Green Building Forum - Internal insulation on solid walls Fri, 04 Sep 2026 13:44:07 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=19931#Comment_19931 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=19931#Comment_19931 Sat, 03 May 2008 22:51:26 +0100 tony Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=20036#Comment_20036 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=20036#Comment_20036 Tue, 06 May 2008 12:20:31 +0100 Saint Sempatap has been around a few years now . When installed it has been successful in preventing mould growth by raising the face temperature of the internal walls by a couple of degrees, pushing the dew point further into the wall thus avoiding surface condensation in the room. Sempatap “thermal” at 10mm thick is somewhat of a slight misnomer as its thermal performance is easily bettered by even mineral wool and far surpassed by more effective insulations. Roughly you would need 16mm of Sempatap to equate to 10mm mineral wool, 27mm of Sempatap to equate to 10mm of PIR board and 47mm of Sempatap to equate to 10mm Aerogel. So if space is at a premium You would need to look at the top end performers.

Interestingly recently in Italy contractors have completed projects on uneven and curved walls using a 10mm Aerogel fleece by applying bonding plaster to the wall and whilst still wet pushing Aerogel fleece into it. Leaving that until the next day to go off they then finish traditionally with more bonding plaster and then a skim coat. I’m not sure if they used the occasional polypropylene fixing for added mechanical strength in places but if not it might be a good idea. This has allowed them to follow the wall contours exactly and thinly.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=32965#Comment_32965 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=32965#Comment_32965 Wed, 17 Sep 2008 14:36:34 +0100 chocolatepixie
One room of my house is very exposed - 2nd storey, 4 external walls (old brick construction, 200yrs old), windy location...

Have been planning to insulate this room with sheeps wool but...

1. noted foster tom's comments on internal insulation leaving walls with no warmth to dry them out - how big an issue is this? (given that at the moment its the humans that are suffering from the lack of heat!)

2. if i go ahead with the sheeps wool, given that i want to put a good thickness (approx 6") how would you recomend doing this - build a stud wall? or, as nothing is square, could I screw, say, 3" battens to wall with frame fixings and then screw more 3" battens to the first ones?

3. i am concerned about the wool getting damp - especially from moisture in the air inside the house (from people insisting on breathing all day and all night...) which will presumably condense as warm moist air passes thru the insulation towards the cold exterior walls. Does the wool need a breathable membrane on both sides of it?

4. I was planning to use reeds and clay plaster but have been recomended to use foil-backed plaster-board. I can see the sense in adding to the heat retention but won't this prevent the walls from breathing?]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33016#Comment_33016 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33016#Comment_33016 Wed, 17 Sep 2008 21:55:38 +0100 Nick Parsons
Tyvek, 75 x 50 battens with 75 sheep's wool, 75 x 50 battens at rt angles, 75 sheep's wool, foil-backed pl'bd with good joints, or vapour control layer (vcl) and std pl'bd.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33597#Comment_33597 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33597#Comment_33597 Wed, 24 Sep 2008 17:32:36 +0100 chocolatepixie
However 75mm sheepswool is only 3" of insulation and I really want to put 5 or 6" so that this room does not need any additional heating (beyond what rises through the house from 2 wood stoves)

How can I do that?]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33610#Comment_33610 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33610#Comment_33610 Wed, 24 Sep 2008 19:31:51 +0100 tony Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33612#Comment_33612 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33612#Comment_33612 Wed, 24 Sep 2008 19:39:13 +0100 Rachel Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33771#Comment_33771 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33771#Comment_33771 Fri, 26 Sep 2008 10:59:41 +0100 Welsh Builder
Clay subsoil prevents water draining away, unlike porous limestone.

Lime plaster/wash, done correctly, breathes and will actually pull moisture out of a wall. But clay?

