ROANOKE TIMES
Copyright (c) 1996, Roanoke Times
DATE: Sunday, December 15, 1996 TAG: 9612170094
SECTION: HOMES PAGE: D-2 EDITION: METRO
COLUMN: Hints for Homeowners
SOURCE: STEVE ELDER
Read any good plywood lately? You can learn a lot just by being able to decipher the grade stamp found on most plywood panels.
The information given by the stamp will enable you to use the product effectively and efficiently. It will also help prevent application errors that can come back to haunt you later.
There is a wide variety of plywood products.They can be classified by size, thickness, species of tree, strength rating, location of use, veneer grade, type of core and so forth. When selling plywood to homeowners, most lumber yards usually just distinguish between ``exterior'' and ``interior'' because they don't want to confuse the buyer by naming all the possible categories. What they actually mean is construction-grade plywood as opposed to plywood that is intended for finish work, such as interior paneling or cabinet-making.
Construction plywood is manufactured according to Voluntary Product Standard PS 1-83, a standard developed jointly by the plywood industry and the Department of Commerce. About 75 percent of mills making structural plywood belong to the American Plywood Association. APA, which changed its name in 1994 by adding ``the Engineered Wood Association,'' also sets standards for a number of other engineered wood products, such as specialty plywoods, oriented strand board (OSB), overlaid panels and plywood beams. Products that are made by APA member mills and meet the PS 1-83 standard, will bear an APA grade stamp that looks like one of the following examples:
figure l figure 2
These stamps contain the pertinent information about the plywood bearing them. In figure 1, the bold-face numbers 48/24 indicate the maximum center-to-center roof and floor span rating. This sheet of ply can be used over roof trusses up to 48 inches apart or over floor joists up to 24 inches apart. The ``23/32 inch'' denotes the thickness of the panel. ``Sized for spacing'' means that a 48-inch-by-96-inch panel will actually measure from 1/16 to 3/32 of an inch less in each dimension. This will allow for the recommended 1/8-inch spacing between installed panels and accommodate the slight expansion plywood will undergo due to increased job-site humidity.
The word ``exterior'' refers to exposure durability. There are four exposure classifications: Exterior, Exposure 1, Exposure 2 and Interior. Panels rated ``Exterior'' are designed for permanent exposure to weather. Panels labeled ``Exposure 1'' have the same waterproof glue but are intended for protected applications. Carpenters frequently call Exposure 1 panels ``CDX'' and mistake them for an exterior panel. In reality, CDX (which is usually roof sheathing) will withstand several job-site wettings, but it is not intended for permanent exposure. An ``Exposure 2'' panel is an interior panel with an intermediate glue type; it can withstand occasional conditions of high humidity and water leakage. An ``Interior'' panel means just that - it is for unprotected use only in interiors. When problems involving delamination (separation of the plies) occur with plywood, it is usually because somebody used an interior-rated piece of plywood for an exterior application.
In figure 1, the designation ``RATED SHEATHING'' appearing under the APA logo means that the panel is performance-tested. It must meet certain requirements of static and impact load capacity, fastener-holding ability and bond durability. Rated sheathing is normally chosen for structural applications such as floors, walls and roofs. The stamp in figure 2 appears on plywood manufactured with an emphasis on appearance as well as strength. Such plywood is used for the underside of soffits, wall paneling and some paint-grade cabinetry. The term ``group'' indicates the species of tree used to make the veneer. Group 1 species (such as birch, yellow pine and Douglas fir) make the strongest and stiffest plywood. In descending order of strength are groups 2-5, which include Western hemlock, various firs, spruces, cedars and pines.
The letters ``A-C'' refer to the veneer grade of the face side and back side, respectively. Grade A means the veneer is smooth and paintable with a limited number of repairs. Grade B indicates a solid surface but does permit tight knots. Some open defects and veneer splits are permitted in grade C, and grade D can have large knots and knotholes.
Do not confuse these veneer grades with the rating system for the hardwood plywoods that are used for cabinetry and furniture-making. Hardwood veneers are graded by the Hardwood Plywood and Veneeer Association.
Lastly, if you are curious about where plywood was born, the three digits in the middle of the lower black line indicate the number of the APA-member mill where the plywood was manufactured. Always check the grade stamp when purchasing plywood to be sure you got what you ordered and to double-check that what you ordered is what you need.
