A window in the slope, chosen for the spot beneath it.
Roof windows chosen for the bed, the desk or the top stair, then fitted with the flashing your roof covering needs.
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Ten years on our workmanship. In writing.
The full guide
A roof window is a window set into the slope of the roof, flashed in so the rain runs over it. It brings daylight and fresh air to rooms in the roof, to landings and to dark back bedrooms. This guide starts with the spot you want lit and works up through the window, the roof covering and the rules.
Callout 1
Anyone typing roof windows Derby into a search box has usually got a particular room in mind. It might be the box room that has never been more than a store, the landing that needs a bulb on all day, or the loft the family hopes to turn into a bedroom. The product is a window set into the slope of the roof. The question that matters comes first, and it is about the room.
So we begin with a spot. Stand where the light is missing and look up. Is it the head of a bed, the edge of a desk, the top stair, the basin in a shower room? A roof window lights a patch of floor and wall directly below and beside it, and the angle of the roof decides where that patch falls. Move the window a hand's width up or down the slope and the light lands somewhere else. That is why we start the survey indoors.
The sash of a roof window opens, and its frame lies level with the roof surface, sealed by flashing into the tiles or slates around it. It is made in standard sizes by the big manufacturers, and it can also be built to order when the opening is awkward. It is different from a roof lantern, which stands up from a flat roof as a glazed structure, and different from a flat roof rooflight, which is a pane or dome over a kerb. Those are covered on our pages for roof lanterns and flat roof rooflights. If your roof is pitched and you want a window you can open, you are in the right place.
In the trade the product is a roof window or a rooflight; most homeowners say skylight. All three words describe the same idea from different sides, and the regulations treat them differently, which is covered further down. For now the useful thing is that a roof window is built to be reached and opened, so it goes where a person can get to the handle or where a pole or electric motor can.
Derby's older streets are lined with Victorian and Edwardian terraces, its suburbs with interwar and post-war semis, and its edges with newer estates. Each gives the roof window a different job.
In a terrace the dark places include the back bedroom over a rear outrigger, the stair that rises between two party walls and the bathroom with no outside wall. A window on the rear slope can reach all three. In a semi the roof is usually bigger than the rooms below it, so the loft is the obvious prize. In a newer house with a small attic space the same window turns a storage void into a study, provided the headroom is there.
Extensions come into it as well. A kitchen extension with a flat roof wants a rooflight or a lantern, but the pitched roof of the original house next to it may need a roof window to light the room behind the extension, which has lost its outside wall. We look at the two roofs together, so the new light and the old one do not fight each other.
The free survey is done in the room, at the spot, and then in the loft or on the roof. We note the pitch, the rafter spacing, the covering, the ceiling height and the direction the slope faces. We mark the spot on the floor and look up the line of sight to the roof. Then you get a fixed written quote with the size, the type and the flashing set out, and the figure stays the same on the day. You can ask for the survey through the form at the quote band, or on WhatsApp on 07880 284133.
Before you book, it helps to know what you want the window to do. Is it mainly for daylight, mainly for ventilation or fresh air, or for the view? The answer steers the choice between a centre-pivot and a top-hung unit, which gets its own page: Centre-Pivot or Top-Hung Roof Windows.
Move the window a hand's width along the slope and the light lands somewhere else.
Callout 2
People ask for a roof window to get more light, and that is a fair reason. Glass in the roof slope sees more sky than an upright window of equal area, because there is no neighbouring wall, fence or eave blocking the view upwards. How much more depends on the pitch and the direction it faces, so we size from the room and not from a rule of thumb.
Daylight from above is gentle and falls deep into a room. A south-facing slope brings strong sun and a lot of heat on a summer afternoon, and a north-facing slope brings an even, cool light that suits a desk or a studio. East gives morning light, west gives evening light. In a bedroom, east is usually welcome and west can be too warm to sleep in, so blinds are part of the conversation. Blackout and pleated blinds made to fit are available for the standard sizes, and manual or electric versions can be added at the time of fitting.
English houses face no daylight rule under the Building Regulations, so nobody dictates how much glass you must have. The decision is yours, and it is a design decision. A small window in the right place often does more than a large one in the wrong place. The wrong place for a desk is a window that puts glare across the screen. The wrong place for a bed is one that wakes you at five in the morning in June.
