Can an old cast-iron rooflight be replaced?

The frame is the part you see, but the replacement is chosen against three other things: the opening in the roof, the covering that meets its edges and the lining on the inside. A VELUX window carries a type sign with a size code. For an old iron unit, we measure the opening instead.

The modern equivalent is the conservation rooflight: a unit that can be low and slim, and can have a central bar, made to sit quietly in an older slope. A new unit brings new glazing with it. The general order of the job is set out under how to replace an old skylight.

Approved Document L (Wales) draws a line that decides which energy figure applies. In the guidance's terms, a roof window lies flush with the slope around it. A rooflight is a glazed unit on a kerb or upstand, out of plane with the roof. The guidance says a new or replacement roof window should meet 1.4 W/m²K or Window Energy Rating band B, and a rooflight 2.2 W/m²K.

How your cast-iron unit is set decides which applies, so we check that before anything is chosen. The guidance also has a fallback for a home of architectural or historic interest. A replacement window or roof window that cannot reach 1.4 may instead meet 1.2 W/m²K at the centre of the pane, or be a low-e secondary glazing arrangement. That fallback does not extend to rooflights. All of this is guidance, so the wording is "should", and the survey settles what applies to your unit.

For a house, the Welsh permitted development rules for roof alterations sit in Class C of the 1995 order. A rooflight can be permitted development if it stands no more than 150 mm proud of the original roof slope and no higher than the highest part of the original roof. That route is closed for inserting a rooflight into a slope when the house stands on article 1(5) land, such as a conservation area, a National Park or an AONB, and also when it sits inside a World Heritage Site.

Whether a like-for-like swap counts as inserting a rooflight is a question for the planning team, and worth putting to them where your house sits on protected land. A council can also remove permitted development with an Article 4 direction. Newport City Council says some of its conservation areas have one, and its conservation area pages are the place to check an address. A flat, for its part, carries no householder permitted development rights.

Listed building consent is needed for work that would affect the character of a building of special architectural or historic interest. It reaches fixtures and details inside the building as well as outside, and applications go to the planning authority for the area, which inside Bannau Brycheiniog National Park means the Park Authority. The Welsh Ministers compile the list of listed buildings, on Cadw's recommendation.

Our guide to listed building consent for rooflights goes through the steps, and the survey tells you what we find on your roof.

Windows, roof windows and rooflights are all controlled fittings in Wales, so swapping one is building work. A repair is not building work, and neither is new glass in the old frame, so far as the energy rules go. Where the work is notifiable, we handle the Building Regulations notification with local authority building control or a registered building control approver. The Building Regulations guide for Wales covers the rest, including ventilation and escape routes from a loft room.

We stand in the room and on the roof side by side. The opening gets measured. The covering around it is looked at, because slate, tile and a flat covering are each dressed round a new frame differently. The lining inside is checked for what needs making good before decorating. Access matters too, for getting a new unit in and the old one out.

After that the price comes as a fixed written quote. You can book through the survey form, or send a photo of the old unit to us on WhatsApp at 07880 284133 first. The page for the whole range is conservation rooflights, and a cost-focused answer sits under conservation rooflight costs.