Long, narrow sitting room with a fireplace and a flat rooflight running down the ceiling

Flat Roof Rooflights in Derby

Daylight for the room that has only a flat ceiling.

A flat roof gives you the freedom to put daylight almost anywhere. We start at the spot you want lit, then work up through the roof.

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Free survey
Fixed written quote
10-year workmanship guarantee

Three places a flat rooflight earns its keep

Kitchen sink under a wide picture window, with a flat rooflight above — Over the far end of the kitchen extension, where the worktop used to sit in shadow.

Plain kitchen with a green island and a flat rooflight letting light onto the floor — Over a plain kitchen with a green island, so the light reaches the floor.

Wooden kitchen units with a patch of daylight on the floor from a rooflight above — Above wooden kitchen units, laying a patch of daylight across the floor.

Ten years on our workmanship. In writing.

Surveyed before we price
A fixed written quote that does not change on the day
Building Control notification handled

How the guarantee works

Frameless flat rooflight on a grey single-ply roof against a brick wall

The full guide

Flat roof rooflights, from the worktop up

A flat roof is the easiest roof to put daylight through and the easiest to get wrong. This guide follows one rooflight from the place it should light, up through the glazing, the kerb and the roof build-up, to the ceiling opening and the paperwork.

Under the opening
Daylight and heat
Glazing choice
Kerb and flashing
Roof build-up
Ceiling and sign-off

Callout 1

Choosing the place the light should land

Flat rooflight or roof lantern for this room

Flat rooflight

Low profile, barely seen from the garden
Most glass for the frame
Suits narrow extensions and corridors
Simple to keep clear of leaves

Roof lantern

Stands proud and lifts the ceiling
Lets light in from several sides
Suits wide kitchen and dining rooms
Needs a deeper, stronger kerb

People ask about flat roof rooflights in Derby by room. The kitchen is too dark. The rear extension feels like a corridor. The garage conversion has a door and no outlook. What they mean is a place inside the room: the end of the worktop where the chopping happens, the dining table, the desk that now lives where the car used to park. A flat roof rooflight is placed so its daylight lands on that place, and everything else follows from there.

Why position matters more than size

A flat roof has no slope to dictate where the opening goes. On a pitched roof the rafters and the slope usually settle the position for you. On a flat roof you can put the opening over the table, over the sink, over the middle of a long room or over a dark inside wall. That freedom is the reason people choose flat roof skylights, and it is also the reason a catalogue size is a poor starting point. A large rooflight in the wrong place leaves the worktop in shadow and the middle of the floor too bright. A smaller unit over the right spot does more.

So the survey begins inside, not on the roof. We stand in the room, note the spot on the plan of your floor, and look at where the existing light comes from. Windows and glazed doors on one side of an extension mean the far side needs the help, and that far side is usually where the rooflight belongs. Then we measure the ceiling, the joists, the wall plate and the roof above, so the opening can be drawn against real dimensions and not guesses.

Rooms that suit a flat rooflight

Flat roofs in Derby turn up in a few familiar places. Kitchen and dining extensions at the back of Victorian and Edwardian terraces, and of interwar and post-war semis, are the most common companion to a rooflight. Single-storey rear extensions often deepen the house by several metres, which leaves the old back room dim. Garage conversions have the same problem with an even shorter list of windows. Porches, utility rooms, bathrooms and hallways under a flat section also benefit, and so do small commercial units such as an office or a treatment room that sits under a flat roof.

If your extension is the reason you are reading, our page on rooflights for single-storey extensions goes through how the opening relates to the rest of the room.

Fixed, opening or a lantern

Once the spot is chosen, the next choice is the kind of unit. A fixed flat rooflight is the simplest option and gives the most glass for the money spent on the frame. An opening unit lets warm air out, which matters in a kitchen. A roof lantern stands proud of the roof and brings light in from its sides as well as from above, so it suits a wider room where you want the ceiling to feel taller. Our roof lantern page covers that style on its own. Where the rooflight will also be stepped on, for example to light a basement or a room below a terrace, a walk-on rooflight is a different product with a different glass build-up.

