cold roof to warm roof

[ludwigMM]

Hi, I am afraid, I made a mistake that i have to correct now. I built up an extension for a kitchen of 5.5x6 metres last year and put a cold roof on it. insulation on the ceiling, all over the place a gap between 100 and 400 mm ( pitched roof ), decking boards from 18mm OSB, fibreglass roof. So far everything is fine, no leaking, no problems. BUT : I noticed that when it was cold I had ice under the OSB boards. If then the ice melts it dropped on my insulation. My trouble now is, can i just build up my warm roof construction on the old roof without removing the fibreglass( this was done last year in spring, the roof is really ok ) but i am feeling more safe with the warm roof construction. However, I know i have to spend money for new insulation and new fibreglass. Only Problem is, can I leave it like it is and start the new one from here, can I leave the insulation on the ceiling? Hope there is anyone to advise me. Thanks for help

 

[tomfe]

How did you tell you had ice on your OSB? How did you get a look into this void?
Is the void vented?
Have you got a vapour barrier on the warm side of your insulation?
Have you checked for leaks?

 

[ludwigMM]

Yes the void is vented, i have a maintenance access in the kitchen. the ice was clearly under the osb boards, u can feel that the place is vented as u can feel the draught. there are definetely no leaks, the place is completely dry, even after heavy rain. the roof is a 6 degrees pitched roof. my idea is, to convert it to a warm roof. i am aware that i have to spend some money, fine. i am only wondering, if i can put the warm roof construction ON the fibreglass or if i have to remove this one. put it on top would be the easiest solution, otherwise i would have to renew all the decking boards as the resin is applied on the boards.

 

[Elastomeric]

As has been asked, what vapour barrier is there ?

 

[ludwigMM]

from inside: ceiling, vapour barrier, insulation, void, timber deck 18 mm, fibreglass roof, finish layer in green. the vapour barrier in between plasterboard and insulation, the fibreglass resin has to be applied directly on the osb boards.

 

[Elastomeric]

I would hazard a guess that your VB is leaking and you have interstitial condensation forming. Ideally you will need to remove Rockwall before converting to warm roof.

 

[rssteve]

Is the access hatch cut into the vapour barrier and making it useless?

 

[ludwigMM]

I am 100 % sure it is not leaking. Even after heavy rain, there are no drops and there are no wet places. Absolutely dry.

 

[tomfe]

It would be best to fix the problem with the roof but to answer your questions.

can I leave it like it is and start the new one from here,

Yes

can I leave the insulation on the ceiling?

No

 

[ludwigMM]

Tomfe, do u mean, i could leave the fibre glass on the osb boards and start completely new with vapour barrier, celotex insulation, new boards and new fibre glass layer but i have remove the old insulation on the ceiling? If so, then this is the answer i was looking for. ( not what i like but its the answer and i know what to do). i personally think that the ice under the boards just came because the top ( outside ) of the fibreglass was frozen, it was -3 degrees that day. like today, everything is fine and working and well vented. was just worried when this ice melts and drops on my insulation. apart from this there is no problem with the roof

 

[tomfe]

Yes I do mean that.

If you have a well ventilated void you should not get any build up of moisture in it unless you are missing the vlc or it is damaged or extremely penetrated (maybe even hardcore) or you have a leak.

 

[catlad]

It sounds like you have to much warm air getting into the roof space.
When you were experiencing the ice on the underside of the roof you
could have laid a piece of celotex/kingspan on the outside of you roof
weighted down with something to see if that helped.