Advice needed on loft conversion's slightly bowed flat roof

theGrinch

We had a leak which started 24-month ago. It created a visible damp patch and if heavy rain a slow drip leak. 

Called a roofer who applied a bitumen layer. That seems to stop it for 12-months. Roofer returned and applied a second layer which again stopped the leak.

I have now noticed that the roof is uneven though there is no further leak. To the eye the uneven-ness are like "a few oranges under a carpet).

Roofer returned to say that the initial leak had caused the plywood to bow (much like a leak would to laminate).

He suggested to leave it for the winter and if it deteriorates then definitely:

a) to change the ply for ply and new roofing material on top.

b) change to marine  ply and new roofing material.

If there is no deterioration then still consider a change to pre-empt future issues.

Would there be any advantage here of marine ply over ply given new roofing material on top regardless.

For the record, he believes something as small as a single misplaced nail hole could have caused the initial leak. And access is relatively straightforward through a loft hatch

FreeBear

Patching a leak from the inside of a roof is doomed to fail fairly quickly. I'm assuming this is a flat roof ?

If so, it would probably pay to strip the whole roof off, insulate the heck out of it, and then put new boards down followed by EPDM "felt". Note - Building Control should be notified if you are replacing more than 25% of a flat roof, but some roofers can self certify the work.

As for suitable boards, OSB sheet is the usual material. Marine grade plywood would be considerably more expensive and not required - The boards will be protected by the felt, so should never get wet.

Tip - Get the roofer to fix the boards down with screws. If you have any plasterboard on the bottom of the joists, screwing the boards down will limit the amount of cracking & nails popping in the ceiling below.

theGrinch

Much appreciated and noted re OSB/screws.

The patching is external as we have access through a loft hatch. 

Thank you. 

Bendy_House

theGrinch said:

Much appreciated and noted re OSB/screws.

The patching is external as we have access through a loft hatch. 

Thank you. 

Do you mean a 'roof' hatch that easily allows you access to the outer roof? Or do you mean a 'loft' hatch that gets you access to a loft void which is under that flat roof?

If the former, then, yes, it must surely be worth stripping that existing outer covering right off, and seeing exactly what needs doing. Sounds like new sheeting - eg OSB - followed by a covering that suits your budget; felt (that's fine if done well), EPDM (usually considered superior) or GRP (generally thought of as the 'best').

Also - DEFINITELY - worth looking at a way to increase the roof slope so that rainwater simply cannot 'pool' on it any more, even if it's slightly wobbly.

Also - DEFINITELY - worth looking at the existing insulation level, and upping that as much as you can.

Put this off until next year (keep leaks at bay by using Cromapol or similar - better than bitumen) and meanwhile have at least 2 other recommended roofers out to assess and quote for a 'recovering'. Listen carefully to what they say, note it down, and come back on here for any clarification required.

If the latter, don't bother with adding 'insulation' to the flat roof as it'll have no effect on your house. Instead, pile up the insulation level on the house's ceilings. But still get quotes for recovering - and increasing the slope - of the existing roof.

theGrinch

Bendy_House said:

theGrinch said:

Much appreciated and noted re OSB/screws.

The patching is external as we have access through a loft hatch. 

Thank you. 

Do you mean a 'roof' hatch that easily allows you access to the outer roof? Or do you mean a 'loft' hatch that gets you access to a loft void which is under that flat roof?

If the former, then, yes, it must surely be worth stripping that existing outer covering right off, and seeing exactly what needs doing. Sounds like new sheeting - eg OSB - followed by a covering that suits your budget; felt (that's fine if done well), EPDM (usually considered superior) or GRP (generally thought of as the 'best').

Also - DEFINITELY - worth looking at a way to increase the roof slope so that rainwater simply cannot 'pool' on it any more, even if it's slightly wobbly.

Also - DEFINITELY - worth looking at the existing insulation level, and upping that as much as you can.

Put this off until next year (keep leaks at bay by using Cromapol or similar - better than bitumen) and meanwhile have at least 2 other recommended roofers out to assess and quote for a 'recovering'. Listen carefully to what they say, note it down, and come back on here for any clarification required.

If the latter, don't bother with adding 'insulation' to the flat roof as it'll have no effect on your house. Instead, pile up the insulation level on the house's ceilings. But still get quotes for recovering - and increasing the slope - of the existing roof.

Thank you. Yes I meant a roof hatch

Bendy_House

In which case, as far as my limited understanding goes, everything but the second-last sentence :-)