IRC's Canadian Construction Materials Centre (CCMC) has just evaluated a product that gives builders in Canada another option for walls and roofs: a single-rib structural insulated panel (SIP) system rather than the currently available multiple-rib structural systems (at conventional spacings of 400 mm or 600 mm). More and more, builders are considering the use of SIP systems because they combine the structural system, wall and roof sheathing, and insulation in a single step.
Developed by Plasti-Fab of Calgary, Alberta, the PlastiSpan SIP system brings the Canadian building market one step closer to offering pure SIP systems that use no ribs. The system consists of a 7/16" oriented strand board (OSB) bonded to both sides of an expanded polystyrene (EPS) insulation core. It incorporates single structural ribs at the panel edges, every 1200 mm, with a specific nailing schedule (see figure). The structural ribs are made of 2x4s for the wall panels and of either 2x10s or prefabricated wood I-joists for the roof panels.
STRESSED SKIN PANELS WITH STRUCTURAL RIBS ARE USED FOR BOTH WALLS AND ROOFS IN THESE HOUSES
CCMC's evaluation confirms that the structural reliability of the PlastiSpan SIP system is equivalent to the structural design principles of CSA O86, the engineering design code for wood. The panels also meet the air leakage requirements described in the National Building Code (NBC), as well as the vapour diffusion control requirements when there is painted drywall on the warm side of the wall assembly and vinyl siding on the cold side.
In addition, CCMC's report looks at the use of the PlastiSpan SIP system without structural ribs in post and beam or timber frame construction (see photo). The report confirms that the wall tables and roof span charts produced with Plasti-Fab's reliability-based model are accurate and comply with the intent of the NBC. It also confirms the system's seismic performance relative to conventional wood-frame shear walls.
PLASTISPAN SIP SYSTEM WALL PANELS
One of the limitations noted in the report concerns roof applications: if the top OSB layer becomes wet during construction, it must dry before installing the low-permeance roof cladding to reduce the risk of trapped moisture. Thus, in SIP construction, there must be extra attention to detail to ensure that drying can occur. In conventional roof construction, trapped moisture is less of an issue because the sheathing can dry toward the attic space. Of course, it is always considered standard good practice for all wood-based products to prevent excessive wetting in the first place.
CCMC Evaluation Report No. 13016-R is available on the Web at: http://irc.nrc-cnrc.gc.ca/ccmc/home_e.html and upon request from CCMC. For further information, contact Mr. Bruno Di Lenardo, CCMC, at (613) 993-7769, fax (613) 952-0268, or e-mail bruno.di_lendardo@nrc-cnrc.gc.ca .