Skylights in Metal Roofs: Key Considerations and Installation Tips

Metal sheets are used on a variety of roofing such as commercial housing, industrial warehouses, factories, horticultural and aquaculture structures and more. Regardless of the type of metal roof structure that’s built, there will always be a need for natural sunlight, which installing skylights in metal roofs will be the logical step. However, careful planning and execution is important when joining two different materials, which is even more so when the materials are under prolonged exposure to the elements.

Common Installation Types for Skylights in Metal Roofs

Standing Seam:

Often considered the best type for skylight installation because it minimizes the risk of leaks.

Corrugated:

More challenging when sealing off the edges due to the ridges and valleys; requires precise flashing when fixed against the wall, or matching ridge caps to seal off the highest point of the roof against leakage.

Fixed Skylights:

Fixed skylights have no openings and are less prone to leaks compared to vented skylights, and can be installed on roof slopes between 5° ~ 10°.

Curb-Mounted:

Curb mounted skylights are required for roof slopes less than 14°. It requires a box structure designed to sit over the curb like a lid on a shoe box set on edge and attached to the roof deck. The box is then ‘flashed in’ with the roofing material for waterproofing. One of the benefits of this design is the ability to replace older skylights without having to re-flash the skylight at the same time.

Deck-Mounted:

Deck mounted skylights are suitable for roof slopes equal or greater than 14°, and more recent design that lowers the profile of the unit. On a deck-mounted skylight design, the curb is the skylight itself. The lower profile provides a better visual appeal, inside and out, and has slightly better energy efficiency compared to curb-mounted skylights.

Key Considerations When Installing Skylights in Metal Roofs

1. Metal Roofing Sheet Profile:

Metal roofs come in different profile shapes and sizes, which will affect the choice of skylights. It is best to fully understand and take into consideration the metal roofing sheet profile before choosing skylights, as sometimes there aren’t matching skylight profiles.

2. Skylight Roofing Sheet Profile:

In some areas, where skylight roofing choices are limited, users might have to compromise by choosing skylight profiles that have a matching metal roofing profile. Choosing skylights that match metal roofing sheet profiles has the advantage of creating a better seal when overlapped and require less effort during installation to prevent water leakage, which is always a concern with any roofing sheet installation.

3. Roof Pitch:

Ensure that the skylight is appropriate for the pitch of the roof. Most manufacturers provide guidelines on suitable pitch ranges.

4. Weather Conditions:

In areas with heavy snowfall or rain, skylights in metal roofs require special considerations to prevent heat loss and condensation. Extra precautions such as more screws per linear meter, more rafters for support, and more overlapping corrugations, are often necessary to prevent leaks.

5. Flashing:

Proper flashing is critical to prevent leaks. Skylight and metal roofing sheets both require specialized flashing kits designed for the specific roof profile and skylight type for a proper seal.

(Read more: Skylight Leaks When It Rains? Causes and Solutions for Sealing!)

6. Thermal Expansion:

Skylight sheets are often made of plastic, which has a higher coefficient of thermal expansion, which means that the size of the sheet changes with the change of temperature, the higher the number, the larger the difference. Metal roofing sheets expand less when compared to plastic skylights, so a thermal expansion hole is only required on the plastic skylight, whereas metal roofing sheets do not. A thermal expansion hole is important to allow for movement without compromising the seal around the skylight.

Skylight Installation Tips

Planning and Placement:

• The first step in installing skylights in metal roofs is selecting the appropriate location. Choose a location that maximizes natural light but avoids shading from nearby structures or trees. For corrugated installations, is it important for the opening side of the corrugation overlap to be opposite the wind direction.
• Plan the placement between roof supports to ensure the skylight doesn’t interfere with structural elements.

Cutting the Opening:

• Use appropriate tools to cut the metal roof, ensuring smooth edges to prevent damage to the flashing and seals.
• Ensure the opening matches the skylight dimensions exactly.

Flashing Installation:

• Use flashing specifically designed for metal roofs. This often includes both base and step flashing to direct water away from the skylight.
• Seal all joints with high-quality roofing sealant compatible with metal roofs.

Sealing:

• Proper sealing is an essential step when installing skylights in metal roofs. Use only Poly-Fast ® Polycarbonate Skylight fasteners when installing corrugated sheets to either metal or timber substrates. This easy to use product will create a thermal expansion hole and fix sheets to the substrates below in one go, eliminating the need to pre-drill, while also sealing off the hole expansion hole with its large EPDM dome washer.
• Use a high-quality, flexible sealant that can withstand thermal expansion and contraction.
• It is recommended to use only neutral based silicone sealant or equivalent when sealing off polycarbonate skylight sheets. In areas where skylight sheets come in contact with metal roofing sheets, it is recommended to use dedicated sealing tape to prevent leakage, and also noise and creaks that come from plastic rubbing against metal.

Insulation and Waterproofing:

• Properly insulate around the skylight to prevent heat loss.
• Ensure that the waterproof membrane around the skylight is intact and well-sealed.

Final Inspection:

• Check for any gaps, loose screws, or potential leak points.
• Test the installation with water to ensure that it is leak-proof.

Maintenance Tips

• Regular Inspections: Routine maintenance is essential to prolong the lifespan of skylights in metal roofs. Periodically inspect the skylight and surrounding roof area for signs of wear, leaks, or damage.
• Cleaning: Keep the skylight clean to ensure maximum light transmission and prevent mold or mildew buildup. Use a soft sponge and warm soapy water to remove dust or stains. For moss, mould, mildew, and lichen, we recommend using 30 Seconds Outdoor Cleaner (Blue label) or equivalent for quick cleans, and 30 Seconds Spray & Walk Away or equivalent cleaning products for a more progressive clean.
• Seal Checks: Check and maintain the sealant and flashing, especially after severe weather events.

Conclusion

Skylights in metal roofs offer numerous advantages, from improved natural lighting to increased energy efficiency. However, their successful installation requires careful planning and execution. By considering the factors outlined above and opting for professional installation, you can enjoy the benefits of skylights in metal roofs for many years to come.

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