Skylights and roof windows in Bognor Regis

People use skylight for everything that lets light through a roof, but the type you choose decides the fitting, the rules and the price.

The word skylight covers several different products, and quotes get confusing when a homeowner means one thing and the supplier means another. A roof window sits in the same plane as the roof slope and opens like a window, usually on a pivot. The best known name is Velux, though other makers sell similar windows, and the trade often says Velux for any roof window, much as people say hoover for a vacuum cleaner. A rooflight is different. Approved Document L, the energy part of the Building Regulations, defines it as a glazed unit installed out of plane with the roof surface, on a kerb or upstand. That describes the fixed or opening units on flat roofs, and it also describes a roof lantern, which is a larger glazed structure standing proud of the roof.

1.1 What each type does well

A roof window suits a pitched roof where you want a view, natural light and ventilation from a loft room, landing or stairwell. Because the glass tilts with the slope, it admits light from the sky rather than from a wall, which is why a dim stair can feel transformed. A flat rooflight is the usual answer on a flat roof over a kitchen, garage conversion or extension. Fixed units give light only; opening ones add ventilation, and electric or rain-sensing versions can be worked from a switch when the unit is out of reach. A sun tunnel carries light through a short tube from a small dome in the roof to a diffuser in the ceiling, so it reaches a bathroom or hall where a window cannot go.

1.2 Materials and glazing

Frames come in timber, painted or sealed, and in plastic or metal, and the glass is usually double or triple glazed with a coating that cuts heat loss. Ask for the glazing specification in writing, because the energy figure for the whole unit matters more than the thickness of the glass, and good quality glazing shows up in that figure. On a sunny south-facing slope, solar control glass or an external blind keeps the room from overheating in summer, which is a real consideration on this coast where roofs take a lot of sun. Energy efficiency is the third reason people fit a roof window, since daylight from above cuts the hours the lights are on.

An old roof window that leaks is not always finished: the flashings, seals or glazing can often be renewed without a new opening.

A roof window that has been in place for a couple of decades will have taken years of sun, frost and driving rain. Seals harden, frames swell and flashings lift. Before suggesting a replacement, we work out which of those has actually failed. A cracked pane, a perished seal and a failed flashing are three separate repairs with three different prices, and a fresh window set into a failed flashing will leak just as the old one did.

3.1 Tracing a leaking roof window

Water reaches the ceiling lining in a few predictable ways. The head of the window, the top edge, takes runoff from the whole slope above, so a lifted head flashing is a frequent culprit. At the sides, the gutter flashings carry water down past the frame, and they can split where they were bent and re-bent. At the sill, the bottom flashing sheds rain onto the course of tiles beneath and can lift in a gale. Then there is condensation, which is not a leak at all, and which shows as water running down the inside of the glass or beading on the frame. It happens when moist indoor air reaches cold glass or frame, particularly in bedrooms and bathrooms. Our guide to a leaking roof window sets out how to tell the two apart.

3.2 When a new window is the better spend

If the frame is rotten, the glazing has failed between the panes or the opening mechanism has seized, a replacement makes more sense than another round of repairs. A like-for-like swap usually keeps the same opening size, so the existing lining and rafters stay in place. Where the old window is a different size to what is sold now, an adaptor or modest trimming may bridge the gap. We tell you plainly which route is right, and give the repair price and the replacement price side by side where both are sensible. A reliable repair needs sound timber behind it, so we probe the framing around the opening before promising that a reseal will hold.

Roof window repair is often cheaper than people expect, because the glass is the part that rarely fails. Flashing kits are made for the make and model, and where an old kit is no longer sold we form the weathering in lead to suit. Photographs of the opening go with the finished job, showing what the work changed.

Most roof windows need no planning application, but they do have rules on position, glazing and thermal performance that you should know first.

For most houses, a roof window falls under permitted development, which means planning permission is not usually needed. Class C of the permitted development rules covers other alterations to the roof of a dwellinghouse, and it carries conditions. The window must not protrude more than 0.15 metres beyond the plane of the original slope, and it must not rise above the highest part of the original roof. Any window in a side-facing roof slope must be obscure-glazed, and it must be non-opening unless the opening parts are more than 1.7 metres above the floor of the room. The obscure glazing applies in every case; the height only relaxes the rule on opening. Flats are excluded because the rules apply to dwellinghouses, which the law defines as not including a building of flats or a flat within one. Our guide to planning permission for a skylight sets out the questions in order.

5.1 Conservation areas, listed buildings and the Downs

A conservation area does not remove Class C by itself, but an Article 4 direction can, and some do. Havant's direction for Langstone, for example, covers roof light windows on the side of a house facing the highway. A listed building needs separate consent for any works that change its special character, whatever the permitted development rules say. A dormer is a different matter: it falls under Class B, which is not permitted development in a conservation area, the South Downs National Park or the Chichester Harbour area, a National Landscape since the 2023 renaming. Check with Arun District Council's planning team, or with your own council, before you order. Inside the National Park the Park Authority itself decides applications in the Arun part, and the district council acts for it in the Chichester part.

5.2 Building Regulations and Part L

Building Regulations are a separate matter from planning. A new opening cuts into the structure, and the Planning Portal says building control is needed where structural alterations are carried out. For smaller jobs it counts roof windows and roof-lights within the building envelope, with a threshold of under 25 per cent of the envelope and under 50 per cent of the roof. Approved Document L, Table 4.2, asks a roof window to reach 1.4 W/(m²·K) or else a Band B Window Energy Rating, and a rooflight to reach 2.2, until 24 March 2027, when the 2026 edition's Table 3.2 takes over with the same values. A replacement should be no worse than the element it replaces. Where a new loft room is being formed, building control also looks at means of escape and ventilation, so ask early. Our short answer on roof windows and Building Regulations goes into more detail.

Two further checks come ahead of any cutting. Bats and their roosts have legal protection, which is why we look for them ahead of any cutting. If the building was built or refurbished before 2000, HSE advice is to assume there is asbestos in it, which matters before anyone cuts through a fibre cement sheet.