SIPs are made from 3 basic components. These components are exposure-rated I oriented strand board (OSB) for the exterior faces, an expanded polystyrene foam core, and a cross-linked structural-rated adhesive. The EPS core and adhesives are capable of withstanding prolonged exposure to moisture. However, the moisture exposure of the OSB is a key element regarding the durability of an SIP.

Exposure-Rated I OSB is designed for limited moisture exposure that may 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 secondary weatherproofing system as soon as possible. This is necessary to protect the OSB from long-term moisture exposure. Installation of the SIPs and secondary weatherproofing system should not be done during periods of heavy rain.

Installation details must ensure that OSB sheathing and other wood components of SIP construction are not subject to moisture during the life of the structure. Moisture exposure could be from outside via bulk water passing through the cladding system or from inside the structure in the form of water vapour. To handle these potential sources of moisture, proper detailing must be achieved.

These key detail considerations help achieve long-term durable SIPs:

1. Application of manufacturer approved sealant at panel joints. Sealant must always be installed in sufficient quantity and applied continuously and uninterrupted.

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 exterior weatherproofing systems that must include a primary and secondary system. The cladding must provide a rainscreen design that provides a pathway for water to penetrate the primary weathering system to drain from the wall. Sheathing must be installed over a weather-resistant rated secondary system such as construction paper or home wrap products (ie Tyvek, home wrap, etc.).

4. Adequate flashing and detailing of all window openings and penetrations. Make sure opening details are consistent with forming a drainage plane that works in conjunction with the exterior weather-resisting system.