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I was thinking of the amount by which you would be raising the top of the roof deck. Would it cause problems where the flat roof intersects with a pitched roof, for example?
Questions About Flat Roof
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The floor of the bedroom (flat roof extension) is lower than those of the house, so the flat roof presumably tucks under the ridge roof.
But I can no longer climb ladders, so I will have to get A N Other to look.
But I can no longer climb ladders, so I will have to get A N Other to look.
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Someone I know suggested dropping the ceiling in the bedroom, clearing out the old rockwool, adding timbers to the underside of the joists to make it deep enough for a headspace and whatever the regulation depth of insulation is - is it 120mm insulation and 50mm headspace?
But then you'd have to make provision for ventilation? At the moment, despite it being a cold roof, there is none.
But then you'd have to make provision for ventilation? At the moment, despite it being a cold roof, there is none.
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I'd consider making a warm roof on top, and if necessary removing the bottom row of tiles from the eaves of the main roof, to make room for the extra height. You'd need a lay board to take the rubber up under the next row of tiles up. A roofer would know how to do this.
That would save any messing around inside, or losing head height.
That would save any messing around inside, or losing head height.
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I have between 150 and 220mm of rockwool between the joists - difference is because of the furrings. Then 50mm of celotex on the joist underside. All taped joints, then the plasterboard. No ventilation. EPDM above.
There is 150mm of celotex in the walls too, but the roof would be the main heat loss surface. In practical terms, it means that for this 5mx3m bedroom there is only a standard 400mm radiator, and it is not on a great deal over the winter as the room stays quite warm despite being north facing and a bit exposed.
So if you are going to re-do the roof for comfort, I would do it from the inside and not mess about externally.
Keep the celotex nearest the room as its the better insulator, and I suspect that it works better for keeping sound and summer heat out by having the rockwool above - plus its easier to pack the void and ensure all gaps are filled.
There is 150mm of celotex in the walls too, but the roof would be the main heat loss surface. In practical terms, it means that for this 5mx3m bedroom there is only a standard 400mm radiator, and it is not on a great deal over the winter as the room stays quite warm despite being north facing and a bit exposed.
So if you are going to re-do the roof for comfort, I would do it from the inside and not mess about externally.
Keep the celotex nearest the room as its the better insulator, and I suspect that it works better for keeping sound and summer heat out by having the rockwool above - plus its easier to pack the void and ensure all gaps are filled.
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To be fair Woody, although I have one flat roof similar to yours, it's not how you're meant to do a cold roof. In theory, any gaps in your Celotex could let moist air through to condense at the dew point, without any ventilation to carry it away.
I agree though that it would be less faff to do it from the inside, now we know that the flat roof abuts a pitched roof. I thought perhaps the OP might prefer not to lose headroom. But your way is easier.
I agree though that it would be less faff to do it from the inside, now we know that the flat roof abuts a pitched roof. I thought perhaps the OP might prefer not to lose headroom. But your way is easier.
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Thanks, guys. I shall speak to my professional!
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OK. I realise it's been a while, but I am now (fanfare!) ready to push ahead with insulating our cold roof flat roof.
I am very limited as to what I can do now, but we are planning to strip off the manky old plasterboard then put Celotex or Kingspan between the joists.
There are many websites on this topic saying this method of insulating cold roofs is now frowned upon and even banned under Scottish BR's.
The complaint is that despite trying to ensure ventilation, condensation can still occur and the roof will quickly rot.
So, is it still a good idea?
The joists are something like 8.5" deep and 2" across. I guess I'll need 150mm and an insulation- backed plasterboard to cover? Is 35mm sufficient?
Cheers.
I am very limited as to what I can do now, but we are planning to strip off the manky old plasterboard then put Celotex or Kingspan between the joists.
There are many websites on this topic saying this method of insulating cold roofs is now frowned upon and even banned under Scottish BR's.
The complaint is that despite trying to ensure ventilation, condensation can still occur and the roof will quickly rot.
So, is it still a good idea?
The joists are something like 8.5" deep and 2" across. I guess I'll need 150mm and an insulation- backed plasterboard to cover? Is 35mm sufficient?
Cheers.
L
Leofric
If you are employing an architect they should sort all this out for you.
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The architect disappeared into the ether and the SE just said something about "levels of insulation commensurate with the latest BR's.
There is no structural work being carried out. I got the SE to visit to comment on various small cracks appearing in the building (nothing to do with the flat roof extension).
These various cracks he said were down to thermal expansion, nothing to worry about. Use a flexible filler in the course of your redecoration, he said.
There is no structural work being carried out. I got the SE to visit to comment on various small cracks appearing in the building (nothing to do with the flat roof extension).
These various cracks he said were down to thermal expansion, nothing to worry about. Use a flexible filler in the course of your redecoration, he said.
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