How to Choose the Right Sun Tunnel
A practical guide to choosing the correct tube size, rigid or flexible shaft, roof system and installation position—without buying a product that is too small, too flexible or unsuitable for your roof.
Start with the room and the roof—not the product name
A sun tunnel works best when you only need daylight, the room is below a roof, and there is a practical route between the roof and ceiling. The correct model is then chosen around the required light level, roof pitch, roofing profile and obstacles in the roof cavity.
It uses a compact roof opening and a ceiling diffuser rather than a large glazed shaft.
A sun tunnel delivers light only. It does not provide the open-sky appearance or airflow of an opening skylight.
Where sun tunnels make the most sense
They are particularly useful for rooms that feel dark during the day but do not need a large feature skylight.
Hallways & entries
Brighten a landlocked corridor and reduce the need to switch lights on during the day.
Bathrooms & toilets
Add privacy-friendly daylight. A separate exhaust system is still required where ventilation is needed.
Robes, pantries & laundries
Useful in compact utility spaces where windows are absent and a large skylight would be unnecessary.
Kitchens & living areas
Possible with a larger or multiple tubular system, although a full VELUX skylight may create a better result in major rooms.
Three components create the daylight
A tubular skylight is not simply a plastic dome. Its performance depends on the complete system and how well the route is designed.
The roof collector captures available daylight. A reflective tube carries that light through the roof space. The ceiling diffuser then spreads it into the room below.
Roof collector
A glazed roof module or optical dome captures direct and ambient daylight.
Reflective tunnel
A rigid or flexible shaft transfers the light from the roof to the ceiling.
Ceiling diffuser
The diffuser softens and distributes the daylight across the room.
Sun Tunnel Quick Chooser
Use these four questions to narrow down the likely solution. The result is a starting point only; roof access and cavity inspection can change the final recommendation.
Rigid or flexible sun tunnel?
Choose the most direct high-performance route that the roof cavity allows. Flexible tubing is useful, but it should not automatically be treated as the better or easier choice for every home.
Rigid tunnel
Usually the preferred option when there is a clear route.
- Highly reflective, smooth internal surface
- Generally stronger daylight transmission
- Better suited to longer roof-to-ceiling distances
- Elbow sections can allow controlled changes in direction
- Can often be extended with the manufacturer’s matching rigid sections
Flexible tunnel
Useful when a short route must work around roof-space obstacles.
- Bends around trusses, ducts and restricted areas
- Best kept as short, open and gently curved as practical
- Multiple tight bends and compressed sections reduce performance
- Not the first choice for a long shaft when a rigid route is possible
- Product-specific length and roof limits still apply
VELUX and MaxLight options explained
Central Skylights supplies and installs both systems, so the recommendation can be based on the room and roof rather than forcing one brand into every property.
| System | Nominal size | Roof application | Best suited to | Important detail |
|---|---|---|---|---|
| VELUX TWR rigid Performance choice | 350 mm tunnel | Pitched roofs, generally 15°–60° | Clear or mostly direct paths; longer runs; hallways, bathrooms, robes and compact internal rooms | Standard rigid tunnel is about 1.65 m and can be extended with matching rigid sections, up to the manufacturer’s stated limit. |
| VELUX TWF flexible Obstacle route | 350 mm tunnel | Pitched roofs, generally 15°–60° | Shorter routes that must work around trusses, ducts or other obstructions | Keep the tube stretched and bends gentle. It is selected for routing flexibility, not maximum output. |
| VELUX TCR rigid Low-pitch option | 350 mm tunnel | Flat and low-pitch roofs, generally 0°–60° | Shorter, unobstructed paths beneath low-pitch roofing | Uses a curb-mounted dome and requires a correctly designed custom flashing; flashing is not supplied by VELUX. |
| MaxLight ML250 Compact rooms | 250 mm tube | Model and flashing selected to suit the roof | Toilets, robes, pantries, laundries, smaller bathrooms and narrow hallways | A compact ceiling diffuser and smaller roof opening. Manufacturer room-coverage figures are a guide, not a guaranteed lux level. |
| MaxLight ML400 / ML400H Larger spaces | 400 mm tube / hybrid diffuser | Model and flashing selected to suit the roof | Larger kitchens, wider hallways, dining areas and rooms needing a broader spread of light | For a major living area, compare one larger tunnel, multiple tunnels and a full skylight before deciding. |
Product specifications can change. Final model selection should be checked against the current manufacturer documentation and the actual roof conditions.
How large should your sun tunnel be?
Room area matters, but it is only one part of the answer. A small unit on a very short straight run may outperform a larger unit with a long, shaded or heavily bent route.
Small spaces
For a toilet, pantry, robe or short narrow hallway, a 250 mm MaxLight or 350 mm VELUX can be considered depending on the desired brightness, tube route and ceiling appearance.
Medium rooms
Bathrooms, laundries and small kitchens need more careful positioning. A 350 mm VELUX or 250–400 mm MaxLight may suit, depending on the drop and the room’s existing windows.
Large rooms
For a large kitchen or living area, compare a 400 mm system, multiple tunnels and a full skylight. One small tunnel may create a bright spot without lighting the whole room evenly.
Your roof profile can decide the product
“Metal roof” is not one universal condition. Corrugated iron, Trimdek and Klip-Lok require different flashing details, and low-pitch roofs require a product designed for that application.
Tile or corrugated roof
VELUX TWR and TWF packages include integrated flashing intended for tiled and suitable low-profile corrugated roofs. The exact tile profile, pitch and roof condition still need checking.
Trimdek or Klip-Lok
The standard VELUX TWR/TWF integrated flashing is not intended for these wide-span profiles. A different product or carefully designed site-specific solution may be needed.
