Do I need approval for a skylight or a new window?

Replacing a window with one of the same size in the same opening is usually straightforward. Creating a new opening is different, because you are cutting members that were carrying load and creating a new hole in the weatherproof envelope.

What is being considered

• Structure. Rafters, trusses or wall studs cut for an opening need a trimmer or a lintel, and a truss in particular must not be cut without an engineer's design.
• Weatherproofing. A skylight is a hole in the roof, and the flashing detail is what determines whether it leaks in ten years.
• Overlooking. New windows facing a neighbour above a certain height typically trigger planning controls about privacy.
• Fire separation. Openings near a boundary can be restricted or require specific construction.
• Energy performance, since glazing area and type feed into the thermal assessment.

Skylights specifically

• A shaft through the roof space needs to be lined and insulated, or it becomes a thermal weak point and a condensation trap.
• Tubular skylights are far less disruptive than a framed opening and suit small dark rooms well.
• An openable skylight adds ventilation, which is genuinely useful in a bathroom or kitchen, and adds another way for water to enter if the seal fails.
• Position matters for heat. A large west-facing skylight over a living area can make a room unusable in summer.