Where to Put a Skylight: Start From the Spot You Use

Stand in the room on a grey afternoon and ask where it feels darkest while you are doing something. A kitchen is rarely dark in the middle of the floor. It is dark at the worktop, where you are chopping with your own shadow across the board. A landing is dark at the top of the stairs, where you pause with a basket of washing. A study is dark at the desk, because the window is behind you or beside you.

Write those places down. Two or three is plenty. Each one is a candidate for its own daylight, and each one points at a different part of the roof.

A rooflight set over the middle of a room often lights the floor and leaves the working places in shade. A rooflight set a little to one side, so the light falls across the worktop or onto the desk, does more with the same size of opening. That is why a survey starts in the room with a tape and not on the roof with a ladder.

Mark it on the floor

The simplest test is also the cheapest. Put a piece of masking tape on the floor where you stand to cook, read or wash. Look straight up from that tape. Whatever is above it, a plasterboard ceiling, a sloping rafter, a loft void, is where the opening has to connect with. Then picture the daylight coming down in a slanted shaft rather than a straight tube, because the sun is rarely overhead in Derby. We come back to that angle in the chapter on pitch and direction.

Some rooms forgive a loose position. Others punish it. These are the ones where a few hundred millimetres decide whether the daylight is useful.

Kitchens and kitchen extensions

The worktop and the hob are the places that need light, and they usually sit against a wall. A rooflight placed over the island may be glamorous but leave the sink in shade. On a flat-roofed extension, a roof lantern can sit above the dining table with a smaller rooflight covering the worktop. If the room is open plan, think about the table and the worktop as two separate places with two separate answers.

Landings and hallways

A stairwell is often the darkest part of a house because it has no outside wall of its own. A rooflight directly above the stair, or above the landing, lights the treads from above and helps the whole upstairs feel less shut in. Where the loft is in the way, a sun tunnel can carry daylight down through a small ceiling circle without any structural change to the roof beam above. Our guide to sun tunnels for hallways and landings covers that case.

Bathrooms and en-suites

The basin and the mirror are the places to light, not the bath. A rooflight over the bath looks good but leaves the face in shadow when you shave or put on make-up. Place it so the light falls toward the mirror, and choose obscured or tinted glass if neighbours overlook the roof. Bathrooms also benefit from a unit that opens, because steam has somewhere to go.

Loft rooms and bedrooms

The bed, the dressing area and the desk need different things. A bed wants gentle morning light that does not hit the pillow. A desk wants steady light from the side. Roof windows in a sloping ceiling should sit at a height where you can see out when seated or standing, which depends on the pitch. The roof windows page goes through the options in more detail.

Studies and utility rooms

A desk in a room with one small window is the classic case for a rooflight. Place the unit so the daylight comes from the left or right of the screen, not from behind it, and glare stays low.

The best spot on the floor does not always have a convenient roof above it. Between the room and the sky sit a ceiling, perhaps a loft void, and a roof made of timbers that carry the weight of the tiles. Any of these can move the opening a little, and sometimes they decide it outright.

Rafters and trimming

Pitched roofs are built from rafters laid at regular spacing. A roof window is made to fit between two rafters, or a pair of them, and where it is wider than the gap the rafters on either side of the opening are cut and the load is carried round the opening by a trimmer timber above and below. That is normal work, and it is why the width of an opening is linked to the rafter spacing. A unit that fits the gap exactly is simpler to install than one that does not, which is one reason standard sizes exist. The VELUX size codes guide explains how the codes map to widths and heights.

Purlins, ridge and chimneys

Purlins are the horizontal timbers that support rafters mid-slope in many older roofs. An opening that hits a purlin may be shifted a few hundred millimetres up or down, or the purlin may be supported differently by a structural engineer. A chimney stack, a valley or a hip can also move the opening. None of these usually makes a rooflight impossible. They make the first position on the plan the thing you adjust, and the surveyor will tell you which direction is simplest.

Flat roofs and joists

On a flat roof the joists run in one direction, and the opening is shaped by where they lie. An opening that runs along the joists is easier than one that cuts across them. A flat rooflight sits on an upstand or kerb, built so water drains away from it. Our guide to flat rooflight kerbs and upstands covers the detail.

