Building with SIPs

SIPs or Structural Insulated Panels are the key ingredient in making every PEA Builders’ house strong, well insulated and amazingly tight.

Strength: The osb skins on SIPs act similar to an I-beam or I-joist. Dimensional lumber is glued and nailed into the factory cut channels creating a double sided I-beam of sorts. This makes a wall section of SIPs 2 to 3 times stronger than conventional stick frame construction, because loads are transferred through both sides of the osb skin. This also creates an ideal situation for meeting the strict wind loads in WI building codes. The whole house becomes a “Shear Wall” able to handle transverse loads much higher than metal braced or single sheathed exterior plywood structures.

Insulation: The insulation value per inch of Polystyrene in SIPs, although not  high at about 3.7 per inch, is continuous. Consider the insulation value of an R-13 SIP wall vs. an R-13 fiberglass/stick wall. Since the stick wall has 25% of its exterior insulation surface in studs, it has a considerable loss of insulation value. And since only the plate material changes when SIP walls get thicker, it costs very little to upgrade to thicker walls. We typically use 6″ or 8″ with an extra layer of foam on the exterior for a water barrier, which gives us R-values of 26 and 34 respectively.

Air tightness: Probably the most important aspect of SIPs is how air tight they are. Fewer pieces and heavy attention to caulking make SIPs up to 4 times tighter then stick walls. Non-uniform stud cavities and poor quality installations are the norm with fiberglass insulation. Although many different band-aide approaches have been developed to counteract these failures, nothing comes close to the simplicity of SIPs. Continuous polystyrene insulation surrounding the whole house gives performance values for air tightness that rival that of the German “Passive Haus”. With 8″ SIP walls, PEA Builders regularly gets ACH (Air Change per Hour) numbers under .6 ACH @ 50 pascals or .05 ACH (normalized). That’s about 70% better than “Energy Star” standards.
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