Can You Put a Skylight in Any Roof?

The roof decides the type, not the answer

The short question hides three separate ones. Is the roof the right shape? Is the structure strong enough? Is the covering one we can weather properly round a new opening? Each has a clear answer once someone has looked at the roof from above and from inside the loft.

A pitched roof, such as a tiled or slate roof on a house, takes a roof window fitted in the slope. On a flat roof a rooflight goes on a raised upstand, and the glass is laid to a slight fall so rain runs off. Between the two sit lanterns, sun tunnels and walk-on glass. All of them are covered from the main skylight and rooflight page.

Pitched roofs

A roof window is built for a sloping roof, and each model has a range of pitches it works within. Too steep or too shallow and the sash will not hang or drain as designed, so we check the pitch with a level before anything else. Plenty of ordinary house roofs sit well inside the range. Where a roof is a little shallow for the window you like, a different model, or a flat-topped rooflight, can solve it, and the survey tells you which.

Plain tiles, interlocking concrete tiles and slate all take a roof window. Each has a flashing kit made to suit its profile, so the water is carried round the frame and back onto the roof covering. We match the kit to your tile, and if the covering is old and brittle we say so at the survey, because lifting tiles round the opening is easier when they are sound.

Flat roofs

Flat roofs are where a rooflight does its best work, because the roof is the only surface that faces the sky. The glass goes on an upstand, a short raised kerb on the roof deck, insulated all round, and the roof covering is lapped up the sides of it. Never think of it as flush. The glass sits proud with a slight fall, so rainwater runs off rather than pooling.

A flat rooflight is also the route to a bright room in an extension, kitchen or hallway where the sides are closed in. Straight up is clear, where a window in the wall is aimed at somebody's fence. The daylight guide shows why a pane overhead carries light deeper into the room.

What sits under the roof

The covering is the visible part. The part that matters most is what carries it. A skylight needs an opening cut through the roof, and that opening interrupts rafters or joists. Those members have to be trimmed, meaning the cut ones are tied back into the neighbours with new timbers, so the load goes round the hole. Think of it as a bridge: the timbers either side of the opening do the work of the ones that were cut.

That is routine on a sound roof. On a roof with undersized timbers, damp or rot, or a roof truss that cannot be cut without an engineer's design, the survey picks it up and the quote reflects it. Trussed roofs need particular care because the timbers are designed as a system. Whatever the survey finds, you see it written down before any work starts. That includes the cost of any strengthening, so there is no surprise once the roof is open.

Loft space matters too. Water tanks, cables and stored boxes near the opening are moved aside before the cut, and the insulation round the new frame is built up so the warmth of the room is not lost through the gap.

Roofs that need more thought

A few roofs are not a straight yes.

• Thatch has no flashing route, and a window in it is specialist work.
• A listed building, or a house under an Article 4 direction, has planning rules that can change what you may fit.
• A roof with a solar array may leave too little clear space for the opening.
• A very low pitch or a green roof calls for a rooflight rather than a roof window.

None of these is a reason to give up without asking. Each has a route, and several simply change which product is the right one, or add a step before the work starts. Whether your street sits in a conservation area is a question for the planning team at the council, and our Milton Keynes planning guide covers the route for a new opening.

What the visit settles

Someone visits, free of charge, and checks four things: the pitch, the covering, the timbers and the room below. A fixed written quote follows, one that holds on the day, and the finished job meets current Building Regulations with the plaster done. If the roof turns out to be a poor candidate, you hear that straight away and nothing is lost.

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