The short answer is simple: The first and most important requirement is that the panel material meet building code requirements. These requirements can be met by using ½” CDX plywood. But there are many other types of Wood Structural Panels that can be used to board up openings. Some exceed the capability of ½” CDX plywood, while some are worse and should be avoided.
1. Interior vs. exterior plywood panels
As the name implies, interior panel material should not be used as shutters or for opening protection. Interior panels are not designed to withstand outdoor humidity, moisture, rain and UV light. Examples of interior use panels are particle board as well as cabinet grade, AC and BC rated plywood. These products contain a resin or glue that dissolves in water and cause premature delamination. In contrast, exterior ½” CDX sheathing grade plywood is manufactured with an exterior grade glue. Periodic rain saturation does not adversely affect the glue but could cause decay to the wood. See moisture sealing panel below.
2. Panel thickness
The building code requires a minimum thickness of ½” (actual thickness 15/32”) or 7/16” OSB (Oriented Strand Board) panel. 3-ply, ½” plywood is most commonly used for opening protection. 4-ply ½” plywood has recently become available and is well worth the additional few dollars per panel as it provides additional impact protection and is not as likely to bow or warp. Many insurance based organizations that push “Code Plus” (better than code) will require 5/8” thick plywood. PlyFASTner Plus® can be used with any thickness of plywood panel. Caution should be taken, since the additional weight of 5/8” thick plywood makes installation more difficult and the fact that the thicker plywood only provides a minimal amount of additional protection.
3. OSB or plywood
Both meet the International Code Council’s definition of Wood Structural Panels and can be used for Opening Protection. Both are manufactured with exterior grade glue. Oriented Strand Board does not hold up well to the coastal humidity unprotected. Also, OSB which was designed as a sheathing material which is intended to be supported (nailed) around the perimeter AND interior studs spaced 16” apart. It does not fare well when spanning over 24”. Even with a material cost significantly less than plywood, PlyFASTner still does not suggest using OSB. Plywood provides greater longevity and superior strength. When properly stored flat (vertically or horizontally) and care given to drying out panels after use, plywood CDX sheathing will last as long as the sheathing under the shingles on a roof. See PlyFASTner recommended panel rack.
4. Treated, painted or sealed panels
Although the use of pressure-treated and Ground Contact Pressure-treated plywood is recommended for storm shutters to extend their useful life, it has been determined that treated but unsealed plywood can absorb up to twice its weight in water. A full sheet, saturated with water, could weigh as much as 135 pounds, making very difficult to move and take longer to dry out.
Painting plywood storm panels is not recommended. Paint relies on adhesion to the surface. Even good wood primers with multiple coats of paint will expand and eventually crack allowing moisture into the core of the panel. This accelerates the decay and compromises the adhesion of the paint.
The best way to preserve plywood panels is with an exterior grade moisture sealer. Sealers do not rely on adhesion but on penetration of the pores to repel contact moisture. There is no coat to crack or peal. Sealing pressure-treated plywood is the best solution to preserve plywood panels but more than doubles the cost of ½” CDX plywood.
To learn more, please visit our website and in particular we would refer you to our Learn More section. As well if you would like to purchase our Plyfastner Plus system, you can purchase it on line here.