no frost on new extension roof.

[jwpetal]

Hi. This morning we woke up to a frosty morning and quickly went to look at our new extension roof. Our old lean to of an extension had no insulation and so having a new 'solid' roof was, to us, quite exciting.

All around we say frost on our neighbors roof, but not ours. When I approached our builder about this, he said we should not have frost on our roof. I fairly certain this is not true. what I do know is that he put celotex in between the joists and then over the joist to regulation - approved by building control and signed off.

It is a pitched roof to 13 percent - is it possible that some tiles do not frost?

I can feel a draft coming through the roof from where our down-lighters have not yet been placed as we are to do another coat of paint. should there be air coming between the insulation and the ceiling? He mentioned needing to put a sealant on the outside, which may explain the draft. But still unsure about the lack of frost. Thanks for any help on this. our builder has tried to cut corners a couple of times so want to check.

 

[footprints]

I would have thought with downlighter holes in the ceiling there must be a fair amount of heat going up I would wait and see what happens when the lights are in place.

I guess you could block them on a temp basis to see what happens. I am no sparks but I believe the downlighters should have some kind of smoke hood over the top which should help too, not sure wether you can insulate over the hood afterwards, no doubt someone on here can confirm.

I would expect a well insulated roof to have frost if the others do.

 

[Alastairreid]

How deep is the celotex between and over rafters?

I'm assuming vaulted ceiling! The downlighter holes wont be helping matters but would expect frost on other areas of the tiles.

 

[catlad]

Sounds like a cold roof design, but if you are having a lot of down lights then that will certainly hinder that design.

 

[jwpetal]

thank you for the feedback.

The extension is 4.2 m x 5 m and has a pitched roof to 13 degrees. We put in 10 down lights and the insulation in total 125 celotex in total - I think 25 between rafters and 100 under, which could explain the cold as the denser part of the insulation appears to be what we cut into. If I'd known that the downlights could cause a draft I wouldn't have done it. Oh we, live and learn. We got him to seal all the places outside that the air might be coming through and we'll see how it goes tonight. They are painting tomorrow and then the ligths will be placed. I hope all that works.

 

[jwpetal]

I have found out we have a cold roof design. The architect and building control have not been terribly helpful. They've just said that there should not be a cold draft going through.

The builder said that he did the downlights so that they did not have to cut into the celotex, but this could mean that he moved the insulation and changed how the venting works causing an incorrect draft. Does that make sense? The architect mentioned this also.

The only other option is to cut into the celotex and ensure the lights are tightly fitted to avoid the this draft problem.

the building control person suggested similar and was surprised that the builder had not done it this way.

What confuses me is that Celotex guidelines say not to cut into it due to fire risk and insulation issues. Is this a concern or is this normal practice?

thanks for your help.