How much does a roof lantern cost to fit?

A lantern is a made-up structure of frame and glass that stands proud of a flat roof, and every part of it can vary. Its footprint is the first lever: a lantern over a hallway is usually a smaller unit than one over a kitchen and dining space. Its shape comes next, since a plain pitched form and a more elaborate one are not the same job to make.

A figure only means something once the roof has been seen, which is why none is printed here. Each of these parts answers to something the survey can measure, and the survey always comes before the fixed written quote.

The specification then changes the figure again:

• Frame. The frame's make and finish are chosen with the glass.
• Glazing. Double or triple glazing, laminated panes and self-cleaning coatings all alter the unit.
• Opening vents. A fixed lantern is the simplest, and any opening part adds to it.
• Blinds. If the room below is used in the evening, blinds are worth deciding from the start.

A lantern is not set straight onto a flat roof. It stands on an upstand built around the opening, and the upstand is part of the price. For its own lantern, Brett Martin specifies a builder's upstand of 150 mm or more and recommends that it is built level. A slope of up to 5° is tolerated, though the maker cautions that the result will probably look lopsided.

That is one maker's advice about one product, and the survey shows what your roof needs. Where the existing roof has no upstand, building one is a job in its own right, with the structure, insulation and covering to match. Where one exists, it has to be sound and the right size for the lantern you choose.

A lantern on a new extension adds a question of timing, because the upstand is part of the roof build. If your extension is still being planned, say so on the form, and the survey can take that into account.

Below the lantern, the ceiling is opened to the new light and then finished. Joists around the opening are cut and trimmed where needed, the loads they carried are taken round it, and the edges of the opening are lined and plastered. Making good the ceiling and decorating it often matter as much to the room as the glass does.

Access adds to the cost on a flat extension at the back of a house. A lantern is delivered as a large, careful piece of work, and getting it to the roof through the house, over it or by equipment can change what is needed on site. We price the route we find at the survey.

A lantern normally stands well over 15 cm proud of the roof, so adding one to an existing flat roof normally falls outside permitted development in Wales and needs planning permission. We confirm this with the council at the survey. For a lantern that goes on as part of a new extension, the position is something we also confirm with the council before work starts.

On Building Regulations, Approved Document L (Wales) sets figures for roof windows and rooflights and does not name roof lanterns, so we also confirm the standard that applies to yours. Where the work is notifiable, we handle the Building Regulations notification with local authority building control or a registered building control approver. Our guide to lantern planning and Building Regulations sets out the detail, and the planning guide covers conservation areas and listed houses.

A lantern is a long-lived feature of the room, so it helps to weigh the price against the room at the times you use it. By day the glass fills the space. After dark it reads black and mirrors the room back at you, which is why blinds for the evening are worth choosing at the same time as the lantern.

The lantern worth-it question and our lantern or flat rooflight comparison help with that choice. For a flat unit, see the flat rooflight cost. The costs page explains what shapes a price in Newport. Book the free survey through the form, or send photos to WhatsApp on 07880 284133.