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Many of us have rooms where we have to switch on the lights during the grey days of winter, particularly in semi-detached and terraced houses where the windows are only at the front and back. There is only so much you can do to bring light into the centre of the home from two end walls, but you can look to the roof for light.

Light from above is better than light from the side. A rooflight, or skylight, that is half the size of a window will provide twice the light. Laid on the slope of your roof, a rooflight is likely to suffer from none of the shading obstructions that can bedevil a wall window, and since the light hits it more squarely, much more passes through.

Conservation style rooflight

Kit form skylights are designed for easy installation

The manufacturers of roof windows have targeted the loft-conversion market, and in doing so have developed their products for remedial installation rather than new build. For those of us looking to convert to greener homes, this is a happy coincidence. The windows are attractively priced, easy to fit into an existing roof and, to cap it all, have wooden frames rather than plastic. But why draw light into our lofts if we aren’t converting them you may ask. The answer is that while letting daylight into your loft is still a good idea, getting it down into a room is even better, and this is the objective. Creating a light well between the ceiling and the rooflight isn’t difficult in modern homes where the roof often has a shallow pitch.

Light wells can be constructed from a timber framework that supports a plasterboard lining, and can also be insulated as necessary from the cold part of the attic, but now they are available with fitted sun tubes as well to extend further into the rooms below. The rooflight and light well can be installed between the rafters and ceiling joists, or these can be cut back and the opening trimmed to allow a larger assembly to be fitted. Usually the trimming timbers are doubled around the opening to support the cut rafters and joists, but since this is a structural alteration, you should take advice from a professional. Building codes and regulations usually apply to structural alterations like this.

Penetration of light through rooflights on flat and sloping roofs is enhanced by shaping the light well

Rooflight structure trimmings around opening

If your roof is made from a series of trusses, under no circumstances should you cut them without obtaining an approved structural design. Trussed rafters comprise a web of thin timbers, joined by metal plates, which work in tension and compression, and they can’t be cut and altered like a conventional ‘cut-and-pitch’ roof structure. Most trusses are set 600 mm apart, and slender rooflights are made to this width, which means that you won’t need to cut through the sloping rafters or the ceiling ties.

Using 50 mm x 50 mm softwood and 9 mm plasterboard to form the shaft will keep the weight of the structure down to a level that the trusses should easily support, but if necessary bearers can spread the load over several of the ceiling ties.

Of course some of the light will be lost as it travels down the shaft, so it pays to keep it as short as you can, installing the roof window lower, rather than higher, on the roof. If the shaft ends up more than 1 m high, you will start to lose much of the light’s brilliance. You can improve matters by painting the shaft white to reflect the daylight and splaying out the base as the ceiling joists allow to create a ‘bell’ shape that is wider at the bottom than the top. More than anything, a south-facing rooflight can bring a little sunshine into a dark part of your home, whether it’s over the stairs or in a bedroom.

Channelling the light down even farther to the ground floor can be done, but it requires either a larger well or a shaft with a highly reflective surface. A larger light well will take up valuable floor space upstairs, so instead pipes made from shiny metal sheeting can be used to create sunshine ducts, or light tubes, that beam the daylight down from the roof. In this case, the rooflight bit is little more than an acrylic dome or pyramid, while the pipes are only 300 mm or so in diameter, but they can be effective. The smaller ones have the benefit of fitting between floor joists and rafters without the need for cutting and trimming if you can get the alignment right, but they do tend to lose their effectiveness over a distance. I’ve planned to install a 300 mm diameter example, south-facing, that is about 3.6 m high from roof to ground-floor ceiling to boost the daylight in my kitchen, but I am aware that this is stretching its capabilities, and it may not prove as effective as I would like.

Pyramidal rooflight

The angle of light through skylights

Cross-section shows a ventilated roof cavity maintained around skylight skylight

Cross-section shows a thermal break between skylight and roof