A flat roof with roof lantern, built to stay dry

The brief: a flat roof that carries a lantern

A roof lantern is a glass feature set into a flat roof to flood the room below with daylight. It looks wonderful on the first sunny day and it creates a problem on the first wet one, because every edge around the glass is a place for water to get in.

The brief on this project was a new flat roof built around that lantern: the whole roof covered, every edge dressed up the lantern frame, and no weak joint left for the weather to find.

What makes a flat roof with a roof lantern hard

A flat roof is never completely flat. It carries a fall so water runs to the outlet, and anything that interrupts the fall, such as a lantern kerb, makes water look for another way. The covering has to turn up the kerb and finish cleanly under the lantern frame.

Laps matter too. The membrane goes down in strips that overlap, and every lap is sealed. On the finished roof in the main photograph you can see the lines of those strips running across the roof towards the lantern, with the edge of the roof clean and the fence and driveway beyond.

Every edge is checked before the roof is signed off, because on a flat roof the details decide the result, not the size of the surface.

How the roof goes together

The build-up starts with a sound deck. Rotten or sagging boards get replaced before anything else goes on, because a membrane laid over a weak deck fails at the weakest board. Then the covering goes on in lapped strips and the details are formed: the lantern kerb, the edges and the outlet.

A second photograph from another job shows the early stage of the same kind of build: torch-on felt laid over a new deck around a roof light, a fire extinguisher standing ready beside the work, the next roll waiting and the edge details still to come. That is the stage nobody sees once the roof is finished, and the stage we never rush.

The finish

A good flat roof looks dull, and that is the point. No ponding, no lifting laps, no stains running down the wall. The roof in the main photograph is flat, clean and tight to the white frame of the lantern, ready for years of weather.

All work is backed with a 20 year written guarantee, and the paperwork is issued when the job is complete.

Need a flat roof or an extension roof?

We renew flat roofs of any size, from porches and garages to full extensions. See our flat roofing, felt roofing and garage and extension roofs pages for systems and details, then get a free, no obligation quote. We promise to beat any written quote.