On stripping a small flat roof recently over a bathroom we soon could see that the decking was rotten.
Surprisingly this was a close boarded roof, of 6×1 planks, and should have been in good shape – but all were totally perished as were a few joist ends.
The actual flat roof itself only had a few cracks so we were surprised as to why the timbers were so bad.
On further investigation we found an extractor fan was fitted in the bathroom ceiling but had no way of venting outside, the hot wet air was simply discharging straight into the ceiling void beneath the decking.
And slowly rotting the timbers supporting the flat roof. Apparently the fan was fitted 20 years ago, no wonder the timbers were gone.
New decking was fitted, joists replaced and a vented air system installed to allow air movement in the roof space.
Needless to say we fitted a proper extractor fan and flue pipe; and we did it properly unlike the ‘builders’ who caused the problem in the first place.