reasons why synthetic paper underlayment may not always be the best choice for roofing projects.
Synthetic paper underlayment has certain drawbacks related to the number of nails required for installation and the damage those nails can cause, which can make it less effective in some roofing scenarios. Here’s a detailed breakdown:
1. Increased Nail Density Requirement
Synthetic underlayment often requires more nails (or staples) for secure installation compared to traditional felt. This is because its lightweight nature makes it more prone to wrinkling or shifting under wind pressure or during installation.
Manufacturers’ guidelines often mandate closer nail spacing, especially in high-wind or steep-slope applications, which increases the number of penetrations in the roof deck.
2. More Nail Holes = More Potential Leak Points
Every nail driven through the underlayment and into the roof deck creates a potential entry point for water. Even when nails are properly installed, the increased density of nail holes raises the likelihood of water infiltration, especially if:
Fasteners are overdriven, creating tears in the underlayment.
Nails are driven at an angle, compromising the seal around the hole.
Roofing materials above shift due to wind or thermal expansion, loosening nail seals over time.
3. Nails Compromise Synthetic’s Waterproofing
Unlike felt, which can self-seal around nails to some extent, many synthetic underlayments are not as forgiving. The waterproofing integrity of synthetic material depends heavily on proper installation and the quality of the fasteners.
When synthetic underlayment is punctured, it cannot "heal" around nails, leaving gaps that can allow water to seep through, especially under conditions of wind-driven rain or ice damming.
4. Risk of Wind Uplift and Tearing
In regions with strong winds, synthetic underlayments often require additional fasteners to prevent wind uplift. However:
The lightweight material is more prone to tearing around nail holes during high winds, which can compromise the underlayment's integrity.
Once tearing begins at a nail hole, it can propagate across the underlayment, creating larger vulnerabilities in the roof.
5. Potential Damage to Roof Deck
The increased number of nails can also damage the roof deck itself, especially on older structures where the decking material may already be weakened.
Over time, repeated nailing (e.g., during reroofing projects) can degrade the structural integrity of the roof deck, leading to the need for costly repairs or replacement.
6. Labor-Intensive and Error-Prone
The higher nail count required for synthetic underlayment makes installation more labor-intensive. This increases the risk of human error, such as:
Misaligned nails missing the roof deck entirely.
Overdriven nails that create small tears around the fastener, leading to leaks.
Inconsistent nail patterns, especially on slopes or edges, which can leave the roof vulnerable to wind-driven rain.
7. Impact of Thermal Expansion on Fasteners
Synthetic underlayment can expand and contract with temperature changes. This movement can:
Stress the areas around nails, enlarging the holes over time.
Loosen fasteners, reducing their effectiveness and potentially leading to leaks.
Conclusion:
While synthetic underlayment offers advantages like lighter weight and resistance to tearing during handling, its reliance on a high density of nails introduces significant vulnerabilities. More nail holes mean more potential for water penetration, and the material’s inability to self-seal around those holes further diminishes its effectiveness. For long-lasting performance, careful consideration of installation practices and site conditions is critical when using synthetic underlayments.
