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Loft thermal insulation minimum size requirement?

Hi, we have had a survey competed on a property we are in the process of buying and it's been flagged up that the insulation in the loft doesn't meet the required size standards. It's only 200mm thick and apparently it should be 300mm.

We have had a couple of quotes come back on MyBuilder to replace the insulation, but there have been conflicting answers about the size standards. Some say it should be 300mm and some say the 200mm is fine as it is.

Does anyone know what the standard requirement should definitely be please? And is there a website I can refer to, if required to be replaced, to prove the standards required?

I hope you can help. Any answers and advice will be greatly appreciated! :)

2 Answers from MyBuilder Insulation Installers

Best Answer

As far as im aware,current regs require 270mm of insulation.This would be 100mm between the ceiling joists and 170mm on top but running in the opposite direction ie OVER the joists.I think 300mm is only required in new builds.


Answered 23rd Sep 2011


the thickness will vary as to the product and their U value, so once you decide on the product you can check the thickness required. i usually specify 300mm standard rockwool but this can be reduced. the other thing is you can just add another 100mm straight onto 200mm thats there. Also one other thing, the government does give grants for such work.

best regards



Answered 23rd Sep 2011

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