An internal bathroom is the room a sun tunnel was invented for. It has no external wall, it is used every day, it is the room people most dislike having no daylight in, and the privacy problem that complicates a window does not arise overhead.
Why it suits this room particularly
Four things line up, and they rarely all line up anywhere else.
- No external wall. There is no window option, so the alternative is permanent artificial light.
- Privacy is automatic. Nothing overlooks a ceiling diffuser, so no obscured glass, no blind, no compromise.
- Small room. A modest tunnel lights a bathroom properly, where it would only glow in a large space.
- Daily use. The benefit is felt every morning rather than occasionally.
What it does to the room
More than the light level suggests, and people describe it consistently.
A windowless bathroom under artificial light reads as an interior space at any hour. The same room with a tunnel reads as connected to outside: you can tell it is morning, you can tell it is raining, and the light changes through the day.
People report leaving the light switch alone for most of the year, which is a saving and is not the point. The point is that the room stops feeling like a cupboard.
Privacy, which is the whole advantage
Worth being explicit because it is the reason this beats a window even where a window is possible.
A bathroom window needs obscured glass, or a blind, or both, and every one of those costs light and needs attention. A ceiling diffuser needs none, because there is nothing above it that can see in.
The exception is a property overlooked from higher ground, and even then a diffuser is not transparent: it is a translucent panel spreading light, not a view. Nobody sees into a bathroom through a sun tunnel.
Ventilated versions
The variant specific to this room and worth knowing about.
Some sun tunnel systems offer a version incorporating a ventilation path alongside the light tube, or a diffuser that accommodates an extract point. It uses one ceiling opening and one roof penetration for two purposes.
Where it works, it is neat: a single tidy circle in the ceiling doing the job of a rooflight and a fan. Where it does not is where the extract requirement is more than the system provides, in which case the two are separated.
It is worth asking about rather than assuming a tunnel and an extract have to be separate items.
A tunnel does not ventilate
The point to be clear about, because the two get conflated.
A standard sun tunnel is a sealed light pipe. It admits daylight and no air. It does nothing for humidity, nothing for extract, and nothing for the requirement a bathroom has under the Building Regulations.
Which means the extract fan is still needed, unless a ventilated system genuinely satisfies it. A tunnel that made the room bright and left it steamy has solved one problem.
Humidity, and why the tube cares
The technical consideration specific to this room.
A bathroom generates a great deal of water vapour in short bursts. The tube passes through a cold roof space, and the diffuser at the ceiling is a surface between a very humid room and a cold pipe.
Which makes a bathroom the worst case for condensation inside a tunnel, and it is why the sealing and insulation of the run matter more here than anywhere. That has its own page and it applies with particular force to this installation.
Sealing at the ceiling
The detail that decides whether it works, and it is easy to skip.
The diffuser is a penetration through the ceiling of a very humid room into a roof space. Unsealed, it is a route for that humid air to pour into the roof, where it condenses on cold surfaces and wets insulation and timber.
Sealed properly, the tube is a closed pipe and the humid air stays in the room where the extract can deal with it.
It is the same principle as sealing a downlight or a loft hatch in a bathroom ceiling, and it matters for the same reason.
Electrical zones
A consideration where a light kit is being added, and it is worth naming.
Bathrooms are divided into zones for electrical purposes, and what may be installed in each is defined. A light fitting within a zone has to be suitable for that zone and rated accordingly.
A sun tunnel diffuser with an integrated light kit is a light fitting in a bathroom ceiling, so the same rules apply as to any other. Which zone a ceiling position falls into depends on its distance from the bath or shower.
The electrician doing the work establishes that. What matters at specification is choosing a light kit with an appropriate rating rather than a general purpose one.
Where the diffuser goes
Position matters more in a small room than in a large one.
Centrally is the default and it is not always right. Over the shower, light falls where somebody is standing and the diffuser is in the wettest zone. Over the basin, it lights the mirror and the person using it, which is where light is most wanted.
In a small bathroom the difference between those positions is a metre and it changes how the room works. It is worth deciding rather than defaulting.
Steam on the diffuser
An honest characteristic worth mentioning.
