Hi Guys. I have read with interest all the comments about what constitutes a warm flat roof and what makes it a cold roof.
It would appear that one can avoid venting a cold flat roof if an effective moisture barrier is created (such as using foil backed insulation board with tape etc). Our building inspector seems to say that you can not have an effective moisture/vapour barrier if you have downlighters set in to the ceiling.
Any views/useful advice.
The alternative will be to vent the whole area which is a daunting task. It all happened because the flat roof 'office' is being converted to a 2 bed flat and in order to meet u values we have to put 7 cm insulation under the joists (in most cases - in some 3.5 inside and 3.5 under to keep a reasonable ceiling height). But there was already 7 cm insulation between the 9 inch joists (which looks as though it has been fitted in direct contact with the underside of the roof). The BI is saying that what was a 'warm' roof has now become a 'cold' roof because of the added 'ceiling' insulation. This does not seem to make sense from a physics point of view
With regard to the previous/existing situation, I have worked in this 'office' for nearly 25 years and not had a problem either with cold or condensation.
Denis
It would appear that one can avoid venting a cold flat roof if an effective moisture barrier is created (such as using foil backed insulation board with tape etc). Our building inspector seems to say that you can not have an effective moisture/vapour barrier if you have downlighters set in to the ceiling.
Any views/useful advice.
The alternative will be to vent the whole area which is a daunting task. It all happened because the flat roof 'office' is being converted to a 2 bed flat and in order to meet u values we have to put 7 cm insulation under the joists (in most cases - in some 3.5 inside and 3.5 under to keep a reasonable ceiling height). But there was already 7 cm insulation between the 9 inch joists (which looks as though it has been fitted in direct contact with the underside of the roof). The BI is saying that what was a 'warm' roof has now become a 'cold' roof because of the added 'ceiling' insulation. This does not seem to make sense from a physics point of view
With regard to the previous/existing situation, I have worked in this 'office' for nearly 25 years and not had a problem either with cold or condensation.
Denis