A roof window that opens does a job a fixed rooflight cannot. Warm air rises, and an opening window high in the slope lets it leave. Open a window low in the house and a roof window at the same time and the air moves through on its own. That makes a loft room much easier to live in during a warm spell. Many models also have a ventilation flap in the head of the frame that lets in fresh air while the sash stays shut, which is useful in a bathroom or a child's room at night.
Where the window is out of reach, an electric opening unit with a rain sensor can be fitted. That is its own product, covered on our page about electric opening rooflights. If you want a very large amount of fresh air, or a window that opens on a switch above a stair, that is worth reading.
Brighter rooms tend to feel larger and calmer, and a room in the roof with proper daylight is simply one that gets used. A study that is lit from above is a room people want to sit in. A landing that has its own light stops being a corridor you hurry through. We would rather describe those things plainly than promise a feeling. What we can say is that the right window turns a dead spot in the house into one you stand in on purpose.
Choices that go with the window change how it performs. A laminated inner pane helps with noise from rain. A tinted or coated outer pane cuts glare and some of the heat. Triple glazing improves the thermal figure further and costs more, so it is worth it in some rooms and not in others. We go through the options at the survey and write the choice into the quote so that it is clear what you are getting.
Callout 3
Roof windows come in a handful of forms, and the choice matters more than people expect. The two main opening types are centre-pivot and top-hung, and there are fixed and conservation versions alongside them. Each answers a different question about the room.
The full comparison, with sizes and pitches, is on our page Centre-Pivot or Top-Hung Roof Windows. What follows is the short form.
The sash turns on a hinge across the middle. The handle is at the top, so you reach up to open it, and the lower half swings out while the upper half swings in. The window can then be turned right round, which brings the outer pane inside for cleaning without leaning out of the roof. It is the familiar type and the standard in most manufacturer ranges. It suits pitches from low to steep, and it sits well in a room where the sill is at a normal height.
The sash is hinged at the top and swings out from the bottom, like a hatch. The handle is at the bottom. The big difference is the view. Because the sash hinges at the top, the window opens clear of your head, and you can stand close to the glass and look out. It suits a stair, a landing or a room with limited headroom. It is also the type that can be fitted with a restrictor and an extra-wide opening for ventilation. It does need clearance outside for the sash to swing.
A fixed unit does not open, so it is for daylight only. It is the right choice over a stair where nobody could reach the handle anyway. A conservation roof window is made with a slim, flat-fitting profile, typically with a cast metal look and a single central glazing bar, to suit period roofs and listed or conservation-area buildings. That is its own range and its own planning conversation, covered at conservation rooflights. Check with the council before you order one.
Frames are made in timber with a polyurethane finish, in white painted timber and in uPVC. The outside is covered in aluminium or a similar weatherproof cladding, so the outer surface of most roof windows is metal whatever the frame inside is. uPVC is easy to wipe down and suits bathrooms and kitchens. Timber looks warmer and suits bedrooms and studies. All have double glazing as standard in the better ranges, with triple glazing available.
The standard range covers most openings, and sizes are built from a width and a height. When a roof has no standard-sized gap, for example between a chimney stack and a purlin, the unit can be made to measure or the opening built around a standard size. We measure for both and say which is better in the quote. Tell us if you are replacing an old window in an opening you want to keep, and we will see whether a modern size fits the old hole.
VELUX is the name most people know, and we fit it. There are other manufacturers with their own ranges. Which is right depends on the roof, the pitch and your budget more than on a name. Our page on which roof window brands are worth considering goes through how to weigh them. For the VELUX range itself, see our VELUX windows page.
The standard range covers most openings. Awkward ones are built to measure.
Callout 4
The window is only half the job. The other half is the join between the window and the roof, and that join depends on what the roof is covered with. A flashing that suits a flat concrete tile will leak on a profiled one, and a slate roof needs a different kit again. It is the part that decides whether the window stays dry.
Every roof window is supplied with flashing designed for a range of coverings. The kit has to match the profile of the tile or slate, the way it laps, and its thickness. A mismatch leaves gaps that rain is driven into. Before we quote, we look at what is on the roof, and we write the matching kit into the quote.
