Cutting a hole in your roof

Why this job feels scary

You are cutting the one panel that faces the sky. Done carefully it is routine. Done casually it becomes a leak that lives with you for years. Take a calm afternoon, not a rushed hour before dark.

Prep that actually matters

Confirm there is nothing above the headlining: braces, looms, aerials, foam fill. Choose the fan size first and use its template, not a sketch from memory. Mask a wide area so swarf does not scratch paint. Have sealant, butyl, primer and the right fasteners ready before you cut. If anything is missing, stop. A half-finished roof hole overnight is a bad plan in UK weather.

Decide now how you will reach the seals later for maintenance. Solar and racks often land around the same patch of roof.

Cut and seal

Mark from inside and out, and compare the marks. Drill corners, cut slowly with a fine blade, support the offcut, then file the edge smooth. Etch-prime and seal the bare metal the same day. Dry-fit the fan until it sits flush and square. Bed it on the sealant system the manufacturer specifies, not whatever tube is open in the shed. Clamp or weight it for the full cure time.

Hose-test from every angle the next day, including under the lip. Fix any weep before lining. Water that gets under cladding is miserable to find later.

Weight, height and neighbours

A roof fan is not heavy, but it sits high. Log it in the weight tracker. If you also run solar and a rack, think about combined roof load and cable glands through the same panel. Leave tidy service loops and label the fan switch so future you is not guessing.

A roof hole without proper edge treatment is how vans rust from the top down.

Figures in this guide are planning estimates. Confirm weights and prices against real products, and have gas and electrical habitation work signed off by a qualified person.