What are Structural Insulated Panels and how do they work in Alaska?
Structural Insulated Panels, or SIPs, are prefabricated building panels that combine structural elements, insulation, and sheathing in one product. SIPs can be used for the walls, roof and floor of a building in place of more traditional construction methods, such as stick-framing. A SIP typically has a foam insulation core with a structural sheathing panel bonded to both faces. Sheathing panels are usually made of industry-standard OSB or plywood.
Building with SIPs
Constructing a home from SIPs begins at the design phase: builders must work with the SIP manufacturer since the panels are specific to the design. Once the building plans are finalized, SIPs are made and shipped to the job site. The panels are labeled so builders know exactly where each panel goes in the building.
As they are erected, the panels must be joined together according to manufacturer specifications. For instance, many panels are joined with splines that are secured with screws. When the structural connections between panels are being made, it’s critical to seal the joint between the panels to ensure it remains airtight. Air sealing the panel joints can be accomplished using sealing agents such as caulk, adhesive, mastic, spray foam or tape. A tight seal is also necessary in order to prevent moisture from entering the panel, which can lead to structural deterioration of its components over time. Some building inspectors may require a 6-mil polyethylene sheeting vapor retarder be installed on the interior side (warm side) of the SIPs once the panel construction is completed.
Electrical outlets and wiring are usually installed into recesses and holes pre-cut into the panels, both on the interior and the exterior as needed. Any special considerations for running electrical systems or other mechanical penetrations through the SIPs should be addressed with the manufacturer during the design phase.
Benefits and Concerns
There are several potential benefits to building with SIPs. For one, the absence of an air-permeable wall cavity prevents convective heat losses from occurring within the panels. Large panels will have fewer framing members than a stick-framed wall, which reduces heat losses due to thermal bridging. With an experienced crew, SIP buildings can be erected quickly, a big advantage in climates with short building seasons. Properly constructed, a SIP panel home can achieve a high level of air tightness and energy efficiency.
On the other hand, a SIP home can fail badly if it is not assembled and sealed properly. And because panels come pre-cut, builders also do not have much flexibility in on-site design changes. An experienced builder who can work through a home design with the manufacturer and who doesn’t cut corners with sealing panel joints is a necessity.
Depending on the situation, SIPs can be either cost-effective or cost-prohibitive. The design services and shipping costs may drive the price of SIPs above that of conventional framing materials. However, this can pay off in reduced labor costs if a trained crew erects a building quickly, or if several buildings of the same design are being erected.