How much does a conservation rooflight cost?

A conservation rooflight is slim and sits low in the slope, and the size you pick sets the first part of the cost. A wider unit means more glass and a longer frame. The wider the unit, the more of the slope has to be opened up.

A unit can be made to measure where the opening does not match a standard size. Fixed units are the simplest. One that opens adds the mechanism, and an electric one adds the wiring that powers it. VELUX says the roof windows in its solar and electric range have a rain sensor built in, which shuts the window itself when rain begins.

After size, the glazing specification is the next thing that shifts the figure. The sheet VELUX publishes for its conservation roof window gives one glazing build-up as a laminated inner pane of 6.8 mm, a 16 mm argon-filled gap, and a toughened pane of 4 mm on the outside. Its range also includes an easy-clean coating, safety lamination and a rain-noise option, and which ones are offered differs with the window and glazing variant.

Self-cleaning glass is a further choice. Pilkington's Activ range is listed for roof glazing, and a coating like that is easier to justify where the outer pane is hard to reach on a steep slope. Frame colour and finish are matched to the slate and the house, and that decision is made before an application goes in.

Here two identical units can end up well apart. Slates around the frame are lifted, lapped over the flashing and set back in courses, and that is slow, careful work on an older roof. A new opening also means cutting the roof. What is left must bear the unit's load, or be reinforced until it does, and gov.wales gives both as grounds for Building Regulations approval of a newly installed rooflight.

Replacing a unit already in the slope can save part of that. The opening and the framing around it already exist, and the question is whether they are sound. The size code on a VELUX window's type sign gives its width and height, which helps when the new unit is meant to match the old one. If the framing or the roof covering has to be renewed, the saving shrinks, and the survey tells you which case you have.

Approved Document L (Wales) is guidance, and the figure for the glass depends on the type of unit. A new or replacement roof window should be no worse than 1.4 W/m²K, or Window Energy Rating band B. A rooflight, meaning a glazed unit on a kerb or upstand, should be no worse than 2.2 W/m²K.

A home of architectural or historic interest gets some room for manoeuvre on the window side. Where a replacement roof window there cannot reach 1.4, the guidance accepts 1.2 W/m²K at the centre of the pane, or low-e secondary glazing. Rooflights get no equivalent concession. Which type your roof takes is settled at survey, and it feeds into the glazing choice and so into the price.

Putting a rooflight into a roof slope in a conservation area, the Gower AONB, Bannau Brycheiniog National Park or a World Heritage Site is not permitted development in Wales, so it needs a planning application, and the council charges a fee for that. The rules are set out in our answer on whether a conservation area rooflight needs planning in Wales.

A listed house also needs listed building consent where the work would affect its character, applied for through the local planning authority. Building control comes in as well. Where the work is notifiable, we handle the Building Regulations notification with local authority building control or a registered building control approver.

Slate condition, the timbers, the slope and the consents all show up only on site, and a figure from a photograph would have to guess at each. So we start with a free survey, and you receive a fixed written quote. The completed work carries a 10-year workmanship guarantee in writing.

The conservation rooflights page covers the full range, and the costs page deals with the other products. To book a visit, ring 01792 929062 or use the form at the foot of the page.