Cavity wall Insulation Options on self-build 2024

If it were me, I'd go for option 1 - tried & tested. When I built here, it was a 100mm cavity with 60mm insulation batts and 40mm gap. Works fine.

Attention to detail is important though. The batts/ slabs should all fit in snugly against the inner leaf, held in by plastic clip on the wall ties. There should be no gaps left - the stuff I used was tongue and grooved board, which when fitted together give a good fit. When cutting odd bits though, it only takes a minute to cut a wee groove with the trowel to get a good fit. If you're doing the work yourself, you'd do this but I wouldn't be convinced many block layers would be too bothered with this. I had a look at various houses under construction when I was doing my own bit, just to see how detail was handled. Saw everything from excellent neat work to downright shoddy practice, with notable few wall ties and insulation flapping about with gaps etc.

Having observed the walls afterwards before rendering, could see the rain soaking through the outer leaf on exposed side. The render and paint helps greatly but bound to be some moisture dripping down.

Another poster here recently was of opinion that with insulation you're chasing your tail to some extent, any insulation improves but that diminishing returns sets in. They were saying that 'air tightness' is as important and of course ventilation. So not just insulating but reducing the warm air that you pay to heat from escaping too readily.

Q1. For those of you who have built in the west of the country classified as having severe weather exposure, what method did you go for and why?

200mm pumped cavity - Why, I can nail stuff to my walls whereever I want and am certain that the walls are full of the product as designed and should work as expected . It was also cost effective for my project. 0.18 Conductivity.

Q2. Any method above that you would avoid like the plague? Any negative experiences.

No - no experience of the others.

Q3. Did you get help with reaching the decision ( did you have an independent expert help assessing your site situation, topographical survey etc).

BER man advised it was sufficient, engineer very happy with system.

Q4. If ye did a board install did you monitor the installation of insulation yourself or rely on contractor? (As mentioned I've no knowledge of construction at all but trying to learn as much as I can.)

With the pump you will see where they drilled into the walls, you can push a pen or stick in and feel the insulation inside to confirm for yourself that it is in there.

One problem with the wider cavity, is that the footings have to increase in width as well - more concrete, more cost and more carbon etc

I am a Quantity Surveyor and a Self Builder.

If I was redoing my house again in the morning, it would be ICF no question. Make all rooms divisiable by 600mm and away you go.

Few of my friends have gone the ICF route since. Some job.

To answer the OPs question. Option 1 would be the only way to go. I live on the West and the horizontal rain we get is mad.

Whatever you do, dont do option 3... just dont.

Icf is simply non fit for purpose in the wilds of the west of ireland.

I see some improvements being made to detailing but overall innterms of weathering, it's a no from me.

Local to me, one Engineer has moved totally to ICF and basically is using one builder for them all.

They are having multiple leaks. The system is crap and if leaking when new, will only get worse.

We see hollowblock houses being successful in cities but try building one in Blacksod or somewhere like that.

From the detailing I've seen within Icf, it is hopeless.

Yeah like others have said when it’s done right it’s A1, the detailing around ops is what I got stuck on and ruled it out for myself from then.

Secondarily you needed someone familiar with ICF construction when it came to every trade so local recommendations were not great.

You may say that but I don't agree with it as a system for severe weather locations.

It's absolutely dependent on the external render. A failure of the render via any form of crack and water is entering and then it's anyone's guess where it appears.

The detailing around windows surely can be done well but is it being done well on most sites.

I don't know your experience with driving rain on West Coast but it will test most systems.

I've seen window systems fail here in storm where it took prolonged use of high pressure washer to reproduce leak with everyone blaming dpc when in fact it was within the window.

I'm made a conscious decision to not get involved with ICF builds for the foreseeable. Ive also moved to specifying 13N concrete blocks throughout.

Reading forums from uk a few years back pretty much confirmed my thinking with people having leaks at random locations internally due to water gaining entry at crack or penetration and travelling along poured concrete outer surface and entering at a weak point.

I'm also aware of an early adopter commercial development that had to introduce a block outer leaf due to weathering issues but detailing has moved on since then I'd agree.

When i say render, im referring to all applicable wet finishes. What is your proposed finish for use all over the country taking into account traditional appearance of a rural dwelling?

I said I'm referring to all types of wet finishes.

A rendered finish is traditional to the west of ireland.

What would you intend to finish with if building 100s of rural houses?

Stone finish is traditional to parts of the country where suitable stone was available.

Where I'm from, the houses are a loose rubble stone construction with render finish from day one.

You are not offering any great ideas. For.someone pushing the system as the future, I'd have thought you.might have more Insight.

I'm an insured professional. A claim would be seriously damaging to my business.

Systems that are unproven for the weather conditions are not even a consideration for me as no doubt when the sh1t hits the fan, the only insured person will come down with the lot.

Nap plaster finish is generally specified as one of the planning conditions. It was for mine anyway, not in the west but doubt it’s much different.