The insulation will eventually dry out - if it dries out quickly this could indicate a cavity with a lot of air flow, which is what you don't want. Of course it depends upon the extent of the building and how far up the walls have gone. IMO the insulation will not recover its expanded state of its own volition once it has sagged due to the weight of water (rain)

I have found that very few builders have good attention to detail and typically they hate doing remedial work. The insulation is in the cavity and the thickness of the material would have been as detailed on the plans. The thickness actually achieved will be of little concern to the builder in the same way as gaps at the insulation joins will also not bother the builder - once the walls are up no one can see what has happened! Of course your builder may be different...........

How would anyone know if their house was loosing 10% more heat than the house down the road that was built in the dry?

Posted By: WillInAberdeenThese mean that the cavity is (by design) often a bit damp and CW insulation is expected to cope with being wetted and dried throughout its life, so organic material is not used.

But CW insulation installed at build is fixed to the inner leaf so there will be a gap between the insulation and the outer leaf so the insulation should not get wet.

Wot philedge said +1

Better define what damp means then

Just dont build with cavities! I realise I'm being glib, but the original purpose of the cavity was to prevent damp, by creating an air break. Now we fill it with insulation!
Just be certain that the external skin is properly watertight. Render, cladding, etc.

Tony, your build is full fill with no render is it not?

Unrelated to Tony's house, but this won't help: https://www.bbc.co.uk/news/business-46454844

OP should let the builder know when the building is complete a thermal imaging camera will be used to view the quality of the fitting of the insulation. If this shows incorrect fitting it will be the builders liability.

Posted By: djh

Posted By: DonkeyOP should let the builder know when the building is complete a thermal imaging camera will be used to view the quality of the fitting of the insulation. If this shows incorrect fitting it will be the builders liability.

Good idea but might prove difficult in practice...................... Might induce the builder to do a good job though!

+1

Posted By: philedge

Posted By: Donkey If this shows incorrect fitting it will be the builders liability.

Cant really see any builder taking down the outer leaf of a new build to remedy a "leak". Best ditching the bricky and getting one that sees thermal "leaks" the same way as a plumber sees water leaks ie not acceptable.

I think the point is that if the builder knows up front that his cavity insulation work will be checked with a thermal camera then the need for the camera will diminish (to zero?) because the builder will not want to be called back and shown evidence of his bad workmanship.

Is an IR camera really good enough to see <10mm gaps through the masonry?

you need to choose the right time to use the IR camera i.e. warm the house for a good time and take the picture when the weather is frosty - preferably in the negative.

Posted By: philedgeRealistically what is your bricky/builder going to do with what would a completed house by the time you can do a meaningful I R survey?

Best ditch the bricky/builder at the start of the job if your not happy with the detail

The same as any other claim about faulty CWI.
Ditching the builder is only of benefit if the next one is better.
I have found that supervision is about the only thing that works to get builders to pay attention to detail. The aim here would be to focus the mind of the builder to the fact that checks are and will be made regarding his work and any remedial action will be sought. Errors have to be brought to attention at the time and excuses not accepted (especially "we always do it that way!"). Once the standards are pointed out and spot checks are made and the builder knows that you mean business then usually things improve.
If not - change the builder - if you can find one in your time scale.

On the topic of IR cameras, does anyone rate the online hire route?

Our new build isn't quite as toasty warm as I (and my family) were hoping. Since the timber cladding is only just about to go on, I'm wondering about running around with an IR camera now before we really are too late to get at any gaps.

Only problem is the new cameras all begin upwards of £200 for a half decent resolution and I'm not planning on doing this as a career.

Most hire places seem to lend them out at about £70 a day so the difference isn't that much but it's one less depreciating asset to own...plus they post out and collect so it looks like a fairly easy arrangement.

What I don't want is to pay all that money for one that's uncalibrated and has been dropped a few times. Has anyone tried the hiring route?

I borrowed an IR camera, then hired someone with their own camera who knew what they were doing and the difference was significant... The cost of the latter was not that bad.

http://www.earth.org.uk/thermal-imaging-survey-of-house.html

Damon

Posted By: KBabsDuring this wet weather, my fibreglass cavity wall insulation is getting wet while the walls to an extension are going up. I asked the building to cover them up but he said it doesn't matter as it will dry out.

Whether or not they will dry out, a good builder should be installing the batts following the requirements of the Agrément Certificate (whether or not you required them to do so in your contract).

At least in the case of Rockwool the certificate requires protection against rain - "Exposed areas of batts should always be covered at the end of the day’s work or in driving rain (and also specifies other requirements that are frequently ignored through ignorance or laziness - leading with the the outer leaf first, use of cavity boards, correct installation of wall ties, correct butting of batts, etc.)

Failure to follow such requirements may constitute a breach of their contract with you.