Skylight Ideas for Extensions

Chapter 1

Start from the shape of the extension

The best extension skylight ideas come from the plan, not the product brochure. Work out where the new room will be darkest and what happens in that spot, and the right rooflight, its size and its position tend to follow.

Three extension shapes come up again and again on Cambridge houses. The side return fills the narrow alley beside the back addition of a Victorian or Edwardian terrace, the sort of house that lines the streets off Mill Road, through Romsey and Petersfield and into Chesterton. The single-storey rear extension pushes the back wall of a semi or detached house out into the garden, common on the 1930s semis of Cherry Hinton and Arbury and on village houses in Histon or Great Shelford. The wraparound does both at once, filling the side return and running across the back to make an L-shaped room.

Each shape has its own dark zone, and each dark zone suggests a different pattern of roof glazing. A side return is long and narrow with one tall wall beside it. A rear extension is deep, with good light at the garden doors and very little at the old back wall. A wraparound has an inside corner that neither the side glazing nor the rear doors can reach. The ideas below are grouped by shape so you can go straight to yours, and each one comes with a plain description of the light it gives through a Cambridge year.

A word on names. The trade tends to say rooflight while search boxes tend to say skylight; on this page the two mean the same thing, a glazed opening in the roof. A roof lantern is the raised, pitched version that sits on an upstand, and a roof window is the opening unit that sits in a sloping roof. For the wider picture of how we plan and fit any of them, start on the skylight and rooflight installation page.

Chapter 2

Side-return extensions: lighting a long, narrow room

A side return turns a dark alley into part of the kitchen, but it also puts a roof where the sky used to be. The ideas that work here run with the length of the room rather than across it.

The glazed strip. A long, slim rooflight running most of the length of the extension, set against one of its two walls, is the classic side-return idea. Light comes down in a narrow band and lands on the wall below it, and a lit wall behaves like a large, soft lamp for the rest of the room. Where the strip sits beside the old house's flank wall, it lights the brickwork you have kept, and exposed gault brick looks good under daylight. Where it runs along the boundary side, it lights the new wall and keeps the glass away from windows on your own house. On the boundary side, the fire rules for roofs close to a boundary or party wall come into play, and the answer depends on the wall and the product; our guide to Building Regulations for rooflights explains why that zone matters.

A lean-to slope with roof windows. Many side returns have a single sloping roof falling from the house towards the boundary. Two or three roof windows set in that slope give more view of the sky than flat glazing of the same size, because a sloping pane faces part of the sky rather than straight up. If the slope faces south or west they bring direct sun onto the worktop, which is welcome in March and hard work in July, so the glass and blinds need thought. A pitched slope also sheds rain quickly, and roof windows open for ventilation, which suits a kitchen. Our roof window installation page covers the product side.

A row of flat rooflights. Where the side return has a flat roof, a line of two to four square or rectangular flat rooflights spaced along its length gives more even light than one long strip, with solid roof between for downlights, extract ducting and a cooker hood. The trade-off is visual: a run of separate openings reads as a pattern on the ceiling, while a single strip reads as one clean line.

The neighbour's side matters in all three. The back addition next door is often two storeys high and may have windows looking across your roof, so glass on the boundary side can be seen from upstairs. Our guide to rooflight privacy and overlooking deals with that directly.

Chapter 3

Single-storey rear extensions: the dark join with the old house

In a rear extension the garden doors do their job, and the gloom collects where the new room meets the old back wall. The roof glazing should go there first.

The junction slot. A strip of glazing running the full width of the extension, tight against the old house wall, is one of the strongest ideas for a deep rear extension. It puts daylight exactly where the plan is darkest, washes the old wall with light, and marks where old and new meet. It also sends light back into the room that used to have the garden window, which is often the one that suffers most once the extension is built.

A lantern over the table. A roof lantern centred over the dining table gives the room a focal point and a generous amount of sky. Its raised form catches light from several directions, and the upstand hides the flat roof build-up. The lantern works best when the table's position is fixed at design stage; move the table later and you are dining beside the sunlight rather than under it. Our page on roof lantern installation covers sizes, glazing bars and upstands.

A spine of flat rooflights. Two or three frameless flat rooflights in a line down the centre of the room light the floor evenly from front to back and leave clear roof for everything else the ceiling has to carry. Frameless units keep the view of the sky uninterrupted, which suits a minimal kitchen. More on the specification sits on our flat roof rooflight installation page.

These ideas combine well. A junction slot at the back and a lantern over the table in the middle, with the garden doors at the front, gives a deep extension three sources of daylight at three depths. The effect is a room where the light level stays steadier as you walk from the garden to the hall, instead of falling away.

Chapter 4

Wraparound extensions: the inside corner

A wraparound gives you an L-shaped room with light from the side and from the garden, and a stubborn dark zone where the two arms meet. That corner, and the old middle room behind it, are where the roof glazing earns its keep.

A corner lantern. Setting a roof lantern over the point where the side arm turns into the rear arm lights the part of the plan furthest from both the side glazing and the garden doors. Because this is often where the kitchen island or the table ends up, the lantern also gives the busiest part of the room its best light.

An L of glazing that follows the old walls. A slim rooflight that runs along the old back wall and then turns to follow the flank wall traces the outline of the original house. It lights both old walls and pulls daylight into the middle room from two sides. This takes more careful structural planning, because the steels that carry the new roof usually run along exactly the same lines.

Separate lights for separate jobs. A wraparound often holds two or three activities: cooking in the side arm, eating and sitting in the rear arm. A roof window or flat rooflight over the worktop, and a larger unit over the sitting area, lets each part of the room get light suited to its use, with a different blind or glass choice for each if the orientation differs.

