Flat roof rooflight installation in Exeter

A flat rooflight is a rectangle, square or circle of glazing on a frame that sits just above the roof covering. Unlike a roof lantern, it has no ridge and no hips. Its glass is level or almost level, so it looks from outside like a dark panel set into the roof, and from inside like a clean opening in the ceiling.

It suits a surprising range of rooms, and the roof usually tells you which one.

Rear extensions with a low ceiling

Many flat roofed additions are kept low on purpose, to stay clear of a first floor window or to respect height limits. A lantern can feel too tall there, and a flat unit gives the daylight without adding to the profile. Across Exeter, from Pinhoe and Whipton to the newer streets near Newcourt, these single storey additions are common.

Corridors, halls and landings

An internal hallway between two rooms in a 1930s semi in Heavitree, or a bungalow in Exmouth with a flat roofed centre, has no wall to put a window in. A flat rooflight over the passage gives the whole space daylight from above.

Bathrooms and utility rooms

A small fixed or opening unit over a bathroom lights the room without overlooking it, and in a flat roofed utility or rear porch it gives a room with no window a pleasant ceiling.

Garages, garden rooms and outbuildings

A converted garage with a flat roof often needs light at the back of its deep floor plan, and a garden studio benefits from daylight overhead that does not eat into the wall space.

Shape is a free choice more often than people expect. Rectangles and squares are the everyday shapes, but circular units, long narrow ones that run along a corridor, and wide units made from several panes all exist. The shape should follow the room below. A square landing wants a square unit, a long galley kitchen wants a long one, and a round tower room or a curved wall can take a round one. Whatever the shape, the opening in the ceiling takes on the same outline, so it is worth sketching it on the ceiling in chalk before anything is ordered.

A flat unit is not always the best choice, and we go through the decision in flat rooflight or roof lantern: which suits your extension. The short version is in the table below. For a taller, more architectural feature over a kitchen island, our roof lantern installation page is the place to start.

The material on top of your roof decides how the rooflight is weathered in, so it is the first thing we look at on a flat roof. Three coverings account for nearly all flat roofs in Devon homes.

A rooflight can go on any of these, but not in the same way.

GRP

Glass reinforced plastic, or fibreglass, is laid wet over a deck and cures into a continuous skin. It is a popular choice on extensions built in recent decades. The rooflight upstand is wrapped in the same laminate, so the covering and the kerb become one continuous surface.

EPDM

A single sheet of synthetic rubber, bonded to the deck and turned up the sides of the upstand. It is flexible and tolerant of movement, which suits timber decks, and the rooflight kerb is wrapped in the sheet with careful corners.

Felt

Built up felt systems, often a torched cap sheet over underlayers, are widespread on older flat roofs. The upstand is dressed with felt layers that overlap the roof covering, and the join is the part that wants the most care.

A rooflight can go on any of these, but not in the same way. We have set the differences out in flat rooflights on GRP, EPDM and felt roofs. Age matters as much as type: an old felt roof that is near the end of its life is better renewed around the new unit than left to meet it, and a quote that ignores that is only half a quote.

Decks matter too. A flat roof sits on timber boards, plywood or concrete, and the rooflight upstand has to be fixed to something sound. Where a deck has swollen or softened over the years, we say so at survey and price the sound boards into the job, because a new rooflight is only as secure as what it is fixed to.

If a flat roof is being re-covered in any case, that is the best moment to add or replace a rooflight, because the upstand and covering can be built as one job. Ask for the two to be priced together.

Flat rooflights come in stock sizes and as made-to-measure units, and the very largest are built from several panes joined together. What is possible depends on the glass, the frame and the structure holding it up, and how big can a flat rooflight be sets out the limits. A wide opening has knock-on effects below the roof: the joists either side must be trimmed and carried, and a very wide span can bring in calculations or a steel beam.

Inside the frame sits a sealed double or triple glazed unit. It has a low emissivity coating, a gas fill between the panes and a warm-edge spacer round the perimeter. The outer pane is toughened. An inner pane of laminated glass is good practice and industry guidance for anything overhead, because laminated glass stays in one piece if it cracks, and we suggest it above any room that gets used. What glass goes in a flat rooflight compares the specifications, and our energy efficient rooflights page explains U-values.

