As building envelope consultants working in the varied climates of New York and New England, one of the most overlooked stressors on roofing systems is something we feel every summer—heat. Roofs, particularly low-slope systems, can easily exceed surface temperatures of 150°F on sunny days. These extremes, compounded by large daytime and seasonal temperature swings, can push materials beyond their flexible limits, especially in older systems or those with poor detailing.
Understanding why these failures occur and what can be done about them is essential for long-term roof performance and capital planning.
Understanding Thermal Expansion and Roof Behavior
1. Material Movement Is Predictable—But Often Unaccounted For
Every material has a coefficient of thermal expansion. Some single-ply membranes like PVC and TPO expand and contract significantly more than traditional built-up roofs or modified bitumen systems. When these materials are constrained—by fasteners, parapets, or penetrations—they develop internal stresses. Over time, those stresses lead to membrane cracking, tenting, or seam failure.
2. Where Failure Begins: Transitions and Terminations
The most vulnerable areas on any roof are at terminations, penetrations, and flashing interfaces. These are also the exact places where thermal stresses are most likely to be concentrated. When different materials expand at different rates, it’s not uncommon for sealant joints to split, laps to peel open, or stress points to fatigue.
3. Aging Accelerates Breakdown
The older the membrane, the more brittle it becomes. Think of how a rubber band becomes less elastic over time and eventually snaps. The same degradation process—UV exposure, oxidation, plasticizer migration—happens to roofing membranes. When compounded with movement, it’s a recipe for failure.
Strategies for Existing Roofs
Spring & Fall Inspections
Catch minor damage before it becomes major. Seasonal inspections can identify early signs of movement—tenting, splitting, displaced flashing—and allow for targeted maintenance before water gets in.
Ventilation & Insulation Improvements
Poor attic or plenum ventilation exacerbates heat buildup. Excessive thermal cycling (think: attic at 140°F, rooftop membrane at 160°F, followed by a cool night drop to 65°F) causes more expansion and contraction than a system designed with better thermal balance. Upgrading ventilation or insulation can mitigate these stresses.
Reflective Coatings
Adding a reflective, elastomeric roof coating can reduce surface temperatures significantly—often by 30–50°F. This not only cuts expansion stresses but improves energy performance, particularly in compliance with ASHRAE 90.1 and local energy codes like NYC’s LL97 or Boston’s.
Prompt Repair of Minor Damage
Hairline cracks and open seams rarely stay small. Once the membrane is compromised, moisture infiltration can begin, and in freeze-thaw climates like the Northeast, this accelerates deterioration through cyclical expansion from water intrusion.
Best Practices for New Roofing Systems
Material Selection Matters
Not all membranes behave the same. Consideration should also be given to single-ply vs. multi-ply built-up systems depending on use and maintenance expectations.
Single-ply roof systems are popular for their lightweight, cost-effective, and versatile applications in roofing projects. They are ideal for various types of roofs, including exposed, green, and ballasted roofs, and are suitable for both new builds and refurbishments.
Key features include:
- Single-ply membranes can be made from materials like PVC and TPO, offering flexibility and durability.
- They allow for fast and clean installation, making them suitable for large flat roof projects such as factories and warehouses.
- These systems can support green roofs and solar PV installations, contributing to sustainability.
- They are designed for fast-track construction, reducing labor costs and time.
- Overall, single ply roofing systems provide a reliable and efficient solution for various roofing needs.
Multi-ply roof systems provide several layers of defense, unlike single ply membranes. When properly installed, mod bit membranes provide thickness stability with longer life spans. Key features include:
- System is composed of multiple layers: base sheet, modified bitumen membrane, and cap sheet.
- Highly resistant to weathering, general wear and tear.
- Exceptional waterproofing compared to other roofing materials.
- Flexible to expand and contract with temperature changes.
- Suited for commercial, industrial, and residential use.
- Offers high tensile strength, energy efficiency, and UV reflection.
- Multi-ply systems create a strong barrier against leaks.
- Composed of alternating layers of asphalt, synthetic rubber, and a reinforcing scrim.
- Weather and UV-resistant, and watertight.
Allowing for Movement
Proper installation of expansion joints—especially at large uninterrupted field areas or structural transitions—is critical. So is avoiding “over-fastening” membrane systems, which restrict their natural movement.
Cool Roof Technologies
Installing cool roofing assemblies, such as those certified by CRRC (Cool Roof Rating Council), can significantly lower membrane surface temperatures. In certain retrofit cases, vacuum insulated panels (VIPs) can allow for high R-value performance with minimal thickness, helping meet energy code requirements without compromising existing flashing heights.
Professional Installation Is Non-Negotiable
Many summer-related failures stem not from the membrane itself, but from poor substrate prep, improper fastening, or ignoring engineer’s or manufacturer installation guidelines. Remember, manufacturer’s have a minimum requirement to obtain a warranty, that doesn’t always equate to best practices to maximize life expectancy! Always insist on certified installers and documented QA/QC procedures.
Warning Signs to Watch For
- Membrane bridging or wrinkling at parapets or penetrations. Bridging typically occurs when the parapet flashing is a continuation of the field sheet instead of being independent of it.
- Cracked, curled, or visibly brittle membrane sections.
- Open or pulled-back flashing at equipment curbs.
- Interior staining or mold at ceiling or upper wall corners.
These symptoms often indicate a combination of heat stress and material failure—and warrant immediate investigation.
Long-Term Protection Is a Strategic Decision
Roofing systems don’t fail overnight. They degrade over time—accelerated by solar radiation, thermal cycling, and deferred maintenance. Incorporating seasonal inspections, understanding how your specific materials perform under stress, and implementing a proactive repair and coating strategy can extend your roof’s service life by years, if not decades.
As with any building envelope element, the earlier a professional is engaged, the more options and cost-effective interventions are available. Building owners and facility managers who treat their roofs as assets rather than liabilities often see the best long-term outcomes.
Peter Holt
Sr. Building Envelope Consultant
Duffy Engineering
