I live in a 1970s block of flats with a flat roof, which is now beyond patching and needs stripping and rebuilding.
I'd really appreciate a bit of independent advice regarding the rebuild, as roofers have a vested interest in putting forward their own proposals.
We've engaged a building surveyor and he has presented his proposals; however, a trusted roofer I discussed them with is not convinced.
The decking is woodwool without a cement screed. In addition, the existing roof has a miserable fall of one and a half inches in 11 feet. It really is a flat roof.
The surveyor proposes:
1. Strip existing felt off.
2. Fit tilting fillets and OSB to give improved falls to valleys feeding to existing rainwater pipes.
3. Fit polyurethane insulation slabs on a vapour barrier.
4. Lay a high performance torch-on felt underlay and mineral-faced cap sheet.
5. New edge detail because new roof surface would be 150mm higher than present.
The roofer has commented that putting OSB over the existing decking (with the tilting fillets in between) is not a good idea - it could induce sweating; however, with the thermal insulation on top of the OSB/vapour barrier, I'm not sure this is a valid comment as the decking and OSB would now be in a warm roof in theory.
I also need to be convinced that the OSB can be properly attached to the existing structure.
The roofer also does not like the mineral-faced capsheet because he says it's difficult to get a good edge joint. He prefers (if I've understood it correctly) to use a 4mm high-performance capsheet painted with solar reflective paint after laying.
I'd be most grateful for any thoughts and comments on the above.
Many thanks
Martin
I'd really appreciate a bit of independent advice regarding the rebuild, as roofers have a vested interest in putting forward their own proposals.
We've engaged a building surveyor and he has presented his proposals; however, a trusted roofer I discussed them with is not convinced.
The decking is woodwool without a cement screed. In addition, the existing roof has a miserable fall of one and a half inches in 11 feet. It really is a flat roof.
The surveyor proposes:
1. Strip existing felt off.
2. Fit tilting fillets and OSB to give improved falls to valleys feeding to existing rainwater pipes.
3. Fit polyurethane insulation slabs on a vapour barrier.
4. Lay a high performance torch-on felt underlay and mineral-faced cap sheet.
5. New edge detail because new roof surface would be 150mm higher than present.
The roofer has commented that putting OSB over the existing decking (with the tilting fillets in between) is not a good idea - it could induce sweating; however, with the thermal insulation on top of the OSB/vapour barrier, I'm not sure this is a valid comment as the decking and OSB would now be in a warm roof in theory.
I also need to be convinced that the OSB can be properly attached to the existing structure.
The roofer also does not like the mineral-faced capsheet because he says it's difficult to get a good edge joint. He prefers (if I've understood it correctly) to use a 4mm high-performance capsheet painted with solar reflective paint after laying.
I'd be most grateful for any thoughts and comments on the above.
Many thanks
Martin