Exterior rainscreens provide a small (roughly 3/4 inch) air gap between siding finish material and the home’s weather resistant barrier. This gap allows any inadvertent water infiltration to drain away via gravity, while also creating space for stack effect air flow that promotes drying of the exterior wall system. JLC has published numerous articles on the benefits and components of rainscreens, including Steve Baczek's classic, Rainscreen Basics,and veteran builder Doug Horgan’s recent article providing criteria for when rainscreens are most essential.
In this article, I share rainscreen flashing and trim details for our Queen of Zero project, a new high-performance single-family home in Maryland (zone 4A). Our exterior finish material is horizontal HardiePlank lap siding, and our exterior wall insulation is continuous R-26 expanded polystyrene (EPS) via structurally insulated panels. Thus, based on climate and material selections, as well as the homeowner’s interest in “future proofing” the house for resilience in an increasingly stormy, hot and humid climate zone, the upgrade to a full rainscreen-type install promised a strong return on investment.
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