Cavity wall Insulation Options on self-build 2024

Option 3 is the worst.

Option 1 and 2 are more common.

Option 1 would have to be the kingspan kooltherm phenolic board (and I'd up that spec to 120mm to be comparable with the 150mm full fill board.

You have another option. 200mm pumped bead

hydrus21

I read a lot on these boards about damp penetrating and tracking through the outer skin of a cavity wall. I agree that this is the case with a

porous brick finish but with a block finish, isn't it down to the render & paint / cladding etc. on the block to repel the damp?

https://www.boards.ie/discussion/comment/121622064#Comment_121622064

where is that question coming from in relation to this thread?

There are plenty of areas where damp can penetrate. Every single junction is a weak point.

Plus you haven't allowed for interstitial condensation which will occur within the cavity, usually on the inner face of the outer block leaf.

That also needs to be accounted for.

bfclancy2

https://www.boards.ie/discussion/comment/121622091#Comment_121622091

because the OP is talking about wind driven rain hitting the walls, and yes render will repel that

https://www.boards.ie/discussion/comment/121622132#Comment_121622132

But the post I replied to make no reference to the question in the OP. IE the performance of bead insulation

anyway, anyone with a gable facing north west along the coast knows how good, or not, paint and render is for repealing Atlantic weather.

markw7

https://www.boards.ie/discussion/comment/121622091#Comment_121622091

On the interstitial condensation - what measures can one take in a new build to mitigate it, apart from moving the dew point outside with ewi?

https://www.boards.ie/discussion/comment/121622882#Comment_121622882

you ensure all your DPC, trays, weep holes etc are installed correctly.

its not something you can remove when choosing cavity insulation, so you have to plan for it.

markw7

https://www.boards.ie/discussion/comment/121622913#Comment_121622913

Ah ok, thanks. Would 130mm board in a 150mm cavity leave enough space in the cavity or is space even required - what would you go for yourself, 130mm or full fill board?

Furze99

https://www.boards.ie/discussion/2058331483/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.

https://www.boards.ie/discussion/comment/121622953#Comment_121622953

the kooltherm K106 board product allows a residual cavity of down to 10mm (but this is considered a "full fill" product)

the other kooltherm products require a 40mm cavity.

in my experience most of engineers dont have an issue with extending the cavity to 160mm in order to install a 120mm kooltherm board product with 40mm cavity, especially in a single storey house.

i have heard different claims from builders about post installation issues with the 150mm full fill xtratherm (unilin) board [swelling below dpc level being an issue]

so my standard specification at the moment is 120mm of the K8 board in a 160mm cavity

thomas 123

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.

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.

In a cavity wall system, the system is designed around a wet outer leaf so it is not correct to say render will keep moisture out.

I'm not a fan of pumped bead or full fill boards given the extreme weather in West of Ireland.

Partial fill board with 40mm clear cavity is my preferred spec.

Furze99

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

https://www.boards.ie/discussion/comment/121623364#Comment_121623364

Why isn't icf more popular here.

Tefral

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.

https://www.boards.ie/discussion/comment/121623402#Comment_121623402

That's my thinking, ireland seems ripe for this solution

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.

https://www.boards.ie/discussion/comment/121624277#Comment_121624277

This all sounds like poor construction detailing. Quality of install coupled with finishing materials would solve for that.

thomas 123

https://www.boards.ie/discussion/comment/121624277#Comment_121624277

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.

SodiumCooled

I think anything less than a 200mm pumped cavity is a compromise in a new build nowadays imo. 150mm cavities should be a thing of the past really I’m surprised they are still being designed into new builds. Also using board insulation will leave gaps, it’s near impossible to get right.

insulated slabs are a hindrance as they prevent using the thermal mass of the wall. Shows poor understanding by the engineer.

We aren't in the west but did a 250mm cavity, we had 200mm in our mind but the architect more or less insisted on 250mm.

https://www.boards.ie/discussion/comment/121624939#Comment_121624939

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.

https://www.boards.ie/discussion/comment/121627027#Comment_121627027

Why render it. Who suggested rendering. There are various other more suitable options. Render is crap on block houses as it is. Destined to crack.

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?

https://www.boards.ie/discussion/comment/121631057#Comment_121631057

There's a multitude of finishes available even more so on the continent.

There's nothing traditional about cement render no idea where this notion stems from.

https://www.boards.ie/discussion/comment/121631065#Comment_121631065

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?

https://www.boards.ie/discussion/comment/121631113#Comment_121631113

Stone is traditional to the west of Ireland but sure look let's stick with what's there.

Typical mentality though no wonder our building methods are nothing like what you'd get in Germany for example.

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.