What is Sheathing Plywood? How to Use It

Sheathing plywood can be used for structural and non-structural work in a residential or construction setting. It’s thicker than your average plywood board, but it’s the same as any other type of plywood. It’s made from layers of veneers that have been glued together and tightly compressed. It also contains minimal knotholes to offer better insulation and water resistance.

You can use sheathing plywood for any woodworking project, including cabinets or wall panels, but it’s not recommended. Because sheathing needs to be strong, thick, durable, and (usually) waterproof, you’re better off using a different type of plywood for other construction projects, like cabinet-grade plywood or hardwood.

Keep reading to learn what is sheathing plywood, what sheathing is for, and what the best types of plywood are for sheathing.

Is Sheathing the Same as Plywood?

Sheathing is what you do to walls, roofs, or flooring to strengthen the structure or add padding for insulation, soundproofing, or waterproofing purposes. Most sheathing is performed using plywood or OSB (Oriented Strand Board), but you can also use foam board or structural fibreboard.

Sheathing plywood is the same as standard plywood, but it’s normally named as such in stores because of the qualities it possesses that make it better for sheathing than other types of plywood. Because of its unique qualities, sheathing plywood is also more expensive than standard plywood.

Usually, sheathing plywood is made from lower-density softwoods and is either OSB, Marine Grade, or ACX plywood. These are the most durable and waterproof types of plywood that are best used for exterior sheathing.

The adhesive used to glue the core veneers is also generally made from phenol-formaldehyde for sheathing plywood, as this offers maximum strength and durability to secure the layers together. Other types of plywood usually contain urea formaldehyde or melamine.

Sheathing plywood also needs to meet building code requirements for residential construction. The required plywood thickness varies depending on the project. For example, plywood designed for exterior wall sheathing needs to be at least 3/8 inch (0.95) or thicker.

What is Sheathing For?

Sheathing is for walls, roofs, or floors and adds structural or non-structural support. It involves using wood (typically plywood or OSB) or another strengthening board to reinforce existing structures (like roofs, trusses, or joints) or to insulate/soundproof interior walls and flooring. There are three types of sheathing: roof, wall, and floor.

Most sheathing is done using plywood, but you can also use fibreboard, cement board, gypsum, foam boards, or glass mat. However, these can’t be used for all types of sheathing. For example, fibreboard is good for wall sheathing to provide insulation, but it isn’t structurally strong, so should be fitted with particle board or plywood to offer strength and padding.

Types of sheathing

	Wall Sheathing (Interior & Exterior)	Roof Sheathing	Floor Sheathing
What Is It For?	Offers extra strength, insulation, soundproofing, and better aesthetics to interior and exterior walls. Walls are typically sheathed with plywood or OSB for insulation and reinforcement, or tiles/wall paneling for aesthetics.	Provides lateral support to the roof frame by distributing weight more evenly across the entire roof, rather than only via the rafters and trusses. It can also be laid to prevent leaks and provide a foundation for laying shingles or for decorative purposes in an attic.	Covers the floors and is installed over a floor frame to provide structural support and a strong platform to walk across. It can be used in construction sites to bear load or in residential settings as a subfloor.
Best Material to Use	PlywoodOSBTilesCement BoardGypsumGlass MatDecorative Wall Panels	PlywoodOSBFibreboard	PlywoodOSB

Why is It Called Sheathing?

Sheathing means to encase or protect something. When used in the context of construction, sheathing means reinforcing (i.e., encasing) something to make it stronger, sturdier, and more waterproof/insulated. When you are reinforcing walls, floors, or roofs, you are “sheathing” them because you are encasing the areas by adding plywood (or another material) to make them more suitable for daily use.

Is Sheathing Ply Waterproof?

No, sheathing ply is not naturally waterproof. Plywood used for sheathing is constructed of veneer sheets glued tightly together. It’s strong, durable, and ideal for use on interior and exterior construction projects. There are different types of plywood available, and some are more moisture-resistant than others, like Marine Grade or Water Boiled Proof (WBP) plywood.

You can make plywood waterproof by sealing the surface and edges with epoxy synthetic resin or oil-based polyurethane. Both sealants can be used on sheathing ply indoors, like in bathrooms or high-humidity areas, and externally, like on sheds, outhouses, or roofs.

When using epoxy externally to make painted or stained plywood waterproof, it’s best to apply a UV-resistant sealant after the epoxy has set. This will protect the finish from discoloration and prolong the epoxy’s lifespan.

Can You Use Sheathing Plywood Outside?