A diffuser in a steamy bathroom will mist over during a shower, like every other surface in the room, and clear as the room does. That is not a fault and it is not condensation inside the tube.
Where it does not clear, or where marks build up on the room side, that points at the extract rather than the tunnel. A room that stays humid for an hour after a shower is a room that needs its ventilation looking at.
Cleaning it
Straightforward and worth knowing.
The room side of the diffuser is reachable and cleans like any light fitting, and in a bathroom it needs it a little more often because of the humidity and whatever gets sprayed about.
The inside of the tube is sealed and does not need cleaning, which is one of the advantages of the product. The dome on the roof needs an occasional clear of leaves and, on this coast, salt film.
The loft bathroom case
A different situation worth separating, because it comes up constantly here.
Where a bathroom is in a converted loft, there is usually roof directly above and no roof space at all. That is a rooflight situation rather than a tunnel one: a roof window in the slope gives light, view and ventilation together.
A tunnel belongs where there is a roof space between the room and the roof, which means a bathroom on a floor below the top one, or a bungalow.
The bungalow case
The most common sun tunnel installation we do, and the bathroom is usually the room.
Bungalow plans put bathrooms in the middle where there is no external wall, and a bungalow has a shallow roof space directly above with a short run to the roof. That is close to the ideal geometry for this product.
Short run, straight route, generous diameter, and a small room to light. It is why the results in a bungalow bathroom are frequently better than people expect, and it has its own page.
Where the room is on a middle floor
The harder case and it is worth being straight about.
A bathroom on a first floor of a two storey house, with a bedroom above it, has no route to the roof at all. A tunnel cannot pass through a habitable room.
Where a run can be found through a cupboard, a void or the corner of a room above, it may be possible and it is a considerable intervention. More often the honest answer is that a tunnel is not available in that position and the ventilation and lighting are dealt with conventionally.
What size
A bathroom is a small room, which is why this product suits it, and the diameter still matters.
A generous diameter on a short run delivers a genuinely well lit bathroom. A narrow one delivers a glow that makes the room feel better without lighting it.
Given that the run in a bungalow bathroom is short, the diameter is where the money should go, and going up a size is usually the best value decision on the job. Selection has its own page.
Light kits
Worth considering here more than in most rooms.
A bathroom is used before dawn and after dark for a good part of the year, so a tunnel alone leaves the room needing its normal lighting anyway. A light kit in the diffuser means one fitting serves both, and the ceiling has one circle in it rather than two.
In a small bathroom, where ceiling space is limited and everything is visible, that tidiness is worth something. Light kits have their own page.
Comparing it with the alternatives
| Sun tunnel | Roof window | Artificial only | |
|---|---|---|---|
| Needs | A roof space above | Roof directly above | Nothing |
| Daylight | Yes | Yes, more | None |
| Ventilates | No, unless a ventilated system | Yes, if it opens | No |
| Privacy | Complete | Complete overhead | Complete |
| Ceiling intrusion | One small circle | A full opening and reveal | A fitting |
| Disruption | Modest | Structural | None |
The middle column wins where the room is directly under a roof. The first wins where it is not, which in a bungalow bathroom is most of the time.
What it will not do
Three things, so expectations are right.
It will not ventilate, unless a ventilated system is specified. It will not give a view, because a diffuser is translucent rather than transparent. And it will not light the room at night without a light kit.
What it does is put daylight into a room that had none, every day, with no privacy compromise. That is a narrow benefit and it is a real one.
Building Regulations
Forming an opening in a roof is notifiable, and a bathroom brings the ventilation requirement alongside it.
Where we are notifying Building Control we will say what the ventilation provision has to be, because the tunnel does not satisfy it and the room needs extract regardless. The completion certificate comes to you.
What we check on a sun tunnel
We check whether there is a roof space and a workable route before anything else, because that decides whether this is a tunnel job at all. We seal the diffuser to the ceiling properly, because a bathroom is the worst case for humidity in a roof, and we say plainly that the tunnel does not replace the extract fan.
An internal bathroom is the room this product exists for. Sealed at the ceiling and ventilated properly, it is one of the most satisfying things we fit.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.