Homes are our first concern, though a small commercial roof gets the same method. The method is the same. Choose the spot, measure the room, then design the opening.

If you would like the spot checked before anything else is decided, the free survey form is the place to start. No figure is given until we have looked at the roof, the spot and the room around it.

On a flat roof you can put the opening anywhere, which is exactly why it should be put somewhere on purpose.

Callout 2

How much daylight, and how to keep it comfortable

Natural light is the reason for the whole job, and a flat roof is a generous place to collect it. A horizontal opening sees the whole sky. A window in a wall sees a slice of it, and the house, the fence and the neighbours take much of what is left. That is why a modest rooflight can brighten a room more than a larger window in the same room.

There is no daylight rule to meet

Building Regulations in England do not set a daylight requirement for houses, so there is no minimum glazed area to hit and no formula that gives the right answer. The right size comes from the room. We look at how deep it is, how high the ceiling sits, where the existing windows face and where you work or eat. Then the opening is sized so the light reaches that spot without turning the room into a greenhouse.

Light well and ceiling height

The shaft between the rooflight and the ceiling opening is called the light well. In a flat roof it is short, because the roof build-up is not thick and the ceiling is close to the roof deck. A short well delivers more light than a long one, and splaying the sides of the well (angling them outwards towards the ceiling) spreads daylight further across the floor. Plain white or pale reveals reflect more than dark ones. We settle the depth and the splay at the survey, because they depend on the joists and the insulation above.

A flat-roof job, from survey to clear-up

Free survey
We measure the room, mark the spot, and check the ceiling, joists and roof covering.
Fixed written quote
You get the unit, the kerb and the finishing in writing, and the figure stays put when the day arrives.
Notification
Building Control is notified before work begins, where the job needs it.
Opening and kerb
The roof is opened, the structure is trimmed and the kerb is built and insulated.
Unit and weatherproofing
The rooflight is fitted and the covering is run up to the kerb.
Finish inside
The light well is lined, the ceiling is made good and the site is left clean.

Heat gain and glare

A rooflight that faces the sun can warm a room in summer. The first remedy is glazing. A solar control coating on the glass cuts the heat that comes through without turning the room dark. The second is ventilation, which is where an opening unit helps, since warm air rises to the highest point in the room and can leave there. A third is a blind. Electric or solar-powered rooflight blinds can sit inside the light well. If you want a rooflight you can open from the sofa, our electric opening rooflights page explains how those units are controlled and what they need in the way of power.

Glare matters at a desk or a television. Positioning the rooflight to one side of the screen, not straight above it, solves most of it. This is another reason the survey starts from the spot where you sit.

Condensation and ventilation

Kitchens and bathrooms put moisture into the air, and a cold pane of glass is the first place it settles. Good double glazing with a warm edge spacer keeps the inner pane warmer, which reduces condensation on the glass. An opening rooflight lets the damp air out directly. If you have a unit that now mists between the panes, that is a different fault: the seal has failed and the glass cannot be dried out. The answer is a replacement unit, and our misted rooflight replacement page explains how that works.

Fixed or opening for ventilation

Choosing an opening unit is mainly about the room. In a kitchen or bathroom, where moisture and cooking heat gather, venting at the highest point helps. In a hall or a dry utility run, a fixed unit is simpler and costs less to keep. We will say which suits your room when we have seen it.

A horizontal opening sees the whole sky, which is why a modest rooflight can outwork a larger window.

Callout 3

Glass, polycarbonate and the type of unit

A flat roof rooflight is a glazed unit on a frame. The choices are what it is glazed with, whether it opens, and whether anyone will walk on it. Each one changes how the rooflight looks from inside, how it behaves in cold and hot weather, and how long it lasts.

