Skylights and rooflights in Caerleon

Light arrives early in June. Before the alarm goes, the sloping ceiling of a loft bedroom can already be bright, because a roof window faces the sky with nothing to soften what comes through it.

The fix for that is a blackout blind, best chosen together with the window rather than added later. At the survey we ask which model you want, how the blind will be worked once the sash is out of easy reach, and whether anyone in the house is a light sleeper. The blind is picked off the maker's list for that window, so we settle the pair as one decision.

The same glass behaves differently in the evening. Once the lamps are on, a roof window reads black and mirrors the bed, the wardrobe and the lampshade, so the room looks smaller until the blind is down. Knowing that in advance helps with placing the window: a position over the foot of the bed puts the reflection somewhere calm, while a position directly above a bedside lamp does not.

One window or two is a fair question for a long sloping ceiling. Two side by side spread the daylight across the room, whereas a single window gives one bright patch that moves across the floor as the morning goes on. The survey sets the size and number against the rafters and the floor area, not against a catalogue.

Air matters as much as light under a roof. Heat builds in the highest part of a sloping room, and a sash that opens gives it somewhere to go. If an old window is being replaced, Approved Document F (Wales) expects the room to be ventilated no worse than before, and if trickle vents were on the old window, those on the replacement should be no smaller.

Reach is the next question. VELUX says a built-in rain sensor closes its solar and electric roof windows once rain starts, and that sensor belongs to those windows alone, so ask which model is being put forward.

The Building Regulations treat a roof window as a controlled fitting, which makes putting one in building work. Where the work is notifiable, we handle the Building Regulations notification with local authority building control or a registered building control approver. Approved Document L (Wales) gives 1.4 W/m²K, or Window Energy Rating band B, as the figure a roof window should meet. Our page on roof windows covers the range.

What happens to a kitchen ceiling once supper has been cooked? On a flat-roofed extension the answer is condensation. Steam from the hob finds the rooflight glass first, because that glass is often the coolest surface around, and it runs down to the edge of the reveal.

Opening helps. A rooflight that opens, or an extractor that vents outdoors, carries the damp air away before it settles. Our page on electric opening rooflights covers the powered kind, which can be worked by a switch for glass beyond arm's reach above a worktop.

Rainclear's installation guide advises a slope of at least 5 degrees on the kerb under its flat glass rooflights, to keep water from pooling, and VELUX says its flat roof dome is designed for pitches from 0 to 15 degrees. Both numbers belong to the named makers' own products, and each product has its own limits, so we read the roof before we choose.

The glass goes dark with the evening. When the sun has gone, an overhead rooflight mirrors the pendant lights and whoever is at the sink. A square, well-lined reveal gives a quiet dark panel, and rough plasterwork around the opening shows up at night far more than by day.

A taller lantern is another route if the room has height to spare. Before work starts, we confirm with Newport City Council how planning treats a lantern built on a new extension. The pros and cons of each are weighed in lantern or flat rooflight?