The pitfall here is too much glass in total. With side glazing, big garden doors and several rooflights, a wraparound can become bright, hot and glary in summer, especially where the rear faces south or west. It is worth adding up all the glazing, not just the roof glass, before settling the pattern.

Chapter 5

Pitched and vaulted extension roofs

Not every extension has a flat roof. A pitched roof with a vaulted ceiling changes the options, and roof windows set high in the slope can light a room in a way flat glazing cannot.

Roof windows placed high on a vaulted slope see a large area of sky and throw light deep into the room below. Placed lower, they give a view out to the garden or the trees, which some people value more than the extra light. A pair of windows either side of a vaulted ridge, one on each slope, lets morning and afternoon light into the room from opposite directions, which evens out the day.

On a garden room or a village cottage extension in a conservation area, flush-fitting roof windows keep the roof plane clean and are more likely to sit comfortably with the planning officer. Where the extension is visible from the street, the number, size and position of rooflights can matter as much as the extension itself, and our guide to planning permission for rooflights covers how the local councils handle this.

A centre-pivot roof window lets furniture sit close underneath and puts the handle at the top of the sash, which can suit a high vaulted ceiling where the window is out of reach anyway; top-hung windows give a clearer view when opened. For windows that are out of reach, an electric opener with a rain sensor removes the need for a pole. Our page on electric and opening rooflights covers the controls.

Chapter 6

Small rooms inside the extension

Extensions often create small internal rooms with no outside wall: a utility, a downstairs WC, a pantry or a boot room. These need a different idea from the main space.

A small opening flat rooflight over a utility room gives daylight and a way to let out steam from the washing machine and dryer. In a WC or shower room, it gives privacy from neighbours as long as nothing looks down on it. Where the small room sits under a pitched roof, a single small roof window does the same job.

Where the small room is some way from the roof, perhaps under a first-floor room that the extension has left in place, a sun tunnel can bring daylight down through a reflective tube. It gives a steady, even light rather than a view of the sky, which is exactly what a hallway, pantry or WC needs. Our page on sun tunnel installation explains diameters and routes.

Chapter 7

Testing each idea against the Cambridge sky

An idea that looks good on a plan has to work under a real sky. In Cambridge the midday sun stands at about 14 degrees above the horizon in late December, about 38 degrees at the equinoxes and about 61 degrees in late June, and every idea above behaves differently across that range.

That low winter angle matters most for side returns and wraparounds. At 14 degrees, a wall casts a shadow roughly four times its own height at noon. The two-storey back addition next door can therefore shade a long stretch of your roof for weeks around the shortest day, and a strip of glazing on that side will receive sky light but little or no direct winter sun. That is not a failure; it is steady, glare-free light. It just means the extension needs enough glass to feel bright on sky light alone.

In June, at 61 degrees, the same wall shades very little and the sun comes almost straight down through any flat rooflight. A glazed strip or lantern on a south or west-facing extension then puts a sharp pool of sunlight on the floor, worktop or table for much of the afternoon. Glass with solar control and a suitable blind can keep that manageable. Our guide on which way a skylight should face goes through each slope in detail.

Glare is the other test. A rooflight that throws sunlight across a television, a computer screen or someone's eyes at the table will annoy every day. Checking where the pool of sunlight falls at different times of day and year, and moving the opening or choosing a different blind, is far easier on paper than after the roof is built. That is the core of our light planning approach.

Chapter 8

Settling the idea before the build starts

The time to choose the pattern is at design stage, before the steels, joists and ceiling are fixed. Moving a rooflight later means changing structure that has already been built around it.

A glazed strip or junction slot needs the steel beam and the roof joists arranged to leave the opening clear. A lantern needs a trimmed opening and an upstand at the right height. A row of flat rooflights needs the joists spaced so the openings fall where the plan says. None of this is difficult when it is drawn in from the start. Our answer on when a skylight should be planned in an extension sets out the stages.

A few points to settle with your designer and builder early:

• Where the table, island, sofa and television will sit, so the rooflights can be placed to suit them.
• Which way each part of the roof faces, and what the neighbouring buildings will shade through the year.
• Whether any rooflight needs to open, for steam, summer ventilation or both, and how it will be reached.
• The total area of glazing across walls and roof, not just the roof lights on their own.
• Where downlights, extract ducts and speakers must go, so they do not end up competing with the glazing for ceiling space.

Rooflights in a new extension are normally covered by the extension's own Building Regulations application rather than a separate one, and where our work is notifiable we handle the Building Control notification. Planning depends on the extension and the house: many single-storey rear extensions fall within permitted development, while side returns on terraces and anything in a conservation area may need an application. When the idea is settled, book a light survey and we will confirm it on your roof and put it in a written light plan with the quote.

Chapter 9

Questions people ask

Is one large rooflight better than several small ones in an extension?

Neither is better in every case. One large unit or lantern gives a strong focal point and a big view of the sky, which suits a dining table or a corner. Several smaller rooflights spread the light more evenly along a long room and leave ceiling space for lighting and extraction. The shape of the extension and where the dark zone falls usually decide it.

Will a skylight in a side return get direct sun in winter?

Often very little. With the noon sun at about 14 degrees in December, a two-storey wall next door can shade a narrow side return for much of the winter. The rooflight will still bring in useful sky light, which is soft and glare-free, but the design should not rely on winter sunshine to make the room feel bright.

Can I add rooflights to an extension that is already built?

Yes, in many cases a flat rooflight or roof window can be added to an existing extension roof, as long as the joists, the roof covering and the ceiling allow it. The position is limited by the structure already there, so it pays to survey the roof and check the light before choosing the size.