There are many types of prefabricated structured insulated panels (SIPs) available. The most common have a core of expanded polystyrene (EPS) insulation sandwiched between OSB sheathing. They are built and cut to size in a factory, including openings for windows and doors, and are shipped to the job site ready for installation. Factory production and the use of engineered and recycled wood products offers the potential for a more precise product, less waste, a speedy jobsite build, and lower embodied carbon.
As the name implies, SIPs can be structural, and used for both walls and roofs, or they can be combined with timber frame, or post-and-beam construction, where appropriately sized posts, beams, and trusses carry the structural loads. This allows for fewer studs in the panels, which reduces thermal bridging and increases the overall R-value of the system. Panel joints are glued and taped and installed to create an airtight building assembly. As with all tight buildings, homes constructed using SIPs cannot rely on passive ventilation and must have well-designed active ventilation systems.
The use of SIPs results in faster construction on-site but requires careful planning involving all trades. The placement of windows, HVAC systems, plumbing, and wiring must be designed ahead of time, as changes later will be costly and complicated.
Using a SIP as a rim joist, as shown in this detail, is one way to provide continuous insulation and air-sealing in an area of the home that is often overlooked. In a conventionally framed floor, the rim joist (also known as a band joist) is set in line with the outside edge of the mudsill. The exterior sheathing is in direct contact with the rim joist and wall above. This creates a cold rim joist, with the potential for condensation to occur, and thermal bridging at each…