Best method of insulating basement walls and ceiling

9 Jul 2009
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United Kingdom
Hope this is OK to post here...

I have a semi basement ( I live on a hill slope from front of house down to the back ), above which is my kitchen / diner. The basement ceiling is timber floorboards resting on timber joists. I want to convert the basement into usable space, Ive had a damproofing consultant confirm that there is minimum damp present, but I will tank it using tanking slurry or the like to be on the safe side. I want to insulate the walls and floor and ceiling and was recommended thermal boarding ( plasterboard? ) for the walls. I want to make sure the ceiling is properly insulated as the room above gets very cold in the winter. Whats the best method here? He suggested celotex but would standard glass fibre / rockwool be just as good? Do I need any kind of condensation membrane on the ceiling before I board it after the insulation install? What about ventilation? the room has a small pvc window with vent, is that sufficient? Thanks for reading, any suggestions welcome. Dan
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If you are using a render to prevent damp ingress then you cannot fix anything through it. So insulated plasterboard on dabs would be a good choice. You could fit rockwool within a stud wall provided you only fix at the head and base and your base fixings do not penetrate whatever damp proofing you are applying (if any). You would need typically about twice the thickness of rockwool to do the same job so when you add the cost of building a stud wall as well I doubt you'll be saving that much.

If you are insulating the floor and walls then why are you insulating the ceiling? Is there any heating?
thanks for the quick reply.

The room wont be connected to the central heating as will only be used infrequently, so will have electric heating as and when required. If I could use a suitable floor insulation ( current floor is concrete ) and avoid the need to insulate ceiling then fine.

Only issue is the ceiling is about 2 metres high and I dont want to lose too much height off the floor as I am also 2 metres tall. So my preferred solution would be minimum thickness ( but max effectiveness ) insulation for the floor and then whatever is cost effective yet also efficient for the ceiling ( between joists ). Any thoughts regarding condensation, venting? Thanks !
PS the house has cavity wall insulation too.

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