Plywood Size For Subfloor (Interesting Facts)

If you go to the market, you will find about three different subfloor materials – particleboard, oriented strand board (OSB), and plywood. Oriented Strand Board (sometimes known as “Chipboard”) and Plywood are usually the most common. But most builders prefer to use plywood because it is stronger, more rigid, suitable for all flooring, easier to install, and does not swell when it is wet. So, plywood is often called a superior material even though it is more expensive.

In this article, we will closely examine the best kind of plywood for your floor as well as the required thickness and strength for your home or building.

Plywood Size For Subfloor

What kind of plywood do you use for the subfloor?

Plywood sheets are designed to have a rough side and a smooth side. The rough side usually faces down, and the smooth side usually faces up. They also come in sizes – some are 4 x 8 ft, while others are 4 by 12 ft.

If you are considering using plywood for the subfloor of your next building, then you should be using either of these two kinds:

  • Standard Plywood
  • Tongue-and-Groove Plywood

(Tongue-and-Groove Plywood is often considered better than Standard Plywood)

The Tongue-and-Groove Plywood Sheets are more commonly used. They are so-called because all the four sides of the sheet have edges in the shape of a protruding tongue and a corresponding groove for them to interlock with other sheets like puzzle pieces.

When these plywood panels are installed, the edges fit into one another to prevent movement around the panel edges and this gives your building a very stiff foundation.

But you must ensure that the plywood panels are properly nailed or glued to the joists where necessary. You should also exercise some caution though, as the tongues can break off easily.

Some of the other things you have to consider in picking the best kind of plywood for your subfloor include – Insulating Capacity and Thickness.

  • Insulating Capacity of the Plywood:

Your subfloor has a great role to play in helping your feet stay warm on the floor during winter by preventing the escape of heat. It can also shut heat out of your home during summer so your feet can be cold or at least less warm.

This ability of the subfloor material to conserve heat or shut it out is called the Insulating Capacity. It is labeled on the material as the “R-Value.”

Generally, if your subfloor material has a very high R-value, it will be able to shut heat out during summer and conserve heat during winter than another material with a lesser R-value.

So in determining the best kind of plywood for your subfloor, you must consider one with a very high R-value to get the best insulating ability for your home.

(This is especially important since plywood generally has a lower R-value than Oriented Strand Boards of the same thickness)

  • The thickness of the Plywood:

Thicker subfloor materials generally have higher insulating ability than thinner ones.

So another thing you have to consider in deciding the best kind of plywood for your subfloor is the thickness of the sheet.

If you are worried about your feet staying flat and even on the floor of your building, then you have to pay even greater attention to the thickness of the plywood used.

The spacing between your floor joists is usually an important factor that determines the most suitable thickness.

But make sure to check with your local code authorities for the recommended thickness and consult with your builder or an experienced technician.

What thickness of plywood do I need for a subfloor?

Your subfloor provides the foundation for the flooring of your home or building. It also helps to reinforce your floor through the way it is screwed or nailed to joists at the base of the building.

Hence, the thickness of your subfloor has a lot to do with the kind of support you want to give your main floor, how durable and smooth you want it to be, and how much noise you will like it to insulate your building against.

For example, if your subfloor has a thickness of less than ½-inch, then there is a very high likelihood that it will dimple or cup in the middle in no time, and this might be a problem if your main floor is vinyl or tile.

You are also likely to regularly hear a creaking noise or sound as a result of wearing down of nails if your subfloor has a thickness of less than ½-inch.

These thickness values are seen as two numbers separated by a forward slash. They are referred to as “Span Rating”.

If you are using plywood as your subfloor material, then you need to pay attention to how wide apart your floor joists are, to determine the thickness of the plywood required.

Most old/traditional buildings have their floor joists spaced at 24 inches apart while most new/modern buildings have their floor joists spaced at 16 inches apart. But it is still advisable to measure the joists yourself, especially for new buildings.

The National Wood Flooring Association recommends that if your joists are between 19.2 and 24 inches apart, then your plywood panel should have a thickness of 7/8-inches or more.

Also, if your joists are apart by 16 inches or less, your plywood panel should have a thickness of 5/8-inch or less.

Can I use 1/2 inch plywood for the subfloor?

If your floor joists are less than 16 inches apart, then you may use ½-inch plywood for your subfloor.

Is 1/2 plywood strong enough for a floor?

While plywood with very high thickness is likely to be more durable, it is also equally very heavy.

So plywood of ½-inch might just be strong enough to not place too much load on the building. But you must ensure that the floor joists are not more than 16-inches apart so the sheets do not sag.

Also, if you plan to complete the floor in the attic or turn the building into a living space, then ½-inch thick plywood might not be strong enough.

If you proceed with it regardless, then the extra weight placed on the subfloor due to people walking around might cause your thin plywood sheet to flex over time – and this will damage your flooring.

Can you use 3/8 plywood for the subfloor?

You can use 3/8-inch plywood if your floor joists are less than 16 inches apart.

But you have to consider the insulating ability and consult with your builder if can support the main floor you intend to place on it.


The space between joists determines the most suitable size of plywood to be used for your subfloor. But you should also consider the R-value and Span Rating for insulation and strength.