Read any good plywood lately? You can learn a lot just by being able to decipher the grade stamp found on most plywood panels.
The information given by the stamp will enable you to use the product effectively and efficiently. It will also help prevent application errors that can come back to haunt you later.
There is a wide variety of plywood products.They can be classified by size, thickness, species of tree, strength rating, location of use, veneer grade, type of core and so forth. When selling plywood to homeowners, most lumber yards usually just distinguish between ``exterior'' and ``interior'' because they don't want to confuse the buyer by naming all the possible categories. What they actually mean is construction-grade plywood as opposed to plywood that is intended for finish work, such as interior paneling or cabinet-making.
Construction plywood is manufactured according to Voluntary Product Standard PS 1-83, a standard developed jointly by the plywood industry and the Department of Commerce. About 75 percent of mills making structural plywood belong to the American Plywood Association. APA, which changed its name in 1994 by adding ``the Engineered Wood Association,'' also sets standards for a number of other engineered wood products, such as specialty plywoods, oriented strand board (OSB), overlaid panels and plywood beams. Products that are made by APA member mills and meet the PS 1-83 standard, will bear an APA grade stamp that looks like one of the examples shown.
These stamps contain the pertinent information about the plywood bearing them. In figure 1, the bold-face numbers 48/24 indicate the maximum center-to-center roof and floor span rating. This sheet of ply can be used over roof trusses up to 48 inches apart or over floor joists up to 24 inches apart. The ``23/32 inch'' denotes the thickness of the panel. ``Sized for spacing'' means that a 48-inch-by-96-inch panel will actually measure from 1/16 to 3/32 of an inch less in each dimension. This will allow for the recommended 1/8-inch spacing between installed panels and accommodate the slight expansion plywood will undergo due to increased job-site humidity.
The word ``exterior'' refers to exposure durability. There are four exposure classifications: Exterior, Exposure 1, Exposure 2 and Interior. Panels rated ``Exterior'' are designed for permanent exposure to weather. Panels labeled ``Exposure 1'' have the same waterproof glue but are intended for protected applications. Carpenters frequently call Exposure 1 panels ``CDX'' and mistake them for an exterior panel. In reality, CDX (which is usually roof sheathing) will withstand several job-site wettings, but it is not intended for permanent exposure. An ``Exposure 2'' panel is an interior panel with an intermediate glue type; it can withstand occasional conditions of high humidity and water leakage. An ``Interior'' panel means just that - it is for unprotected use only in interiors. When problems involving delamination (separation of the plies) occur with plywood, it is usually because somebody used an interior-rated piece of plywood for an exterior application.
In figure 1, the designation ``RATED SHEATHING'' appearing under the APA logo means that the panel is performance-tested. It must meet certain requirements of static and impact load capacity, fastener-holding ability and bond durability. Rated sheathing is normally chosen for structural applications such as floors, walls and roofs. The stamp in figure 2 appears on plywood manufactured with an emphasis on appearance as well as strength. Such plywood is used for the underside of soffits, wall paneling and some paint-grade cabinetry. The term ``group'' indicates the species of tree used to make the veneer. Group 1 species (such as birch, yellow pine and Douglas fir) make the strongest and stiffest plywood. In descending order of strength are groups 2-5, which include Western hemlock, various firs, spruces, cedars and pines.
The letters ``A-C'' refer to the veneer grade of the face side and back side, respectively. Grade A means the veneer is smooth and paintable with a limited number of repairs. Grade B indicates a solid surface but does permit tight knots. Some open defects and veneer splits are permitted in grade C, and grade D can have large knots and knotholes.
Do not confuse these veneer grades with the rating system for the hardwood plywoods that are used for cabinetry and furniture-making. Hardwood veneers are graded by the Hardwood Plywood and Veneeer Association.
Lastly, if you are curious about where plywood was born, the three digits in the middle of the lower black line indicate the number of the APA-member mill where the plywood was manufactured. Always check the grade stamp when purchasing plywood to be sure you got what you ordered and to double-check that what you ordered is what you need.
Steve Elder is a Roanoke home inspector. Questions and comments may be sent to him in care of The Roanoke Times, P.O. Box 2491, Roanoke, Va. 24010-2491.
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