Glass or polycarbonate

Sealed double glazed glass units are the usual choice for a room that people sit in. They give a clear view of the sky, a cleaner look from inside, and good thermal performance. Triple glazed units add insulation where it matters, such as a north-facing room that you want to keep warm. Polycarbonate is lighter and cheaper to fit and is common on older porches, lean-to roofs and garages. It can discolour and become brittle with age, and cracking at the fixings is a frequent reason people ask for a replacement. Neither material is a bad choice in itself. They suit different rooms. Our page Polycarbonate or Glass for a Flat Rooflight? sets out how to decide.

Frames

Frames come in aluminium, uPVC and, for some systems, timber or a composite. Aluminium frames are slim and strong, which suits a bigger span with a neater look. uPVC frames are common on stock units and are well suited to modest openings. The frame also affects how much heat is lost around the edge of the glass, so a thermally broken frame helps the overall performance.

Energy performance

The energy rules sit in Approved Document L (Part L 2021), Table 4.2. For an existing home, a new or replacement lantern or other rooflight is held to 2.2 W/m²K. A unit classed as a roof window gets the stricter window limit, which allows 1.4 W/m²K at most, or band B on the Window Energy Rating scale. Which applies depends on how the unit is classed. We confirm that at the survey and specify a unit that meets the limit, so the installation passes. For more on glazing and heat loss, the energy efficient rooflights page covers it in more detail.

Fixed, opening and walk-on in one view

The table below sets the three main types next to each other, because the choice often comes down to what the unit has to do besides let light in.

Fixed, opening or walk-on, side by side

How the three main flat rooflight types compare.
Type	Opens	Best for	Watch for
Fixed flat rooflight	No	Halls, offices, dry rooms	No venting
Opening flat rooflight	Manual or electric	Kitchens, bathrooms, extensions	Needs power if electric
Walk-on rooflight	No	Terraces, basements, link roofs	Thick, laminated glass
Roof lantern	Optional vent	Wide kitchen extensions	Deeper kerb needed
Pyramid or dome	Sometimes	Small square openings	Less light per size

Callout 4

Kerbs, upstands and the watertight line

The most important part of a flat roof rooflight is the part you never see once it is finished. That part is the kerb: a short upstand built around the opening that the rooflight sits on. The kerb lifts the unit clear of the roof surface, and the covering climbs its sides to seal the junction.

What the kerb is for

Water on a flat roof moves slowly, and in heavy rain it can lie against anything that stands in its way. A rooflight fixed straight on to the flat surface would be sitting in a puddle. The kerb raises the frame above the water line, gives the roof covering a vertical face to turn up, and carries the insulation that stops the edge of the opening becoming a cold bridge. Kerbs are made from timber, from a purpose-made prefabricated kerb, or built into the structure as part of an extension roof. The height above the finished roof surface is set by the roof covering manufacturer's detail and the unit's own requirements, and we confirm it against your roof at the survey. A shortcut here is the usual reason a flat rooflight leaks later.

For the detail behind the kerb and why it matters, see our page on kerbs and upstands for flat rooflights.

Flashings and the roof covering

The roof covering is turned up the face of the kerb and finished beneath a cover flashing, or sealed into a trim, depending on the system. In a single-ply membrane roof the covering is bonded or welded to the kerb. On a GRP roof it is laminated into the kerb face. On felt or built-up roofs, upstand layers are lapped and sealed, and lead or aluminium flashings may protect the top edge. The covering has to be compatible with the roof beneath. A mismatch of materials is a common source of trouble. We look at the existing covering at the survey and choose a method that suits it.

Fall and drainage

A flat roof is not flat in the geometric sense. It is laid to a slight fall so water drains to an outlet or a gutter. A rooflight kerb interrupts that flow, and rain has to be led round it. Water can pond behind the upstand on the uphill side if the build-up is not set out well. We therefore check the fall and the position of the outlets when we plan the opening, and where the fall needs a small tapered section on the uphill side, we include it in the quote. The unit itself sits level on the kerb, so the question people often ask is whether the rooflight needs a fall of its own. Our page Does a Flat Rooflight Need a Fall? answers that directly.

