01The idea
A rooflight that sits level with the roof
Flush-fitting means the glass lies almost in the same plane as the tiles or slates around it, instead of standing up from them.
Look at an older skylight from the garden and you will often see a box, a dome or a raised frame sitting on top of the roof. A flush-fitting rooflight is the opposite. The frame is slim, the glass is close to the surface, and from the street it reads as a thin line of glass in the slope, not an object stuck on the roof.
It is the standard shape of a conservation rooflight, which is why the two phrases get used together. The point of the design is that the roof keeps its own character. A flush rooflight does not break the pattern of the tiles, throw a shadow across the slope or catch the eye the way a bulky unit does.
If you are searching for a flush fitting rooflight, the thing to hold onto is simple: the less the unit projects, the more flush it is. Nothing makes a window perfectly flat, because the glass has to shed water and the frame has to sit on something. What you are choosing is how close to flat you want to get.
- 150mm, the most a rooflight may project beyond a roof slope under Class C permitted development
- 2.2W/m²K, the Part L limit for a replacement rooflight
- 1.4W/m²K, a figure a good double glazed rooflight can reach
02How it is built
What makes the profile so low
Slim metal frames, a short step up from the roof covering and a seal that lies close to the glass do the work.
The frame is usually aluminium or steel, made thin because the metal is strong enough to carry the glass without a big timber section. Modern frames include a thermal break, a strip of insulating plastic between the outer and inner metal, so the thin frame does not carry cold into the room. A timber lining or a plaster reveal inside finishes the opening.
On a pitched roof the unit is fixed to the rafters and then flashed, which means a strip of metal is dressed over the roof covering at the edges so water runs over it and away. A flush design uses a low, tight flashing set to the thickness of the slate or tile. That is why it matters that the person fitting it knows your roof covering: plain clay tiles, concrete interlocking tiles and slates all need different flashing kits.
On a flat roof, the equivalent is a low-profile unit with a minimal upstand. The upstand is the raised collar the rooflight stands on. We cover that side in flat roof rooflights and on the page about what a roof lantern upstand is.
| Feature | Flush-fitting | Standard raised unit |
|---|---|---|
| Frame width | Slim | Wider, more visible |
| Height above roof | Close to the slope | Stands clear of the slope |
| Look from the street | A thin line of glass | A box or a frame |
| Best for | Period roofs, protected areas | Many ordinary extensions |
03Warmth
Is a flush unit as warm as the others?
It can be, and it needs the same insulation detail at the edge as any other rooflight.
Flush does not mean thin glazing. Inside the slim frame there is still a double glazed sealed unit with a low-e coating, a warm-edge spacer and argon in the cavity, and some flush units take triple glazing as well. What a thin profile changes is how much frame there is to lose heat through, and a smaller frame area can be a small gain.
The weak point is the joint where the frame meets the roof insulation. Because the unit sits so low, the insulation has to be carried right up to the edge of the opening, with no gap and no squashed section. Our glazing has a warm-edge spacer built in, and we keep that joint in mind on every job.
We go through the numbers in are conservation rooflights energy efficient, and the different glass options on rooflight U-values explained.
04Choosing one
When flush is the right call
Pick it for how it looks from outside and for the rooms where a slim frame also helps the daylight.
A flush rooflight is the usual answer on roofs that people care about visually: Victorian terraces, converted barns, village cottages and any street where the council cares what it sees. It is a sensible choice on ordinary houses too, simply because a tidier roof looks better, and because a thin frame lets in a little more glass for the same opening.
In a conservation area, flush rooflights are what planners usually expect to see. Class C permitted development still applies to many houses, but an Article 4 direction can take it away, and a listed house must have listed building consent before any work. Check with the council before you order. We explain the steps on skylight planning permission and the style on conservation rooflights explained.
- We survey the roof and note the covering, the pitch and the rafter spacing.
- We agree the size and the glazing bar pattern with you in a written quote.
- The frame is fitted and flashed to the roof covering.
- Insulation and the lining are tied in, and floors and furniture are protected throughout.
- Where the work is notifiable, the Building Control notice is ours to deal with.
The full range sits on our conservation rooflights page.
Flush fitting: leaks, cleaning and looks
Is flush-fitting the same as conservation?
Close, but not identical. A conservation rooflight is flush-fitting with a slim frame and often glazing bars. Flush describes the profile and conservation describes the whole style.
Does a flush unit leak more?
Not if it is flashed to suit the roof covering. A flush unit depends on neat flashing detail, which is why the fit matters as much as the product.
Can a flush rooflight go on a flat roof?
Yes, low-profile flat roof units exist, though they still sit on a small upstand so water drains away from the glass.
Does flush mean fixed?
No. Opening versions exist, but the moving sash needs more depth, so a fixed pane is the flattest.
