What is Plywood?
Along with concrete blocks and lumber, plywood is one of the main staples of residential and commercial construction. Plywood is made from thin wood veneers or “plies” that are then glued together, pressed and heated to form sheets. The wood grain of the plies is rotated 90° with each alternate layer to reduce expansion and contraction of the wood. This gives plywood stability and resistance to shrinkage, breaking, warping, and cracking. The more plies a sheet has, the stronger and thicker the board is.
The Plies of Plywood
The layers of veneer or plies of the plywood help determine the strength of the sheet. Plywood must have a minimum of three plies and are usually combined in an odd number of layers. Also, plywood sheets that have a different number of plies can have the same thickness. The most common plies are:
- 3-ply is one of the most common types of plywood. With three layers of veneer, it’s strong and durable. It can be a desirable choice for indoor use with a more decorative look than plywood with more layers.
- 5-ply refers to the five layers of veneers. This is a common type of plywood that is suitable for a wide range of miscellaneous and construction uses where rigidity and strength are needed.
- Multi-ply plywood is used mostly for exterior use and roofing. Usually designed with seven or more layers, it creates an extraordinarily strong, durable home frame material that will withstand wind and weather damage.
Plywood Grades
Plywood receives grades (ranging from A to D) based on the number of blemishes on the product.
- Grade A: Both the face and back are nearly free of defects, with a smooth, sanded surface and virtually no knots. Ideal for cabinet doors and furniture and can be painted or stained.
- Grade B: Also sanded smooth, but the face and back have a few defects. These blemishes may have been repaired filler. Cheaper than Grade A.
- Grade C: Unsanded, with tight knots up to 1-½-in width. Larger sections that have been patched and filled. Good for subflooring or other applications where appearance is not important.
- Grade D: Also unsanded, with knot holes up to 2-½-in width. Generous patching and filling with some unrepaired defects. Like Grade C, good for structural uses where it will not be seen.
When two grades are indicated, such as A/B, the A refers to the face and the B refers to the back. This can save costs to the mill. The most common is B/C-grade, which is a mix of B-grade on the face side and C-grade on the back side.
Plywood Ratings
In addition to grading, plywood is also rated for where it should be used and the ability to withstand moisture.
Exterior: These panels are waterproofed to tolerate adverse weather conditions. Exterior rated plywood is used on outdoor buildings that will be exposed to the elements.
Exposure 1: These panels have been waterproofed but only for the construction period. They are not manufactured for extended exposure like exterior panels are.
Exposure 2: The plies in this plywood have a transitional adhesive that is not designed for long-term water exposure and thus not fully waterproof. Occasional exposure is okay, but Exposure 2 panels are best for interior use.
Interior: These panels have no waterproofing at all and should not be exposed to moisture. They are intended for interior use only.
Structural 1: These panels are constructed to be earthquake resistant and are rated for seismic retrofitting. Only Structural 1 panels can be used in this type of construction work.
Plywood Sizes
Plywood panels are available in three main sizes: 4-ft x 4-ft, 4-ft x 8-ft, and 4-ft x 10-ft.
You should choose the thickness depending on what type of project you have. Plywood is usually made from 1/8-in thick to more than 1-1/2-in thick. Most common plywood thicknesses are 1/4-in, 1/2-in, and 3/4-in.
Exterior & Interior Use
Exterior plywood is used outside the home where durability is required. Bound together using water-resistant glue that doesn’t wear off easily, this plywood is wind and weather resistant. Some of the most suitable applications for exterior plywood are walls, roof linings, and outdoor structures.
Interior plywood is not very resistant to outdoor elements and tends to degrade quickly when exposed to moisture and heat. Some of the popular applications for interior plywood include indoor furniture, interior cladding, and craft projects. Check out our article Simple DIY Plywood Projects to Upgrade Your Home for great ideas to make.
Sanded Plywood
A sanded plywood face provides a beautiful high-quality surface that is ready for finishing. It is used where the outward appearance is important. It is resistant to dents, scratching and gouging. And thanks to being sanded at the mill, minimal if any additional sanding is required for most applications.
Typical construction uses include stair treads and risers, cabinets and built-ins, shelving, paneling, accent panels, and furniture projects.
Plywood Sheathing
Exterior plywood sheathing is used on weather-protected building exteriors like roofs and walls underneath siding. Sheathing is normally rated CDX, with a C-grade face, D-grade back and X for weather exposure. It has exterior rated glue to stand up to the elements.
Plywood Underlayment
Plywood underlayment is water repellant and thicker than normal plywood, ranging from ¾-in to 1-1/8 in. It is a durable, single-layer flooring panel for use under hardwood flooring, carpet and pad, and tile and vinyl floor coverings.
Look for tongue and groove panels for a squeak-free floor. The sheet should be labeled “T&G”.
Hardwood & Softwood Plywood
Hardwood plywood is made from oak, maple, poplar, birch, and walnut trees. It is designed for demanding end uses. Having between three and seven layers, hardwood plywood is characterized by its excellent strength, stiffness, and durability. Hardwood plywood has outstanding surface hardness, making it damage and wear resistant. This tough exterior makes it a choice for packing cases, speaker boxes, and furniture.
Softwood plywood is usually made either of Douglas fir, pine, Southern yellow pine, and whitewood and is typically used for exterior frame sheathing, roof sheathing, and sub-flooring. Softwood plywood is also ideal for projects like sheds, plant boxes, doghouses, and shelving.
Plywood Project Panels
Plywood project panels are convenient, pre-cut boards ideal for fast and simple DIY tasks. Available in a variety of wood types, plies, and alternative materials, they’re perfect when you already have your project measurements in hand. Easy to work with and beginner-friendly, they’re an excellent choice for anyone starting out in DIY. And for more creative projects, our article How to Bend Plywood the Easy Way will show you how to form sheets to fit your projects.
Plywood Sheathing vs. OSB
Plywood sheathing and OSB (Oriented Strand Board) are both universally used structural panels in construction, especially for walls, roofs, and subfloors. Here’s a breakdown of their key differences:
Material Composition: Plywood sheathing is made from thin layers or plies of wooden veneer glued together. OSB is made from wood strands compressed and bonded together in a crossways-oriented configuration.
Strength: Plywood is stronger overall, impact resistant and better able to hold nails and screws. OSB is comparable strength-wise, but the edges can swell when exposed to moisture.
Moisture: Plywood can withstand water better as it dries faster and is less likely to swell and warp. OSB will absorb water more slowly but will retain it longer if not adequately sealed.
Appearance: A smooth and uniform surface are features of plywood. OSB has a rougher, chip-like appearance that is typically left unfinished and hidden from sight.
Cost: Plywood is usually a bit more expensive due to the manufacturing process and better materials. OSB is more budget-friendly, making it a popular choice where costs are concerned.