Skylights vs. Solar Tubes (Tubular Daylighting Devices)

The names vary: solar tube, sun tunnel, light tube, tubular skylight. The Energy Code and the Residential Code call them tubular daylighting devices, or TDDs. This comparison is part of our California window guide. If you already have a skylight that needs replacing, see our sibling guide on skylight replacement.

How each one works

Skylight

A glazed unit set into the roof, with a framed and finished shaft connecting it to the ceiling below, or no shaft at all in a vaulted ceiling. You see the sky through it. Direct sun comes through it and moves across the room during the day. It can be fixed or can open for ventilation.

Tubular daylighting device

A small clear dome on the roof, a tube lined with highly reflective material running through the attic, and a diffuser set in the ceiling that looks like a light fixture. Solatube describes its system as designed to capture sunlight at the rooftop, redirect it down a highly reflective tube, and diffuse it throughout an interior space. There is no view and no opening. Residential tubes are commonly 10 or 14 inches in diameter.

VELUX makes two kinds of its Sun Tunnel: a rigid tunnel for a straight, clear path to the roof, and a flexible tunnel that bends around obstructions. It notes that rigid tunnels give brighter light and that longer runs may reduce brightness.

Side by side

We do not publish prices here, because the spread is wide and driven by the roof and ceiling more than the product. The direction is reliable: for a room under an attic, a tube costs noticeably less than a skylight with a shaft. For current budgeting see our cost hub.

Light: quantity and quality

A skylight delivers far more light than a tube, simply because it is many times larger. It also delivers a different kind of light. Direct sun through a skylight is bright, warm and moving. It makes a room feel open. It also causes glare on screens, fades whatever sits in the sun patch, and can be too much over a bed or a desk.

A tube delivers even, diffused light with no beam and no glare. Solatube states that its 14-inch residential model delivers daylight to spaces up to about 300 square feet, a figure it bases on a short tube and the dome in direct sun. The light dims with clouds and at the ends of the day, as it does with any daylighting.

How much reaches the room depends on things you can control at installation:

• Tube type. Rigid tube gives brighter light on a direct path. Flexible tube is for routing around an obstacle.
• Length and bends. Shorter and straighter is brighter.
• Dome location. A dome on a south-facing roof slope in full sun outperforms one shaded by a chimney, a tree or a second story.

Heat gain and energy

Any hole in an insulated ceiling loses heat in winter and gains it in summer. The difference between the two products is mostly one of scale.

A skylight on a south or west roof slope in Sacramento faces the high summer sun that vertical windows largely escape. With clear glass or a plastic dome it can overheat a room. Low solar gain glass, an interior blind, and careful placement on a north or east slope all help. The light shaft matters as well: its walls are attic-facing surfaces and need to be insulated and air-sealed like an exterior wall. Our page on the best windows for cooling explains the solar heat gain coefficient.

A tube has a small opening, so its total heat gain and loss are small in absolute terms. Per square foot, though, a basic tube is not a good insulator. The Energy Commission's compliance manual works an example of a tube with a single-pane diffuser: treated as a metal-frame, fixed, single-pane skylight, its default U-factor is 1.19 and its default SHGC is 0.83. Those are poor numbers, which is why the code pays attention to the diffuser. A dual-pane diffuser at the ceiling, at the plane of the insulation, is what earns a tube its exception.

Tubes also need care in the attic. The tube passes through unconditioned space, and warm, moist indoor air that gets into it can condense. Solatube's own guidance acknowledges that condensation can occur when warm, moist air enters the tubing. Sealing the ceiling ring and choosing a product with a sealed, dual-pane diffuser both reduce it. Bathrooms are the room where this matters most.

How Title 24 treats each

Both are fenestration under California's Energy Code. The prescriptive treatment differs.

Three practical consequences:

• Ask for a dual-pane diffuser. It is the condition for the tubular exception, and it is the better product anyway.
• Count the area. Three square feet is roughly five 10-inch tubes or two 14-inch tubes plus one 10-inch. A house full of tubes can exceed it.
• The compliance manual states that the U-factor of an excepted tube still must not exceed 0.40. A product's certified rating, not the default table, is what gets it there. Ask for the rating in writing.

