Robg.
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.

From wall:

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.

Try reading it again it was 150mm !

How does clay plaster breathe?

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.

Hi Tony,
Can that process work in reverse?

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.

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.

Hi Nick
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.

Hi to all,

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!

NTP,

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!

Hi NTP. Have you considered Aerogel?

Can you really not lose more than 50mm on external walls. This can be an issue in rooms the size of toilets, and on stairwells but in any sensible sized room you really won't notice when it's done. I worried about this in first house (35mmphenolic+12mm plasterboard boards), but really it seemed exactly the same size afterwards, and that was a fairly small 2-up 2-down semi. In this house I'm doing 100mm PUR+plasterboard. And even that hasn't made any detectable difference to room sizes (although they are reasonably generous rooms here). I will probably have to do thinner in downstairs loo and on stairwell.

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.

Wookie,

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.

By the way, does anybody know a decent builder (based in London) that can help with my project?

So Lee whats your ballpark figure, supply and fit external 100m EPS with thro-colour render finish on a standard 3 bed semi , per m2
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