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Choosing Rooflights

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Rooflights will flood interiors with more high-quality light than vertical windows — and might be your only choice of a new window anyway. Melanie Griffiths explains how to choose.

When Are Rooflights Best?

Rooflights are the perfect way to introduce natural light into areas where conventional windows cannot be installed, or would be aesthetically obtrusive. Loft conversions are an obvious example, but also lean-tos and dark corridors.

However, there are also instances where you won’t have any other choice, such as barn conversions, where strict planning laws often prevent the insertion of new openings, as Matthew Slocombe of SPAB 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, elaborates: “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 original Victorian models – the period in which they were invented, for agricultural buildings – and 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.

Which Type of Rooflight?

The term ‘rooflight’ has several meanings within the window industry. Many presume the Velux-type windows — but when H&R recently asked Velux about its ‘rooflights’, the initial response was, “Sorry, Velux doesn’t do rooflights — just roof windows.” Meanwhile, dozens of glazing companies claim their glass ceilings are actually rooflights. So when you start to think of rooflights as simply a way of introducing daylight from above, the term starts to make a lot more sense.

There are several types of rooflight, both fixed and opening — referred to as ‘in plane’ or ‘out of plane’, depending on whether they are flush, like the Velux type – installed in either a random, chequerboard fashion, or evenly spaced upon a mid-roof slope – or raised sculptural lanterns. Typical bespoke sculptures are pyramids, pitched polygons, barrel vaults, ridgelights and vertical glazed panels. But the options don’t end there. Rooflights can serve as viewing boxes at the top of staircases, or as openings onto roof gardens — you can even specify flush, walkon rooflights if you’re brave enough.

Frame Materials

Your rooflights’ material must work in close complement with that of your windows. Metal is perfect for period properties, barn conversions and sleek, contemporary houses alike, with both steel (often required for barns and homes in Conservation Areas) or aluminium being the options.

Timber is a long-time favourite on homes of any style, but getting onto the roof to maintain the timber can be an awkward task, so consider timber-aluminium composites, which offer the look of wood inside but are lower maintenance outside. PVCu is an option, but it will not provide the slim frames that metal is capable of, nor the natural look of wood. It is, however, inherently low maintenance.

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

Glazing Options

Rooflights need to comply with Part LA of the Building Regulations, last revised in October 2010, with the required U-value satisfied. It can be a complex area and factors such as your roof pitch and whether you’re building new or replacing/adding a rooflight to an existing home, impact upon the U-value required. Extensive ‘glass roofs’may be subject to more stringent control, while slight relaxation may be granted where the aesthetics of a rooflight are of primary concern, such as on listed homes.

“Building Control states that new rooflights to existing homes should usually have a maximum average U-value of 1.6W/m2/K. This is typically achieved with a combination of 6mm and 10mm toughened glass, with an argon-filled 16mm cavity,” says Charlie Sharman of Cantifix. “Different suppliers will use different combinations, but check with your supplier that the glass specification satisfies Part LA. A ‘low-emissivity’ coating on the glass will reduce U-values further.” Triple glazing will help improve thermal efficiency too, as well as offering good soundproofing.

Where overheating is also a potential concern then solar control glass is an option. “It can help reduce solar glare by up to 72%, and be of particular benefit to south-facing homes,” says Apropos’s Phil Buckley.

Bear in mind that a tinted glass, such as ‘blue’ or ‘bronze’, can also reduce glare, but will have an impact on the amount of light entering your home. So if you hope for maximum light transmission, you’ll have to specify ‘clear’ glazing.

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, which in turn 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,” says Sharman.

Finally, give thought to safety. “All glass used should be toughened (to prevent it from shattering if broken), but if the roof is particularly high above floor level (5m+), then glass should also be heat soaked to strengthen further,” concludes Cantifix’s Sharman.

Advice from the Experts

Maximising light
Kevin Brennan, Head of Sustainability, Velux Company Ltd (0870 166 7676)

“As a general rule, you need to provide glazed areas equivalent to 10% of the room’s floor area to achieve adequate daylighting. The overall effect is improved dramatically by increasing this ratio to around 20% and also by using several smaller windows rather than one or two large ones. When a new extension is built the room is usually longer, meaning daylight has further to penetrate into the house. With rooflights you can make the room feel brighter, larger and more welcoming.”

Design Possibilities
Paul Trace, Managing Director, Tuscan Foundry Products (01409 255120)

“Although conservation roof - lights authentically replicate a traditional Victorian design for period properties, their low profile and fine lines of steel have infinite design possibilities with modern-day architecture. They also benefit from having high specifications of glazing, including self-cleaning glass. And not only do they provide a solution to lighting up dark areas, but they are energy efficient due to the amount of natural light they let in, which in turn will reduce energy costs.”

Gallery Listings

1.. Cantifix’s Slideglaze is an electrically operated sliding roof, available up to 7m2 and with option for rain sensors. The glass can also be engineered to be walked on when closed. A 2m2 option costs from £7,500 installed — the larger model shown costs approx £12,000 installed (020 8203 6203)

2. Glazing Vision’s Flushglaze Rooflight — this 1x1m model would typically cost £1,658 excl VAT (glazing-vision.co.uk)

3. Lumen Rooflight’s low-profile Lumen LR5 conservation rooflight, from £640 (0330 300 1090)

4. This bespoke rooflight, from Mumford & Wood’s Garden Room collection, is made from premium engineered timber with BSI energy-rated glazing and efficient sealed units which reduce solar gain. From around £4,000 excl VAT (01621 818155)

5. This bespoke rooflight from Apropos includes two electronically controlled vents, toughened float and low-E glass, and has a centre-pane U-value of 1.10W/m2K. From £13,000 excl VAT (0800 328 0033)

6. Lumen Rooflight’s EVO 3 Landscape is a contemporary ‘frameless’ rooflight — from £1,696 fixed or £2,862 opening; both prices excl VAT (0330 300 1090)

7. Clement Windows’ Conservation Rooflight lies flush with the roofline, and comes in two profiles — one designed for tile or thicker roofing types, and a thinner profile for slate roofs. £399 excl VAT (01428 643393)

8. Cantifix’s glass roof appears frameless from the interiors. From £1,500 (supply only) at Cantifix Direct (020 8203 9203)

9. Glazing Vision’s bespoke Sloped Sliding Rooflight features one section which slides over the roof — other variants are available. From £15,000 (0333 8000 881)

10. This bespoke structurally glazed lightwell (almost 3.5m wide), from architectural glazing specialist Cantifix, features three double-glazed panels structurally bonded with silicone to create a frameless appearance, and costs approx £15,000 installed. Smaller variations cost from around £10,000 installed (020 8203 6203);

11. This bespoke Brett Martin Ritchlight Ultra skylight includes a thermally broken kerb which helps reduce the risk of condensation, POA (024 7660 2022)

12. The Rooflight Company’s low-profile Neo™ rooflights, shown here installed flush with the roofline and with the company’s flashing kits, which provide additional protection from water and wind ingress compared to traditional lead soakers. (In this installation the centre pane achieved a U-Value of 0.6W/m²K.) The Neo can be specified in steel or Fortecom®; the latter is designed for marine environments. POA (01993 833155)

13. Velux’s GGU Centre-Pivot roof window features a timber frame with moulded polyurethane finish — making it ideal for humid rooms such as kitchens and bathrooms. The rooflight rotates 180° for easy cleaning. From £360 incl VAT (01592 778225)