The ceiling opening

Inside, the daylight has to get from the roof to the room. In a loft conversion or a sloping ceiling that is a short splay. In a house with an unused loft above, the light well between the roof and the ceiling is lined, insulated and finished, and it is wider at the bottom than the top to spread daylight. The angle of that well matters as much as the size of the glass.

Where a rooflight sits on the roof changes the kind of light it gives. Three things matter. How steep the roof is, which way the slope faces, and how high up the slope the unit sits.

Steep and shallow pitches

On a steep slope, such as a Victorian terrace or a converted attic, a roof window is almost vertical when seen from inside. It looks out and across, more like a wall window. On a shallow slope, such as a post-war semi or a low dormer, the same unit looks nearly upwards, and the light goes deeper into the room. A shallow roof also tends to carry more direct sun through the glass on summer middays, so shading and glazing choice deserve a thought.

North, south, east and west

A north-facing slope gives even, cool light all day and little glare, which suits a desk or a studio. A south-facing slope gives more light and more warmth, which is lovely in winter and sometimes too much in July. East gives morning light and west gives evening light. If you cannot decide, ask which part of the day you actually use the room. A kitchen used at breakfast suits an east-facing rooflight. A sitting room used in the evening suits one that faces west.

Heat gain is real, and glazing and blinds can manage it. The energy efficient rooflights page explains how the glass specification changes how much warmth comes through, and the answer on heat loss covers the winter side.

High or low on the slope

Higher on the roof, a unit lets light travel deeper into the room, and the view tends toward sky. Lower down, it gives a view out and a flatter angle of light. For a standing view from inside, the bottom edge of a roof window is commonly set to suit the person who will use it, and the surveyor will mark that height with you, not for you.

A few rules affect position, and they are worth checking before you fall for a plan.

Building Regulations

Cutting a new opening changes the roof structure, so it counts as building work and needs approval from the local authority or a registered building control approver. The notification is ours to make whenever the job requires one. Swapping an old unit for a new one of the same kind still falls under Part L, which holds roof windows to a tighter energy limit than rooflights. The figures are published on gov.uk.

Nothing in the Building Regulations demands daylight in an English house, so no room is ever required to have a rooflight. The decision is yours, and it is about how the room feels and works.

Escape windows

A loft bedroom raises fire escape questions. Under Approved Document B, a roof window qualifies as an escape route only if the room is no more than 4.5 m off the ground. On a two-storey house the loft cannot rely on a roof window for escape and needs a protected stair, whereas a bungalow or chalet bungalow with rooms in the roof can rely on one within that height. The clear opening must reach 0.33 m² and no side may measure under 450 mm, which ties position to size, and the bottom edge has to be reachable.

Planning

Planning is a separate hurdle. Ordinary houses are generally covered by permitted development rights with strings attached, while flats, listed buildings and conservation areas are handled differently, as set out in our planning guide. The position on the roof can matter for those conditions, particularly on a side-facing slope.

The free survey is where the floor tape meets the roof. Pricing waits until someone has looked at the spot, the room around it and the roof above. You show us where you stand, we look up, then we go into the loft or onto the roof and check what is there.

We measure the rafter spacing and note the roof covering, because a slate roof, a plain clay tile roof and a profiled concrete tile roof are flashed differently. We check the pitch, the aspect and anything that might move the opening. We look at the ceiling and the light well that would carry the daylight down. Should the address sit in a conservation area, be a flat or be listed, we say so early, so the plan does not run into a rule later.

A fixed written quote follows, and the figure holds when the day comes. If the plan needs adjusting because of what the roof turned out to hold, the adjustment is made on paper before it is agreed, not on the roof afterwards.

Derby houses and where they point

Derby has Victorian and Edwardian terraces near the centre, interwar and post-war semis in the suburbs, and newer estates on the edges. The roofs differ, and so do the answers. A terrace with a rear slope often takes a roof window above a stair or a back bedroom. A semi with a good loft may suit a sun tunnel or a roof window over the landing. A newer house with a flat extension is often the best case for a lantern or a flat rooflight over the dining table. Where the house lies inside the Derwent Valley Mills World Heritage Site, or in a conservation area, check with the council before settling on a plan. Our guide to conservation areas and rooflights in Derby goes further.

If you already know the spot

To start, describe the room and the spot in the survey form, or write to us on WhatsApp, 07880 284133. A photo of the room and a note of where you stand is plenty to start. Whether a particular roof can take a unit at all is dealt with in a separate piece, which roofs can take a unit.