The Energy Code also specifies how visible light transmission is rated for tubes, under a separate NFRC procedure from the one used for windows and skylights. For most homeowners that matters only as a reminder that tube brightness claims are measured differently from skylight ratings and are not directly comparable. Background on the code is on our Title 24 page and on what Title 24 is; the label is explained in how to read an NFRC label.

Building code points

• Testing and labeling. Section R324.6.9 of the 2025 California Residential Code requires unit skylights and tubular daylighting devices to be tested by an approved independent laboratory and labeled with the manufacturer, performance grade rating and inspection agency.
• Skylight glazing. Skylight glass has to be one of the materials permitted in Section R324.6.2, with retention screens in some cases. Details are in our skylight replacement guide.
• Low-slope roofs. Unit skylights on roofs under 3:12 pitch need a curb at least 4 inches high unless the manufacturer's instructions say otherwise.
• Ventilation. The Residential Code counts openable skylights among the openings that can provide a habitable room's required natural ventilation. A tube cannot contribute.
• Wildfire zones. In fire hazard severity zones, roof penetrations and glazing fall under California's Wildland-Urban Interface Code. Ask the manufacturer whether the dome is approved for those zones. See wildfire-resistant exteriors.

Both installations cut the roof covering, so a building permit is generally required. Check with your building department.

Installation and leak risk

A tube is the simpler installation. The roof hole is small and round, the flashing is typically one piece made for the roofing type, and the tube usually passes between rafters or trusses without cutting them. Inside, the only finish work is a round hole in the ceiling. Solatube says its systems can be installed on practically any roof type, with self-mounted and curb-mounted options.

A skylight needs a larger opening. In a stick-framed roof that usually means cutting a rafter and installing headers; in a trussed roof, trusses generally cannot be cut without an engineer, so the skylight has to fit between them or the design changes. Then comes the shaft: framing, insulation, air sealing, drywall and paint. That interior work is why a skylight costs more than the unit price suggests.

On leaks, the tube has the advantage of less perimeter and simpler flashing. A skylight installed with the manufacturer's engineered flashing kit, underlayment and correct step flashing is also dependable; the bad reputation comes from site-built flashing and sealant. In both cases, the best time to install is during a reroof, when the flashing can be integrated with new underlayment.

Which to choose

Choose a solar tube when:

• The room is a hallway, closet, laundry, interior bathroom or stair landing that needs light and nothing else.
• There is an attic between the ceiling and the roof, and a shaft would be deep.
• The roof is trussed and you do not want to involve an engineer.
• You want daylight without a sun patch, glare or added summer heat.
• Budget and disruption need to stay low.

Choose a skylight when:

• You want to see the sky, or want the room to feel larger.
• The ceiling is vaulted, so there is no shaft and the skylight is directly overhead.
• You want ventilation, such as in a bathroom, a kitchen or the top of a stairwell.
• The room is large and needs more light than a tube or two can supply.
• The roof slope faces north or east, or you are willing to use low solar gain glass and a blind.

Choose neither when the room could have a window. A vertical window gives light, view, ventilation and an escape route, with none of the roof risk. Our guide on choosing a window style is the place to start, and if a window already exists and is just too dark, replacing tinted or heavily coated glass may help more than you expect; see window film versus replacement.

Sources

• 2025 Building Energy Efficiency Standards: Section 110.6(a), Section 150.1(c)3A with Exceptions 2 and 3, Sections 150.2(b)1A and 150.2(b)1B
• 2025 Single-Family Residential Compliance Manual, Chapter 3 (Examples 3-8 and 3-9, tubular daylighting devices; skylight exceptions)
• 2025 California Residential Code, Chapter 3: Sections R319, R324.6 and R325.1
• Solatube: 290 DS tubular skylight, residential FAQ and tubular skylights overview
• VELUX: Sun Tunnel skylights buying guide and Mounting and Flashing

Working with Heritage Exteriors

We are a window, door and siding contractor, so our honest first question is whether a window would solve the problem better than anything through the roof. Where a skylight or tube is the right answer, we can help you check the Energy Code figures and coordinate with a roofer. Licensed in California, CSLB #1055919. Call (916) 546-2991.