The short answer
Yes. A flat roof takes a rooflight on a kerb, and with no tiles or slates to cut around it is among the easier roofs to open up. What settles each job is the framing under the covering, the fall of the roof and the state of its surface, and then whether the finished unit stands high enough to need planning permission.
- Free survey, fixed written quote
- 10-year workmanship guarantee
What lies under the covering
From above, a flat roof looks like a single surface. Underneath it is a deck on joists, with insulation somewhere in the build-up and a waterproof layer on top, and each part affects the opening. The joists run one way, and an opening wider than the gap between two of them means cutting a joist and carrying its load round the hole on new timbers. We find the direction and spacing from the loft space or the ceiling below, and those measurements decide which sizes are realistic.
The waterproof layer matters as much as the structure. A new kerb is dressed into the existing covering, so the sound area around the opening has to hold the new joint. If the surface is blistered, cracked or ponding near the spot, we point it out at survey and quote the covering work alongside the glass, because a rooflight set into a failing surface starts life with a weak joint.
Fall comes next. Flat roofs are built with a slight slope to carry water to a gutter or an outlet, and a kerb must leave that route clear. Our page on upstands and kerbs goes into heights and detailing.
| Part of the roof | What we find out |
|---|---|
| Joists | Direction, spacing, and whether the opening needs a trimmed joist |
| Deck and insulation | The build-up that sets how tall the kerb must be |
| Waterproof covering | Its condition around the spot where the kerb will be dressed in |
| Fall | The line rain takes to the outlet and whether the kerb crosses it |
Which rooms suit it
A ground-floor shower room built into the back corner of a house often has a frosted window the size of a tea tray and little else. A rooflight over the cubicle sends daylight onto the tiles, and an opening one gives steam a way out. The hall inside a flat-roofed porch is another case: a glazed front door lights the first step or two and the run behind it stays grey. A bedroom above an old garage, with a flat roof over its ceiling, gets sky where its one window faces a boundary fence.
Where the flat roof covers a deep ceiling build-up, the opening passes through more depth, and that changes how the inside of the opening is lined. We sketch the section for you at survey. If the room sits under a pitched slope further along the house, a different product fits, and roof windows are the place to start.
Rules that sit alongside the roof
A rooflight on a kerb stands out from the roof surface, and that projection is what the planning rules measure. On a house, a rooflight is usually permitted development if it stands no more than 150 mm proud of the original roof, frame included, and no higher than the highest part of that roof. A roof lantern normally goes beyond 150 mm, so it needs planning permission unless the council confirms otherwise. Flats and maisonettes sit outside householder permitted development altogether. The detail, including cases where rights have been taken away, is in our planning guide for flat roof skylights.
Any fresh hole through the roof counts as building work too. The structure round the hole and the thermal performance of the glass come under Building Regulations, and a rooflight in an existing dwelling has to reach 2.2 W/m²K under Part L. We handle the Building Control notification where the work is notifiable.
Fixed, opening or electric
Once the roof has said yes, the room picks the unit. A landing or hall only needs light, so sealed glass is enough. A bathroom or kitchen gains from a vent. Where the roof is out of reach, a motor and rain sensor save climbing a ladder. Our answer on choosing a skylight for a flat roof sets these options side by side, and for what moves the figure on a quote, see flat roof skylight cost.
To have your own roof read, send a photo of the ceiling and the roof above it to WhatsApp 07880 284133, or book a free survey.
