Rooflight and skylight fitting in Ponthir

How do you open a window that sits high on a slope? At the foot of a loft stair it is a short stretch to a handle. Over a bed, behind a desk or above a wardrobe, the handle can be hard to reach, and that single fact settles more window choices than any brochure.

Manual roof windows can open with a handle or a pole. Electric and solar versions can open from a switch or a remote, which suits glass that is out of reach, or a household that likes to air the room without getting up. VELUX describes a rain sensor that closes the window by itself when rain starts, fitted to its solar and electric models. It is a VELUX feature, and another maker's range is judged on what that maker says.

Early light is part of the choice. A loft room that faces the morning sky is bright long before the household is ready for it, and the blind, rather than the glass, decides how dark the room gets. We pick the blind with the window, and we ask who sleeps in the room.

Fresh air matters under a roof. Heat rises into the high end of a sloping room, and a window that opens lets it out. An electric opening unit can release warm air without anyone climbing up to it. Our page on choosing between electric and manual compares the two for rooflights.

Ventilation is also a rule, not only a comfort. On a replacement window, Approved Document F (Wales) wants the house to be no worse ventilated afterwards. That is checked against the vents on the old window, and it can affect which sash we offer.

The paperwork follows the work. A new rooflight will generally need Building Regulations approval, and where the work is notifiable we handle the Building Regulations notification with local authority building control or a registered building control approver. For the glass, Approved Document L (Wales) gives 1.4 W/m²K or band B as the level a roof window should meet.

Ask yourself who uses the room most. A teenager's loft bedroom, a home office and a guest room each want something different from the same slope, and the answer changes the blind, the handle height and the opening method we suggest.

Evenings bring the mirror effect. Lit from below, a roof window over the bed reads as a black panel with the lamp in it. A blind pulled across makes the room feel finished, and it is the same blind that keeps the dawn out.

Think of the smallest room in the house. A downstairs cloakroom, or a hall toilet, often has no outside wall at all, so the only light it ever gets is the one on the ceiling.

A sun tunnel suits a room like this. Reading from the top, the dome sits on the slope, the tube crosses the loft, and the diffuser finishes the ceiling. The dome gathers daylight, the tube carries it down and the diffuser spreads it through the room. By dusk the daylight is gone, and what is left is a pale disc overhead.

The loft is the test. The tube needs a path between slope and ceiling, past tanks, cables and timbers. A short run is the simplest case; a bend is a question for the product and the loft together. The choice between a rigid tube and a flexible one is compared in its own guide.

On the roof, the flashing around the dome has to suit the covering, so we note whether it is slate, clay tile or concrete tile, and which slope sees the most open sky. Inside, we look at what the diffuser will sit above, whether that is a ceiling of plasterboard or something older.

Not every room should have one. A bedroom wants darkness at dawn, and a tube may have no way to provide it. A cloakroom, a hall or a walk-in wardrobe has no such problem, which is why these are the rooms we think of first.

Where in the room the diffuser lands matters too. Over the basin, over the door or in the middle: the best spot depends on where you stand and where you look. We note it at the survey, with the loft route, before anything goes on the quote.

After dark the diffuser is the only sign of the tube, and the cloakroom light does the rest. Because the room is small, the light fitting and the diffuser end up close together, so we look at how they sit side by side on the ceiling before deciding where each goes.

Value is a fair question for a small room, and are sun tunnels worth it? looks at both sides.