Strength Characteristics

Walls

SIP walls are structurally superior to conventional stud framed walls. The core of rigid foam provides shear strength while the interior and exterior layers of OSB provide tensile and compressive strength. A panel's structure can be compared to that of an I-beam; the OSB functions like the flanges of an I-beam while the foam core serves much like the web. According to Building Systems Magazine, a SIP built home is three times stronger than a conventionally constructed home.

Roof and Eaves

SIP’s roof panels can be made with OSB splines where the face panels are designed to carry the entire load or they can be made with splines designed to share the load. In areas with 20 pound live load requirements the most economical spans are in the 10 to 12 foot range where a 2x-by shares the load.

Roof overhangs are normally a simple extension of the SIP panel and are ready for attachment of the facia and soffit trim. Where the slope dimensions exceed the 24 foot length manufacturing limitation, splines between panels can be extended so that a stick-built overhang can be added to the roof assembly.

Axial Loading

Structural insulated panels have superior axial load-bearing capacity (the strength to support vertical loads from the roof or floor above) when compared to a conventional framed wall that is capable of supporting vertical loads only where studs are located. The exterior sheathing, typically plywood, provides no support due to the gaps between the sheets. SIP'S, in contrast, can use all their capacity to support vertical loads because the OSB is prevented from buckling by the continuous reinforcement of the foam core.

Resistance to Shearing

A SIP wall is superior to a framed wall in its resistance to shearing forces as well (known alternatively as racking). This is a critical structural attribute for resisting extreme wind, hurricane and earthquake conditions.

Local Loads

SIP’s also exhibit other superior structural/strength characteristics. They are highly resistant to local loading; fasteners with proper anchors for railings, cabinets, fixtures, wall-mounted brackets, etc. can thus be anchored anywhere on a SIP’s wall.

Buckling

A SIP wall has great resistance against buckling and bending when compared to a stud framed wall. Single panels can be used for walls of up to 24 feet in height allowing for greater load capacity and wind resistance. SIP’s can be designed to both the Hurricane Code requirements and the Earthquake Code at very little additional cost.

Roofs

The structural superiority of SIP’s are also relevant to roof applications. Sloped roof panels naturally create a cathedral ceiling on the interior of the structure.

Bending Strength

The horizontal loads imposed on buildings by earthquakes or extreme winds can be effectively resisted by a SIP building because the roof can flex and act as a diaphragm. Because SIP’s provide the bending strength necessary to withstand live (snow) and dead (roofing and equipment) loads, they usually can span freely from the ridge beam to exterior walls, or between widely-spaced beams or purlins. If greater rigidity is required, SIP’s may be manufactured with increased bending strengths and reduced deflection.

Connections and Joints

SIP’s superior performance characteristics are dependant in part on the tight connections at the joints between panels, as well as the connections between panels and such other adjacent structural elements as beams, purlins, and columns.

Panels are joined together by fitting a 2 inch wide spline matching the thickness of the panels having the same depth as the foam core. Each panel edge is pre-routed to fit half of the width of each spline. The 2 inch splines, which fuse the individual panels into a single cohesive structural element, are essential to the performance of the entire wall.

Openings and Inserts

Rough openings for doors and windows are pre-cut at the factory. Headers must be installed for window or door openings of more than 4-to-6 feet and can usually be eliminated for smaller openings. The normal technique consists of routing out approximately 1-1/2 inches of foam around the perimeter of all rough openings for 2-by framing installation. The framing works effectively as both a fire-block and nailing surface. When nailed to panels above rough openings, the framing let into the panel adds to the box beam effect.

To accommodate electrical wiring, panels come with pre-routed electrical wiring chases. These chases create a network of cored-out space through which wiring can be run from the building exterior or basement up through walls and floors to the attic. Wiring chases are pre-drilled vertically at panel edges or horizontally at pre-determined locations above the finished floor. Receptacle outlets and switch boxes are usually attached to panel splines or hung on brackets attached to the interior facing material.