Please enlighten me.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33796#Comment_33796 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33796#Comment_33796 Fri, 26 Sep 2008 15:59:50 +0100 tony Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33806#Comment_33806 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33806#Comment_33806 Fri, 26 Sep 2008 19:53:53 +0100 Michael1 Can that process work in reverse?]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33814#Comment_33814 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33814#Comment_33814 Fri, 26 Sep 2008 20:51:10 +0100 joe.e Posted By: Michael1Hi Tony,
Can that process work in reverse?
Yes - clay dries out quite fast.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33928#Comment_33928 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=33928#Comment_33928 Mon, 29 Sep 2008 13:46:07 +0100 Welsh Builder Posted By: joe.e
Posted By: Michael1Hi Tony,
Can that process work in reverse?

Yes - clay dries out quite fast.

Yes, but is it releasing the vapour back into the air or just spreading the moisture evenly through itself? If the latter, the wall will gradually become saturated.

Breathability means that a material must release water vapour not just pull it in then spread it evenly throughout itself through diffusion/capillary action.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34502#Comment_34502 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34502#Comment_34502 Sat, 04 Oct 2008 18:29:43 +0100 greenladywell
I have a ground floor flat in a converted 1900 Victorian property. I'm about to get double glazing (wooden sash) and want to get the floors and walls sorted at the same time. Having done lots of reading up I'm currently veering towards Kingspan/Pavadentro on the walls (but am worried about the comments above about damaging the wall fabric) and hemp batts with insulation boards underneath under the floor boards, then get the floor boards repolished and sealed (I'm loathe to get carpet as as asthmatic). Will this do it or do I also need a waterproof membrane somewhere under the floor?! Anyone know of any good installers in London who can do this for me? Many thanks (off to put another jumper on now . . . )]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34509#Comment_34509 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34509#Comment_34509 Sat, 04 Oct 2008 19:04:42 +0100 joe.e Posted By: Welsh BuilderYes, but is it releasing the vapour back into the air or just spreading the moisture evenly through itself? If the latter, the wall will gradually become saturated.

Breathability means that a material must release water vapour not just pull it in then spread it evenly throughout itself through diffusion/capillary action.
A bit of both, but it does release it into the air at a good rate and will eventually dry right out. But I should stress that I've got no experience of using clay plaster in a building, only of the behaviour of clay on its own.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34568#Comment_34568 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34568#Comment_34568 Sun, 05 Oct 2008 22:17:51 +0100 Nick Parsons
Nick]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34624#Comment_34624 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34624#Comment_34624 Mon, 06 Oct 2008 15:27:42 +0100 greenladywell Yes, I've seen that, and I also went up to visit the house that Camden Council have retrofitted. I know roughly what I want done (wall insulation, underfloor insulation, it's finding the person to do it. I've had one builder do a quote today who didn't impress me much, but got another one coming around who has done similar work before using Pavatex and sounds more hopeful.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34645#Comment_34645 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=34645#Comment_34645 Mon, 06 Oct 2008 18:04:54 +0100 arthur And what windows are you going for? Are you having double glazing put into existing sash frames?]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53402#Comment_53402 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53402#Comment_53402 Tue, 05 May 2009 18:20:47 +0100 NTP
Could you please help with some advice?

I have a three bedroom flat in a converted Victorian house. It’s in good condition (ok to live in for a while) but needs some refurbishment. I am hoping to start with the two bedrooms on the top floor and then continue with the rest. In other words do it bit by bit so that I can live in and at the same time control the costs better by not doing it all together. This winter I felt that the whole flat was quite cold. The gas bill was sky high and I thought that it might be useful to insulate the external walls and save some cash. I looked around for different options and found that plasterboard with integrated insulating material (British Gypsum) is the best option (I might be wrong here). However, this is where the problem comes, my sash windows come out of the wall (inwardly) only as much as the plasterboard that I’d like fitted on (2.7 cm). My builder said that it wouldn’t look aesthetic and the sashes will lose their charm. Well, this is fair point so I thought maybe we could pull the windows inwards a bit and then fix the plasterboard to the walls. He wasn’t sure whether this would work and said he’d never done it before.

