Rooflights and skylights around Abersychan

Start from the roof window already in the slope. If it is a VELUX, a metal label at the head of the sash carries its size code, and it comes into view as soon as the sash is swung open. VELUX windows built after 1968 all have one. The code is short, and VELUX's published chart turns it into a width and a height, as the table shows for three common ones.

VELUX's chart is the authority, so each code is read against it, and the sign appears on each VELUX window built since 1968. A photograph of the label before the visit saves a trip to the loft.

With the size known, the next question is whether the opening is sound. Putting a new roof window into an existing opening can involve less building work than forming a new one, so the opening is looked at before anything is ordered. The page on VELUX size codes goes through the system in more detail.

If the window serves a loft bedroom, a blind is half of what makes the room usable. A blackout blind shuts out the early light in summer, and with the blind raised the glass reads as a black panel that mirrors the lamp after dark. Both belong in the choice, so the blind is picked alongside the window and not afterwards.

Energy is the other check. Approved Document L (Wales) says a new or replacement roof window in an existing home should meet 1.4 W/m²K or Window Energy Rating band B. It is guidance on what the regulations are aiming at, and the maker's sheet for a given model shows where it stands.

Ventilation comes along with a replacement. Approved Document F (Wales) wants a home to be ventilated at least as well after the work as it was beforehand, so a replacement for a window with trickle vents is expected to keep vents no smaller than the originals, controllable by the occupant or automatically.

Fitting or replacing a roof window is building work, and where it is notifiable we handle the notification with local authority building control or a registered building control approver. A repair is not building work, and changing nothing but the glass, while the frame stays put, is not building work for the energy rules.

When the clocks go back, extension glass goes dark early, and the room under it shows what it was built for. A lantern over a kitchen or family room stands proud of the flat roof on its upstand, with pitched glass that gives the ceiling beneath a high centre. By eight in the evening the glass is black and the lamps are doubled in it.

Which suits better, a lantern or a flat rooflight? Each has its place, and the comparison of lantern or flat rooflight lays out the differences. A lantern asks for more height above the roof line and gives the room more ceiling to look at.

The roof is where the planning question sits. A lantern stands noticeably above a flat roof, so on an existing roof it usually brings a planning application rather than relying on permitted development. A lantern planned as part of a new extension is a separate question, and Torfaen is asked how it is treated.

Inside, the lining decides how the glass looks after dark. A deep reveal with square returns frames the black panel, while a rough one leaves shadows. We talk it over at the survey and note how thick the roof is from the joists to the covering.

Brett Martin recommends building the upstand for its roof lanterns level. The upstand is therefore the first detail the survey measures, ahead of the glass.

The choice between fixed and opening deserves its own conversation. An electric opening rooflight is one option where a switch or handset suits, and a flat rooflight can be had in an opening form too. Glass that opens lets steam and cooking air out of the room, which a fixed lantern cannot do.

Cooking and washing-up put moisture into the air, and cold glass can collect it first. An extractor that vents outdoors is the first answer, and an opening rooflight is the second. A lantern is a fixed structure unless the maker offers an opening version, so whether to ask for one belongs in the conversation before the order.