Because flat glass looks straight up, it takes high summer sun full on. A room facing south or west may feel warm by mid afternoon. Solar control glass cuts the heat that gets through while still passing daylight, a self-cleaning coating helps a level pane shed the dust and pollen that settle on it, and blinds under the frame give you shade on demand. An opening vent lets hot air out at the top of the room. Solar control glass for rooflights goes through the coatings and the trade-offs.

Planning is one question and Building Regulations another. A flat rooflight may raise either, both or neither, and where the work is notifiable we handle the Building Control side for you.

On the planning side, a house rooflight generally comes under the permitted development right in Class C (Schedule 2, Part 1, General Permitted Development Order), so long as the unit rises 150mm or less above the roof plane and does not exceed the ridge or roof top. A flat rooflight on a shallow upstand may sit inside that limit, while a taller kerb could go beyond it, so the height above the roof surface is the measurement to watch. On a new extension the rooflight is normally judged along with the extension itself, and the approved drawings should show it. If you want certainty, a Lawful Development Certificate from the local planning authority puts the answer in writing.

A new opening in an existing flat roof means cutting joists, which counts as a structural alteration

Not every home can lean on permitted development. Flats and maisonettes have none of the householder rights, and a listed building requires listed building consent for external alterations. A conservation area allows Class C in principle, though an Article 4 direction can remove it. Parts of our area lie inside Dartmoor and Exmoor National Parks, which are Article 2(3) land with narrower rights. The authority that decides is Exeter City Council, East Devon, Mid Devon, Teignbridge or Torbay, or a national park authority, according to your address. Rooflight planning and Building Regulations in Devon widens the picture.

Building Regulations are firmer. A new opening in an existing flat roof means cutting joists, which counts as a structural alteration, and the new unit has to meet the limiting U-values in Approved Document L Volume 1, 2021 edition. That needs Building Control approval. Swapping a complete rooflight, frame and glass, is notifiable as well, because a rooflight counts as a controlled fitting. Changing only the sealed glass inside a sound frame is not notifiable.

Fire guidance may apply too. A rooflight near a boundary can be caught by Approved Document B, so we look at the position when we survey. When the work is signed off you get a completion certificate. Keep it with the house papers, because a buyer's solicitor will ask for it.

Every flat rooflight is priced after a survey, since identical glass can cost quite different sums on two roofs. The written quote splits the work into lines, and the costs page gives general market ranges and explains how a quote is assembled.

The quote also tells you what is not in the price, which is just as useful. If scaffold, an engineer's calculations or the renewal of old covering are needed, they are listed as lines, so there is no surprise on the day the roof is opened. Ask any installer for the same, and for the lining and decoration to be written down.

The inside is where many quotes go vague.

Begin with the unit. Its size, shape, frame, glazing and whether it opens all feed in. A circle or a very large pane costs more than a standard rectangle, frameless costs more than framed, and electric operation, a rain sensor and blinds each add a line.

Then the roof. The easiest case is a new extension with the opening already framed. In an older roof, joists must be cut and carried, which may mean an engineer's calculations or a steel beam. Tired covering may have to be renewed round the opening, and occasionally the whole roof is better dealt with in one go. Access counts: a back roof with no side passage might need scaffold or a careful lift.

The inside is where many quotes go vague. A straight lining costs less than a splayed one. Lime in an old house takes longer than a gypsum skim. A deep shaft needs more board and more finishing than a shallow one. Building Control fees sit on the quote too. At survey we ask five things, and they set most of the price:

• how wide the opening is, and what carries the joists beside it;
• what covers the roof, and how old that covering is;
• how deep the shaft is, and what shape the lining takes;
• what the ceiling is made of, and which plaster suits it;
• whether you want a vent, blinds or solar control glass.

The schedule writes the lining, plaster and decoration down, so you can lay our quote next to another and compare it line by line. Our guarantee page explains the 10-year workmanship guarantee, which stands behind the roof work and the room work together.

Not if it is specified and finished well.

Generally yes, once the joists, deck and covering have been checked. The opening is cut and supported, a new upstand goes up and the covering is dressed over it. What the joists look like decides how simple it is. Whether a flat rooflight can be added to an existing roof goes through each stage.