Tube, shaft or roof window?
| Tubular skylight | Skylight with a light shaft | Roof window | |
|---|---|---|---|
| How light gets in | A small dome and a mirror-lined tube to a ceiling diffuser | A glazed unit in the roof and a boxed shaft down to the ceiling | The window sits in a sloping ceiling, with no shaft |
| Suits | Hallways, bathrooms and small rooms | Living areas and kitchens that want real daylight | Raked ceilings, attics and lofts |
| Size guide from Your Home | 1 to 2% of floor area for high-performing tubes | 3 to 5% of floor area | 3 to 5% of floor area |
| Roof pitch, VELUX ranges | 15 to 60 degrees for its standard sun tunnels, 0 to 60 for its TCR | Flashings for 15 to 90 degrees | Flashings for 15 to 90 degrees |
| Can it open? | No | Fixed, manual, electric and solar models | Many do, like a normal window |
How big should it be?
Smaller than you'd think. Your Home, the Australian Government's guide to sustainable houses, says a skylight or roof window can let in more than 3 times as much light as a vertical window the same size. It suggests about 3 to 5% of the floor area for conventional skylights and roof windows, 1 to 2% for high-performing tubes, and spacing of about 1.5 times the floor-to-roof height.
There's a legal ceiling as well. Under the 2022 edition of the building code's housing provisions, roof lights serving a habitable room are limited to a total of 5% of that room's floor area, with limits on heat loss and heat gain (clause 13.2.4, which doesn't apply in NSW). If you want a lot of light in a big room, ask about two well-spaced smaller units rather than one large one.
For tubes, Solatube says its 250 mm model lights about 19 m2, its 350 mm model about 28 m2 and its 530 mm models about 46 m2, based on a 1.82 m tube, a 2.4 m ceiling and the dome in direct sun. Those are a seller's best-case figures.
Straight, angled or splayed shaft?
With a flat ceiling, the shaft is the part you'll live with. A straight shaft runs plumb from the roof opening to the ceiling. An angled shaft lets the roof unit sit on a sunnier or less visible part of the roof than the ceiling opening below. A splayed shaft flares out towards the ceiling, so the opening in the room is bigger than the one in the roof and the light spreads wider.
Length matters. The code sets the allowed solar heat gain by shaft length, and tubes have limits: VELUX says its rigid sun tunnels extend up to 6 m, and Solatube quotes 6 m, 9 m or 12 m depending on the model.
The framing in the roof space decides what's possible. A wide shaft may mean cutting and supporting rafters or trusses, which is structural work and may need approval. In the NT, adding a skylight to an existing house needs a building permit, with some exemptions. Elsewhere, ask your council or a building certifier.
Will it make the room hot?
It can. Your Home says roof glazing takes in almost twice as much heat as an unprotected west-facing window of the same area, and sloped glazing loses heat about 40% faster than vertical glazing.
So the glazing matters as much as the size. The Window Energy Rating Scheme (WERS) rates skylights on U-value, which is heat loss, and SHGC, which is how much of the sun's heat gets through, so compare those figures. Opening models can let hot air out, and VELUX sells fixed, manual, electric (with a rain sensor) and solar-powered versions.
Climate plays a part too. Your Home says tubular skylights work best in sunny, clear climates, while roof windows and conventional skylights suit places with more cloud.
Tile or metal: getting the flashing right
The flashing, the skirt of metal or moulded material that sheds water around the opening, is what keeps a skylight dry. VELUX says its flashing systems are designed to shed water without relying on sealants that can break down. On metal roofs, BlueScope says skylights often need specialist flashing, and on low-pitched roofs a penetration that blocks the sheet channels needs a head gutter above it to divert water.
Who fits it matters. In NSW, putting in skylights is roof plumbing work, and Queensland's roof tiling and roof cladding licences both cover skylights and flashing roof penetrations. Our licence guide shows how to check in your state.
In bushfire-prone areas, Your Home says skylights must comply with AS 3959 for the home's bushfire attack level, and the code limits combustible skylights to 20% of the roof area.
Skylights make a roof fragile
Safe Work Australia says polycarbonate or plastic skylights are a sign a roof is likely to be fragile, and Laserlite, which makes polycarbonate sheet, says never to walk on it or put your weight on it. Stay off the roof and leave the work to the installer. Old skylights and roof manholes can be asbestos cement, so have an older one checked before it's cut out. And Solatube warns never to block a tubular skylight with window tint or anything flammable, because that creates an extreme fire hazard.
Planning a skylight for a flat ceiling
Decide what you want from it
Light only, light and fresh air, or a view of the sky. That points you to a tube, an opening skylight or a fixed one.
Pick the spot from inside
Choose where you want the light on the ceiling, then have the installer check what's above it: trusses, wiring, ducts and the distance to the roof.
Size it to the room
Use Your Home's guide of 3 to 5% of floor area for skylights, or 1 to 2% for tubes, and stay inside the code's 5% limit for habitable rooms.
Choose the glazing
Compare WERS ratings for U-value and SHGC, especially on a north or west-facing slope.
Match the flashing to the roof
Ask which flashing kit suits your tiles or sheet profile and your roof pitch.
Check approvals and licences
Ask your council or a certifier whether the job needs approval, and check the installer's licence covers skylights.
What you can do, and what needs an installer
You can
- Measure the room and work out the size guide
- Mark where you'd like the light on the ceiling
- Look into the roof space from the manhole for obvious obstacles
- Compare WERS ratings and warranties
- Check the installer's licence
Leave to a roofer
- Cutting the roof and fitting the unit
- Flashing to suit your tiles or sheet profile
- Framing and lining the light shaft
- Wiring for electric units, by an electrician
- Removing an old skylight that might be asbestos cement
What we'd put in
For a dark hallway, bathroom or small room, we'd fit a tube and enjoy the free daylight. For a living area, we'd choose a skylight with a splayed shaft, glazing with good WERS figures and an opening model if the room gets stuffy, sized to Your Home's guide rather than as big as possible. On a west-facing slope we'd go smaller again, and we'd make sure the installer is licensed for the flashing on our type of roof.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.