Short answer
A skylight is built to keep rain out, and whether it does depends on three things: a unit that suits the pitch of the roof, a flashing or upstand fitted to suit it, and a roof around it that drains. Water inside the room is not always a leak, since condensation and mist between the panes are different matters.
Free survey / fixed written quote / Building Control notification handled / 10-year workmanship guarantee
The junction is where the work is
Rain meets glass first, but glass is not where the fitting effort goes. Water has to find a way past the point where the unit meets the roof, so that line is the one to get right. On a pitched roof, that means a window flashed into the tiles or slates around it. On a flat roof, it means a kerb or upstand with the surface falling away from the unit.
Manufacturers set terms for the roof as well as the unit. Brett Martin's bulletin for roof lanterns specifies a builder's upstand 150 mm tall at the least. VELUX gives pitch ranges for its products, such as 10 to 20 degrees for the low-pitch roof window. A unit placed on a roof outside its stated range has a problem before any rain falls.
Leak, condensation or mist
Three kinds of wet mark get reported as leaks. They look alike from the bed or the sofa, and each has its own cause. Telling them apart saves a wasted afternoon with a ladder.
Can point to condensation
- Beads of water on the inner face of the glass or frame
- Worse in a kitchen or bathroom, or after cooking and showers
- Forms where humid indoor air touches the coolest surface
Can point to a leak
- A mark or drip that follows rain, even in a dry, still room
- A stain at the edge of the lining where unit meets roof
- Water that arrives with wind-driven rain
Mist between the panes
The third is a fog you cannot wipe off, because it sits inside the sealed unit between the panes. That is a sealed-unit matter, and the answer on whether a misted rooflight is a problem explains it. Condensation that keeps returning is a ventilation question. Under Approved Document F (Wales), a swapped window should leave the home no less ventilated than before, and a trickle vent or a fan that is switched on carries the rest. A bathroom roof window that steams up after every shower is telling you about the room, not the roof.
When the window is open and the weather turns
Some rain simply walks in through a window left open. A manual one over a landing is easy to forget when the forecast turns mid-morning. VELUX builds a rain sensor into its electric roof windows so that they close themselves, and how a rain sensor works goes through the idea. The sensor answers the open-window problem. A flashing is a separate job, and the sensor sits beside good fitting rather than replacing it.
Flat roofs and standing water
A flat rooflight lives with water in a way a pitched window does not. In its flat glass rooflight guide, Rainclear suggests sloping the kerb by at least 5° to minimise water pooling. Water that stays on the glass or its surround after the rain has stopped suggests the fall needs looking at, and the page on water sitting on a flat rooflight goes further. If an old VELUX has let you down, swapping an old leaking VELUX sets out the options.
What to note before you call
A few observations narrow things down before anyone climbs a ladder. Which room is it, and does it hold a bath, a hob or a clothes airer? Does the mark come after rain, after a shower, or on cold mornings? Is it at the edge of the lining or in the middle of the glass? Is the window one that opens, and was it open? The answers show whether to look first at the junction, the fall or the ventilation of the room, and they make the survey easier to read.
What stands behind our fitting
No price is given until the roof and the room have been seen, and it arrives as a fixed written quote. Our work is covered by a written 10-year workmanship guarantee, set out on the guarantee page. The products that suit a wet roof are on the roof windows and flat roof rooflights pages. Phone 01792 929062 or book a survey.