus=302670#Comment_302670 Mon, 31 Jul 2023 14:31:30 +0100 Rick_M