Parapet walls are frequent sources of thermal bridging and air leakage in commercial and multifamily buildings. This article outlines effective strategies to detail parapets while preserving all four control layers: water, air, vapor, and thermal.
Parapet Design Challenges
Parapets create interruptions in wall and roof continuity, increasing risks of air infiltration, condensation, and thermal bridging. Improper transitions at the roof membrane, sheathing, and insulation layers can also result in water intrusion and decreased durability of roof edge materials.
Control Layer Strategies
- Extend the air barrier membrane continuously from the wall sheathing up the back and over the parapet cap
- Use compatible roof membrane flashing or transition tapes at the parapet base and wall tie-ins
- Install continuous rigid insulation or tapered mineral wool over the parapet face and top
- Use metal coping caps with continuous cleats and drip edges to shed water
Thermal Bridging and Fire Resistance
Parapet blocking and backer studs often create a direct path for heat loss. Offset wood framing or use insulated nailers and fasteners designed for low conductivity. In fire-rated parapets, wrap mineral wool or install non-combustible parapet blocking and extend roof membrane under coping metal per UL parapet assembly designs
Inspection and Detailing Tips
- Overlap air barrier and roof membrane by 6” minimum with compatible primer or flashing tape
- Install slope-to-drain at parapet caps to prevent ponding
- Use stainless fasteners and continuous cleats for coping attachment
- Visually inspect for air gaps or thermal discontinuities at parapet ends and joints
Mockups should include the entire parapet return to evaluate membrane compatibility, coping attachment, and thermal alignment.
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