Skylight and rooflight fitting in Abertillery

Victorian terraces in general tend to share one plan. The town centre itself mainly developed in the late 19th century. A front room, a middle room and a kitchen at the back, with a bathroom or lean-to beyond. The kitchen sits furthest from the street, and its one window faces a yard or a narrow garden, so the room is often the dimmest on the ground floor by the time the morning has gone.

A flat rooflight over the back addition changes that. The glass stands up on an upstand set into the flat roof and puts daylight into the middle of the room, where a wall window cannot. If the roof is pitched at the back instead, a roof window does the same job from the slope.

Gov.wales gives four reasons that a first rooflight usually brings the Building Regulations into the job. To make the opening, the roof structure usually has to change. The roof has to bear the weight of the new unit, or be strengthened to do so. The unit has to meet the energy standard. And where the opening sits close to a boundary, fire performance has to be considered.

That last reason matters in a terrace, where the neighbour's roof is only a few metres away on one side or both. The position of the opening relative to the boundary is something we look at on the survey.

A terrace with a dark middle has another answer. The stairs and landing of a house like this sit away from every wall that has a window, and a sun tunnel can carry daylight to them from the roof, though only while it is light outside. Our sun tunnels page sets out where one makes sense, and a clear loft route is the first thing it needs.

For the energy figure, Approved Document L (Wales) says a new or replacement rooflight in an existing home should meet 2.2 W/m²K. Where the work is notifiable, we handle the Building Regulations notification with local authority building control or a registered building control approver.

At supper time the new glass turns dark and holds the cooker hood and the pendant, so the lining round the opening gets as much attention as the glass.

A lamp-lit room on a winter evening shows up every flaw in the glass above it. A pane with a cloudy film between the layers, a roof window that never clears, or a rooflight with moisture trapped inside is hard to miss when the room below is bright and the outside is black.

Two routes follow. Where the frame is sound, the glass can be replaced and the frame kept. Where the whole unit is tired, the window or rooflight is replaced. Our misted rooflights page covers the signs and the choices, and the page on replacing the glass in a VELUX goes into that case.

The paperwork differs. Replacing a window or roof window like for like is still building work, according to Approved Document B (Wales), and replacing only the glass while keeping the existing frame is not building work for the energy rules, according to Approved Document L (Wales). The Building Regulations still apply to a swap of the whole unit, and we handle the notification where the work is notifiable.

A replacement window carries ventilation with it too. Approved Document F (Wales) asks for vents no smaller than the old ones, controllable by the occupant or automatically, if the old window had them.

Glass that cleans itself is one more thing to ask about for a rooflight out of reach. Pilkington names roof glazing among the uses of its Activ range, a coating that works with daylight and rain, and that is Pilkington's description, not ours.

Photographs of the unit from inside, taken when the room is bright, help us tell a clouded seal from a dirty outer pane. A shot of the whole unit from below and a close one along the edge of the glass are enough to send with the quote request, along with the street and the room.