Has anybody done internal insulation in a Victorian conversion? Did they have to fiddle with the windows to fit plasterboard on the walls? Or did they go for a different type of insulating materials, perhaps thinner? Would Kingspan help in my case?

In another forum somebody mentioned that 9 inch victorian wall doesn't need to be insullated and fixing/restoring/replacing the sashes will do the job. What do you think?

Thanks for your advice!]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53406#Comment_53406 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53406#Comment_53406 Tue, 05 May 2009 18:49:02 +0100 Moderator
There will be a comprehensive story about it and how anyone could copy the system in the Summer 2009 edition of Green Building magazine (out middle of June). The building is over 200 years old.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53415#Comment_53415 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53415#Comment_53415 Tue, 05 May 2009 19:52:36 +0100 Nick Parsons
27mm won't anywhere near meet Building Regs (assuming 9 inch solid brick). Approx 65mm of phenolic foam laminate (55 foam, 10 pl'bd) will. If you are doing more than 25% of the external wall area you need either to meet U = 0.35 or prove to Bldg Control that you cannot, on either technical or financial grounds. See p.23 of Approved Doc L 1 B (http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADL1B_2006.pdf).

Simply take off the architraves and increase the depth of the boxing.

''In another forum somebody mentioned that 9 inch victorian wall doesn't need to be insullated and fixing/restoring/replacing the sashes will do the job. What do you think?''

What do I think? Urgghhhh!]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53431#Comment_53431 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53431#Comment_53431 Tue, 05 May 2009 22:23:37 +0100 NTP
At least I am now aware that 27 mm won't give me any benefit. The whole idea was to re-plaster the place and while doing so to check if internal insulation is feasible and easy/cheap to do. Anything above 30mm would reduce usable floor area to a level that I don't feel comfortable with. Unfortunately, my rooms aren't big enough for 65mm.

As per the sashes, thanks for providing valuable advice. This will increase the cost since a specialist needs to be involved. Thus, insulation is becoming even more difficult project.

One thing though I wasn't aware with is that I need comply with building regulations. Well, it's my first home so I suppose I can be forgiven.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53439#Comment_53439 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53439#Comment_53439 Tue, 05 May 2009 23:19:12 +0100 Mike George Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53448#Comment_53448 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53448#Comment_53448 Wed, 06 May 2009 00:09:10 +0100 NTP
This is the last option on my list. I am going to call the suppliers this week. However, I hear it's quite expensive. Do you have a rough idea how much per square meter?]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53453#Comment_53453 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53453#Comment_53453 Wed, 06 May 2009 02:12:21 +0100 wookey
All the expense is in the work, rather than the insulation itself, so do try to go as fat as you can - it'll probably not get done again for many years.

27mm is not 'no benefit' - it will make your walls a factor of 3.6 better (from U of 2.2 to 0.6 ish). (for PIR boards, 0.85, factor of 2.5 for EPS boards)The 35mm PIR we put on our 9" walls was a huge improvement. But as stated it could get you in trouble with the building inspector, and you really should do a bit better than that.

Re moving windows. It is best in terms of removing thermal bridges to line up windows with the insulation, otherwise there tends to be a nasty bridge spoiling your good work right round each window. So if you could move them out into the foam then that would be optimal. The fixing details could be tricky for this though, as you have to attach them to the solid wall. Angled brackets holding the windows in place before the insulation goes on might be best solution. It's important to ensure finished construction is airtight whilst making a mess - that means a vapour control layer attached to window frames and to insulation, or into plaster.

I've ben doing just this for last couple of weekends here.

If you decide that moving the windows is too much work, then bringing insulation right up to frames, and round the reveals is next best. This insulation usually has to be thinner (limited by frame width).

You ask if 'kingspan' would help. I assumed that was what's on the back of your boards, but perhaps they are XPS or EPS (polystyrene)? If you are short of space then you want PUR or PIR back boards (PIR is best per thickness, and of course most expensive) (or aerogel which is even bester and seriously expensive). EPS or XPS would be false economy here.

