A misted roof window is the same failure as any other
A roof window has a sealed unit in it exactly like a window in a wall: two panes bonded to a spacer bar with a drying agent inside. When that seal goes, the cavity starts breathing damp air, the drying agent fills up and moisture condenses between the panes where nothing can reach it. In a roof it tends to show as a milky haze or as tide marks low down in the pane. It cannot be dried out or cleaned, because the water is sealed inside the unit — the unit is what gets replaced, not the window.
Glass above your head has to be laminated, and that matters
This is the part worth knowing before anybody quotes for it. A window in a wall can be toughened all through. Glass fitted overhead cannot, because toughened glass breaks into thousands of granules and gravity brings them straight down into the room. Overhead glazing is made with the room-side pane laminated, so if it breaks the pieces stay stuck to the plastic interlayer and the pane holds together in the frame. A roof window unit is normally toughened on the outside and laminated on the inside, and any replacement has to be built the same way. If a price for roof glass looks surprisingly low, that specification is the first thing to ask about.
Cracked and broken roof window glass
Roof glass takes more than most. Branches and hail hit it, and it takes the full swing of the sun which can crack a pane on its own — a thermal crack usually starts square to the edge and wanders, and it happens where one part of the pane is shaded and the rest is baking. Because the inner pane is laminated, a cracked roof window normally stays in one piece rather than coming down, but it still wants replacing rather than leaving through a winter.
Handles, catches, hinges and the control bar
Plenty of roof window problems have nothing to do with glass. The bar along the top is the handle and the vent on most models, and its catch wears until the window will not pull up tight. The friction hinges that hold the sash part-open go slack with age, so it drops shut or will not stay where it is put. The locking catch that holds the sash in the reversed position for cleaning is a common failure and a genuinely unsafe one. All of these are replaceable parts.
Water coming in that is not the window's fault
Rain running in around a roof window is more often the flashing than the window. The kit of flashings and soakers that ties the frame into the tiles is what keeps water out, and if it has been disturbed, badly formed at the outset, or the tiles around it have slipped, water gets in past a perfectly sound window. Condensation is worth separating too: water on the room side of the glass is warm damp air meeting cold glass, which is ventilation, not a fault. Misting sealed between the panes, where you cannot wipe it, is the unit.
Find the data plate before you ring
Every roof window carries a plate with its model and size code on it, and that code is what a replacement unit or a spare part is ordered against. On most makes you swing the sash right over as though you were cleaning the outside, and the plate is on the top edge of the sash. Photograph it and send it with your enquiry along with a picture of the window itself, and you can usually have a price without anybody coming out.
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Common questions
Can just the glass be replaced, or does the whole window have to come out?
In most cases the glazing unit is replaced and the window stays in the roof. The model and size code on the data plate is what decides it — on some older windows the unit is not available separately and the sash is replaced instead, which is still far less work than taking the frame out of the roof.
Where do I find the model number?
Swing the sash over as if you were cleaning the outside of the glass and look at the top edge of the sash. There is a plate there with the make, the model and a size code on it. A photograph of that plate is the single most useful thing you can send with an enquiry.
Does it need scaffolding?
Usually not. Most roof windows are designed to rotate through 180 degrees and lock, so the outside of the glass and the glazing beads can be reached from inside the room. What is needed depends on the window and where it sits, so it is worth asking when you send the photographs.
It is misted up. Is that the same as the condensation I get in the morning?
No, and the difference is where the water is. Condensation you can wipe off with your hand is on the room side of the glass and comes from warm damp air meeting a cold pane — that is a ventilation matter. Misting you cannot reach is sealed between the two panes, and that means the unit has failed and needs replacing.
Water comes in when it rains hard. Is the window leaking?
More often it is the flashing rather than the window. The flashings and soakers that tie the frame into the tiles are what actually keep the water out, and slipped tiles or disturbed flashing will let water in past a window that is in perfect order. It is worth having the whole detail looked at rather than assuming the window is at fault.
Can you change the glass for something different while you are at it?
Often yes. If a unit is being replaced anyway, it can usually be specified with solar control glass to cut the heat in a south-facing room, or with a higher specification for noise. The room-side pane stays laminated whatever else changes, because that is what overhead glazing requires.
Where we cover
roof window and Velux repairs across the West Midlands and the towns around it, including: