Cavity wall Insulation Options on self-build 2024

ros89

Hi Folks,

I know the topic of insulation has been done to death over the years so I apologise in advance.

About to start a new self-build in the West of Ireland. Going with standard block build. Engineer has started construction drawings and has asked us what type of cavity insulation we'd like to use. Going out to tender for a contractor as I've no knowledge,skill or mates in construction! :(

He's given us a few options to start thinking about for a 150 mm cavity.

1. 110 mm partial fill board to meet minimum building regulations.

Couple of people I've spoken to have gone with this option. Their reasoning is that leaving 40 mm air gap protects against wind driven rain. However you are placing a high level of faith in block layer that they're laying board tight to inner leaf. Otherwise it's a waste of time due to thermal looping effect.

2. Full fill 150mm board (cavity therm seems to be one of the most commonly discussed here on boards. .ie)

No real air gap but from what I understand the design of the board seems to help run water ingress from wind driven rain back out towards the outer leaf . The jointing also appears to ensure a better seal between boards in the wall. However the engineer told us that many block layers absolutely hate this system.

3. 150 mm pumped bead and add insulated plasterboard to inside of wall. However I've had the suggestion from a few company reps I've spoken to to widen the cavity to 200mm and pumping with bead. This removes need for adding insulated plasterboard to inner wall.

My main concern with the bead method is weather here in the west of Ireland with the wind and rain being so bad. I know companies talk of the beads water resistance and shape guiding water down towards the ground as opposed to bridging into inner leaf. The NSAI standards for these insulation types strongly suggest getting a topographical survey of the site area to determine wind and rain exposure if considering this option so it doesn't give me much confidence on what the reps are saying.

On the other hand bead seems to be the least headache in getting the job done. But it's for the wrong reasons in that I may lack trust that the boards are being placed right. No offence meant to the trade out there but just with the cost of build nowadays I'm stressed to get the bones of the house right from the get go.

I guess what I'm trying to gauge here is

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?

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

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

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.)

Thanks

Biker1

What does your BER assessor recommend?

sydthebeat

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?

sydthebeat

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

sydthebeat

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?

sydthebeat

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.

sydthebeat

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.

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.

mickdw

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

listermint

Why isn't icf more popular here.

Tefral

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

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.

listermint

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

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

mickdw

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.

listermint

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.

mickdw

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.

listermint

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.

mickdw

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?

listermint

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.

mickdw

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?

listermint

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.

mickdw

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.

listermint

https://www.boards.ie/discussion/comment/121631207#Comment_121631207

Traditional would be a lime render. Are you lime rending all the new builds out west ? Interesting.

SodiumCooled

https://www.boards.ie/discussion/comment/121631224#Comment_121631224

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.

listermint

https://www.boards.ie/discussion/comment/121631392#Comment_121631392

I've an acrylic render on mine 6 years now. Perfect finish on top of EWI.

Still wondering how some builders in the West are getting their detailing so wrong.

mickdw

No, but appearance wise, the majority would be white render finish. You.might be interested to know that the rural housing guidelines call for traditional detailing YET they are not asking for thatch roofs. It's more proportion, appearance and scale.

A simply detailed dwelling of proportion similar to old cottage with a simple rendered finish is deemed to be suitable..... and yes plan ing department are quite happy with any of the multiple render systems available.

They will even accept that the front door may not be a wood product as long as it has the appearance of wood. Imagine that.

MakersMark

You should be going externally insulated on a new build.

davegilly

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

Why not #3?

If you have a house that only has 100mm cavity as it was started 15 years ago and left idle when structure was built until now, what would you suggest?

mickdw

What's in the cavity?

SodiumCooled

https://www.boards.ie/discussion/comment/121631638#Comment_121631638

Because you want to heat up the thermal mass of the walls which in turn give the heat back to the house (assuming they are well insulated on the cavity side from losing it to the outside world). Putting an insulated slab on the wall prevents this process.

Plenty of new builds do it and it shows very poor understanding of thermal management in the house by the designers.

Thats new builds though it might make sense on a retrofit where there isn’t sufficient cavity though external insulation would be a better option there.

