EWI vs drylining when walls already pumped

houseyhouse

We have pumped cavity walls (1970s house). Are we better off getting EWI or dry lining to further increase wall insulation? Our architect favours EWI but builder has said he personally doesn’t like it (but he’ll do it no problem).

Cost is a concern, too. The cavity walls were pumped by the previous owner with the grant so we can’t get a grant for wall insulation. It’s a semi-d and only the front wall and a small section of upstairs rear wall will still be external walls after we extend but the cost of doing the EWI is still €8k.

Yellow_Fern

From a theoretical point of view, excluding costs EWI is usually better. Can ruin the outside look of the house though.

MicktheMan

https://www.boards.ie/discussion/2058327040/ewi-vs-drylining-when-walls-already-pumped

EWI is, in so many ways, far superior to IWI. There have been plenty of discussions on this topic on boards over the years.

EWI is really great IF heat conduction through your external walls is the main mechanism of heat loss from your house.

I don't want to drag the thread off topic but I'm just wondering if you have hit all the low hanging heat loss fruit first before contemplating extra wall insulation? What I'm getting at here is your air tightness and ventilation.

Have you had an air tightness test done for instance?

Who are advising you to further insulate your walls? (do they sell insulation per chance?)

Very often there can be major wins here without breaking the bank especially if cost is an issue.

Can you afford to spend big on EWI (or IWI) to find out afterwards that the expected improvements are not there because something else (such as draughts) is the real heat loss issue!

houseyhouse

https://www.boards.ie/discussion/comment/121501362#Comment_121501362

We’re doing an extension and retrofit. I‘ve no doubt current airtightness is poor but it should be good by the end of the build. The architect said we would need additional wall insulation to qualify for the heat pump grant and our BER survey did have the walls at only moderate despite being pumped. But EWI is so expensive and we’re over budget so we were considering internal instead.

listermint

https://www.boards.ie/discussion/comment/121501710#Comment_121501710

EWI is more superior given you're application. Its better.

You're budgets is yours and unfortunately no one can spend your money for you

Biker1

https://www.boards.ie/discussion/comment/121501710#Comment_121501710

Your Architect says you need extra insulation to qualify for the heat pump grant!!! Unless he has done a technical assessment he cannot make a statement like that.

houseyhouse

https://www.boards.ie/discussion/comment/121502150#Comment_121502150

We have had a BER survey to prepare for the retrofit so maybe that’s where the idea came from?

houseyhouse

https://www.boards.ie/discussion/comment/121501740#Comment_121501740

Ok, thank you. The builder says he doesn’t like the EWI because you have to heat all the way out to the external leaf so I thought maybe there wasn’t a huge difference in suitability.

I’ve seen an article online from August saying EWI is between €90 and €120 per square meter including installation. Does that sound right? We’re being quoted €8k for under 50sqm (so €160/sqm). Over a quarter of that is windows and doors and we’re already paying for new cills separately so the cost seems very high compared to the online estimate.

listermint

Price seems about right. Don't mind the builder your walls should act as a heat sink that's half the point of it and also a key part of how underfloor heating operates as an example.

He probably does install the stuff hence will ward you off it.

Water John

Does the BER have taken into account that the walls are pumped? It may not be if the assessor hadn't evidence that it was done. I'd examine the BER and the recommendation sheet with it, to see why the house might be failing to make the BER required for HP. Is it fireplaces or gas fire or things like that?

houseyhouse

https://www.boards.ie/discussion/comment/121503092#Comment_121503092

I think so. There was a previous grant which the assessor knew about. Just checked and the walls were rated ‘fair’.

Water John

A pumped wall is the usual insulating upgrade done. I don't see how it was rated fair. The rating he applied to it, needs to be drilled into. I would worry that this, or other such issues are what are lowering your BER rating, likely lower than it actually will be. It's worth pursuing to identify why you're not eligible for HP grant alone.

Water John

Don't wanting to be sending you on a wild goose chase, but worth a consideration.