Sun tunnel or rooflight for a dark room

A sun tunnel collects light on a small dome on the roof and carries it down a reflective tube to a diffuser in the ceiling. A rooflight is a glazed unit set into the roof itself, directly over the room it serves. The first moves light along a pipe. The second removes the roof from the equation.

That difference explains nearly everything else in this guide. A tunnel is narrow, so it gives a pool of light about the size of a ceiling light fitting, brighter than you would guess from its size but confined. A rooflight is as large as you choose to make it, so it gives a room a whole patch of daylight with direction and depth, and you can see sky through it if the room sits directly under the roof slope.

Both suit the case where the wall beside the room is shared, buried or overlooked and a window is not an option. Neither needs planning drama in the ordinary case, though we check the address before we promise anything. The plain mechanics of the tunnel are in our guide to how a sun tunnel brings daylight into a dark room, and the tunnel service as a whole is on the sun tunnel installation page.

Three facts about the room decide the matter before any product is named. Ask them in this order.

1. Is there a roof directly above the room, or is there another room, a loft floor or a long roof void in the way?
2. Does the room need a spot of light or a proper daylight source, somewhere you read, cook, dress or work?
3. Will the room be used in the evening and at night more than at midday?

If another storey sits over the room, a rooflight cannot reach it, and a tunnel has to pass through the floor above, which is sometimes possible and sometimes not. Our answer on whether a sun tunnel can pass through an upstairs room covers that case. If the room is directly under the roof, as in a loft conversion or a single-storey extension, the rooflight is open to you and usually wins on quality of light.

If the room only needs to stop being a cave, a bathroom with no window, a hall that swallows the light from the front door, a landing at the heart of the house, then a tunnel is usually the proportionate answer. It is a smaller hole, a quicker job and a lighter touch on the ceiling and the roof.

The plain difference in light is size. A tunnel dome is typically a few hundred millimetres across, and the tube narrows what arrives. A rooflight can be a metre or more on a side, and the light comes in unrestricted by a pipe.

A tunnel gives a soft, even glow from one point. It is ideal where the job is to lift a space from gloomy to bright, because the diffuser spreads what arrives without glare. The tube also works against height: light has to bounce down its length, and every metre of tube and every bend takes a little away. Long, straight runs do better than short, twisted ones. We go through that trade in tunnel length, bends and how much light arrives.

A rooflight shares more of the sky. It lights a larger area, it moves across the floor through the day as the sun travels, and it shows you the weather, which for plenty of people is the real appeal. The room gets daylight that feels like daylight, with a direction to it, where a tunnel gives a lamp that happens to be solar.

On a grey Sussex afternoon both collect less, because both depend on the same sky. A rooflight is bigger, so it gathers more of a dull day, but a tunnel still brightens a room on overcast days more than people expect. Our answer on whether sun tunnels work on cloudy days is the plain account of what to expect.

This table sets the two against the points people ask about most. Each row is a general comparison, and your own roof and room will shift it.

The table has no overall winner, and that is the point. A tunnel leans towards the small, awkward, buried room. A rooflight leans towards the room that will be lived in for hours.

Every hole in a roof is a thermal event. The question is how big the hole is and how well it is built, since the glass and the tube are both weaker than an insulated roof.

A tunnel is a small opening, and its dome is usually double layered. The tube passes through the loft insulation, which is the detail that decides how much heat you lose in winter. A well-built tunnel is wrapped or boxed so that the loft insulation stays continuous around it. A poorly wrapped one leaves a cold column in the ceiling, which is where condensation starts. We have written separately about sun tunnels, loft insulation and heat loss and preventing condensation in a sun tunnel, and both are worth reading before you commit.

A rooflight is a larger area of glazing, so the specification matters more. Modern double or triple glazed units with a low emissivity coating, warm edge spacers and an insulated frame keep winter loss low, and the same coating helps to hold back summer sun. Energy performance for rooflights is set by Building Regulations Part L, and our page on energy efficient rooflights explains what a good specification looks like.

In summer the picture reverses. A south-facing rooflight of generous size can overheat a room if nothing is done about it. Solar control glass, an external blind or an internal blind brings that back under control. A tunnel admits far less heat because its opening is small and the tube attenuates some of it on the way down, which is why people ask about it. Our answer on whether sun tunnels make a room hot in summer goes through it. A tunnel rarely causes a heat problem, and a rooflight can, but the fix is a specification choice that we make with you at the survey rather than a reason to avoid the rooflight.

Disruption is where the tunnel earns its reputation. The work is a small hole in the roof covering, a flashing set into the tiles or slates, a length of tube through the loft and a neat cut in the ceiling. It is measured in hours rather than days in the ordinary case. Our note on how long it takes to fit a sun tunnel sets that out.

A rooflight asks for more. The opening in the roof is bigger, so rafters or joists are cut and trimmed. Inside, a pitched roof needs a lined reveal or a short light shaft to carry the opening from the roof plane down to the ceiling. The plaster finish around that reveal is the job that takes the time, because it has to dry and then be painted. On a flat roof the work is a kerb, a membrane dressed up to it and a ceiling opening beneath, which is a different sort of job again. Both are covered in our pages on roof window installation and flat roof rooflight installation.

Think about the room too. A rooflight sends dust into the space below during the cut, so anything you care about in that room is best moved out first. A tunnel confines the mess to the ceiling and the loft. If a bathroom or a nursery has to stay in use, that can decide the matter alone.

The roof covering matters for both. A plain concrete tile roof takes either without fuss. Natural slate or old clay tile takes more care, and the tunnel flashing has to be matched to the covering, as our guide to fitting a sun tunnel through a tiled or slate roof explains.

