How to Install a Tubular Skylight (Sun Tunnel) in a Shingle Roof
A round hole between rafters, a flashing base, a reflective tube and a ceiling diffuser. No structural changes when it is planned right.
- Intermediate
- 3 to 5 hours
- Updated
The short answer
A tubular skylight is installed by locating a spot between rafters and ceiling joists, cutting a round hole through the ceiling and the roof, flashing the roof base under the shingles above and over the shingles below, running the reflective tube down from the dome to the ceiling, and fitting the diffuser. The hole is commonly 10 to 14 inches across. Follow the kit's instructions for angles, extensions and sealing.
A tubular skylight, also called a sun tunnel or solar tube, brings daylight into a room through a reflective tube that runs from a small dome on the roof to a diffuser on the ceiling. It suits places a regular skylight will not: closets, halls, small bathrooms, stairwells and rooms with a deep attic above. There is no view, but it provides a lot of light for a small hole.
They are also a simpler install. The round hole, commonly 10 to 14 inches across, usually fits between rafters and ceiling joists, so there is no need for headers or a cut rafter. The dome and the roof flashing base are the main leak risks, and both follow the lapping logic of any skylight flashing.
Kits differ in how the tube is sectioned, how it angles and how the base is shaped for different roofs. Follow the instructions for your exact kit. If you are still choosing, see skylight types.
Tools
- Drill with a long bit
- Reciprocating saw or jigsaw
- Stud finder
- Plumb bob or level
- Hook blade utility knife
- Tin snips
- Caulking gun
- Tape measure
- Screwdriver or drill driver
Materials
- Tubular skylight kit with dome, flashing base, tube sections and ceiling diffuser
- Tube extensions or adjustable elbows if the run needs them
- Self-adhered membrane or sealant as the kit specifies
- Roofing nails or screws from the kit
- Foil tape for tube joints
- Insulation wrap for the tube in the attic, if the kit recommends it
Safety first
- Work tied off on the roof. WorkSafeBC requires fall protection at 3 metres (about 10 feet) and wherever a fall could cause serious injury.
- Check the attic for wiring, ducts and plumbing before you cut. Turn off power to any circuit in the area.
- Cut a ceiling hole from below first with a small pilot hole, so you know what is above it before any saw goes in.
Step by Step
Step 1: Pick the location from inside and check the attic
From the room, pick a centre point. Drill a small pilot hole up through the ceiling and push a wire through it so you can find it in the attic. Check the space around the hole: the tube needs a clear, roughly round path about the width of the tube plus a little extra.
Go into the attic and look at what is near the pilot hole: joists, rafters, cables, ducts. Move the location if needed. Try to keep the tube as straight and short as possible, since every bend and extra foot of tube reduces the light.
Step 2: Transfer the location to the roof
On the roof, look at the spot. You need room above it for the flashing base to tuck under the shingles, and room below for the base to lap over the shingles. Avoid valleys, chimneys and the area close to the eave or ridge, where there is not enough space to flash properly.
Keep the dome out of heavy shade if you can, since the dome collects the light. If the light path needs an angle, plan it with the kit's adjustable elbows, which are normally included for roofs with slope.
Step 3: Cut the ceiling opening
Trace the ring or template from the kit around the pilot hole and cut the drywall with a drywall saw. Catch the dust. Move any insulation out of the tube path but keep it from falling into the hole.
Fit the ceiling ring or mounting plate as directed, leaving the diffuser itself until the end.
Step 4: Cut the roof opening
Mark the hole from the kit template centred on the marked point. Remove the shingles and nails around the hole in an area as large as the flashing base, and a little more. Cut the deck with a jigsaw or reciprocating saw, cutting through the underlayment as well.
Keep the hole clear of any rafter. If a rafter ends up in the path, move the location slightly rather than cutting it.
Watch out: Do not cut into a rafter or truss. Shift the location instead. Trusses are engineered as a system and cannot be cut.
Step 5: Install the flashing base
Apply a strip of self-adhered membrane around the hole first if the kit or roof calls for it. Then slide the upper edge of the base under the shingle courses above the hole, lifting the nails if needed, and set the base so the lower edge rests over the shingles below.