Furze99

https://www.boards.ie/discussion/comment/121631447#Comment_121631447

How will that advice look in 20 years time?

Tefral

https://www.boards.ie/discussion/comment/121631638#Comment_121631638

Apples and oranges.

You don't do it on a new build where you have a choice not to. If its a retrofit we'll... you have no choice but to do it.

Dont Be at It

https://www.boards.ie/discussion/comment/121623077#Comment_121623077

What's the difference between the k8 and Tw50?

sydthebeat

https://www.boards.ie/discussion/comment/121739257#Comment_121739257

completely different materials

the K8 is phenolic foam

the TW50 is polyisocyanurate.

phenolic has a better thermal conductivity value than the polyiso.

both require a min 40mm residual cavity

Dont Be at It

https://www.boards.ie/discussion/2058331483/cavity-wall-insulation-options-on-self-build-2024

We went with option 1 with house current under construction. In practice it seems like it's hard to avoid bits of gaps between internal leaf and insulation. Does this cause much of a reduction in insulation performance?

thomas 123

https://www.boards.ie/discussion/comment/122045653#Comment_122045653

I think it would reduce performance significantly. A decent builder in here may advise.
If it was my house I would not want any holes in it anyway.

Biker1

Unfortunately blocks are not all exactly the same thickness and the blocklayer will be lining them up from the side he is working from so any differences will be on the insulation side. Also if the insulation is not stacked on the flat it can end up with bows. There is a way of ensuring that the insulation is in full contact with the inner leaf and that is to bring up the inner leaf three rows ahead of the outside and fit the insulation as you go. Rarely done this way though.

Dont Be at It

Insulation boards are in very good shape and there's a tongue and groove on them which is good for preventing gaps between boards, at least.

Any idea if the gaps where the insulation is a bit out from the block causes much of a downgrade in thermal performance of the insulation? Hard to quantify I guess.

mickdw

What I've found over the years is that despite what appears to be an excellent idea re the tongue and groove, in reality, a board with straight cut edges fits better. The ones with the groove tend to climb more and basically if they are climbing, they are not fitting together right.

Material type is even more important and a board that is alittle soft will tighten much better than a super rigid one.

The boards without the tongue creat less waste too as they can go in in various orientations.

Cavity insulation in general in my opinion only reaches a fraction of its theoretical insulation value. Not so much due to uneven block thickness but due to difficulty in fitting around dpc trays, loose fitting at corners, gaps when blocklayer couldn't be arsed etc.

It's still my preferred method in terms of safety from water penetration and no danger of pressure within the cavity as is a problem with some of the injected systems.

thomas 123

https://www.boards.ie/discussion/comment/122047494#Comment_122047494

Sorry, misread what you said initially, I'd imagine not an issue at all really at a guess. If a bit of heat does get in there it either has to go through the wall plate or back into the wall, or through the insulation.

dathi

https://www.boards.ie/discussion/comment/122047494#Comment_122047494

https://www.kore-system.com/cavity-wall-insulation-the-devastating-effects-of-thermal-looping/

a bit about it here

Dont Be at It

Seems that gaps between boards is the main issue that you want to avoid.

Had similar concerns re the injection system. Not sure new blocks would deal with it.

joeyanne

We are currently building and going with 150mm cavity of full fill beads and insulated plasterboard on external walls.

I see a number of people saying this is the worst option but after watching both my sister in laws do builds and go with 110mm insulation in 150mm cavity, I can safely say this is not an efficient option. They had two different builders and gaps could be seen in both builds. Which significantly reduces the efficiency of the insulation. It's near impossible to ensure the insulation is being installed correctly and gaps are always going to happen.

SodiumCooled

It’s not that it’s terrible it’s just losing the advantage of the thermal mass (plus the nuisance of having slabs on the wall for hanging things). A bigger pumped cavity is the best option removing the need for the plasterboard while staying away from rigid board which is as you say nearly impossible to get right. Most block layers don’t want to know about it anymore either as pumping is the norm - one of the first things they asked when I was getting quotes was is the cavity being pumped. Now blocklayers aren’t too pleased on the large cavity either as they have to lean out a lot more with blocks but it’s certainly less hassle than putting in board insulation correctly.