Internal wall insulation - thinnest, latest, best approaches?

[Daniel_E_B]

Narrow Victorian semi so single skin walls and no desire to lose significant floor area. I'm installing PIR board beneath the ground floor but what are the latest and greatest options to lower external wall thermal conductivity? I've read about various insulating plasters, renders, aerogels etc but no plasterer I speak to seems to know anything about them. Does anyone have knowledge or experience?

 

[jeds]

Aerogel gives the highest thermal value but isn't readily available and if it was would be very expensive. Thermal plasters won't provide anything like a reasonable upgrade in thermal value.

Best option is PIR insulation; either PIR + board finish or thermal laminate, incorporating the board. The only question is how much and how to fix? Personally I would advise 52.5mm (minimum) thermal laminate or 62.5mm. These won't reach current regs but will be a significant increase. What is the state of the plaster at present - is it solid?

 

[Daniel_E_B]

Yes, plaster is solid and paper-lined. Dot and dab on plaster? I don’t want to lose floor space with battens.

 

[Mr Chibs]

Strip paper off, and fix boards directly to walls, as Jeds has said 62.5mm would be better, I have this, made a massive difference in comfort.

Fixings recently discussed here:

 

[Dereekoo]

don't dot and dab to solid brick walls??? - https://www.kingspan.com/gb/en/prod...ds/kooltherm-k118-insulated-plasterboard/?s=d

 

[jeds]

No problem with dot and dab on solid walls, as long as the wall is protected (externally) and dry. In order to dot and dab onto plaster though, the plaster must obviously be sound and it should be primed and prepared. Feb Bond Blue Grit or similar.

 

[Daniel_E_B]

I have to admit, in my kitchen which is the most exposed, chilly area of my property and where space really is an issue, I am tempted by this Proctor product, Spacetherm WL (wall liner) which is a board comprising 10mm of an aerogel mat bonded to 3mm of magnesium oxide sheet. It is specifically designed to be bonded directly to the interior of solid walls using Insta Stik foam adhesive. They say it is breathable and will bring a typical solid external wall U value from 2.1 down to about 0.8. Which is not the 0.3 demanded by the regs when refurbishing but would still be a massive improvement. It's not cheap at > £70 for a 1200x600 board but there doesn't seem to be anything comparable on the market.

 

[freddiemercurystwin]

All that money for the sake of an inch or summink.

 

[Daniel_E_B]

Ach, you're probably right. Maybe I'll do PIR or phenolic plasterboard in the kitchen.

 

[JohnD]

How thick is the old plaster?

 

[jeds]

People always stress about losing 25-35mm of space but, once done, you won't even notice it.

 

[Daniel_E_B]

How thick is the old plaster?

Um, not more than 11 or 12mm in total I reckon. Maybe a bit less.

 

[JohnD]

Hardly worth hacking off, then?

 

[Daniel_E_B]

True

 

[robinbanks]

Aerogel gives the highest thermal value but isn't readily available

I thought that honour went to VIPs, aerogel as a material being the winner but by the time it's incorporated into a useful form of insulation it dips somewhat. In either case, they're considerably more expensive than PIR or phenolic

Daniel, have you looked at the possibility of external wall insulation?

no plasterer I speak to seems to know anything about them

Common or garden trades won't have much of an idea about novel, modern concepts like insulation, air tightness etc; generally you need to engage specialists if you want to incorporate into your home's fabric anything that's been developed in the last few decades