Roof Windows and VeluxInstallation in BathDaylight In, Water Out

Flashing kits are made for specific covering types, and using the wrong one is the single most common cause of leaks. Slate and other low-profile coverings need a different kit from deep-profile interlocking concrete tiles, because the depth of the tile controls how the side flashings must sit and where water is directed.

The kit works as a system: a head section that carries water around the top of the window, side sections that channel it down past the frame, and a sill section that returns it back onto the covering below. Each part must be lapped correctly with the others and with the surrounding slates or tiles, so the water path is continuous from the top of the roof to the gutter.

Cutting a rafter to make an opening removes part of what holds the roof up, so the load must be carried around the hole by trimmers fixed between the adjacent rafters. Where a window spans more than one rafter, the doubling and fixing specification matters, and it is not optional.

Position matters for the result as much as the structure. Head height, sight lines from a seated or standing position, the location relative to valleys and chimneys, and whether the window sits in a slope that will shed water cleanly all inform where the unit should actually go.

The distinction is straightforward once you know what to look for. A flashing leak follows rain, particularly wind-driven rain from one direction, and shows at the head or sides. Condensation follows cold weather and internal humidity, shows on the glass and the reveals, and can be worse when it is not raining at all.

Condensation is normally addressed by insulating and detailing the reveal properly, splayed at the bottom, vertical at the top to promote air movement over the glass, and improving ventilation in the room. We will tell you which problem you have before quoting a fix.

Older units that no longer seal, lock or close are usually best replaced with a modern unit into the existing opening, which is a considerably smaller job than a new installation. Modern units bring better thermal performance, integrated ventilation flaps and easier operation.

Where a loft is being converted, planning for ventilation and shading at the same time, rather than after the plastering is finished, avoids re-opening finished work later.