Weather protection for SIP (structurally insulated panels)
SIPs are manufactured from 3 basic components. These components are Exposure Grade I Oriented Strand Board (OSB) for the exterior faces, an expanded polystyrene foam core, and a crosslinked structural grade adhesive. The EPS core and adhesives are able to withstand prolonged exposure to moisture. However, exposure to moisture for OSB is a key element regarding the durability of a SIP.
Exposure Rated I OSB is designed for limited exposure to moisture that can occur during construction, but SIPs must be covered during storage to protect them from exposure to rain, snow, and other elements. After installation, SIPs should be covered with a weatherproof secondary system as soon as possible. This is necessary to protect the OSB from long-term moisture exposure. Installation of SIP and secondary weather resistance system should not occur during periods of heavy rain.
Installation details should ensure that OSB siding and other wood components of SIP construction are not subject to moisture for the life of the structure. Exposure to moisture could be from outside through bulk water making its way through the cladding system or from inside the structure in the form of water vapor. To handle these potential sources of moisture, proper details must be done.
These key detail considerations help achieve long-term durability SIPs:
1. Application of manufacturer approved sealant to panel joints. Sealant should always be installed in a sufficient quantity and applied continuously and uninterruptedly.
2. Proper use of SIP tape or vapor retarders as required. Selection and location depend on building use and weather conditions.
3. Proper use of code recognized outdoor weather resistant systems that must include a primary and secondary system. The siding must provide a rainscreen design that provides a path for water to penetrate the primary weatherability system to drain from the wall. The siding must be installed over a secondary system that is classified as weather resistant, such as construction paper or home wrapping products (i.e. Tyvek, home siding, etc.).
4. Adequate flashing and detailing of all window openings and penetrations. Make sure the detail of the openings is consistent with the formation of a drainage plane that works in conjunction with the exterior weather resistant system.