Welsh slate roofs are part of the older Derby terrace stock. Slate lies flat and thin, so the flashing is a flat-profile kit with soakers that tuck under each course. Each slate beside the opening is lifted and cut so it fits snug, and there is no way to hurry that. If the slates are brittle with age, some will break as they are lifted, and we would tell you when we saw a pattern of that at the survey.
| Covering | Profile | Flashing | Care point |
|---|---|---|---|
| Welsh slate | Flat, thin | Slate soakers | Brittle old slates |
| Concrete tile | Thick, profiled | Deep apron kit | Cutting beside frame |
| Plain clay tile | Small, many laps | Plain tile kit | Relay in order |
| Staffordshire blue | Dense, dark clay | Tile-matched kit | Hard to replace |
| Flat roof | No pitch | Not a roof window | Use a kerb rooflight |
Interwar and post-war semis are tiled in interlocking concrete tiles. They are thick and profiled, so the flashing kit includes a deeper apron and side pieces that rise over the profile. The tiles beside the window are cut with a cutting disc and set into the flashing so the water runs over the top, and not into, the join.
Plain clay tiles are small and overlap in many layers, and they are the covering to handle with care. Staffordshire blue clay tiles are dense and dark, and they can be hard to replace like-for-like. We lift them, set them aside and relay them in order, and a roof with brittle or irreplaceable tiles is flagged before the day.
A roof window needs a pitch to work properly, so on a flat roof it needs an angled upstand of its own. A flat roof takes a rooflight on a kerb, or a lantern. If your kitchen extension has a flat roof and the house has a pitched one, you may need both, and the surveyor will tell you which goes where. Our page on flat roof rooflights covers the flat side, and orangeries and conservatories with a glazed roof are a different product again.
Under the flashing, the window needs a lining and an insulation collar. Both are part of the kit. They keep the warm side warm and stop condensation forming on the frame. The details matter more in a cold loft than in a room that is already insulated and heated. We fit the collar and check the roof insulation meets it before the lining goes in.
Callout 5
A roof window job is shorter than people expect, and more orderly than they imagine. For a straightforward single window expect usually one or two days up on the roof, with the inside finished after. It needs a dry day for the opening to be made, and we plan the work around the weather.
You get a free survey first, and nothing is priced until we have stood in the room and looked at the slope. The quote that follows is fixed and written down, and the figure holds on the day. We also order the window and the matching flashing and lining kit. If the opening needs a structural change, such as cutting a rafter, there will be a trimmer and a plan for it, and where the job is notifiable, we make the Building Control notification ourselves.
The covering is lifted around the opening and set aside. Where the rafters have to be cut, they are doubled up and trimmed around the new frame, and the frame is fixed to them. The flashing goes in from the bottom up, which is the reverse of how it feels, because water runs down. Each piece laps over the one below it. Last of all, the tiles or slates are put back and the sash is hung.
The roof is made watertight at the end of each day, so nothing is left open overnight.
The floor spot is marked, the opening measured and the covering checked from outside.
Size, type, flashing kit and lining are written down, and the figure holds.
Covering lifted, rafters trimmed and doubled, frame fixed and the roof made watertight.
Flashing laid bottom up, covering relaid, then the sash and glass fitted.
Insulation collar, splayed lining and ceiling finish, then a clean room.
Inside, the lining is built from the frame down to the ceiling, usually splayed so that the light spreads wider as it comes down. A splay is the angled surface between the window and the ceiling, and it makes a difference to how bright the room feels. The plasterboard is taped and skimmed, or an off-the-shelf lining is fitted, and the room is left clean. Decorating is up to you or your decorator, and you should allow for the plaster to dry first.
When the window goes into a loft that is already a room, the ceiling is whatever the loft conversion made it. When it goes into a cold loft over a landing, there is an opening to be formed through the ceiling joists, a light well to be built, and boards to be fixed. The light well is the shaft from the window down to the ceiling. In a shallow loft it can be a few centimetres; in a deep one it can be a metre or more, and its walls are lined white to carry the light down.
