Deck-Mounted vs. Curb-Mounted Skylights: Which is Better for Waterproofing?

When choosing a skylight for your roof, understanding the differences between deck-mounted and curb-mounted designs is crucial for ensuring proper waterproofing and long-term durability. This document outlines the key distinctions and explains why curb-mounted skylights are generally better for waterproofing.

Deck-Mounted Skylights

Deck-mounted skylights are installed directly onto the roof deck, offering a sleek, low-profile appearance. However, they come with notable challenges for waterproofing. Here are the main features and considerations:

• Design: The skylight frame attaches to the roof deck, and an integrated flashing system is used to create a watertight seal.

• Installation Process:

  • A self-adhesive underlayment is applied around the skylight’s perimeter.

  • Flashing is secured to direct water away from the opening.

• Advantages:

  • Sleek design blends with the roofline.

  • Ideal for modern architectural styles.

• Challenges:

  • The flashing for deck-mounted skylights is typically smaller and less robust than that used for curb-mounted designs. This can lead to water infiltration if the flashing is overwhelmed during heavy rainfall or snowmelt.

  • Installation precision is critical to avoid leaks, leaving little margin for error.

  • Integrated flashing systems may be less adaptable to certain roof types or climates.

Curb-Mounted Skylights

Curb-mounted skylights sit on an elevated curb, typically constructed on-site, which raises the skylight above the roof plane. This design offers distinct advantages for waterproofing:

• Design: The skylight frame is mounted on the curb, while the curb itself is separately flashed to create a waterproof barrier.

• Installation Process:

  • The curb is wrapped with a waterproofing membrane.

  • Step flashing is installed along the sides, with head and sill flashing at the top and bottom to channel water away.

• Advantages:

  • Elevated design reduces the risk of water infiltration.

  • Flashing for curb-mounted skylights is larger and more robust, offering better protection in extreme weather conditions.

  • Better suited for climates with heavy rainfall or snow.

  • Easier to replace or repair without disturbing the roof deck.

• Challenges:

  • May require more materials and labor for curb construction.

  • Slightly higher profile may not suit all aesthetic preferences.

Why Curb-Mounted Skylights Are Better for Waterproofing

1. Elevated Position:

   • The curb raises the skylight above the roof surface, providing an additional layer of protection against water pooling and infiltration.

2. Larger Flashing System:

   • Curb-mounted skylights use larger, independently installed flashing, which significantly reduces the risk of leaks compared to the smaller flashing on deck-mounted systems.

3. Independent Flashing:

   • Flashing is installed around the curb, creating a robust waterproof barrier. This design is more adaptable to roof irregularities and complex configurations.

4. Ease of Maintenance:

   • Curb-mounted skylights can be replaced or repaired without disturbing the surrounding roof structure, reducing the likelihood of accidental damage or future leaks.

Conclusion

For homeowners and roofing professionals prioritizing long-term waterproofing and durability, curb-mounted skylights are the superior choice. While deck-mounted skylights may offer a streamlined look, the elevated position and robust flashing of curb-mounted designs provide unmatched protection against water intrusion, particularly in areas prone to heavy rainfall or snow. Investing in a curb-mounted skylight ensures greater peace of mind and a more resilient roofing system.

Pictures From: https://www.columbiaskylights.com/why-skylights/curb-mounted-or-deck-mounted/ and https://www.veluxusa.com/