Is it really a leak?
Before anything is taken apart, work out whether water is coming in from outside or forming inside. Note when it happens:
- During or just after rain: almost certainly a leak.
- On cold, dry mornings, or after cooking, showers or drying washing: probably condensation on the glass or reveal.
- Only in wind-driven rain from one direction: a leak at one side, often at a fixing or a corner.
- Weeks after heavy rain, as a stain spreading in the ceiling: water may be tracking along a joist from further away.
Condensation is common and is covered in our rooflight condensation guide. The rest of this page deals with water coming in from outside.
Where do rooflight leaks usually start?
| Cause | What you see | The fix |
|---|---|---|
| Failed sealant or fixings | Drips at the frame edge, often at one corner or along one side | Lift the unit, clean back, re-bed on fresh sealant or tape, refix to the maker's spacing |
| Membrane short or perished at corners | Water running down the reveal corners | Cut back to sound membrane, form new corners, dress the covering up and under the frame |
| Upstand too low | Leaks in heavy rain or snow melt, staining at the bottom of the reveal | Remove the unit, raise and insulate the kerb, re-weather, refit |
| Ponding against the kerb | Standing water on the roof long after rain, leaks at the low side | Correct the falls, add a small raised saddle to divert water, move outlets, raise the kerb |
| Blocked drainage | Water backing up on the whole roof, leaks after heavy downpours | Clear outlets and gutters, fit guards, then check the kerb detail |
| Failed glass seal | Misting or droplets between the panes | Replace the sealed unit or the rooflight |
Sealant, fixings and membrane corners
Every rooflight sits on a bedding layer, either a sealant bead or a compressible sealing tape, and is held down by screws or brackets. Over time sealant can harden and crack, especially where it was applied thinly or to a dirty or damp surface. Fixings can work loose, or were never placed where the maker wanted them, letting the frame lift slightly in wind. A bead of new sealant smeared over the outside rarely lasts. The lasting fix is to lift the unit, clean the kerb top back to bare material, re-bed it on the specified product and fix it at the maker's spacing.
The corners of a kerb are where the roof covering has to fold in three directions at once. If the membrane was cut and filled with mastic, or stops short of the top of the kerb, water finds the gap. Older felt also perishes and splits where it bends. The fix is to cut back to sound membrane and form proper corners, using pre-formed pieces on rubber and single-ply, or laminating the corners in on fibreglass, with the covering carried up the kerb and finished under the rooflight frame.
Low upstands, ponding and drainage
An upstand that is too low lets standing water, splashback and drifting snow reach the joint under the frame. The height commonly cited for rooflight upstands is at least 150 mm above the finished roof, and roofs that have been overlaid or insulated over the years often leave old kerbs well short of it. Ponding makes it worse: if the roof falls towards the kerb, or the outlet is blocked with leaves and moss, water sits against the low side. Fixing this may mean raising the kerb, adjusting the roof falls around it, clearing and guarding outlets, or a combination. Read our upstand height guide for the detail.
Failed glass seals
If you can see misting, droplets or a white bloom between the two panes of glass, the seal around the sealed unit has failed. Water is not coming into the room, but the glass will lose insulation and the view will get worse. It cannot be wiped away. The fix is a new sealed unit or, where the glass is bonded into the frame, a new rooflight. Check the product warranty first, since this is usually a product issue rather than a fitting one. See rooflight glass replacement.
What does a leak repair visit involve?
Leak investigation and repair visits are charged, and the price is confirmed with you before booking. On the visit, the fitter inspects the roof and the inside, checks the kerb height, membrane, corners, fixings and drainage, and where it is safe, runs water over the suspect area to find the entry point. Simple faults, such as a blocked outlet, can often be put right there and then. Bigger faults, such as a low kerb or a perished roof, get a written repair quote. If the unit is still under the maker's warranty, or the fitting is under a workmanship guarantee from whoever installed it, contact them first. See rooflight leak repairs.
How do you stop it leaking again?
- Have outlets and gutters cleared of leaves and moss each autumn, from a safe position or by someone equipped for roof work.
- Look at the kerb corners and frame edges from a window or the ground once a year, and photograph anything that changes.
- Keep up any checks the maker's warranty requires. One maker makes an annual inspection of fixings, vents and sealing tape a condition of cover.
- Never stand on, or rest a ladder against, a frame or glass that is not designed to be walked on.
- When the roof is re-covered, make sure the new covering is taken up the kerb and finished under the frame, and that the kerb still stands high enough above the new surface.
Repeat leaks often come from a repair that sealed over the symptom and left the cause, so ask any repairer what caused the leak, not just what they will seal.
What should you do until it is fixed?
- Do not go on the roof yourself, particularly when it is wet.
- Catch the water, and move furniture and anything electrical away from the drip.
- If water is near light fittings or switches, turn the circuit off and get an electrician to check it.
- Take photos and notes of when it leaks and in what weather; this speeds up diagnosis.
- Check, from the ground or a window, whether the roof outlet is visibly blocked.
Send the photos and notes through the quote form and we will confirm the visit price.
Questions
Can a leaking rooflight just be resealed from outside?
Sometimes, for a short time. A bead of sealant over the outside joint can slow a leak, but if the bedding under the frame has failed, or the membrane is short at the corners, water still finds a way in. A lasting repair usually means lifting the unit, correcting the cause and re-bedding it.
Is a rooflight leak covered by my warranty?
It depends on the cause. A failed glass seal or a cracked frame is usually a product issue under the maker's warranty. A leak at the kerb, corners or fixings is usually a fitting issue for whoever installed it. Some warranties are voided by poor fitting, such as a kerb lower than the maker allows.
Why does my rooflight only leak in heavy rain?
That pattern often points to water reaching a height it normally does not: ponding against a low kerb, a blocked outlet backing water up, or wind pushing rain under a frame edge. Light rain drains away before it reaches the weak point. Checking kerb height and drainage is the first step.
Do you charge to look at a leak?
Yes. Leak investigation and repair visits are charged, because they take time on the roof and often need water testing. The price is confirmed with you before the visit is booked, and any further repair is quoted in writing before it is carried out.
