Exterior gypsum sheathing is widely used in non-combustible wall assemblies for its fire resistance and compatibility with WRB systems. This article reviews the types, installation methods, edge and fastener detailing, and temporary moisture protection strategies.
Types of Exterior Gypsum Sheathing
- Glass-Mat Faced: e.g., DensGlass®, GlasRoc® – mold/moisture resistant, non-paper
- Paper-Faced: Suitable for interior partitions only – not water-resistant
- Fire-Rated Core: 1/2″ or 5/8″ thickness – required in fire-rated assemblies
Installation Guidelines
- Use corrosion-resistant fasteners (screws or nails) – 8″ o.c. edges, 12″ o.c. field
- Sheathing should be gapped 1/8″ at ends and edges to allow expansion
- Stagger vertical joints – never align four corners in one location
- Install with the long edge horizontally for added racking strength
Moisture Protection and WRB Integration
- Use fluid-applied or self-adhered WRBs over gypsum sheathing for waterproofing
- All vertical and horizontal joints must be sealed with approved tape or flashing
- Protect exposed sheathing during construction – max 12 months (typically 6)
- Install cladding anchors and furring through sheathing into framing
Field QA and Long-Term Performance
- Document sheathing condition at time of WRB installation
- Photograph seams and corners to verify proper flashing coverage
- Ensure no damage or exposure of gypsum core before cladding is applied
- Reinspect prior to installation of rigid insulation or rainscreen components
Sheathing should be handled with care to avoid edge chipping and must be stored off the ground and protected from bulk water at all times on site.
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