Cantilevered floor systems are frequently used in residential architecture. They provide an opportunity to capture additional square footage without enlarging the house’s footprint. But they can be problematic if not detailed well—leading to moisture issues and occupant discomfort. Correctly positioning the water, air, vapor, and thermal control layers is crucial.
In the control layer hierarchy, bulk water management comes first. An overhanging floor system inherently protects the wall assembly below but we should still strive for appropriate water management within the wall assembly itself. In this detail, we used Zip R-6 sheathing, a type of OSB backed with 1 in. of laminated rigid-foam insulation with an integrated weather-resistant barrier (WRB). Using Zip R means there is no need for an additional weather barrier. Once installed, all the joints should be wiped cleaned, sealed with Zip tape, and rolled with adequate pressure. (Click here for “Zip Sheathing Tips.”) The taped Zip R will handle the field of water management.
To reduce stress on the WRB, a drainage/ventilation plane is created on the face of the Zip R sheathing using 1×3 wood furring strips spaced 24 in. on center to align with the 2×6 stud framing below. A corrugated vent strip runs along the bottom of the gap, allowing for proper drainage and adequate ventilation; it also keeps bugs and critters out. In this case, the exterior finish—cement board siding—is installed on top of the furring strips.
With the water management control layer positioned for success, the next consideration is air leakage. Air-sealing protects against the transfer of energy either by heat loss or heat gain through the building assembly. Restricting the flow of air diminishes the energy penalty. A good air-sealing strategy also prohibits moisture from moving along an air stream and hitting a cold surface, where it can condense…
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