Standing in a dim hallway or a windowless bathroom, the question is usually the same: what is the best way to get daylight in here? Two products answer it. A roof window is a proper glazed window set into the slope. A sun tunnel is a small dome and tube that pipes light down to a round diffuser. They are not rivals so much as tools for different rooms.
The deciding facts are mostly about the house rather than taste: what sits above the room, how much headroom there is, and whether you want a view and fresh air or simply light. Weigh those three and you will usually know which way to lean before anyone visits.
What each one actually is
A roof window is a glazed frame fitted into the pitch of the roof. It opens, it frames the sky, and it needs a room directly beneath the slope so the light has somewhere to land. How one is put in is described under roof window installation.
A sun tunnel has no view at all. The dome collects daylight, the mirror-lined tube carries it, and a frosted diffuser spreads it. Nothing opens and nothing is electrical. It is a way of getting light into a room that has no outside wall and no slope above it.
The test: what is above the room?
This single question settles most cases. If you can stand in the room and see the underside of the roof overhead, as in a loft bedroom or an attic bathroom, a roof window can go straight above you. If there is a ceiling, then a loft space, then the roof, a window has nowhere to be, because the opening would have to run through the loft as a shaft.
That is a rule of thumb, not a law. Some houses allow a light well, which is a lined shaft that widens towards the room, and a few lofts are converted so that a tunnel is not needed. The survey is where we find out.
Light, view and air
A roof window gives you more of everything a window gives: a brighter room, a view of sky and treetops, and fresh air when it is opened. A sun tunnel gives only daylight. It cannot be opened, and nobody will see through it, which is exactly right for a bathroom.
| Daylight | Window: generous. Tunnel: gentle and even |
|---|---|
| View | Window: sky and roofline. Tunnel: none |
| Ventilation | Window: opens. Tunnel: fixed |
| Roof cut-out | Window: rectangular, trimmed into the rafters. Tunnel: round and small |
| Room it suits | Window: under the slope. Tunnel: below a loft or ceiling void |
| Privacy | Window: blinds if needed. Tunnel: frosted by design |
Landings and hallways
An inner hallway or a stairs landing has no wall to put a window in, and in a terraced house it often has no slope directly overhead either. Here a tunnel is the natural choice. Because the diffuser is on the ceiling, the light falls down the stairwell, and the doors off the landing open on a brighter space.
The exception is a landing at the top of a loft conversion, where a roof window above the stairs can do the job and give a view as well. Our guide to sun tunnels for bathrooms and hallways goes further into those two rooms.
Bathrooms
For a bathroom the picture changes. In a loft conversion, a roof window over the bath or basin is a lovely thing, with the right glass and a blind for privacy. In a first-floor bathroom with a loft above it, a sun tunnel brings in light without worrying about neighbours or overlooking.
Whichever you choose, a bathroom makes moisture a point of attention. A window can be opened to clear steam, while a tunnel depends on a good extractor fan. Either way the fitting details matter, and we plan them at the survey.
The work involved
A sun tunnel is generally the smaller job. The cut in the slope is a circle, so only a small area of covering is lifted, and the structure is barely disturbed. The tube is run through the loft, and a diffuser goes in the ceiling.
A roof window needs a rectangular opening, with the rafters cut and a trimmer fixed on each side, plus a flashing and insulation collar. It takes longer, and it brings more dust to the room beneath, which is why we cover floors and furniture first. Where the room allows it, the extra work buys a lot more than light.
How different houses tend to answer it
Every house is its own case, but the shape of a home often points one way. Many Victorian and Edwardian terraces in York have a landing at the top of a narrow stair with a loft directly above it. That is classic sun tunnel territory. The back bedroom, if the loft has been converted, is classic roof window territory.
A 1930s semi often has a hipped roof, a loft that is open or boarded, and an inner landing between three doors. Again the tunnel suits the landing and a window suits any room made in the roof. A bungalow is different. With a single storey, the ceiling and the roof are close together, so a tunnel is short and efficient, and rooms that sit under the slope can take a window if the ceiling is raked.
Newer extensions with flat roofs invite a third option: a flat rooflight. When the room needs a large amount of light and a view of the sky, flat roof rooflights deserve a look beside the other two.
