Does anyone know about insulating lofts / condensation / ventilation issues?

[Masood]

Not really a plumbing question but there are some very knowledgeable chaps on here so... My roof is tiles on close-boarded timber planks (sarking board I think?) and as far as I can tell, no felt or breathable / waterproof membrane.

I want to insulate and board the roof to make the loft warmer and less dusty - only for storage, not converting it. Various websites refer to regs requiring an air gap, with ridge and eaves ventilation to prevent "interstitial" condensation whatever that is.

My roof has no vents at the moment. Can anyone advise as to whether I need vents? If I cut celotex and install between the rafters, in direct contact with the timbers, would that cause problems?

Cheers!

 

[stani]

I think you need an air gap, our lads did some a few months back, I wasn't on it but pretty sure they' had to leave 25mm

 

[rpm]

Overheard some roofers talking about this in the pub, 2 vents needed (1 each end) to allow circulation of air or ........................

Sorry mas I stopped listening at this point but could ask tomorrow night if your still looking.

 

[Masood]

Overheard some roofers talking about this in the pub, 2 vents needed (1 each end) to allow circulation of air or ........................

Sorry mas I stopped listening at this point but could ask tomorrow night if your still looking.

Thanms mate but been doing some reading and I need to leave a 50mm gap between boards and insulation. I'm not sure whether I'd need to have vents as well, but I may put some in just to be on the safe side...

 

[Deleted member 7121]

Thanms mate but been doing some reading and I need to leave a 50mm gap between boards and insulation. I'm not sure whether I'd need to have vents as well, but I may put some in just to be on the safe side...

It's to stop cold bridging, also make sure you use foiled back plaster board.

 

[Masood]

It's to stop cold bridging, also make sure you use foiled back plaster board.

If I use foil backed celotex would I still need foil backing on the plasterboard??

 

[Atouchofgas]

Yep as the foil backed plasterboard acts as vapor barrier across the whole area not just in between the rafters

 

[justlead1]

I can see you have had some good information. Which gives me the opportunity to say i make sheet lead roof vents should you need them.