Fasten only where the instructions show, usually along the upper corners and sides, with nails or screws covered by the next course or sealed as directed. Every piece laps over the one below, as in all flashing. See the lapping logic in the shingle lapping rule.
Step 6: Attach the dome to the base
Clean the collar, add any supplied gasket and set the dome. Fasten with the screws provided. Some domes lock with a clip or ring. Check that the dome sits evenly all the way around with no gaps.
Domes are plastic or acrylic and can crack if screws are overtightened. Snug them evenly.
Step 7: Run the tube from the roof to the ceiling
Work from the roof down. Each section slides into the next with the upper section on the inside, so any condensation runs down the inside of the tube toward the room rather than out through the joint. Secure each joint with screws or foil tape.
Use as few bends as possible. Support the tube in the attic with the straps supplied. Some kits recommend wrapping the tube in insulation in cold attics, which also helps prevent condensation on the tube.
Step 8: Fit the diffuser and check the seal
Attach the tube to the ceiling ring, seal the joint with foil tape and install the diffuser. Some diffusers have a built-in seal or second pane that also helps prevent condensation.
On the next rain, look at the ceiling around the ring. If there is a stain, it may be condensation from warm air leaking up into a cold tube. See how to fix a leaking skylight.
Tube Length, Angle and Light
Light drops off as the tube gets longer and as it bends. A short, straight tube with a high-reflectance lining delivers the most. Long runs usually need a larger diameter or more efficient reflective film, and kits give length limits.
Condensation and Insulation
A tube passes through a cold attic. Warm moist air from the room can condense on the inside of the tube, or on the diffuser. Seal the ceiling ring and diffuser, tape the tube joints and, where the kit recommends it, wrap the tube in insulation. See how attic ventilation works for why attic air matters.
Common Mistakes
- Skipping the attic check. Wiring, ducts and rafters in the path force a messy relocation after the hole is cut.
- Cutting a rafter. The small hole does not justify any structural cut. Shift the location.
- Putting the flashing base over the upper shingles. Reverse lapping drives water under the base.
- Too many bends. Every elbow loses light and makes the room darker than expected.
- Loose or untaped tube joints. Warm room air reaches the cold tube and condenses.
- Overtightening the dome screws. It cracks the plastic.
When to Call a Professional
Call a roofer if the roof is steep, high, tile or metal, or if the path requires going through a truss roof or complex framing. The dome and base are a roof penetration, and the flashing needs to be woven in correctly.
If you are not comfortable working at height, have a roofer install the roof side and finish the ceiling yourself.
Fraser Roofing does free roof inspections across the Fraser Valley, from Hope to Abbotsford. See our Skylights service or the towns we cover.
How to Install a Tubular Skylight (Sun Tunnel): Questions
How big a hole does a tubular skylight need?
Residential tubular skylights commonly need a hole between 10 and 14 inches across, though sizes vary by model, so check the kit's template. That is small enough to fit between most rafters and ceiling joists without structural changes. Larger diameters give more light but need more space in the attic.
Can a tubular skylight leak?
Yes, at the dome seal or the flashing base if they are installed badly. Water can also appear from condensation inside the tube or at the ceiling, which looks like a leak. A properly flashed base that laps correctly with the shingles, and well sealed tube joints, prevent both.
Can you install a sun tunnel in a room with a floor above?
Not directly, because the tube needs a clear path from the ceiling to the roof. In a two-storey house, a tubular skylight can only light the top floor unless the tube passes through a chase or closet. Check the path carefully before choosing a location, since structure and ducts often get in the way.
Do tubular skylights work on cloudy days?
Yes, but they deliver less light. Daylight through a tube is diffuse and reduces with the brightness of the sky, so on dark Fraser Valley winter days you will still get some light, but much less than on a bright day. Larger tubes and shorter, straighter runs help a lot.
Related Guides
All Skylights guides|The full How-To Library
This guide is general education. Always follow the product manufacturer's installation instructions, the BC Building Code and WorkSafeBC requirements, which take priority over anything written here.
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