I would be a little worried that there would be a danger of interstitial condensation in the insulation with that thickness of insulation. I have similar walls (though drier region) and went for : stone wall, lime render (as flattening layer and airtight layer) 60mm wood fibre board (fixed to wall with plastic pins), lime render, limewash. 20mm boards around window reveals. Airtight tapes embedded in backing render taped to windows/doors/joists. If possible make sure the woodfibre boards go all the way up the wall at ceiling level and is joined to too insulation.
I also installed Mvhr (not knowing if it would strictly be necessary but I ended up with an air test of 1 ACH and anything better than 3 requires mechanical ventilation).

It has worked very well for me - nice comfortable and dry environment. I had the advantage o taking the house back to a shell to do the work and maybe you don't. The backing layer online render is easier if you have relatively flat walls as you want to avoid voids behind the woodfibre board. But I think it is a better way to go than your plan.

And just I be clear - no membrane in my build up!

Brilliant thanks. sorry for the late reply, I work on an island now and then and so was out of touch for longer than is polite after asking a question..!

Those articles are very reassuring, although wood fibre seemed to increase wall humidity the most, so perhaps blown cellulose may be the thing to use especially as it gets into all of the nooks.

jfb - I have found myself looking at mechanical ventilation too, - I had a design done which looked a bit OTT but I was going to basically extract from bathrooms and kitchens and vent into far corners of bedrooms etc and hope fir the best.

any advice on insulating up into the joist space above the wall??

Andy

how do you make it air tight - say if you were using wood fibre? Do you mean tape it and put in a membrane? Really want to avoid membranes where possible.

And on the off chance any knowledge on open cell pour foam insulation behind lath and plaster? I spoke with one of the scientists who has installed it in Aberdeen and actually the interstitial humidity is similar to the cases you pointed me to - slightly higher and slower to dissipate but never reaching worrying levels..

cheers again!

andy

I don't understand the point of the first video. Blocks aren't airtight, so what's the point of sticking to them? I can see the point of sticking Fentrim to a parge coat and then overcoating with a finish coat.

And the second video???? Stainless steel all around the window? What's the point? At least it's not mild steel. I'm happy with steel brackets or with a few pegs underneath like I think Tony used, but continuous metal all the way around the window??

Posted By: Rick_Membed the tape in your parge coat

This I understand

I don't know if the tape would stick well enough directly onto uneven stone/brick.

The tapes I used had me prime a concrete surface and then use the non-setting glue product to secure the tape. I suspect that the tape in the video is relying on an airtight seal to the plaster above it.

The bit about using a small, hard roller to make the tape adhere properly is important though. I also found the back of a box knife was useful in some circumstances.

Posted By: Rick_M1st video: If you plaster over the blocks and over the section of the tape that has all the holes in, I can't see why it would matter that the blocks aren't airtight, as they will be behind your air barrier. I must be missing something?

My concerns are that I can't see (a) why is it important to stick the tape to the blocks and (b) what makes the plaster stick to the tape? The Pro Clima equivalent has a fleece layer on the non-sticky side of the tape to help it stick to the plaster, as well as a mesh on the plus version. I don't understand how the Siga version works.

2nd video: They look like brackets to me, not continuous sheet.

Ah yes, apologies. On second viewing I agree. Though I think there are a lot more than needed.

I agree, 20% sounds impossible. Hard to believe that would be published without being flagged. I read the paper years ago but didn't notice that. Also, I don't know if any follow up review has been published which would be more helpful.

My understanding is aerogel is not 4x better than other insulants, but more like 1.7x better. As in, you'd need 17mm of rigid foam to match the performance of 10mm of aerogel.

FYI I linked the videos above as they were the first ones that came up on youtube, nothing more than that.

Not entirely sure about the quality of this report..

Solid Wall Insulation:
Best Practice and Innovation
Report for the Department of Business, Energy and Industrial Strategy

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/658604/BEIS_-_SWI_Innovation_Final_Report_-_FINAL_Approved.pdf

Award for the thread title that I have been waiting over 10 years for.