What is the difference between a skylight and a rooflight?

Everyday word, trade word

Skylight is the word people use at home. It is what goes into a search box, what an estate agent writes in a listing, and what somebody says when they mean glass in the roof of a kitchen. It is clear, it is understood, and there is nothing wrong with it.

Rooflight is the word used by the people who specify and fit them. Architects write it on drawings, roofers say it on site, and manufacturers put it on the technical pages of their literature even when the marketing pages say something else. It carries no extra precision of its own; it is simply the register the trade settled into.

Some of the difference is age. Rooflight is the older English term and once described anything glazed set into a roof, including the cast-iron lights over Victorian workshops. Skylight has always been the plainer word for the same idea. Neither went through any process that fixed its meaning, so both survive, doing overlapping work.

The distinctions some installers do draw

Although nothing is defined, habits exist, and knowing them makes a conversation with a supplier shorter. Three are worth having in your head.

Roof window usually means an openable hinged unit set into a pitched roof, serving a habitable room, supplied with a flashing kit made for the covering around it. The word window is doing real work there: it ventilates, it opens for cleaning, and in a converted loft it may be the unit providing an escape opening.

Rooflight is the broader term. It covers everything a roof window covers, plus fixed units that do not open at all, vented units with a small trickle opening, glazing in flat roofs, and the flush conservation-pattern units made to sit in the plane of the slate rather than above it.

Lantern is the one people are clearest about, because it looks like what it is: a raised glazed structure standing above a flat roof, framed, with a ridge and sloping panels.

These are conventions rather than rules. A supplier may use all three differently, and often does.

Why the label is the least useful part of the conversation

The practical problem with the vocabulary is not that people use the wrong word. It is that two people can agree on a word and still be picturing different objects. Somebody asks for a rooflight meaning something they can open and stand under on a warm evening, and receives a quotation for a fixed pane, or for a vented unit with a small background opening, which is not the same thing at all.

That mistake tends to surface late, which is what makes it expensive. Glass for these units is frequently made to size, so the moment the misunderstanding becomes obvious is usually the moment it is hardest to unwind.

The way round it costs nothing. Describe the thing instead of naming it. Anybody who fits these units for a living will translate your description into a product immediately, and if their word for it differs from yours, that difference will surface in the first minute rather than the last week.

Four things that settle the product

Four pieces of information do more to fix the specification than any amount of arguing about terminology.

The roof, and roughly how steep it is. Pitched or flat is the first fork, and it rules out most of what is confusing you, because very few products cross that line. What the covering is matters too, since stone slate, Welsh slate, clay tile, concrete tile, felt and single ply all take different detailing at the perimeter.

Whether it opens, and why. Ventilation, physical access onto the roof, and providing an escape opening from a habitable room are three separate requirements that narrow the range in three different ways. Saying which one applies is more useful than saying opening.

Whether the room is habitable. A bedroom or a converted loft is a different specification from a landing, a garage or a store, and it changes what Building Control is looking at.

Whether appearance is constrained. Whether the slope is seen from a road or footpath, and whether the building is older, listed or in a conservation area, decides whether a flush unit is needed rather than merely preferred.

Where the words genuinely matter

There is one place the terminology stops being harmless, and that is on paper. A quotation that says rooflight and nothing else has not told you what you are buying, and a written order is the last opportunity to catch a misunderstanding before anything is made.

A quotation worth comparing against another one states the roof it is for, whether the unit is fixed, vented or fully opening, the mechanism if it opens, whether it is manual or motorised, the external finish, and whether it sits flush or on a kerb. On a flat roof it also states whether the glass is specified to be walked on, because that is not something that can be added later without replacing the unit.

If two quotations use different words for what you believe is the same thing, ask both to describe the unit against that list. Where they diverge, one has quoted for something other than what you asked for, and the cheaper number is usually the one that has quietly dropped something.

How to describe what you want

The opening sentence of a useful enquiry sounds something like this: a pitched slate roof at the back of the house, one unit, it needs to open for ventilation, the room is a loft bedroom, and the slope is visible from the lane. That is five seconds of speech and it eliminates most of a catalogue. Say skylight or rooflight, whichever you prefer, and nobody who fits them will be confused.

Our guide to roof windows and rooflights takes the terminology further, with the working distinctions, the choice between centre-pivot and top-hung, and the five questions that settle the product for good. For glazing in a flat roof, the flat roof skylight installation page covers the kerb, the falls and how the covering terminates.

We install new rooflights and full replacements across Oxford and up to twenty five miles by road, we have been doing it for fifteen years, and we handle the Building Control notification as part of the job. We install VELUX, Fakro, Keylite and Roto units, and our workmanship carries a ten-year guarantee.