Heat, glare and blinds
A bigger window lets in more of everything, including summer sun. A room under a south-facing slope can warm up in the afternoon, and a roof window usually wants a blind. Most makers offer blinds made for their windows, and fitting one is a common extra at the time of installation.
A tunnel is gentler. Its light is spread and diffused, so there is little glare and no hot patch on the floor. That is part of why it works in a bathroom or a child's room where you do not want harsh light. If the room faces strong sun and you are weighing both, mention it at the survey.
Safety and escape
If the room is a bedroom, the rules about escape come into the question. A window used as a means of escape must be reachable and large enough, and it only counts for storeys within 4.5m of the ground. On a two-storey house, a loft bedroom is reached by a protected stair, because a roof window cannot be its way out. In a bungalow or chalet bungalow the rooms in the roof sit within that height, so a window can serve.
A sun tunnel is never an escape route, since it does not open. That is fine for a landing, bathroom or hallway, but it means a tunnel will not solve the problem if a loft bedroom needs a way out. We raise it at the survey whenever it applies.
Mistakes that make the choice harder
Three things go wrong often enough to be worth naming. The first is choosing a product from a picture, before anyone has looked in the loft. The second is expecting a tunnel to behave like a window, then being disappointed that there is no view. The third is fitting a window in a room whose ceiling is flat, so the light falls on a loft floor and not on the room.
All three disappear once the route is traced and the room is looked at from inside and above. It takes an hour at the survey and prevents a lot of regret.
- Check what is above the ceiling before choosing
- Decide whether you want a view, fresh air or just light
- Think about privacy and blinds in bedrooms and bathrooms
- Allow for the ceiling to be made good afterwards
Looks from outside
From the street a tunnel is a low dome, much smaller than a window and often hardly noticed. That suits a front slope, where you may want as little as possible to show. A roof window is a bigger feature on the roof, and a pair set in line can look very smart on a back slope, as many period terraces show.
If your house sits in a conservation area, tell us at the start. Rooflights on houses are usually permitted development, but an Article 4 direction can remove that on particular streets, and the council confirms. Our planning guide covers the conditions.
Insulation, glass and thermal performance
A window in the roof is glazing, and glazing loses heat faster than an insulated roof. That is why Building Regulations set standards for new and replacement units. For existing homes, Part L 2021 asks roof windows to reach a U-value of 1.4 W/m²K or Window Energy Rating Band B, and rooflights to reach 2.2 W/m²K. The glass we fit is chosen to meet those figures.
A tunnel has a smaller area of glass, a dome in place of a window, and a tube that is wrapped in the loft. The thermal question is therefore about sealing and insulating the run more than the glass itself. Both products are fitted so that they do not become the cold spot in the ceiling, and the details are given to you at handover.
A quick way to decide
If you are still unsure, run through these questions in order. The first clear answer usually settles it.
- Is there a loft or an attic floor between the ceiling and the roof? If yes, a tunnel is likely.
- Do you want to see the sky or open the glass? If yes, a window is the product.
- Is the room a bathroom, landing or hallway with no outside wall? A tunnel fits.
- Is the room in the roof itself, with a sloping ceiling? A window fits.
- Do you need a legal way out of a bedroom? Then a roof window may matter, and the storey decides.
If the answers pull in different directions, we look at the house together and find the compromise, whether that is one of each or a different product altogether.
When you want both
Plenty of houses end up with one of each. A loft conversion gets its roof windows, and the landing below gets a tunnel so the stairs are not dark. The two work side by side without competing, and fitting them in the same visit means one set of access, one plan for each day and one handover.
If you are weighing up what a tunnel will cost on its own, sun tunnel cost, fitted breaks down the price. If you are still deciding on the tube itself, rigid or flexible is next.
Booking a survey to settle it
Sometimes the only way to decide is to look. At the survey we go into the loft, check what sits above the room, and talk through the options with the real roof in front of us. If a window suits, we say so. If a tunnel does, we say that. There is no charge for the visit.
Everything from roof to ceiling is set out in sun tunnel installation, and the survey can be booked using the quote form that follows.