What are skylights?

A skylight is basically a glazed roof aperture. Being flush with or domed above the ceiling, they let in more light than traditional dormer windows, which jut out at an angle from roofs.

Improvements in manufacture mean skylights are now largely problem-free — as long as they are of good quality and are properly installed, condensation and leaks should not affect modern designs. You can either buy a skylight as a standard unit and get a builder to install it or hire a specialist company that can design versions to order for a particular finish or to fit an awkward space. You could install the most basic form of roof light yourself, but only if you are very competent at DIY.

The options?

There are many different types of skylight. They can be horizontal, or fitted on shallow-pitched roofs. Fixed models are generally cheaper, while adjustable versions can be opened either manually or electronically. Some cutting-edge designs even shut automatically at the first drop of rain. The majority are manufactured for flat roofs, and they can be design features, in the form of traditional roof lanterns, for instance. If you are constructing a skylight for a surface being used as a terraced area or roof garden, consider using modern structural glazing that you can walk on.

One of the most striking uses of roof lights is at the top of a stairwell, flooding light down through the house. For a simple but dramatic improvement to a standard house, get builders to cut a hole in the roof, box in the roof cavity to create a tunnel out of the space, and fit a skylight. Boxing in should cost £300-£400, the window about £1,000 depending on size.

Costs and suppliers

Obviously the cost of installing a skylight depends on its size and the complexity of the job, but the average cost of a 1m sq opening would be about £1,000 plus Vat and additional costs for redecorating. DIY stores sell small skylights from less than £100, but it is worth spending more as cheap jobs are notorious for leaks.

For costs, Glazing Vision has an “online quote generator” offering lots of different options, allowing you to experiment. Velux is the big name in skylights. It has a helpful website with a “visualiser” tool which shows you a before and after effect on different rooms. Some of its models come with built-in retractable blinds. Structural glass costs up to £500 per square metre; it can be sandblasted or acid-etched for non-slip or privacy reasons.

At the top end of the market, Marston & Langinger glass roofs and skylights can be tailored to almost any shape or size. A typical 2m by 3m lantern roof set into a flat roof costs £8,500 plus Vat to install, but that excludes preparation costs — you will need a builder to knock a hole in the roof first. More complicated structures include openable side-lights for ventilation, and they can be square, oblong or octagonal.

The Rooflight Company makes high-quality traditional skylights from £400 — particularly useful if you are in a conservation area. House Couturier makes manual and electric blinds for skylights, and can make bespoke versions for non-standard sizes. Prices start from £400 for manual options and £1,200 for electric models.

Technicalities

With a skylight for a flat roof, it is important to make sure that the upstand along the perimeter of the sky light is to a minimum height of 150mm to avoid flooding. Velux says that, as a general rule, you need a glazed area equivalent to 10% of the room size to provide adequate natural day-lighting, but the effect is improved hugely by increasing the ratio to 20%.

Fitting a skylight is usually a job for professionals; if you do decide to install a roof light yourself, always follow the manufacturer’s technical specification — particularly with regard to sealing the opening and making the job watertight. You should choose a double-glazed model — the huge majority on sale in this country are insulated in order to comply with building regulations.

Is there anything else I need to know?

If you live in a conservation area, you might have to get permission from your local authority. Remember that glazed-in areas can become unbearably hot in summer and cold in winter so you might need blinds or solar-control glass (which has a light tint and reduces heat from sunlight entering the building), or low-E glass which reflects heat. Privacy can also be an issue. If you are spending more than a few hundred pounds, get design help from an architect. Sometimes two or more smaller skylights look better than a larger model, and this can be a cheaper and easier option, too.

You might need to get approval from your council’s building control team, who will ensure you meet insulation regulations. Remember that a skylight can be a security weak spot; make sure that your locks are adequate. Cleaning can also be an issue — unless you have outside access, consider models that swivel inwards so you can clean both sides from your home. A roof light can double as a fire escape, allowing you to comply with building regulations in a loft conversion.

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