SIPs are manufactured from 3 basic components. These components are Exposure I Rated oriented strand board (OSB) for the outer faces, an Expanded Polystyrene foam core, and a crosslinked structural rated adhesive. The EPS core and the adhesives are capable of withstanding long term exposure to moisture. However, the exposure to moisture for the OSB is a key item with respect to the durability of a SIP.
The Exposure I Rated OSB is designed for limited exposure to moisture that can occur during construction, but SIPs must be covered during storage to protect from exposure to rain, snow and other elements. After installation, the SIPs should be covered with a secondary weather resistive system as soon as possible. This is required to protect the OSB from exposure to moisture long term. The installation of SIPs and the secondary weather resistive system should not occur during periods of heavy rain.
Installation details must ensure that the OSB facings and other wood components of the SIP construction are not subjected to moisture over the life of the structure. Moisture exposure could be exterior by means of bulk water making its way through the siding system or from the interior of the structure in the form of water vapor. In order to manage these potential sources of moisture, proper detailing must be accomplished.
These key detailing considerations help achieve the long term durability SIPs:
1. Application of manufacturer approved sealant at panel joints. Sealant must always be installed in a sufficient amount and applied in a continuous unbroken fashion.
2. Proper use of SIP Tape or vapor retarders as required. Selection and placement is dependent upon building use and climate conditions.
3. Proper use of code recognized exterior weather resistive systems which must include both a primary and secondary system. The cladding must provide a rain screen design which provides an avenue for water that penetrates the primary weather resistive system to drain from the wall. The cladding must be installed over a secondary system that is rated as weather resistant, such as building paper or house wrap products (i.e. Tyvek, housewrap, etc.).
4. Proper flashing and detailing of all window openings and penetrations. Ensure that the detailing of openings is consistent with forming a drainage plane which works in conjunction with the exterior weather resistive system.