What is the difference between Exterior and Exposure 1 rated sheathings?
Exterior rated sheathings have a fully waterproof bond and are designed for applications subject to exposure to the weather or to moisture for its entire service life. Exposure 1 rated sheathings, either OSB or Plywood, have a fully waterproof bond and are designed for applications where construction delays may be expected prior to providing protection.
Exposure 1 rated sheathings are made with the same exterior adhesives used in Exterior rated sheathings. However, because other compositional factors may affect bond performance, only Exterior rated sheathings should be used for permanent exposure to the weather. SIPs are not to be used in applications where they will be used for permanent exposure to the weather. A rain screen must be used in conjunction with all siding materials. An acceptable rain screen is any non-perforated housewrap installed per the manufacturer's recommendations or 15# or 30# asphalt impregnated building felt installed shingle style with a minimum 4" lap.
Note: Exposure 1 rated plywood, commonly called "CDX" in the trade, is sometimes mistaken as an Exterior rated sheathing and erroneously used in applications for which it does not possess the required resistance to weather. "CDX" should only be used for applications as outlined under Exposure 1 above.