Experiences with cork cladding?

I’m looking at EWI options for a drafty old solid walled house at the moment. Looked at corksol (decent lambda value: 0.45 or so) but it was too expensive. But I’ve happened across cladding, which seems much cheaper on the materials side. Stuff like this:

Other suppliers exist, naturally, but I’ve not decided on who seems best yet.

What I’d like to know is, has anyone here gone down this path? Are there snags and gotchas awaiting me? I’m trying to get 20-30mm of good, breathable insulation on before mid autumn for reasons I’m sure everyone can guess.

Some architecturally interesting stuff has been done with it:

But I’ve no idea if it is a sane option for retrofit, or if I can just ask a random cladding specialist to have a punt and not suffer disaster afterwards. Any experiences would be hugely helpful!

(Apologies for the similar post to my last one, this one is slightly different!)

This looks like an interesting product. I’m keen to follow your progress. The thermal transmittance is very close to Rockwool EWI batts.

Provided the house is only 2 storeys I would be happy with it. Cork will burn at high temperatures so I wouldn’t add it to anything taller.

I anticipate higher fitting costs than CorkSol or Diathonite as there is more preparation and finishing off than with a spray on solution, so you may not save as much as you expect.

Whichever solution you go for remember not to stop at the soffit but to insulate up to and abutting/overlapping the roof insulation, otherwise you will end up with a cold band around the top of your top floor rooms, which will attract condensation and mould.

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I’ll definitely keep posting. If I can find anyone who’ll do it (or dare to try DIY - not inclined!) I’ll post before and after pics.

As to cost… I’m still working that out. I’m reasonably sure the existing render causes more problems than it solves because it appears to not be breathable. I’m not 100% sure on that, but if I’m right it would benefit from going anyway.

My thinking is that even if it works out as more than CorkSol or Diathonite when removing the render, I’ll be able to get so much more on that it’ll be worth it. I’m going from a u value of 1.35 or so as-is. Being charitable, without the existing render I’d guess that gets to 1.8 or so. Then 30mm of cork would, I’d hope, get us down to 0.5 or lower.

Obviously all guesstimates (except the 1.35) but I’m hoping I’ll get more bang for buck this way. If I can find anyone who’ll quote…!

Good tip on the rockwool by the way: it seems to come in thicker sheets but I’ll take a look.

How are you guesstimating your U values?

I was told that to add the U values of components you add the inverse of the U values, take the inverse of the sum and there you are. If they are available just add the R values and take the inverse.

Incidentally, it is very unlikely that an original render doesn’t breath unless it has had relatively recent paints or treatments. Some treatments done in years gone by have been shown to worsen the situation. I know of a large Edwardian house converted into flats a few years ago and re-rendered to prevent damp ingress. It is now wet and mouldy throughout as the damp was originating in the building and at least some had been escaping through the walls, until they were re-rendered with addmix in the mortar. Not that the landlord believes my explanation. I was asked for advice by one of the tenants.

Heat loss survey gave the figure of 1.35. Removing the render adding 0.5 is a total guess, to be honest. The guesstimate for the cork relates to one of the corksol case studies: they added 6mm of corksol to a building and the claim is that they took the U value down by about a third from 1.5 or so. From that, I’ve compared the lambda values of both (cork panels have lower lambas than cork spray) and have picked a big-ish number (20 to 30mm) on the assumption that would scale roughly linearly.

I realise that’s not quite as it works with diminishing returns etc, but I’d be surprised if I couldn’t lop 1.0 off the U value I have. At some point I’ll sit down and work it all out properly, but I’ve not got round to that bit yet since we’re in the throes of moving and life is a bit mad, so I’m deferring what I can defer.

Alas, before we moved in the house was empty for 18 months and the neighbours paid for it to be painted at the front and side alongside her own. No idea what they used, and they don’t know either. So it could be an… intriguing… voyage of discovery this winter.

Are the neighbours amenable to insulating with you? If not you have to take precautions against a long thermal bridge at the party wall where cold enters around the edge of the insulation through their fabric. Thinking about it, the same applies to loft insulation.

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Possibly. They’ve indicated they’d want some work done alongside ours and I’d been considering asking. Always awkward when money is involved though.

Hadn’t considered the thermal bridging issue there, good shout, thanks!

The cost of doing adjacent properties usually drops for each added property. You should ask for quotes for both scenarios, so that you and your neighbours get a genuine price. When I got my first marital home cavity insulated I asked for a quote for the whole block too (4 properties) in the hope of getting my neighbours interested. The saving was considerable but none of them were interested (that was before you could get it for free in certain circumstances).

Interesting. I’ve had the conversation now and she’s mulling it over - as is the installer!