Replacing roof windows in an existing opening

If the frame is sound and only the glass has misted, a replacement glazing unit or sash from the manufacturer may be available, and that is a repair. If the frame is warped, the hinges worn and the flashing leaking, replacing the whole window with a new one of the same size is the usual route. Making the opening bigger, or adding a second window beside it, is new structural work and belongs with a roofer; our page on installing a new roof window explains what that involves.

The major manufacturers make replacement windows to match their older standard sizes, and many installers can identify the model from the plate on the frame. Note the code on the data plate and the approximate size before you ask for a quote; it saves a visit.

The old sash is lifted out, the frame unscrewed from the roof, and the old flashing and the tiles or slates immediately around it are removed. The new frame goes into the same opening with a new flashing kit and an insulation collar, the covering is relaid around it, and the inside lining is reconnected. On many pitched roofs this is done from inside through the opening, without full scaffolding, though higher or awkward roofs still need access equipment outside.

If the old window was fitted without insulation around the frame, the inside lining may show cold stains or mould. A replacement is the moment to put that right, and it may mean replacing the lining panels as well.

A roof window is a controlled fitting under the Building Regulations, just like other external windows. FENSA states that its scheme covers the replacement of external windows, doors, roof windows and roof lights in existing homes. An installer registered with a competent person scheme can self-certify the work and you receive a certificate; with an unregistered installer, Building Control has to approve it.

The new window must meet current energy efficiency standards, and if it is close to a boundary its fire performance has to be considered. Where the roof window serves a loft room as its escape route, the replacement must not make escape any harder, so do not swap a top-hung escape window for a centre-pivot model without checking.

Replacing like for like does not normally need planning permission. On a listed building, or where a conservation area has restrictions, check before changing the style, for example from a conservation rooflight to a standard frame.

Newer roof windows offer better glazing, laminated inner panes for safety in rooms below, ventilation flaps that let air in while the window is shut, and electric or solar-powered opening for windows out of reach. Rain sensors that close an open window, and external blinds against summer heat, are much easier to order at the time of replacement.

Rooms under roof windows are often the warmest in the house in July. If that is a problem now, say so; glazing with solar control and external shading make more difference than internal blinds.

• make, model and size of each old window and its replacement
• glazing type, opening style and any escape function
• flashing kit for your covering and insulation collar
• internal lining work and making good
• access method, whether inside only or with outside equipment
• certificate route, guarantee and removal of the old windows

Offrano shows your request, without personal details, to window and roofing companies in your area. One company can buy it and pays Offrano for it. Before your details go to that company, we email you its name, address and phone number. The request is free for you and then closes.

There is no guarantee of a taker; unsold requests are withdrawn after 21 days. You are not obliged to accept the quote. Offrano does not check workmanship, so look the installer up on its competent person scheme's register.