Cold to Warm Roof Conversion

securespark · 22 Feb 2020

With reference to this:

https://www.diynot.com/diy/threads/damp-flat-roof.533187/

We have been talking to the guy that did it. He would like to fit ventilation, I would prefer he does a warm-roof.

He has hinted that the en-suite has contributed to the condensation (mainly because of the poorly fitted rockwool that he fitted between the joists), so has been pointing out to me that the en-suite will still generate a lot of moist warm air which will fill the void with condensation.

But my argument is that, with a decent VCL (which the existing EDPM will form), the whole area under the flat roof, including the roof void, will be the same temperature, eliminating the possibility of condensation.

He is unsure.

noseall · 22 Feb 2020

Only someone particularly insane would risk a cold roof detail above a condensation rich room. Bonkers.

Notch7 · 22 Feb 2020

Are you creating a new warm roof, rather than a retrofitted hybrid roof

securespark · 22 Feb 2020

Hmm. Not sure.

The plan is to use the existing cold roof EDPM as a VCL then put rigid insulation on top with a new EDPM layer over.

securespark · 23 Feb 2020

We are not even sure we want the guy back to do any further work given his past record. What would you peeps do?

conny · 23 Feb 2020

More research and then consult someone with a genuine good reputation in this kind of work.

securespark · 23 Feb 2020

Cheers, conny.

Wonder if Notchy is about to expand on his comment?

noseall · 24 Feb 2020

securespark said:
Hmm. Not sure.

The plan is to use the existing cold roof EDPM as a VCL then put rigid insulation on top with a new EDPM layer over.

That will work.

securespark · 24 Feb 2020

My "roofer" is convinced I will still have the same issue with condensation forming in the void 'tween deck and ceiling.

noseall · 24 Feb 2020

securespark said:
My "roofer" is convinced I will still have the same issue with condensation forming in the void 'tween deck and ceiling.

You need a cold spot first. Remove any insulation that is guarding the structure below your new insulation layer and then the structure will gain warmth from the room heating and be at the same temperature as the room.

securespark · 24 Feb 2020

Cheers.

Could this be done after boarding out, or should it be done before?

I have removed the old ceiling and the rockwool in the void above.

The bedroom is over an unheated garage, so the plan is to rip up the floor and fit celotex between the joists, then relay the floor.

Should these works be carried out in a particular order?

Notch7 · 24 Feb 2020

securespark said:
Cheers, conny.

Wonder if Notchy is about to expand on his comment?

I did, but forgot to submit and lost it.

yes it will definitely work, you are creating a true warm roof with a continuous layer of insulation, which are over the top of ceiling joists.

you need to make sure the insulation is returned downwards at fascia and brickwork to remove any thermal bridging.

My only issue is that if you put insulation over the top then cover with an OSB deck -it will need screwing down -which will go through the epdm (although that is also true of a VCL) Alternatively you can stick the PIR down but then you will have the question of whether the sheets will stick to the EPDM.

you can also foil tape all the PIR before putting the top OSB deck on -its another VCL.

nb: if you do your roof and it rains, your warm roof will trap in the moisture -so try and do in a dry spell and get weathered in fully -even if you just cover the roof with a full sheet of dpm and tuck it under the flashing

dont try and adapt your existing roof to a cold roof -Noseall is 100% right -its a bad solution.

securespark · 24 Feb 2020

Notch7 said:
I did, but forgot to submit and lost it.

Bless you!

Notch7 said:
dont try and adapt your existing roof to a cold roof -Noseall is 100% right -its a bad solution.

The surveyor said we need to either ensure good cross ventilation or go for a warm roof.

The roofer who did the refurb said he would fit mushroom vents??

We think a warm roof conversion is a much better idea altogether.

Notch7 · 24 Feb 2020

securespark said:
The roofer who did the refurb said he would fit mushroom vents??

Thats a cop out

Not a solution, just an easy option bodge.

securespark · 24 Feb 2020

I'm beginning to think his roofing knowledge is limited, as he says a warm roof will still create buckets of condensation.

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Cold to Warm Roof Conversion

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