Low-slope commercial roof assemblies require careful thermal design to avoid condensation, improve energy efficiency, and meet fire ratings. This article compares common insulation types and their best use cases.
Overview
Commercial flat roofs use several layers of insulation to meet code-required R-values and prevent thermal bridging at structural elements. These systems often use tapered insulation to promote drainage and combine different materials to achieve fire and moisture resistance.
Insulation Types Compared
- Polyiso: High R-value/inch, commonly used but loses R-value at low temps
- XPS: Closed-cell foam with high moisture resistance and compressive strength
- EPS: Economical but more vapor permeable
- Mineral Wool: Non-combustible and sound absorbing, used in fire-rated systems
🔍 Quick Picks
- Polyiso Roof Board: Rmax Thermaroof Polyiso
- Rigid XPS Foam Panel: Foamular 250 XPS Insulation
- Mineral Wool Roof Board: ROXUL Comfortboard 80
Additional Considerations
Always verify fire resistance using FM or UL assembly ratings. Use cover boards to protect foam layers and ensure adhesion for roof membranes. Tapered insulation systems often combine layers of ISO with varying slopes to meet drainage requirements.
Conclusion
Thermal roof insulation is not one-size-fits-all. Select materials based on compressive strength, fire rating, moisture risk, and installation sequence. Combine with tapered layouts and cover boards for the best long-term results.
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