Keeping it weatherproof

A tidy junction is a watertight junction. Sealed laps, no fixings through the upstand face below the cover flashing, and continuity of the membrane around the corners are the details we care about. Once finished, the rooflight, kerb and roof covering work as one system and carry a 10-year workmanship guarantee, in writing.

A rooflight is only as watertight as the junction that holds it, and the junction is built by hand.

Callout 5

What is in the roof, and what it means for the opening

Behind every flat rooflight is a roof build-up, and the build-up decides how the opening is framed, how thick the kerb has to be, and how the covering is finished. Flat roofs on Derby houses vary a lot, from older felt and bitumen on timber decks to newer single-ply membranes, GRP and metal coverings on recent extensions.

Warm roof and cold roof

In a warm roof, the insulation sits above the deck, and the structure stays on the warm side of it. In a cold roof, the insulation sits between the joists and a ventilated void is left above it. The difference matters because it changes how the kerb is built and where the vapour barrier goes. A rooflight in a warm roof sits on a kerb that is insulated all the way round. In a cold roof, the ventilation path has to be kept open around the opening so the roof timbers stay dry. We find out which you have by looking at the roof edge, the ceiling below and, where needed, a small inspection opening.

What we check on the roof before drawing the opening

Existing covering: felt, single-ply, GRP or metal, and its condition
Build-up type: warm roof or cold roof, and the insulation depth
Joists: direction, spacing and span, so trimming can be designed
Fall and outlets: where water goes, and where it will meet the kerb
Edges and parapets: access, upstand height and flashing detail

Joists and trimming

The opening cuts through roof joists, so the structure is trimmed around it. Short trimmer joists frame the opening and carry the loads of the cut joists on either side. The size and fixing of the trimmers depend on the opening width and the span of the joists. We measure these at the survey and design the framing so the rooflight does not weaken the roof.

Roof lights in an existing roof

People often ask whether a rooflight can go into a roof that is already finished. It can, and the work is more involved than the unit itself suggests, because the existing covering has to be cut, the new kerb tied in, and the covering made good so the old and new parts act as one surface. If the roof covering is near the end of its life, it can be more sensible to renew it around the new opening at the same time. Our our guide to cutting into a finished flat roof goes through that in detail.

Replacing an old unit

Plenty of Derby flat roofs already have a rooflight, often a dome or a polycarbonate sheet, installed some time ago. Where the old unit has cracked, yellowed or let water in, we can replace it. Replacing an old rooflight with a new one counts as controlled work, and Part L sets the new unit's target at 2.2 W/m²K. The replacement is often a chance to improve the unit at the same time, for example by fitting double glazed glass in place of a single skin, or an opening unit where a fixed one used to be.

Pitched roofs with a flat section

Some houses have a pitched main roof and a flat section over a rear kitchen, a bay or a porch. The flat section is where a flat roof rooflight belongs. The pitched part is the place for a roof window or a VELUX, which has its own page: see our roof windows service. A loft conversion or a pitched-roof bedroom is a different job from a flat roof extension, and a different kind of unit suits it.

Callout 6

The ceiling opening, Building Control and the paperwork

The last chapter is the one people forget until it matters. A flat roof rooflight has a ceiling opening inside the room, the paperwork that makes the job legal, and a handful of questions about access and safety. Good planning on each means nothing needs to be sorted out after the scaffolding has gone.

Finishing the ceiling opening

The light well is boarded, plastered or lined, then painted. Where the ceiling is lower, the opening is often splayed so the light spreads across the room, while a deeper well may be kept square. A plasterboard finish gives a clean line that can be painted to match the room. If the rooflight has a blind or an electric motor, the cable run and any switch position are decided during the survey so wiring is tidy and not an afterthought.

Building Regulations and Building Control

Cutting a new opening that changes the roof structure counts as building work, so approval comes from the local authority or a registered building control approver. In the city that means Derby City Council, or an approver you appoint. When the job is notifiable, we send the Building Control notification ourselves, and the fitting follows current Building Regulations. A straight swap of one unit for another is controlled fitting, which brings Part L into play, and a competent person scheme can self-certify it.

