building sciences Truss Roof Vents Figure 2: brutally simple Wall Roof design. Note how we use wood as a thermal break between the trusses and the perimeter structural supporting steel beams. Wood is also used as “furring” to provide a further thermal break between the gypsum board ceiling and the bottom chord of the steel truss. The key to this detail is the sheet metal closure strip that provides air control layer continuity and vapor control layer continuity between the air control layer of the attic assembly and the air control layer of the wall assembly. Ditto for the vapor control layers. You install the sheet metal closure before you set the wood thermal break and before you set your trusses. The sheet metal provides a strip to connect your attic air control layer to. Gypsum board makes a great air control layer. Terminate the edge of the gypsum board ceiling in a “drywall return” and leave a gap to squirt sealant into. Bend the sheet metal closure down over the exterior gypsum sheathing and connect your wall assembly air control layer membrane to the sheet metal strip. Metal Roof Fully Adhered Roofing Membrane Roof Sheathing Metal Roof Deck Gypsum Board Air Control Layer Liquid Applied Vapor Control Layer Vented Soffit 2x Continuous Wood Thermal Break Metal Cladding Hat Channel Thermal Control Layer Water Control/Air Control/ Vapor Control Layer Service Space Interior Lining 2 × 4 Thermal Bridge Furring Sealant Sheet Metal Closure Strip Surface Mounted Fixtures Ducts Ducts Dropped Ceiling www.info.hotims.com/37990-70 66 ASHRAE Journal September 2011