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Suspended Timber Floor Insulation


MikeGrahamT21

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Hi,

 

Never seems to be a firm answer on this...

 

We have 100mm joists with sleeper wall, which we will insulate with 100mm PIR, friction fit, and gaps filled with expanding foam. I have got some Tyvek Supro (breathable roofing felt) left over, and as its airtight to 50pa, I was going to use this across the top of the joists, before the OSB3 goes down.

 

However I've just read online, that its more suitable to have a VCL above the joists, to stop any moist air going underneath.

 

Ample ventilation under the floor and a decent gap.

 

Would you say an airtight VCL may be the best option?

 

Regards

Mike

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If the PIR has a foil face put this uppermost. If practical put the supro underneath the PIR with adhesive or similar. Avoids multiple punctures from OSB fixings. PIR, especially foil faced has significant vapour resistance and acts as its own vapour check so would not bother with VCL if you do not already have it.

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PIR has a double foil face, and its not practical to put supro underneath, i'd probably be able to get it part way, but never with a proper seal, as we don't have a crawl space, theres only 2 bricks worth of room.

 

I had a look on ebay, and managed to get a 75m2 roll of Protect BarriAir for £68, so I'm going to go down the route of VCL on the warm side to protect the timbers best I can (since the reason i'm replacing is because of woodworm infestation which we believe is no longer active, obviously caused by the timbers being too moist, though i think this was more to do with the air bricks being mostly blocked/semi blocked, which now isn't the case), and on top of where the joists are, I'm going to use 50mm butyl tape to seal the penetrations from the screws in the OSB, and be very careful that i'm 100% accurate with my screw placement!

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