The firm gives a 10-year workmanship guarantee, in writing. It covers the fitting, which is the part we are responsible for, and the manufacturer's own guarantee covers the product. The details are on our guarantee page, and the question of what moves the cost is on our costs page, since the survey changes the figures.
Callout 6
A few rules apply to roof windows, and they are worth knowing before you commit. The firm installs to current Building Regulations, and the rest of this chapter sets out what that means for you.
Table 4.2 of Approved Document L (the 2021 edition) sets the heat-loss limit for work on existing homes. Put a new or replacement roof window in, and it is held to the window figure of 1.4 W/m²K. Reaching Window Energy Rating band B is the alternative test. A rooflight takes a looser 2.2 W/m²K, and lanterns fall in that group. The split exists because a roof window is built and used like a window, while a lantern or kerb rooflight is a different construction. Ask for the figure in writing for whatever you are quoted, by us or anyone else.
Cut a new opening and you alter the rafters, which makes it building work. Approval for that comes from the local authority or a registered building control approver. Swapping one roof window for another is treated differently, as a controlled fitting, so the new unit still has to reach the heat-loss figure above, and competent person self-certification is one route for it. The paperwork is our job where the work is notifiable.
A bedroom in the roof raises the question of getting out in a fire. Approved Document B lets a roof window serve as the way out only for a floor that sits 4.5 m or less up from the ground. Convert the loft of a two-storey house and you cross that line, so the answer there is a protected stair. Rooms upstairs in a bungalow or chalet bungalow can rely on the window, because those floors sit within that height. Whichever window is used, the clear opening has to be 0.33 m² or more, and no less than 450 mm across either way. Our page on roof windows for loft conversions goes through head height, stairs and the opening size in more detail.
For a house, planning is normally light touch, because rooflights tend to be allowed as permitted development, subject to conditions, and our planning guide lays those out. A flat or maisonette is different, since householder rights do not extend to it. A listed building generally calls for listed building consent. Where a conservation area applies, the council may have withdrawn the right through an Article 4 direction, so ask Derby City Council first. The Planning Portal at planningportal.co.uk has the official guidance.
That is a fair question, and we answer it with the caveats in Are Roof Windows a Good Idea? If you want the vocabulary first, What Are the Windows in a Roof Called? sorts out the roof window, skylight and dormer.
We cover Derby and about 30 road miles around it, measured by road. Areas covered include Derbyshire towns such as Belper, Ilkeston, Long Eaton and Duffield, and Leicestershire towns on the east side. Homes are our first concern, and small commercial jobs are welcome. If you are not sure whether you are in range, ask in the form at the quote band.
You get a free survey, a fixed written quote and a 10-year workmanship guarantee on the fitting. Each is in writing, so you know what you are agreeing to before work begins.
Nearly every pitched roof can take one, but the pitch decides which type is suitable, and the rafters decide where. Each model has a minimum and maximum pitch, so we check the pitch at the survey before we quote. A very shallow or a very steep slope narrows the choice but rarely closes it. A flat roof takes a different product.
It can, particularly on a south or west slope. The fix is a mix of choices made at the order stage, namely a coated outer pane, an external blind or awning, and an opening sash that lets hot air out. Blinds are cheaper to add at the time of fitting than afterwards, so we raise them at the survey.
Not necessarily. A modern window often fits the old opening, because the sizes are standard, but old frames vary and the flashing may need a new gap. If the old window was a bespoke size, we measure it and either match it or adjust the opening. The replacement must meet the thermal figure for roof windows in the regulations.
Yes, and in an extension that is a common pairing. The pitched roof of the old house gets a roof window, and the flat roof of the extension gets a lantern or a flat rooflight. We look at both in one survey and quote them together, so the two lights do not compete. Our roof lantern page covers the other half.
A straightforward single window means usually one or two days up on the roof. Plastering, decorating and any structural work extend that, and we agree what is included before the day. We choose a dry spell for the roof opening and tell you in advance if the weather moves things.
The firm gives a 10-year workmanship guarantee, in writing. It covers our fitting, such as the flashing, the fixing and the finish. The window itself carries the manufacturer's own guarantee. Both are explained on the guarantee page, and the written quote tells you what is included.
Where do you want the light? Tell us in the form: the worktop, the stair, the desk.
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