A winning rim detail
If you're a SIP builder but don't yet subscribe to Building Systems Magazine, you've missed a nice article on SIP building details. Some of the details written up and illustrated by Jim LeRoy and Ted Cushman in the November/December issue are widely used, but a few may be new to you. One that doesn't show up in most manufacturer's drawings, or in the construction manual on this website (until today), is the SIP rim or band joist.
To install a SIP rim, glue and bolt down a 2x4 bottom plate that is held in 7/16" from the outer edge of your 2x8 mud sill. [Note: when you set your foundation bolts, set them close enough to the outer edge-within 3 inches-and high enough that the bolt can stick up through both the mud sill and the bottom plate; this eliminates the cost of attaching hurricane straps.] Then apply foam-compatible adhesive to both sides and the top of the bottom plate. Now slip horizontal lengths of 4-1/2" thick insulated panel down over this bottom plate and fasten it per manufacturer's specs.
These short SIP panels must be cut, preferably at the factory, to match the height of the floor joists you're using: between 9-�" and 11-7/8" would be the typical height. And the foam has to be recessed both top and bottom 1-1/2" to accommodate both plates. The longer the horizontal lengths of the panels-cut from a few extra 16' to 24' roof panels-the fewer the spline joints you'll have to deal with at the end of each panel. Where you will have posts in the walls above, carrying loads down from a ridge beam, you'll likely need to cut your rim there to embed a section of the post. After all the panels are placed, tie them together with long lengths of top plate; use adhesives and a nailing pattern as specified by the manufacturer (typically on 4" to 6" centers) to attach the OSB facings to the top plate. Fasten the panels at corners with 6" panel screws.
At corners, the crews seal joint with construction adhesive (left) and fasten them with hardened epoxy-coated screws (right).
At this point, install your floor joists. Butt them flush to the SIP rim and toe-nail them to the mud sill and the top plate. After the deck is framed, gluing and screwing down your plywood subfloor ties your floor together.
Is this really worth the trouble? In a word, yes. On-site tests with infrared cameras and blower doors shows that installing conventional rim joists in a SIP house will cause thermal and potential moisture weak points, hence alternatives are strongly recommended. In cold climates, adding an R-11 batt inside the RIP rim should give you all the R-value you need. For an extremely cold climate, you could bump the SIP rim up to a 6-1/2" thickness.