A tunnel is sealed. It brings in light and nothing else, so it does not ventilate the room. A rooflight can be fixed or opening, and an opening model is a real source of fresh air and a way to clear heat from the top of the house on a warm evening.

That matters most in two rooms. In a bathroom with no window, the extract fan is what actually controls moisture, and Building Regulations Part F sets the extract rates for that. A tunnel can sit alongside a fan without trouble, but it cannot take its place. We cover the details of that arrangement in our answer on fitting a sun tunnel in a bathroom with an extractor fan. In a loft bedroom, a rooflight that opens gives you a way to let hot air out that a tunnel cannot. Where you want that opening by remote, electric and opening rooflights are built for it.

A fixed rooflight is also a fair option. A dark room often needs light and nothing more, and a fixed unit is simpler and usually better sealed than an opening one. Choose opening where the room will genuinely benefit from air.

Our work is built around the idea that a hole in the roof can let in more than light. Both options change how the room sounds, in different ways.

A tunnel dome is a thin shell and the tube runs through a roof space that may already be noisy. Rain on the dome can be heard in the room below, and so can rooftop activity and aircraft. A thicker outer dome, a solid tube and a properly fitted diffuser all reduce it. We explain the choices in rain on the dome: keeping a sun tunnel quiet.

A rooflight puts a pane of glass into the roof, and the glazing build decides what you hear. A laminated acoustic inner pane, a thicker outer pane, a sensible cavity and well-seated seals make a large difference over a plain unit. The upstand and kerb on a flat roof matter too. Where the room is a bedroom or an office, that specification is where the decision is made, and we write it into the quiet spec that comes with every quote.

Neither needs to be loud. A tunnel in a hallway is rarely an acoustic question. A large rooflight over a bedroom beneath a flight path, or a lantern over a kitchen, is exactly where sound needs thinking about before anything is ordered.

Rooms fall into rough groups, and each group tends to point one way.

A windowless bathroom, a cloakroom or a utility room suits a tunnel. The room is small, used briefly and wants light without building work. A hallway or landing in the middle of the house suits a tunnel for the same reasons, with the added point that a long hall can take two. Our pages on sun tunnels for windowless bathrooms and sun tunnels for hallways and landings go into each.

A kitchen is more mixed. A small galley kitchen with a room above it may only be reachable by tunnel. A kitchen in a single-storey extension or a bungalow usually suits a rooflight or lantern, because the ceiling is directly under the roof and the room will be used for hours at a stretch. If the choice is a flat rooflight against a lantern, the roof lantern installation page explains the difference.

A loft bedroom, a home office or a studio is nearly always a rooflight or roof window case. The room is under the slope, it will be occupied for a long time and it benefits from a window you can open. A tunnel cannot do that job well.

A room in the middle of the house with floors above it is the real tunnel territory, provided the route through the upstairs can be made to work. Where it cannot, the answer may be better electric lighting and a lighter ceiling colour.

A tunnel usually costs less to install than a rooflight for a comparable room, since it is a smaller product and a shorter job. A large opening rooflight with a shaft, a finish and possibly some structural work costs more, and so does a lantern. The cost is driven by the roof type, the depth of the ceiling to be lined, the size of the opening and the glazing specification more than by the product name. Our costs page explains the drivers as a guide, and we put the actual figure in writing after a survey.

Value is a different question from cost. A tunnel that lifts a dead hallway is often very good value. A rooflight over a room you live in for years pays back in how the room feels every day. If you are unsure that a tunnel is worth it in your house, our answer to are sun tunnels worth it helps you weigh it.

Some rules apply to both options. They are the ordinary Building Regulations that any roof opening meets, rather than anything unusual.

Part L controls the thermal performance of new and replacement glazing and, for new extensions, the proportion of glazing overall. Part F covers ventilation, which is the reason a windowless bathroom keeps its fan. Part K applies to glass that people could fall against or through, and overhead glazing over a place where people stand is usually laminated as good practice. Part B matters where a tube or a rooflight passes through a fire separation in the loft, as our answer on whether a sun tunnel affects fire safety in a loft explains. We install to current Building Regulations, and we handle the Building Control notification where the work is notifiable.

Planning is seldom an issue for a roof opening on a house in its own right, but a conservation area, a listed building or a flat can change that, so we check the position for your address before the work is booked.

The choice is not always either or. Houses with a dark core and a bright loft often end up with both. A rooflight or roof window lights the bedroom under the slope, and a tunnel lights the landing below it. The two do different jobs, and together they lift the whole stairwell.

A room that is partly under the roof and partly not is the other case. A long hall that begins under the eaves and runs back into the middle of the house may take a rooflight at one end and a tunnel at the other. A survey shows what the route allows.

These are the questions that come up most when a homeowner is weighing the two. Each turns on your own roof, and the reasoning holds everywhere.

Is a light tube or skylight better for a bathroom?

For a bathroom with a room above it, a tunnel is usually the practical choice. For a bathroom at the top of the house, directly under the roof, a rooflight that opens can do more, because it lights the room and clears steam. The extract fan stays either way.

Can a sun tunnel replace a window?

It can give a room daylight where no window is possible, but it gives no view and no fresh air. If the room needs either, a rooflight fits better.

Will a tunnel be bright enough for a kitchen?

It can lift a small kitchen, and it is less suited to a large working kitchen where the task areas need strong light. Our pages on whether a sun tunnel can light a kitchen and how much light a sun tunnel gives set out what to expect.

Which is quieter in heavy rain?

Neither has to be noisy. Either can be, if the specification is thin. The quiet comes from the glazing or dome build, the seals and the upstand, all of which are chosen for the room and written into the quiet spec.

If you have a room in mind, get a quote. We will look at the roof, the route and the room, then tell you in writing whether a tunnel or a rooflight is the better answer, and what the quiet spec for it would be.