There is a vital difference between OSB panels and sheathing classified as ‘Exterior’ and ‘Exposure 1’. Utilizing the wrong panels or sheathing could compromise the structure which is exposed to weather. The classifications are based on material composition as well as the durability of the adhesives utilized in the manufacturing process.
Exterior ratings are for panels and sheathing that will be subjected to extended exposure to the elements. Exposure 1-rated panels and sheathing can withstand exposures to inclement weather during construction, but are not suitable for extended exposure. The grade stamp on each panel will indicate whether you are using Exterior or Exposure 1. Using Exposure 1-grade panels and sheathing for applications where they will continuously be exposed to weather conditions will compromise the structure.
Exterior panels are waterproofed which means that they are able to withstand extended exposure to inclement weather.
Exposure 1 classification
Exposure 1 sub-floor and sheathing panels are able to withstand weather it may be exposed to during construction without affecting the structural properties of the panel as well as a certain amount of moisture or humidity inherent in a structure. It is important to note the on-site storage recommendations from the APA which suggest that Exposure 1 panels and sheathing be stacked horizontally on a platform of 4x4s to prevent panels from coming into direct contact with the ground.
It’s also suggested that Exposure 1-rated sub-floor panels and rated sheathing be stored under tarp or roof with adequate air circulation to keep them protected from prolonged rain or snow.
If Exposure 1-rated panels and sheathing do get wet, edge swelling may be experienced. In order to prevent damage, cut the steel bands on the bundles. Allow the panels to dry properly prior to installation.
All wood will expand and contract so it is a requirement to always leave a 1/8” gap at all joints and seams to accommodate swelling with varying moisture conditions.