CDX Plywood for Pole Barn Siding?
We recently had a client order a new post frame (pole barn) building kit package sheathed with 5/8” CDX plywood. The client’s intention – use plywood as a low budget siding. This one waves red flags as CDX plywood isn’t intended for prolonged exposure to weather.

A vital difference exists between Plywood panels and sheathing classified as ‘Exterior’ and ‘Exposure 1’. Utilizing wrong panels or sheathing could compromise a structure exposed to weather. These classifications are due to material composition as well as durability of adhesives utilized in manufacturing processes.

Exterior ratings are for panels and sheathing to be subjected to extended weather exposure. Exposure 1-rated panels and sheathing can withstand exposures to inclement weather during construction, but are not suitable for extended exposure. Each panel’s grade stamp 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 structure.Exterior panels are waterproofed, meaning they are able to withstand extended exposure to inclement weather.

Exposure 1 sub-floor and sheathing panels are able to withstand weather they may be exposed to during construction without affecting a panel’s structural properties as well as a certain amount of moisture or humidity inherent in a structure. Of importance, note APA job site storage recommendations suggesting Exposure 1 panels and sheathing be stacked horizontally upon a platform of 4x4s to prevent panels from coming into direct contact with the ground.
It’s also suggested Exposure 1-rated sub-floor panels and rated sheathing be stored under a 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 each bundle’s steel bands. Allow panels to dry properly prior to installation.

All wood will expand and contract so always leave a 1/8” gap between all joints and seams to accommodate swelling with varying moisture conditions.

In any case, I cannot recommend using CDX plywood of any sort as siding. Looking for low cost and durability in a post frame building siding? Painted steel siding remains to be the best value for your investment.