Don't Move, improve: Raise your glass, please

Roof windows are not just for loft conversions – they can cast your whole home in a new light

Even in the era of the iPod, few products reach that supreme marketing status achieved by the likes of JCB and Hoover, where the brand name describes the product itself. Velux is one such product, and it is hard to think of one more deserving.

Velux, just in case there's anyone out there who doesn't know, makes roof windows, and they open up a whole range of opportunities for improving and converting space within our homes. I remember a tutor at architecture school so smitten by the possibilities that these roof windows provided that he advised us to offer up prayers of thanks to the "Virgin Velux".

Why are they so good? Their most obvious use is in the conversion of loft spaces. Previously, the way to add a window to a loft required structural alteration and extensive carpentry in forming a "dormer" to the roof. This not only needed scaffolding, extensive re-roofing, tiling, lead flashings (to waterproof the junctions), fascias and gutters, but also, more often than not, planning permission.

A Velux generally does not need permission, requires only a simple opening, can usually be fitted from the inside and comes with all the watertight flashings and seals necessary. They are openable for ventilation, can be turned nearly all the way around for cleaning on both sides and offer good thermal performance in winter.

It is true that a dormer window can both add headroom and (sometimes) be attractive externally, but the complexity described above translates directly into expense.

Roof windows are not just for loft conversions, however. They can be used very effectively to bring daylight down from above over stairwells or double-height spaces, or in any room where part of the ceiling slopes with the shape of the roof.

The great thing about bringing in light from above was first explained to me (again) back at architecture school. "Environmental science" was presented as a rather dusty subject. I hope that tutors these days help their students understand the important connection that exists between their "sun-path calculations" and "rainfall charts" with their design projects. One lecture (during which I am forever glad that I stayed awake) illustrated the intensity of light from the sky on an overcast day.

Cutting through all of the jargon of "lux" and "lumens", the essential lesson is that light from directly above is the most intense, whereas light from sideways is the least intense.

All of this means that daylight entering your house via an opening in the roof is much more intense and effective than day-light entering from a window in a wall.

Having publicly the Velux's praises, however, I should point out that they are not always the best answer and there are a whole host of alternatives that suit different situations.

For a start, what if you have a flat roof? Well, various manufacturers make small roof lights or miniature "roof domes" that can bring in daylight via a square or circular hole in the ceiling. The most basic ones are fixed shut and of plastic construction, usually 600x600mm to correspond with standard office ceiling tiles. We have successfully used a series of these in a row to create a line of small openings in a flat ceiling, which can look really cool in the right place.

As they become more elaborate (and therefore expensive) there are openable versions – sometimes automatically openable – and there are larger options. They come with aluminium or timber and glass rather than plastic, and in different shapes, such as pyramids or barrel vaults and enlarged with different sections using glazing bars. Be aware of the potential, not only for heat-loss in winter, but also from uncomfortable heat-gain in full sunshine.

The first new house that our practice designed was entirely orientated around a large central roof-light. The site was extremely tight and windows were mostly impossible due to the danger of overlooking the numerous neighbours. A large opening in the first floor brought light flooding down and filled the house.

One form of roof light that can be effective in older buildings is the "roof lantern". Here a square or rectangular opening in a flat roof has a box construction over it, with windows in the vertical sides with either a solid or glazed roof above. A great example of how this can be used is over a central island in a kitchen, combining a central source of daylight just where it is wanted, a good source of ventilation to extract heat and smells and an attractive centrepiece to the room.

Hugo Tugman runs the design service architectyourhome.com

The lowdown

How much will it cost?

Allow a minimum of £2,000 per Velux window, including installation, unless you are doing several at once. The cost of larger roof lights will depend upon the materials involved, the size of the opening and if any structural alterations are involved.

How much hassle is it?

Having a roof window fitted can be a very simple procedure, taking only a day or two and causing very little hassle and mess (in relative terms). The larger and more ambitious your plans, the more likely they are to involve disruption – for example, forming a roof lantern above an existing kitchen will probably leave you eating takeaways for a couple of weeks.

What's the first step?

If you are thinking of adding a roof window, a good place to start is the Velux website www.velux.com for ideas and available sizes. For something more complex, or if you are concerned about alterations to the structure of the house, it would be sensible to consult an architect who can both advise as to the feasibility of the project, and may have some ideas that you had not considered.

h.tugman@independent.co.uk