Another consideration is that whilst thermal boards are quick and easy it is harder to get a good vapour seal than if you use separate insulating boards and plasterboard. This way you can seal the foil layer between boards together and be sure you have very good airtightness and vapour-proofing. it is also cheaper thhis way (for materials - about 25% I found). but it's more work, so if paying a tradesman then it probably works out more expensive.

hope that helps.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53458#Comment_53458 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53458#Comment_53458 Wed, 06 May 2009 08:14:31 +0100 Saint
With regard to Aerogel, if you contact the Proctor Group you will probably be offered one of their Spacetherm brand solutions where Aerogel is bonded to Fermacell or plasterboard. To make these products the original Aerogel fleece has to be cut to size and then laminated to the substrate board. All these operations add additional cost so a Spacetherm laminate solution incorporating a single layer of 10mm Aerogel will cost probably in the mid £20s/m2
However it is also available in its blanket form i.e not bonded to anything else

On another posting "Paul from Montreal" suggested an alternative method for lining out walls that can also be used easily with Aerogel.

Firstly purchase Aerogel (Space Loft) in its original roll form.
Cut and fit the Aerogel blanket against the wall. This is a temporary fixing done before battens are fixed and can be done by simply hanging the Aerogel fleece using self adhesive pins.
Then fix battens as usual through the Aerogel into the wall using Tapcons or similar (this securely fixes the Aerogel) followed by conventional dry lining over the battens. A VCL can be fitted over the battens first or even on the face of the Aerogel.
By doing this you can purchase the Aerogel fleece in its raw format and avoid the add ons. The fleece is 1.45m wide and can be 50m long if you purchase it in roll form. The price should then be in the £16-18/m2 range]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53614#Comment_53614 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53614#Comment_53614 Thu, 07 May 2009 21:20:25 +0100 NTP
Thanks for your specialist advice. After reading your post I feel like not touching the windows at all. It seems to me that I will need a professional builder to handle the windows and this is going to be expensive. Also it will be difficult to find one that I can trust. So, sadly I will only restore the windows and leave them in their current position.

Your suggestion of bringing insulation right up to frames, and round the reveals somewhat doesn't appeal to me. Wouldn't it look as if the windows have been fitted too deep (outwards)? Also, I have only got 27 mm between the wall and the top of the frames so not much room for insulation.

Therefore, I might go for insulating only the external walls that don't have windows. Perhaps I can fit my radiators below the windows so that they compensate the lack of insulation and help with cold spots in the rooms.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53617#Comment_53617 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53617#Comment_53617 Thu, 07 May 2009 21:32:47 +0100 NTP
There isn't much difference for me between £16-18/m2 and £20s/m2 for the Spacetherm laminate solution. There would have been if I had to do the whole house but in my case, just a few external walls, it is just not a problem.

So, do you think that if I use the Spacetherm laminate I won't have any problems with the Building control person? The 10 mm Aerogel will do a nice job.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53618#Comment_53618 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53618#Comment_53618 Thu, 07 May 2009 21:36:01 +0100 NTP Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53623#Comment_53623 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53623#Comment_53623 Thu, 07 May 2009 22:38:58 +0100 wellburn ie - 10mm aerogel is only about the same as 18mm kingspan - which while being an improvement, - is no where near enough !!! - not for building regs, - not for anyone. - and it is WAY expensive. It really is about labour, - not cost of materials UNLESS you choose aorogel, - so just bite the bullet, - do the maths, - and buy big fat foam boards.]]> Internal insulation on solid walls https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53626#Comment_53626 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=793&Focus=53626#Comment_53626 Thu, 07 May 2009 22:53:17 +0100 jamesingram nice to see some figures ,as I see this as a great way to improve the energy effiecency of a big section of the old housing stock, but if its to expensive it simple wont happen


cheers Jim]]>