Skylights and rooflights fitted in New Tredegar

November takes the daylight early. By late afternoon the sun has gone, and a landing with no window sits dark even before the lamps come on. For a stairwell like that, a sun tunnel brings daylight in from the roof through a tube that ends at a ceiling fitting.

It collects daylight and nothing else, so the benefit ends at dusk. After that the fitting overhead is just a pale circle lit from below by the landing lamp. Think of it as a daytime product for the part of the house that spends the day dark.

The loft decides whether a tube fits. A tube needs a clear path from the roof to the ceiling beneath, and the loft may hold cables, tanks, braces and boxes. The straight ones are simplest to plan, and where a bend is needed the choice of tube matters. For a view of how the tube kinds differ, rigid or flexible is the page to open.

The slope matters, because the roof end wants the most open sky it can have. In a terrace, the neighbouring roofs and chimneys can shade a slope, so the survey notes what stands where.

Not every dark room is a landing. A bathroom with no window and a loft above it is another good candidate, and a walk-in wardrobe works too. A bedroom is the exception. There, a roof window with a blind that blacks out the light is the better pairing, because a tube may not keep out a bright June morning.

After dark the hall is lit the way it always was. A tube adds nothing to the evening, so the existing ceiling light or wall lights stay in charge, and it is worth knowing that before the order goes in.

Doors matter on the way down. A stairwell with rooms opening off it behaves differently from an open hall, since bedroom doors can be shut during the day. Which doors you leave open is worth mentioning at the survey, because the diffuser is placed to light the route and the doorways rather than the centre of the ceiling.

Midsummer nights are short in Wales, and a bedroom in the attic gathers the heat of the day. Two things help: a window that opens, and a blind that keeps out the early light and some of the sun.

For warmth, Approved Document L (Wales) gives guidance rather than a rule. A new or replacement roof window in an existing home should have a U-value no worse than 1.4 W/m²K, or a Window Energy Rating of Band B. The figures for each product are laid out in Part L and rooflights in Wales.

Ventilation is the matter for August, when a shut attic room can feel close well into the night. Approved Document F (Wales) counts an opening window as purge ventilation for a habitable room, provided it opens far enough for its size. Windows that open only a short way do not count at all, and the survey tests the sash against the room's floor area.

Attic rooms bring other parts of the Building Regulations with them. Approved Document B (Wales) covers escape from upper floors and what turning a loft into a bedroom does to the stairway below, and we go through it with you; our Welsh planning guide has the escape measurements. Under the Building Regulations a new roof window in an attic counts as a controlled fitting, and where the work is notifiable we handle the notification.

A roof window also closes the day in a particular way. When the lights go off, the glass turns from a screen showing the room into plain darkness. That is when a blackout blind either helps or does not, which is why the blind is chosen with the window and not afterwards.

Position gets less attention than it deserves, and it is easy to get wrong from the floor. In a wide attic two windows can sit better than one large one, and a single window over the bed puts the early sun on the pillow. Where the rafters allow it, the survey weighs the options with you, standing in the room and looking at the slope from inside.