Flat or low-pitch roof
Use a system specifically designed for low-pitch conditions. The VELUX TCR is a rigid low-pitch model and requires custom flashing formed to drain correctly with the roof.
The best ceiling position is only half the job
A good layout balances where the light is needed inside with where the collector can perform and be flashed safely outside.
Choose the room target
Place the diffuser where daylight will spread usefully, not simply in the easiest ceiling spot.
Check roof structure
Locate trusses, rafters, ducts, plumbing, wiring and insulation before committing to the opening.
Find a clear roof area
Avoid heavy shade, solar panels, valleys, hips and crowded roof penetrations where practical.
Shorten the route
Use the most direct path and minimise bends while keeping the diffuser in a visually sensible position.
Confirm flashing
Match the roof module and flashing method to the actual roof pitch and material.
A sun tunnel is not always the best answer
The right advice sometimes means recommending a different product.
A sun tunnel is likely suitable if:
- The goal is natural daylight rather than a sky view
- The room sits below an accessible roof area
- A practical tube route can be created
- You prefer a compact ceiling diffuser
- The room is small to medium, or multiple units are acceptable
Consider a full skylight if:
- You want the room to feel visually connected to the sky
- You need natural ventilation in a kitchen or bathroom
- The room is large and needs broad, powerful daylight
- You want an architectural feature rather than a ceiling light effect
- A large plaster shaft can be designed attractively
What homeowners are often told incorrectly
Room size is useful, but the tube route, bends, shading, roof position and required light distribution can matter just as much.
Flexible tubing is valuable around obstructions, but a rigid tunnel normally provides a cleaner optical path when the structure allows it.
Corrugated iron, Trimdek and Klip-Lok are different profiles. The roof module and flashing method must suit the actual sheet profile and pitch.
A standard sun tunnel supplies daylight only. Moisture control still needs an appropriate exhaust or ventilation solution.
Output changes naturally with cloud cover, season, time of day, roof orientation and external shade. That variation is part of using real daylight.
The collector penetrates the weatherproof roof layer. Correct positioning, cutting, flashing, sealing and safe roof access are critical to long-term performance.
Photos that help us recommend the right model
A fast photo quote is much more accurate when we can see both the desired ceiling position and the roof above it.
1. The whole room
Stand back and show the room, existing windows and where the diffuser may go.
2. The ceiling
Include lights, exhaust fans, manholes, bulkheads and the proposed location.
3. The roof outside
Show the roof profile, pitch, solar panels, valleys, vents and nearby shade.
4. Roof-space access
Where safe and available, show trusses, ducts or obstacles above the room.
Sun tunnel questions answered
Are sun tunnels worth installing?
They can be excellent value when the goal is to brighten a dark internal room without building a large plaster shaft. They are particularly effective in hallways, toilets, robes, pantries, laundries and smaller bathrooms. A full skylight may be better where you want a sky view, ventilation or a strong architectural feature.
Do sun tunnels work on cloudy Melbourne days?
Yes, they collect available ambient daylight as well as direct sun. The room will still receive light on an overcast day, but the output will be lower than on a bright clear day. Tube type, length, bends and roof position influence how much of that daylight reaches the diffuser.
Is a rigid sun tunnel brighter than a flexible one?
In general, a smooth rigid reflective tube gives light a more efficient path and is preferred for longer or clear routes. A flexible tunnel is selected when obstacles prevent a practical rigid route. A short, well-stretched flexible tube can still perform well in the right application.
What size sun tunnel should I choose?
There is no reliable room-area-only formula. We consider the room size, ceiling height, desired brightness, roof-to-ceiling distance, tube bends, external shade and roof orientation. Compact 250 mm systems often suit small rooms, 350 mm VELUX systems cover many common internal spaces, and 400 mm or multiple systems may suit larger areas.
Can a sun tunnel be installed on a flat roof?
Yes, provided the product is designed for the roof pitch and is flashed correctly. The VELUX TCR rigid model is intended for flat and low-pitch roofs within its stated range and requires custom flashing. Other tubular systems have their own low-pitch roof options.
Can VELUX TWR or TWF be installed on Trimdek or Klip-Lok?
The standard integrated flashing supplied with VELUX TWR and TWF is intended for tile and suitable low-profile corrugated roofs and is not designed for profiles such as Trimdek or Klip-Lok. The site may need another tubular product or a carefully assessed alternative solution.
Will a sun tunnel ventilate my bathroom?
No. A standard sun tunnel provides daylight but does not open for airflow. Bathrooms and laundries still need suitable ventilation or exhaust arrangements for moisture control.
Does a sun tunnel need electricity?
No electricity is required to deliver daylight. Some tubular systems may offer optional electric light or dimming accessories, but those are separate from the daylight function and any electrical work must be completed appropriately.
Can the roof collector and ceiling diffuser be offset?
Often, yes. Rigid systems can use controlled elbow sections and flexible systems can curve around obstacles. However, the more indirect the route becomes, the more light may be lost. We aim for the shortest, straightest practical route while keeping the diffuser in a useful position.
How many sun tunnels does a large room need?
It depends on the room shape and how evenly you want the light distributed. Two smaller units can sometimes produce a more balanced result than one central bright spot. In a large kitchen or living room, it is worth comparing multiple tunnels with a full VELUX skylight before deciding.
Can a sun tunnel leak?
Any roof penetration can leak if the product is unsuitable, poorly positioned or incorrectly flashed. The correct roof module, pitch, flashing method and installation workmanship are essential. Sealant alone is not a substitute for a properly draining flashing system.
Let us compare the room, roof and tube route
Central Skylights can recommend a VELUX rigid or flexible Sun Tunnel, a low-pitch solution, a MaxLight model, multiple units or a full skylight where that will produce the better result.