75mm loft insulation option given PIR boards are unobtanium?

[sjalloq]

So I have a very low pitched roof with a central crawl space that I can't even sit up straight in, i.e. there's not a lot of space. I want to board it so that I can use it for storage and was going to renew the insulation which is some sort of glass fibre type stuff. However, the joists are only 75mm and I was planning on using a Celotex board but have just seen that there's some sort of national shortage and the lead time is 8 weeks plus.

What can I use instead? All the 'wool' type brands seem to be 100mm plus and I'm assuming if you squash it into a 75mm space it won't perform like it is supposed to. Should I just order the Celotex and wait or have I missed a 75mm product that would perform well?

Cheers.

 

[MikeG.]

There are shortages, but some of the seconds dealers have stock, and there are alternative brands available at some builder's merchants.

PIR and mineral wool are not a straight swap for each other. The PIR is almost twice as efficient as mineral wool, so 75mm is the equivalent of 140+mm of mineral wool. Squashing 100mm of mineral wool into 75mm gives an efficiency of the less than if you used 75mm in the first place. Finally, 75mm of anything in that roof is inadequate. Without looking it up I think you need about 230mm or so of mineral wool to be getting near the current U values, and with PIR (Celotext etc) that means at least 130mm. Bear in mind that you should also be getting adequate ventilation into the roof void.

 

[Jake]

Shortage probably due to a certain fire.

 

[MikeG.]

Shortage probably due to a certain fire.

Yes, but not the one you are thinking of. There was a fire in the factory in Germany which produces the base chemicals for most of the PIR board made in Europe.

 

[RobinBHM]

Im fitting 120mm in my loft.

The joistscare 100mm, so Im screwing down some tile batten on each joist to make the difference.

Celetex, kingspan, ecotherm, recticel are all PIR.

I expect if you ring around somebody will have 70mm or 75mm

 

[Phil Pascoe]

https://www.secondsandco.co.uk/product- ... foil-board

This firm is always worth a look.

 

[Harbo]

From what I’ve read, Celotex is not fire proof unless you use the FR range.

Rod

 

[MikeG.]

From what I’ve read, Celotex is not fire proof unless you use the FR range.

Rod

No, but the ceiling is, so the fire resistance of the insulation is unimportant.

 

[sjalloq]

Ah, I forgot to turn on notifications so thanks for all the replies.

MikeG, thanks for the info. I've only got 75mm of space so that's what I'll fit. Either side of the crawl space I'll be able to add more and the roof is vented so I'm not changing that.

I'll have a ring round and see what I can get.

Cheers.

 

[Myfordman]

I can't remember if this stuff comes in 10mm or 5mm steps in thickness but if 75mm is so hard to get why not use two layers of thinner stuff?