Choosing roof panels

Most builders who use SIPs in walls report that installing SIP roofs costs much more than the more traditional roof-truss alternative. However, this cost difference narrows considerably when the upper level is finished as additional living space, either by using a steeper pitch (10/12 or 12/12) or by placing SIPs in kneewalls and then roof panels at a more modest pitch (6/12 or so)

Roof SIPs range in size from as small as 4'x8' elements to as large as 8'x24'. EPS roof panels typically have 7 1/4" cores (+/- R-30) in milder climates with lower fuel costs to 9 1/4" (+/- R-40) in colder regions or where fuel costs are high. With thicker roof panels on a steep pitch, any gable-end overhanging panels need some design thought since they create a wide facia look. Urethane roof panels have a thinner profile (5 1/2" or 6 1/2") and provide higher R-values per inch plus higher R-values for the component (+/- R-35 to R-42). While they are limited in size to 4-foot widths, they offer narrower facia requirements and provide a roof with a higher service temperature.

Small panels can be raised to the roof by hand; that's fine for non-profits and do-it-yourselfers but defeats the speed advantage that SIPs offer. Larger panels (over 4'x12') are normally placed with a crane, which significantly speeds up the shell enclosure process. For those who want an exposed T&G pine ceiling, panels can be ordered from some manufacturers with the T&G pre-applied to the bottom facing; they'll need more care during handling to make sure they aren't marked up.

Roof panels typically are oriented on the building in one of two ways: 1) they run perpendicular to the long walls in a house, either clear-spanning from walls to ridge beams or at least to intermediate load-bearing purlins; or 2) they are placed parallel to the long walls, bearing on roof trusses or purlins and ridge beams. During the early 1990s, the University of Oregon's Center for Housing Innovation developed a lower-cost alternative that eliminates the ridge beam and supporting posts by relying on a structurally integrated SIP roof and SIP floor system; their roof panels attach with an overlapping joint at the peak.

SIP roofs attached to other building systems in cold climates
Straw bale home in Telluride, Colorado

Log home near Jackson Hole, Wyoming.