What pushes a flat rooflight quote up or down

Size of the openingWider spans need stronger trimmers and a bigger unit.
Type of unitOpening, electric and walk-on units cost more than fixed glass.
Glazing and frameTriple glazing, coatings and aluminium frames add to the specification.
Roof coveringA covering that is hard to tie into needs extra detailing or renewal.
Access and heightScaffold, edge protection and crane or hoist needs vary by site.
Inside finishA deep splayed light well takes longer than a flush opening.

Planning permission

For a house, permitted development normally covers a rooflight, with conditions attached. We link those instead of repeating them, so you always see the current text. Our planning guide covers what applies. A flat or maisonette sits outside householder permitted development, so a rooflight there usually needs planning permission first. If the house is listed, almost any change to the roof goes to the council for consent first. Conservation areas can have permitted development withdrawn through an Article 4 direction, which the council can confirm before you order anything. The government's Planning Portal has the national guidance.

Safety on and around the roof

A flat rooflight can look like a solid part of the roof but must not be treated as a walking surface unless it is a walk-on unit. Fall protection matters in any roof access, so edge protection and safe working are part of the plan. If the roof will be used for maintenance, for example to reach solar panels or to clear a gutter, tell us at the survey. A fragile unit in a path that people use is a risk. We can choose a unit with an appropriate load rating or fit protection around it.

What affects the cost

Because every roof differs, we give a fixed written quote after the free survey. The cost module below lists what moves it. The figure on the quote is the figure you sign.

Areas we cover

We fit flat roof rooflights in Derby and about 30 road miles around it, counted along the road. Within that circle sit Belper, Ilkeston, Long Eaton, Burton upon Trent, Ashbourne and the villages between. If your house is near the edge of that radius, ask and we will check by road distance. Homes come first, and a small commercial roof is a fair brief. You can reach us on WhatsApp on 07880 284133, by email at info@skylarkskylightsderby.co.uk, or with the survey form.

Most of the care in a rooflight job goes into what you will never see again once the ceiling is painted.

Flat rooflight questions from Derby homes

Can a flat roof rooflight be fitted to any flat roof?

Most flat roofs can take one, but it depends on the structure and the covering. We check the joists, the build-up and the condition of the roof at the free survey. Where the roof covering is worn, it can make sense to renew it around the opening. The quote then covers the whole job, in writing, before any work begins.

How long does a flat rooflight take to fit?

A straightforward single rooflight usually takes a day or two on the roof. Inside, making good the ceiling and the light well takes longer, because plaster and paint need time to dry. A larger opening, a lantern or a roof that needs new covering takes longer, which the quote spells out.

Will a flat rooflight make my room too hot?

It can if the unit faces the sun and has no answer to it. A solar control coating on the glass, an opening unit to let warm air out, and a blind all help. We choose the combination at the survey, based on which way the roof faces and how you use the room.

Is a flat rooflight classed as building work?

If the opening alters the roof structure, yes, and approval comes through the local authority or a registered building control approver. Fitting a like unit in place of an old one is controlled work under Part L. We send the notification whenever the job needs one.

What is the difference between a rooflight and a roof window?

In everyday talk the words overlap. For the energy rules, a roof window gets the window figure (1.4 W/m²K at most, or band B on the Window Energy Rating scale) and a rooflight or lantern is held to 2.2 W/m²K. We confirm which applies when we specify the job.

Can I walk on a flat roof rooflight?

Only if it is a walk-on unit, built with laminated glass and a rated frame. An ordinary rooflight is not designed to take a person's weight, and standing on one is dangerous. If you need a surface to cross or stand on, ask for the walk-on option at the survey.

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Where do you want the light? Tell us in the form: the worktop, the stair, the desk.

No obligation. We survey before we price.
We cover Derby and 30 miles around.