Walk along a Stroud terrace and you can read the roofs. A slate slope with a small window set into it. A glass lantern over a rear extension. A thin metal-framed pane lying flat in old stone tiles. A dome on a flat garage roof. Each is a different product, built for a different roof and governed by different rules, though people call them all skylights.
This guide tours the four families: pitched roof windows, flat rooflights and lanterns, conservation rooflights, and sun tunnels. For each it covers how the unit works, which roofs it suits and what to watch for when it is fitted. If you only want to know how the two common words differ, roof window or skylight answers that in a page. For the wider service, including fitting and repairs, start at our roof windows and skylights hub.
One question sorts every skylight: is the roof pitched or flat?
Before you compare makers or finishes, look at the roof. A pitched roof is one with slopes, the usual arrangement on a house with a ridge. A flat roof, in practice, falls gently to a gutter or outlet. The two take different glazing because water leaves them in different ways.
On a pitched roof, the glazing sits in the slope, in line with the covering, and water runs over and around it in the same direction it runs over the slates. That is a roof window. On a flat roof, water does not run off quickly, so glazing is raised on a kerb, called an upstand, and the roof covering is lapped up and over it. That is a rooflight. The difference between them is not a matter of branding. It decides the flashing, the repair method and the energy rule.
Two further types do not fit the pitched or flat split neatly. Conservation rooflights are a pitched-roof product designed to sit flush. Sun tunnels are a small dome and a tube that can go into either kind of roof. We take them in turn below, starting with the type you are most likely to be quoted for.
Fixed or opening
Whatever the family, a unit is either fixed, so it only lets light in, or opening, so it also ventilates. Opening units cost more and have more parts to seal, but they give a loft room, a landing or a stairwell a way to shed warm air, and they let you reach the outer glass for cleaning on the pivot types. Our hub page gives the price ranges, and the next sections say which types come in which form.
Pitched roof windows: centre-pivot, top-hung and electric
The pitched roof window is the workhorse of the loft conversion. It is a glazed sash in a frame, set into the slope of the roof and sealed by a set of flashings cut to suit the slates or tiles around it. On a house in Stroud that covering might be natural slate, clay or concrete tile, or stone slate, and the kit changes with each.
How they open
A centre-pivot window turns about a hinge near the middle of the sash. Push the bottom out and the sash rotates, which also lets you clean the outer glass from inside. A top-hung window hinges along its upper edge and swings out like a canopy, giving a clear opening beneath when it is raised. Some units combine both movements. An electric window is operated by a motor. MyBuilder's August 2026 guide lists a standard centre-pivot window at £305 and an electric window at £420 to £590.
Where they suit
A roof window fits where the slope is steep enough to give headroom and the rafters can be trimmed around an opening. The loft of a terraced house on a Stroud hillside is the classic site, with a window on the rear slope for light and air. Placement matters for glare and for overheating, and our answer on where to put a roof window goes into that.
Escape windows
A habitable loft room needs a way out in a fire. Approved Document B describes an emergency escape window as one that opens to at least 0.33 m² of clear space, 450 mm high and 450 mm wide at the minimum, with its lower edge no higher than 1,100 mm above the floor. The rule applies only where the window is within 4.5 m of the ground, so with two full storeys below, a loft window usually sits too high to serve as the escape route. Our guide to Building Regulations for roof windows covers that and the energy limits.
Flat rooflights and lanterns: glass on a kerb
A flat rooflight is a pane or dome of glazing carried on a flat roof, or a roof with only a slight fall. The simplest is a fixed pane in a frame, set on an upstand, which brings daylight into a kitchen or a hallway beneath an extension. Rooflights come as domes, flat glass units, hinged opening units, long narrow strips and walk-on panels. A lantern is a taller, more architectural version, a glazed box with pitched glass sides rising from the kerb, often over a dining area.
The kerb is part of the product
On a flat roof, the upstand is where the weatherproofing succeeds or fails. The roof membrane, whether EPDM, GRP or felt, is carried up the side of the kerb and tucked beneath the rooflight's frame, so the joint faces away from running water. If the kerb is too low, or the membrane stops short, water splashes or ponds against the joint. Water needs a slope to find the outlet, even on a roof called flat. The recommended minimum finished fall in BS 6229 is 1:80 (IKO, February 2021), and a rooflight set where water collects will leak sooner than one placed on the run of the fall.
