Posted By: VictorianecoWe would like to maintain the brick facade

Seems heavy consequences. Any photos?

With such a large overhang, you do have an ideal candidate for EWI. It would make your life a lot simpler than having to deal with IWI and associated thermal bridging. EWI with brick slips maybe? You could even look at installing your ewi with a cavity and carrier board that then holds clay brick slips. Not sure what the costs are but there are options.

If you were to look at a lime render for the ewi then Lime Green is the only company I know at the moment who have develoed a lime render system for woodfibre ewi.

Good luck with it, looks like an exciting project.

What is the floor construction, how will you insulate it? Suspended floor possibly easier to retrofit insulation than a slab?


Been some previous threads about EWI retrofit on cavity walls, the questions were about

- stopping any residual air movement in the cavity that would bypass EWI, and

- how to join the wall insulation onto the floor insulation so there's not a cold bridge all around the wall/floor junction -much easier with IWI than EWI. The wall/ceiling junction is also difficult with EWI especially on gable walls. But making IWI continuous depends on the internal partition wall construction, difficult with solid partition walls, and

-what to do about airtightness between the inside and the wall cavity, if you need to plaster internally for airtightness then you might want to IWI while you are at it.


Is becoming more important to think about the embodied energy/carbon of material/insulations we use, a few years ago that was insignificant compared to energy/carbon from heating, but now ASHP heating is becoming quite low in primary energy and carbon so the balance is shifting. Might be good to avoid too much polystyrene/cement/lime if you can use glasswool/timber instead.

Edit to add: we sank a huge amount of time effort and emotion into retrofitting our previous 'forever' home, however illness in the extended family meant we unexpectedly had to sell it, to move closer to them. We are now retrofitting our next 'forever' home but our learning point was not to commit extravagant effort in the expectation of getting decades of satisfaction/comfort/luxury, we are trying to stay more level headed this time, life is too unpredictable to make plans for 'forever'!

It's all going to come down to what your take is on energy consumption reduction. As noted on the "Circular economy for rare elements" thread, reducing energy consumption is critical with reducing heating need a main priority. If it's going to be your forever home then I'd argue that piecemeal measure - 20mm floor insulation / fill the 2 inch cavity / accept the ASHP sell - will not provide long-term satisfaction.

It's a philosophy thing and if you want to significantly reduce consumption then, I'd go with EWI as it will be much more effective. Looks like there's the potential to slightly reduce ground level and thus EWI below ground floor level. EWI means a much neater thermal envelope, e.g. re triple glazing. Look into lightweight fill of the cavity - not insulation - so as much of the existing walls become part of the thermal mass. Look into digging out the existing concrete floors - much 50s floor construction is poor quality and thus easy to take out (is the garden big enough for 'spoil' landscape features?).

Above all, it's not easy. But don't decide on the basis of opinion, get it modelled, maybe with an EnerPHit plaque as a finishing touch?

EDIT: are you certain there's a cavity? Lots of examples of 50s brick build with all stretchers so it looks like a cavity wall but actually it’s around 10 inch of solid wall.

I agree with John, and I'd also be looking to install UFCH in those new floors.

SimonD said ''If you were to look at a lime render for the ewi then Lime Green is the only company I know at the moment who have developed a lime render system for woodfibre ewi."

SimonD, are you ruling out the Baumit products because the EWI render (MC55) apparently contains a very small proportion of cement? I don't know the proportions but I think it is predominantly llime, but not pure lime? It's great to use.

Fassa do a lime render for use with graphite EPS.

Posted By: Nick ParsonsSimonD said ''If you were to look at a lime render for the ewi then Lime Green is the only company I know at the moment who have developed a lime render system for woodfibre ewi."

SimonD, are you ruling out the Baumit products because the EWI render (MC55) apparently contains a very small proportion of cement? I don't know the proportions but I think it is predominantly llime, but not pure lime? It's great to use.

Fassa do a lime render for use with graphite EPS.

Hi Nick,

Yes, mentioned Lime Green as it's a pure lime (NHL) render and I know some people are keen on this. I do agree with you about Baumit, I myself have woodfibre rendered, well actually I'm still rendering it myself, with Baumit MC55W!

I chose the Baumit because it was the only product available to me in the UK that was an European Technical Assessment approved alternative render to the woodfibre manufacturer's own product. It is really nice to work with.

Good to know about Fassa, that's handy, thanks.

Posted By: John WalshLooks like there's the potential to slightly reduce ground level and thus EWI below ground floor level

No need, for downstand insulation purposes - much more effective is to dig a trench right down to bottom of foundation (but abs no deeper, to avoid undermining the found or reducing its bearing area) and run the EWI right down as deep as that allows. This creates a 'coffer dam' of insulation around a large block of subsoil, which then becomes a slow-changing stabilising thermal mass, part of the house's internal environment. To maximise insulation value, you can prevent standing water in the trench by putting a french drain in the bottom, with sharp clean aggregate and geotextile to prevent silting.

Posted By: John WalshLook into digging out the existing concrete floors

And it goes a long way to making that unnecessary, which is a boon when you don't have to rip out kitchen, cloakroom etc, not even carpets.

This floor insulation won't be as good as you could achieve with a new replacement floor, but could be a worthwhile trade-off. See latter part of http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6562 where an02ew applies Therm to quantifying it.

I used to think that the underground EWI needn't be as thick as above - but now realise that the reverse is true - make it at least as thick if not more.

There's more detail on how to do this - search GBF.

Posted By: fostertomdig a trench right down to bottom of foundation (but abs no deeper, to avoid undermining the found or reducing its bearing area) and run the EWI right down as deep as that allows. This creates a 'coffer dam' of insulation around a large block of subsoil, which then becomes a slow-changing stabilising thermal mass, part of the house's internal environment. ... This floor insulation won't be as good as you could achieve with a new replacement floor, but could be a worthwhile trade-off. See latter part of http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6562 where an02ew applies Therm to quantifying it.

I used to think that the underground EWI needn't be as thick as above - but now realise that the reverse is true - make it at least as thick if not more.

Reading back on that thread, I said at the time that didn't really look like enough insulation - the figures An02ew came up with, were equivalent to about U=~0.9 W/m²K for the floor area of the example house.

Maybe further tweaking of the Therm could get a bit more out of it?

The contours show that the heat wasn't getting through the insulated trench, so it didn't need thicker insulation. Instead the heat was just flowing underneath it. If we think about the 8m width of the house floor slab, compared to the 0.6m-ish depth of the trench, the 'aspect ratio' isn't in favour - really the trench needs to be metres deep if it's going to meaningfully lengthen the heat flow path from the floor to the outside air.

I think if you are going to the trouble of wall insulation, you'd also want floor insulation and you don't want a gap between the wall and the floor insulation.