The Problem
The roof was an artificial slate pitched roof that was leaking. On inspection we realised the slates were not correct for the pitch of the roof, so capillary action was causing water to travel up under the slates and leak. There was also no lead flashing at all.
What We Found
When we stripped the slate roof we were shocked to discover that the pitched roof had been built on top of an old flat roof, which had been left in place. The rafters were not properly secured and were barely hanging on, and there was no wall plate. The whole weight of the pitched roof was resting on the old flat roof.
There was no way we could simply replace the roof covering. Re-covering a structure like this would have hidden a serious safety problem.
What We Recommended
We spoke with the customers and explained that the pitched roof was dangerous and needed to be removed. We discussed the options with them, and explained they also had a condensation problem, caused by a lack of ventilation and two roofs being sandwiched together. We recommended removing the unsafe pitched roof and installing a warm flat roof.
In a warm flat roof the insulation sits above the structure, so the deck stays warm. That removes the need for ventilation and prevents condensation forming inside the roof.
Work Carried Out
- Removed the unsafe pitched roof
- Laid an 18mm OSB roof deck
- Fitted a vapour control layer
- Installed Celotex insulation boards
- Fitted a second roof deck
- Finished with a three-layer torch-on felt system
The Result
A safe, properly built warm flat roof that solves the leaks, the structural problem and the condensation in one go. The customer was left with a 10-year insurance-backed guarantee.
Why an Honest Inspection Matters
This job started as a leak and turned into something much more serious. A quick quote that only replaced the slates would have missed it. Learn more about our flat roofing service and roof repairs, or request a free survey.
What Is a Warm Flat Roof?
In a warm flat roof the insulation sits above the structural deck, so the structure stays warm and there is no cold void where condensation can form. That means no ventilation is needed. The build-up here was an 18mm OSB deck, a vapour control layer, Celotex insulation boards, a second deck, and a three-layer torch-on felt covering.
Why Not Just Re-Slate?
Replacing the covering would have hidden the real problem: a pitched roof resting its whole weight on an old flat roof, with poorly secured rafters and no wall plate. Re-roofing it would have been unsafe, and would not have cured the condensation caused by two roofs sandwiched together.
Questions About This Job
Why was the roof leaking?
The slates were not suitable for the pitch, so water was drawn up under them by capillary action, and there was no lead flashing.
Why did the customer have condensation?
Two roofs sandwiched together with no ventilation trapped moist air, which condensed on cold surfaces.
See our flat roofing service and our guide to flat roof options.