Sheathing plywood is usually water-resistant, so it can be used outside. However, it should still be treated to make it fully weatherproof. Otherwise, prolonged water exposure can cause moisture to penetrate the veneers and cause the wood to warp and rot. When sealing sheathing materials, it’s especially important to ensure any cut edges are sealed properly, as these have been exposed and are most prone to water damage.

How Strong is Sheathing Plywood?

Sheathing plywood is one of the strongest types of plywood. Being designed for permanent structural use and structural strengthening, including walls, floors, and roofs, it’s designed to withstand high impact and hold heavy weights over prolonged periods without bending.

Sheathing boards can be used on the roof of sheds, barns, outbuildings, and houses to strengthen the supporting beams. When fixed to the trusses and floor joists, it can help the roof withstand heavy loads, like snow, without boding.

The strongest type of plywood is Marine Grade, which is made with minimal knotholes and uses high-quality glue to keep the plies together. Its lack of knotholes also makes it the most waterproof type of plywood suitable for exterior wall sheathing. However, it should still be sealed before use outdoors or in areas with high humidity.

How strong the sheathing plywood is depends on its size and thickness. Most plywood can withstand weights between 5-50lbs, with smaller, thinner sheets holding less and larger, thicker sheets holding more. Naturally, the larger and thicker the sheet of plywood, the more it will cost. Learn more about the costs of plywood.

Remember, the thicker the plywood, the heavier it will be. Always ensure the supporting structure can withstand the weight of plywood before installing it. For example, if installing sheathing plywood on attic subfloors, you need to check the ceiling beams and joists can withstand the weight. Learn more about how to choose the right plywood weight and plywood thickness.

What Type of Plywood is Used for Sheathing?

There are four types of plywood best used for sheathing: OSB/particle board, Marine Grade plywood, ACX plywood, and WBP plywood. Each type is best used for different purposes. Remember, sheathing needs to be thick and must meet your local building codes, so always check how thick your plywood needs to be before purchasing sheathing for residential settings.

Here’s a table summary of the types of plywood used for sheathing:

Type of Plywood	Wall Sheathing (Structural Support)	Wall Sheathing (Insulation / Soundproofing)	Floor Sheathing	Roof Sheathing
OSB / Particle Board	No	Yes	No	Yes
Marine Grade Plywood	Yes	Yes	Yes	Yes
ACX Plywood	Yes	Yes	Yes	Yes
WBP Plywood	Yes	Yes	Yes	Yes

Should You Use OSB or Plywood for Sheathing?

You can use both OSB or plywood for sheathing, but there are advantages and disadvantages to using each material. Firstly, OSB (also known as particle board) is not as waterproof as plywood, so it isn’t ideal for exterior sheathing or wall sheathing in high-humidity areas, like bathrooms.

Despite its thickness, OSB is not as strong or durable as plywood. When used as a subfloor, particle board can bode between joists over time. This is especially a problem if used in heavy load-bearing areas, like basements with appliances, garages, or sheds.

However, OSB is cheaper to purchase compared with plywood. It’s also extremely lightweight, making it easier to carry, and very flexible. In addition, it has better insulating and soundproofing properties compared with plywood. This often makes it a better choice for interior wall sheathing.

On the flip side, plywood is strong, durable, and long-lasting. It can withstand very heavy loads without bowing, making it ideal for subfloors. When you use exterior sheathing plywood (also known as Marine Grade or ACX), it is more naturally water-resistant. However, it should still be treated to fully protect it from direct moisture and all weather.

The disadvantage of using plywood for sheathing is that it’s dense. This makes it harder to carry/install alone, especially when using it for roof sheathing. You should always check the joists/trusses in floors or roofs can withstand the weight of plywood before installing. Because plywood is stronger and more waterproof, it’s also more expensive than particle board. 

	OSB	Plywood
Pros	InexpensiveExtremely lightweightFlexible	StrongDurableWater-resistant
Cons	Low water-resistanceSwells when wet	Heavier/denserMore expensive
Best Used For	Interior Roof SheathingWall Sheathing (Insulation/Soundproofing)	Interior/Exterior Roof SheathingFloor SheathingWall Sheathing (All Types)

Summary: Things to Remember

• Sheathing is thicker and more water-resistant than standard plywood
• Use different types of plywood for wall, roof, and floor sheathing
• Sheathing ply is waterproof, but should still be treated for exterior use
• OSB and plywood can be used for sheathing, but plywood offers more universal advantages than OSB
• Always check local building codes and regulations before sheathing