"If the roof's not leaking, where is all the water coming from?"
That was Matt's question. The flat roof over his bathroom had no obvious leaks and had recently been looked at by another company, but inside, the plywood under the roof was swelling, softening and showing moisture damage.
Condensation, not rain
We ruled out rain quickly: the felt was still doing its job. The real problem was the design. The roof was a cold roof, with the insulation below the plywood and no ventilation between the joists, so warm, steamy air from the shower was condensing on the cold underside of the deck and soaking into it.
Day after day the timber soaked it up. When we stripped it back, the boarding and the firrings that give a flat roof its fall had rotted through from below, while the felt on top still looked sound.
The fix: a warm roof
We took the whole build-up off, down to the joists, and rebuilt it as a warm roof: a new plywood deck, rigid insulation boards on top of it, and a new flat roof covering. With the insulation above the deck, the roof needs no ventilation. We went back after the main day to finish the trims.
"A 'cold roof' construction with no through ventilation, shower room below, rising hot air has destroyed the boarding and furring pieces."
Steve Ball, on this job
"John and Steve were a pleasure to deal with from start to finish. They quoted the job and were quickly able to arrange the work without fuss. We had a complex issue with a severely damaged felt-covered flat roof above our bathroom, and they were able to diagnose the issue and repair it for us with a high-quality finish. They were friendly, didn't muck us around, and even came back after the main day of work to do a few small finishing touches. We nearly went with another company that hadn't spotted the real cause, we're so glad we didn't. We'll definitely consider using them again!"
