A tubular daylighting device (TDD), often called a solar tube, sun tunnel, or tubular skylight, is a roof-mounted daylighting system that brings natural sunlight into an interior space through a highly reflective tube. Unlike a traditional skylight, which uses a relatively large glazed opening, a tubular daylighting device captures sunlight through a small roof-mounted dome and directs it through a reflective tube to a diffuser at the ceiling.
TDDs are commonly used in homes, offices, warehouses, schools, and commercial buildings where adding windows or conventional skylights may be difficult. They can provide natural illumination while reducing the need for electric lighting during daylight hours. A typical system consists of a roof dome, flashing assembly, reflective tube, and interior diffuser.
How Does a Tubular Daylighting Device Work?
The process begins at the roof. A transparent dome or sunlight collector captures available daylight and directs it into the tubular system. The light then travels down a highly reflective tube, which can be straight or angled depending on the building configuration. At the ceiling, a diffuser spreads the incoming daylight throughout the room.
Because the roof opening is relatively small, TDDs can require less roof disruption than many conventional skylights. Manufacturers also offer systems and flashing configurations designed for different roof slopes and materials, including shingle, tile, metal, membrane, and other roofing systems.
What Is Flashing on a Tubular Daylighting Device?
Flashing is the weatherproof component that connects the daylighting device to the roof assembly and helps prevent water from entering around the roof penetration. This makes flashing one of the most important parts of a tubular daylighting installation.
A properly selected flashing assembly creates a transition between the TDD and the existing roofing system. Depending on the roof design, the flashing may be a factory-made self-flashing unit, a pitched flashing, a flat or low-slope flashing, or a curb-mounted configuration.
For example, tubular daylighting manufacturers offer different flashing options for pitched and non-pitched roofs. Some systems use seamless, one-piece flashing assemblies to reduce potential weak points around the penetration.
How Is a Tubular Daylighting Device Flashed?
The exact installation method depends on the manufacturer, roof type, roofing material, and roof slope. However, the general process involves several important steps:
1. Select the correct flashing.
The installer first determines the roof type and slope and selects a compatible flashing assembly. Pitched flashings and flat or low-slope flashings are designed differently. Some systems are specifically available for membrane, modified-bitumen, built-up, shingle, tile, or metal roofs.
2. Prepare the roof opening.
The opening is carefully laid out and cut according to the manufacturer’s installation requirements. The location should also be coordinated with the roof deck, insulation, structural components, and interior ceiling.
3. Install and secure the flashing.
The flashing is positioned over the prepared roof opening and mechanically secured according to the manufacturer’s instructions. The goal is to create a stable, weather-resistant base for the tubular daylighting device.
4. Integrate the flashing with the roofing system.
This is critical. The surrounding roofing material and flashing must be installed so that water is directed away from the penetration rather than underneath it. On membrane roofs, for example, the roofing membrane must be properly integrated with the flashing. On shingle roofs, the flashing must be layered correctly with the shingles.
5. Install the dome and tube assembly.
Once the roof flashing is properly integrated, the tubular daylighting components are attached and sealed as specified by the manufacturer. The reflective tube is then connected to the roof collector and interior diffuser.
6. Inspect and test for watertightness.
A professional installation should be inspected for secure attachment, proper flashing integration, and potential water entry. Project specifications may also require water testing after installation and sealant curing.
Why Proper Flashing Matters
A tubular daylighting device creates a penetration through the roof, so even a small installation mistake can become a source of water intrusion. Poorly integrated flashing, incorrect sealants, improper fastening, or incompatible materials can contribute to leaks and premature roof deterioration.
For commercial buildings, the flashing also needs to be compatible with the existing roofing system and warranty requirements. Installation should therefore follow the TDD manufacturer’s instructions as well as the roofing manufacturer’s requirements and applicable building codes.
Final Takeaway
A tubular daylighting device is essentially a compact skylight system that captures sunlight through a roof dome and carries it indoors through a reflective tube. Its flashing forms the critical weatherproof transition between the device and the roof. Proper flashing selection and installation—particularly on low-slope and commercial roofs—is essential for preventing water intrusion and maintaining the roof system’s long-term performance.
For complex commercial roofing applications, a qualified roofing professional should coordinate the daylighting installation with the existing roof assembly rather than treating the TDD as a standalone penetration.
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