DIY Doctor

Insulation Only on Top of Joists and not Inbetween Each Joist?

Postby elara99 » Sat Mar 05, 2016 2:17 pm

Hi all, hope you can help. We are looking to remove some old, dirty, bat-dropping-infested fibreglass from our loft and will be replacing it with Kingspan/Celotex. However we were wondering if it would be OK to just put this on top of the joists, rather than have to cut it to fit in between the joists.

Is there any good reason to *have* to put it down between the joists rather than just lay it on top? wouldn't it still be insulating, albeit a few inches higher up, with a layer of air underneath it?

Any advice would be great. I've not managed to find anything online about this so far, and I've looked quite hard...

Many thanks
(and yes, we know about bats - had someone round to check - they're long gone though now)
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Simply Build It

Postby welsh brickie » Sun Mar 06, 2016 10:47 pm

if you lay it on top, it may condensate underneath causing problems, and you cannot stand on it as it will break/crush. and could cause damage to the ceiling
No air gaps is better, that's why fibreglass is used
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