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How to Choose Rooflights

rooflight windows
(Image credit: getty images)

Rooflights introduce natural light into areas where conventional windows cannot be installed, or would be aesthetically obtrusive, such as:

  • loft conversions
  • lean-tos
  • dark corridors

What is a Rooflight?

Sometimes building terms can be straightforward, and the term rooflight (sometimes referred to as a skylight or a roof window) is a good example.

A rooflight is an opening in a roof designed to let light in.

Behind the apparent simplicity of the definition lies a diverse group of products with differing purposes and very different price points, such as:

  • simple fixed skylights, costing a few hundred pounds at most
  • huge glazed openings sometimes costing as much as a small house.

They are usually manufactured by specialists who rarely produce conventional vertical windows.

Pitched Rooflights

The pitched rooflight came of age in the 1970s when the loft conversion boom started. Before that, the main way of getting light into roof spaces was via a dormer window. They had three problems:

  • They are relatively expensive
  • They are also relatively bulky
  • They break through the roofline

In contrast, planners take a more relaxed view of loft living when the existing roof shape doesn’t change.

The Danish company Velux popularised the pitched roof window in the 1970s and 1980s. Critically, it was possible for a carpenter to fit a Velux in a day, from the inside of the roof, thus reducing the need for scaffolding and tarpaulins.

The success of Velux played a big part in the popularity of loft conversions. There are now several other businesses offering similar products, but Velux remains the best-known brand.

What was once a relatively simple product has become more complex and could include:

There is a wide choice of blinds and awnings, and the rooflights themselves can now be opened manually or automatically, powered either by the mains or solar cells. There is also a range of glazing options to choose from, including triple glazing for energy efficiency.

Off-the-Peg or Bespoke?

Flat roofing is becoming popular again, so we are seeing a growing number of daylighting solutions designed for horizontal use:

  • At the basic end, a polycarbonate rooflight costs as little as £250. It can be double or triple skin and configured to open for venting.
  • Switching to glass roughly doubles the price but adds to the longevity. Velux carries a range of modular rooflights that can be installed in series to give a glass-roof effect.
  • For locations where a conventional rooflight isn’t suitable, the sun tunnel is an effective alternative.

Some specialists supply bespoke glazing solutions for roofs, often combining vertical, horizontal and sloped glazing. Bespoke glazing solutions start at around £10,000 and have almost no upper limit.

The possibilities are extensive:

  • Glazing can be made strong enough to walk on.
  • Glazing can be made retractable so that you can open up the room below to the elements.
  • It can be configured as lanterns or even stairwells for use where the roof becomes a terrace.

Glass is being used as both a walling and roofing element, and bespoke glazing solutions are beginning to move away from the basic rooflight concept. Yet their attraction is much the same: bringing light into dark places.


Modern double or triple glazing is so effective that people are more concerned about summer overheating from rooflights than overall energy efficiency. Summer sunshine can sometimes cause spaces behind the glass to become uncomfortably hot. This is a possibility if the rooflights face south and the room they light is relatively small.

Solutions include:

  • Specifying solar reflective glass, or glass with a low g factor, such as Velux’s Glazing 60, which keeps the solar radiation levels down to as little as 30%. This helps but does dull the quality of the light.
  • Using physical shading, either using removable awnings or fixed panels (brise soleil). These keep off the high summer midday sun but not the lower-angle sunlight enjoyed in the evenings and in winter.

If none of these options are possible, the best approach is to limit the ratio of rooflights to floor area to around 10%. This should provide plenty of light to the room without too much discomfort during heat waves.

Many rooflight solutions come with built-in ventilation, and this can also be deployed to even out temperature differences between inside and out.

Frame Materials

Ensure the material complements or matches your windows:

  • Metal suits period properties, barn conversions and contemporary houses. Steel (often required for barns and homes in conservation areas) or aluminium are the most common options.
  • Timber is popular, but getting onto the roof to maintain the timber can be tricky. Consider timber-aluminium composites, which offer the look of wood inside but are lower maintenance outside.
  • PVCu is a low-maintenance option, but it will not provide the slim frames that metal is capable of or the natural look of wood.

Whatever the material, rooflights must be fitted to allow water to drain away. Weather-resistant flashings can be visually obtrusive but are essential to avoid leaks. Ensure they complement your roof as closely as possible.

Conservation Rooflights

Strict planning laws often prevent the insertion of new openings in cases such as barn conversions.

Matthew Slocombe of the Society for the Protection of Ancient Buildings advises: “Sympathetic detailing is likely to be a condition of consent, especially if the barn is listed or in a conservation area. New openings should generally be kept to a minimum and should be of a simple form that respects the farm building’s character.”

Paul Trace, managing director of Tuscan Foundry Products, adds: “In this situation a conservation rooflight would be required as they are especially designed with a low profile. This means the rooflight will sit flush and not detract from the character of the building.

“Steel conservation rooflights are ideal as they are made specifically to provide slender sections which are unobtrusive.”

Steel conservation rooflights are designed to replicate Victorian models that were originally designed for agricultural buildings. They also have a glazing bar. As well as many barn conversions, they are a requirement in a lot of houses that are listed or in conservation areas.

Other Considerations

Rooflights need to comply with Building Regulations, with the required U value satisfied. It can be a complex area — factors that impact on the U value include:

  • your roof pitch
  • whether you’re building new or replacing/adding a rooflight to an existing home

Extensive ‘glass roofs’ may be subject to more stringent control. Slight relaxation may be granted where the aesthetics of a rooflight are the main concern, such as on listed homes.

If your rooflights will be difficult to access, then selfcleaning glass is a good idea. The surface reacts with sunlight to break down dirt, loosening its adhesion, In turn this allows dirt to be more readily washed away by rain.

For flat rooflights installed with a shallow fall, water droplets can be eliminated by use of a coating product such as Ritec’s ClearShield.

All glass used should be toughened (to prevent it from shattering if broken).If the roof is particularly high above floor level (5m+), then glass should also be heat soaked to strengthen it further.