A sun tunnel is a reflective tube that carries daylight from a dome or flat glazing on your roof down through the loft and into a ceiling below, so you get natural light in a room that has no outside wall for a window. It works where a normal roof window or wall window cannot reach, such as a hallway, landing, bathroom or internal WC. VELUX makes them in two versions, rigid and flexible, and two common diameters, roughly 10 inch and 14 inch, with separate kits for tiled and slate roofs.
They are sometimes called a sun pipe, light tube or light pipe. The idea is simple. Light hits the clear dome or glass on the roof, travels down a highly reflective tube that loses very little of it along the way, then spreads into the room through a diffuser set into the ceiling. On a bright day the effect is closer to daylight than to a light fitting, and there is no running cost because nothing is switched on.
How a sun tunnel works
Every sun tunnel has three parts. On the roof sits the top unit, either a clear domed cap for a pitched roof or flat glazing for a flat roof, fitted into a flashing that weathers it into the covering. Inside the loft runs the tube, which is the part that actually moves the light. At the bottom is a diffuser, a translucent disc flush with the ceiling that softens and spreads the light so you do not see a hard beam.
Because the tube reflects light rather than relying on a straight line of sight, a sun tunnel can light a room two floors down from the roof. The shorter and straighter the run, the brighter the result, which is the first thing to think about when you choose between rigid and flexible.
Rigid vs flexible sun tunnel: which one
The choice comes down to what is in the way between your roof and the ceiling you want to light.
- Rigid sun tunnel. A solid, mirror-finish metal tube for a straight or near-straight run. It reflects the most light, so for the same diameter and a clear path a rigid tunnel gives you the brightest result. Rigid tube can also cover long drops, with runs from about 0.9 m up to 6 m using extension sections, which suits a light travelling a fair way down through the house.
- Flexible sun tunnel. A concertina tube that bends around obstructions such as rafters, purlins, pipework or a water tank. It comes in the 14 inch (350 mm) size. It is quicker to route through an awkward or cramped loft, but every bend costs a little light, so it is best kept short. VELUX recommends keeping a flexible run to around 1.5 m on a pitched roof.
In short, pick rigid when there is a clear line from roof to ceiling and you want maximum brightness, and pick flexible when the loft is tight or something sits in the path. If you are unsure what your roof void will allow, our counter staff have specified these across Sussex and Kent since 1996 and can talk it through with you.
Sun tunnel sizes: 10 inch or 14 inch
VELUX sun tunnels come in two diameters. The smaller is about 10 inch (250 mm, coded 0K10) and the larger is about 14 inch (350 mm, coded 0K14). The bigger the tube, the more light it collects and delivers, so size to the room rather than guessing.
| Diameter | Roughly suits | Typical rooms |
|---|---|---|
| 10 inch (250 mm) | Smaller spaces up to around 14 sq m | Hallways, landings, ensuites, WCs, utility rooms, walk-in wardrobes |
| 14 inch (350 mm) | Larger or darker rooms up to around 19 sq m | Kitchens, family bathrooms, living rooms, home offices |
These are guides, not hard limits. A north-facing room, a long tube run or a lot of bends all reduce the light that reaches the diffuser, so if a room sits on the boundary between the two sizes, the 14 inch is usually the safer choice.
Pitched roof and flat roof versions
Sun tunnels are made for the roof you have. Pitched-roof versions are designed for roof slopes of about 15 to 60 degrees and use a domed top to gather light from a low sun across the day. Flat-roof versions, for pitches under about 15 degrees, use flat glazing that sits above an upstand so water runs off. The two are not interchangeable, so check your roof pitch before ordering.
Tile and slate flashing kits
The flashing is the part that seals the top unit into your roof covering, and it has to match what you have on the roof. There are separate kits for profiled and plain tiles and for slate, because the two sit and lap differently. As a rough guide the flashing is made to weather in with slate up to about 8 mm thick, or profiled tiles up to around 120 mm in profile depth. Get this wrong and you invite a leak, so it pays to order the correct kit from the start.
We stock VELUX rigid and flexible sun tunnels for both tile and slate at our depots, alongside the wider range of roof windows and rooflights and the full VELUX line, from roof windows to flashings and blinds. If you are matching a sun tunnel to an existing tile or slate, bring a sample or a photo and we will pair it to the right flashing.
Sun tunnel vs VELUX window: what is the difference
A roof window like a standard VELUX is a glazed unit set into the roof slope. It gives a view, opens for ventilation and floods a room with light, but it needs the room to sit directly under the roof slope. A sun tunnel gives light only, no view and no opening, but it can reach rooms buried in the middle of a house where a roof window would never work. They solve different problems. If the room is under the slope and you want air and a view, fit a roof window. If it is an internal space that just needs daylight, a sun tunnel is the tool for the job, and it is a smaller, tidier job to install.
Buying sun tunnels in Sussex and Kent
Brian Gow Roofing Supplies has stocked VELUX for the trade and for homeowners since 1996, covering Kent, Surrey and Sussex from four depots with delivery across the South East. Call in for a straight answer on which sun tunnel suits your roof and room, or collect the same day. See our Burgess Hill roofing supplies branch for stock and opening hours, or find your nearest branch to get started.
Frequently asked questions
What is a sun tunnel?
A sun tunnel is a reflective tube that brings daylight from your roof into a room below through a diffuser in the ceiling. It lights spaces that have no outside wall for a window, such as hallways, landings and internal bathrooms. It gives light only, with no view or opening, and costs nothing to run.
What is the difference between a rigid and flexible sun tunnel?
A rigid sun tunnel uses a solid mirror-finish tube for a straight run and delivers the most light, and it can cover long drops. A flexible sun tunnel uses a bendable tube that routes around rafters, pipes or a tank in a tight loft. Every bend loses a little light, so flexible runs are best kept short.
What size sun tunnel do I need?
VELUX sun tunnels come in about 10 inch (250 mm) and 14 inch (350 mm) diameters. The 10 inch suits smaller spaces up to roughly 14 square metres, like a hallway or ensuite. The 14 inch suits larger or darker rooms up to around 19 square metres, such as a kitchen or living room. If in doubt, size up.
Can you fit a sun tunnel to any roof?
Most tiled and slate roofs are suitable. There are separate versions for pitched roofs, about 15 to 60 degrees, and for flat roofs under about 15 degrees, plus matching tile or slate flashing kits. You also need a reasonably clear route through the loft. A flexible tunnel helps where beams or pipes get in the way.
Is a sun tunnel better than a VELUX window?
Neither is better, they do different jobs. A roof window gives light, a view and ventilation but needs the room to sit under the roof slope. A sun tunnel gives daylight only, yet reaches internal rooms a window cannot. Choose a roof window for rooms under the slope and a sun tunnel for landings, bathrooms and other enclosed spaces.
How much light does a sun tunnel provide?
On a bright day a sun tunnel gives daylight comparable to a small window, enough to light a room without switching anything on. The amount depends on diameter, tube length and the number of bends. A short, straight, larger-diameter run gives the most, so a 14 inch rigid tunnel delivers noticeably more than a long, winding flexible one.