Can I convert my current flat roof to a warm roof?

[Ges1]

I've got a flat roof in my kitchen extension, with some pitched perimeter pieces and a roof lantern in the middle.

If I want to switch to a warm roof, can I just rip the membrane off the roof, pull out all the insulation, then put in a vapour barrier, insulation, OSB, new membrane, tuck in around the outside, tape up etc.., or do I have to rip the entire roof off and start with new joists from scratch?

I know there's a lot of variables in play, but in general, when comparing an existing flat roof structure to a warm roof, is this what I need to plan for, or is replacing the entire structure more sensible?

 

[Deluks]

What you propose will mean raising the height of the roof, any rooflights will have to be removed and raised up on new upstands. Then there's any existing flashing details at abutments to consider, as well as making sure any insulation in the walls is extended upwards to meet the new roof insulation.

You can probably use the existing joists if the span tables indicate so.

You'll probably have to take the deck off, if it's in good condition and is held down by screws you might be able to reuse it, but for all the faff involved...OSB is as cheap as chips. (...because that's what it's made of!)

 

[blup]

Design it from scratch, even warm roofs need to release moisture

 

[Ges1]

Sorry guys, forgive me, I realise I asked the wrong question!

What I really mean to ask is - is it possible to reuse the joists from a flat roof and convert to a warm roof?

Yes it will be higher by 125mm, that’s all good, yes to redoing the flashing etc, and having to redo the lights etc..

But, if I rip everything out leaving only the joists, can I the.reuse those joists to make a warm roof?

 

[stevie888]

Joists should be fine as increased weight of Celote is minimal. (You want 150mm now)

 

[Ges1]

OK great, it was the only part of the job I was really concerned about. I didn't fancy having to re-strap new joists and have to chase out everything out of the walls if I could avoid it. Hopefully they're in good condition!

 

[Ges1]

Thanks so much, that was what I hoped. The roof needs replacing anyway, so I figured I might as well switch to a warm roof; good to know I can save the joists.

Thanks for the reply!