The energy rule is different
Approved Document L treats a rooflight differently from a roof window. Table 4.2 sets a limit of 2.2 W/m²K for a rooflight, counted over the unit's outer developed surface, against 1.4 for a window in the slope. A kerb supplied together with the rooflight is judged as one assembly at that same 2.2, whereas an upstand built on site must reach 0.35 at most.
Lanterns and big glazed units are heavy and expensive, and the roof structure under the kerb has to carry them. That is a question for the survey, and often for an engineer.
Conservation rooflights for slate and stone roofs
A conservation rooflight is made for the roof that must keep its look. The frame is slim, often cast or fabricated metal, and the glass sits flush with the covering instead of standing proud. From the lane it reads as a thin dark line in the roof, much like the iron rooflights that old mills and cottages once carried.
Why they exist
Stroud District has 41 conservation areas, and the Cotswolds National Landscape covers a large part of the east. A thick-framed window on a prominent slope can look wrong against an old stone or slate roof. Flush units answer that, and their low profile also helps with the Class C limit that keeps a roof window from standing more than 0.15 m clear of the original roof plane. Our guide to roof windows and planning explains that rule and what Article 4 directions and listing change.
Fitting into stone
On a Cotswold stone roof laid in diminishing courses, where the biggest slates sit at the eaves and the smallest by the ridge, the opening has to work with courses whose length changes all the way up the slope. The stone is heavy, about 1,000 kg per 10 m² in Cotswold District Council's 2000 guidance, so the opening is trimmed with care. We set it out course by course and lay the surrounding slates to suit the frame, with lead where the details call for it.
On a listed house, a rooflight is an alteration, and listed building consent comes before the order. Raise it with the council's conservation officer first.
Sun tunnels: light without a window
A sun tunnel, also called a tubular skylight, is the smallest of the four. A clear dome sits on the roof, a reflective tube runs down through the loft space, and a diffuser panel in the ceiling spreads the light across the room below. There is no view out and no opening sash, only daylight.
Where they work
The tube makes a sun tunnel useful where a window cannot go: a landing or hallway with a roof void above, a bathroom or utility room, a wardrobe space, or a room under a roof where the rafters or a chimney run get in the way. A flexible tube can bend round a rafter or a chimney run, which a framed window never could.
On slate, tile and stone
The dome stands on a collar that must be worked into the covering, and on a pitched roof that is a job for a roofer, not a general builder. On natural slate it is a lead or formed flashing; on stone slate the surrounding courses are re-laid to fit it. Because the opening is small, the work is more contained than for a full window, but the principle is the same: the roof covering has to lap over the flashing, not under it.
A sun tunnel brings no fresh air and no view. If you want ventilation as well as light, you need an opening roof window or another route to daylight.
Choosing between the types for your roof
Start with what the room needs and what the roof will allow. The table sets the four families side by side.
| Type | Sits on | Best for | Watch for |
|---|---|---|---|
| Pitched roof window | A sloping roof | Loft rooms needing light, air and a view | Trimmed rafters, flashing matched to the covering, the 1.4 limit |
| Flat rooflight or lantern | A flat roof, on a kerb | Kitchens and extensions below flat roofs | Kerb height, the fall, the 2.2 limit, weight |
| Conservation rooflight | A pitched roof of slate or stone | Older and listed houses that need a low profile | Consent, course layout, lead details |
| Sun tunnel | Pitched or flat roof | Landings, bathrooms and wardrobes | No ventilation and no view |
Then check the legal side. Whether a roof window needs planning permission depends on Class C and on any Article 4 direction, and every type is a matter for Building Regulations if it alters the structure or must meet a thermal limit. We handle that notification where the work is notifiable.
The survey decides
At the survey we read the covering, measure the rafter spacing and pitch, look into the loft below and plan the scaffold route, with photographs of your own roof taken as we go. After that comes the written quote for the whole job, and the finished work carries our 10-year workmanship guarantee in writing.