The short answer
Make the room safe first and cover the opening from outside if the pane has gone through. Then there are two routes: a new glazed unit fitted into the existing frame, which works when the model is still supported, or a whole new window when parts are no longer made or the frame is worn. A survey tells you which, and a written quote follows.
Making a broken pane safe
Glass hanging over a bed, a staircase or a cooker needs dealing with before anything else. Shut the door on the room, keep children and pets out, wear thick gloves and eye protection, and sweep the floor rather than shaking out the blind. If only the outer pane has gone, the inner layer may still be holding. Where the opening reaches through to the weather, tape a heavy sheet or board across it from inside, so loose fragments stay put and rain stays out until someone can cover it properly from above.
Do not climb out onto the roof to patch it. A roof window sits on a sloping, wet surface, and falls from there are serious. A window that is letting water in comes ahead of routine bookings, and we make it safe first, from outside wherever that can be done safely. Photograph the damage before you tape anything; the pictures help at the survey and should you speak to your home insurer.
Why the glass broke and what that tells us
Causes vary. Falling branches, thrown objects, hail and dropped tools account for impacts. Thermal stress cracks glass that has a sharp edge defect, particularly when strong sun hits one half of a pane that is in shade. A misted or cracked sealed unit with no clear impact point may simply have failed with age. Our page on condensation in a roof window explains how a failed seal differs from damp indoors.
Where the glass is intact but water is coming in, the problem is often the flashing or seal, not the pane. Our page on leaking roof windows covers those cases. A roofer should check the frame, the flashings and the timber trim before ordering glass, so you do not replace a pane on a window that is about to leak anyway.
Option one: replace the glazed unit
Many roof windows are glazed with a sealed double-glazed unit, with a toughened outer pane to resist impact and a laminated inner pane that holds together if cracked. When a manufacturer still supplies that unit, it can be ordered to size and fitted into the existing sash. The frame, flashings and finish indoors stay as they are, which is the least disruptive route and often the lowest in cost.
To order the right part, you need the label on the sash edge or frame, which gives the model and size code. Photograph it, with the date, and send it with a picture of the whole window. Lead times vary with the supplier, so we confirm the date at the survey rather than guess. If the old glass is laminated, the replacement should be matched to the original specification, and your written quote will say what is being supplied.
Option two: replace the whole window
When a model is discontinued, the frame has rotted or corroded, the seals have perished or the glazing cannot be sourced, a new roof window is the better answer. A whole-window replacement is also the moment to consider opening size, glazing type and whether the flashings should be renewed. Our page on fitting a roof window to any roof explains the options for different coverings.
MyBuilder's roof window guide, updated 21 August 2026, gives installation at £350 to £600 for standard jobs including labour and fitting, with scaffolding at about £500 where needed. A brand-new window brings Part L into play: Table 4.2 of Approved Document L gives roof windows a limit of 1.4 W/m²K, with a Window Energy Rating of Band B as the alternative route, and para 4.8 adds that a replacement element must not be worse than the one it replaces. Notification to building control is something we arrange when the job is notifiable, with the consent position talked through at the survey.
Scaffold, access and who does the work
Reaching the window dictates the cost. A window within arm's reach of a flat roof or a low eaves can be done from a ladder or a small platform; one high on a three-storey house needs scaffolding. Ask any quote whether VAT and scaffolding are included, since the totals are affected by both.
Fitting a pane can look like a weekend job, which is why people ask. The risks are real, though: heavy glass, a sloped roof and flashings that must be re-dressed. Our page on fitting a roof window yourself sets out what is involved. For most households the safest answer is a roofer who also checks the surrounding lead and tiles on the same visit.
Getting a quote and next steps
At the visit we photograph the window, its label, the flashings and the trim, and the written quote that follows includes those pictures. If a new glazed unit is all the window needs, that is the job we price, and if only a full replacement makes sense, the quote explains why. Workmanship is guaranteed in writing for 10 years (the guarantee is not insurance-backed), and broken glass and packaging leave with us.
For background on the product itself, start with our skylights and roof windows page. Before you ring on 01793 626096, find the model label and take a clear photograph of it, plus one of the whole window from inside and one from the garden if you can see it safely.