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A rear extension flat roof taken back to the joists and rebuilt properly: rotten timbers cut out and replaced, mineral wool insulation, a new SterlingOSB Zero deck and a three-layer torch-on felt system with a grey mineral cap sheet. Completed July 2026 and photographed on site.
This was a rear extension in Chatham, Medway, and the brief was a complete flat roof replacement rather than another patch on top of what was already there. An adjoining raised terrace area was included in the same job, so the extension and the terrace were finished as one continuous piece of work in the same system.
We inspected the roof first, explained what it actually needed and gave a fixed written quote before anything was lifted. The work was completed in July 2026 by our own team and is covered by our company workmanship guarantee.
Once the old covering came off, the reason for the replacement was in plain sight. The deck was saturated and several of the joists underneath had rotted. That is the part a homeowner never sees from the garden, and it is exactly why laying another layer of felt over the top would have been a waste of money.
A felt-over-felt patch traps the water that is already in the timber instead of getting rid of it. The rot carries on quietly underneath, the deck keeps softening, and within a season or two the new covering starts to dip and split where the structure has given way. You end up paying twice, and the second time the damage has spread further.
So we did it the only way that lasts. Every failed and rotten timber was cut out and replaced with new treated timber, and only once the structure was sound did anything go back over the top.
Every photo below was taken on site by our own team, in the order the work happened.
A flat roof fails at its weak points: joints, fixings and the surface that faces the sun. A bonded three-layer build removes all three.
Each layer is heated and bonded to the one below, so the roof behaves as one continuous membrane rather than sheets sitting loosely on top of each other. If the surface ever takes a knock, there is still material underneath it.
Because the layers are bonded, nothing has to be nailed or screwed through the finished waterproof surface. Every mechanical fixing driven through a covering is a hole, and holes are where flat roofs start to leak.
The grey top sheet carries a mineral finish, and those granules take the sunlight instead of the bitumen underneath. UV is what dries a cheap covering out until it goes brittle and cracks, so the cap sheet is doing real work, not just looking tidy.
The finished extension roof is a sound structure first and a waterproof surface second, which is the right order round. New treated timbers where the old ones had failed, insulation between the joists, a fresh SterlingOSB Zero deck, then three bonded layers of felt finished in a grey mineral cap. The upstands, the wall abutments and the threshold at the patio doors were all dressed and flashed, and the raised terrace next to it was covered in the same system so the two surfaces are continuous.
The customer was on the roof with Cornelius when the job was signed off, which is how we prefer to finish. Cornelius owns the company, he handles every enquiry himself, and he is on the jobs rather than behind a call centre.
Tell us about the roof and we will arrange a free inspection and a fixed written quote. If the deck or the joists have gone, we will tell you straight instead of felting over the problem.
Tell us about the job, we usually reply within the hour.
Prefer to talk? Speak to Cornelius on 07777 735785 or 01753 415 442
Free written quotes. 24hr emergency callout. A local team rated 5.0 by 200+ homeowners.
