How Many Layers Of Plywood For Subfloor? (Best Flooring Practices)


Plywood is a durable wood product that you can use for a variety of projects. In the realm of man-made wood material, it’s particularly suitable for construction projects.

But a subfloor is an extremely important part of properly laying a floor. If you’re using plywood, you need to make sure you’re using the right thickness and number of layers.

The minimum number of plywood layers for a subfloor is one, though you need to be sure you’re using a layer at least 3/4″ thick. If you’re using heavy material, such as stone or ceramic, you need at least two layers of plywood.

What Are All The Layers Of A Floor?

Proper flooring is more than the carpet or hardwood slats you see on the surface. It consists of several layers: the joists, the subfloor, the underlayment, and the surface flooring/floor covering.

Joists

The joists, also called band sills, support the entire floor system, similar to the studs in your walls. They can also house some of your plumbing if reinforced correctly. 

They’re like slats in between the foundation beams, meaning there are large gaps between them. Not all floors require joists, though, such as concrete floors.

Subfloor

Something has to go on top of the joists to actually make the floor walkable, and that’s the subfloor. The subfloor can be made of multiple types of material, but in general, it’s a flat surface that lies across the joists. This creates a smooth, sturdy surface that allows other surfaces to lie on top.

You can technically walk across and place furniture on just the subfloor, but it’s definitely not a good idea. Though it’s strong, it doesn’t offer the full protection of an underlayment, and it’s not at all pleasing to the eye or the bottom of your feet.

Underlayment

To remedy the feel and appearance of a subfloor, you have the underlayment and floor covering. The underlayment is made of softer material than the other layers and is a cushion between the subfloor and the surface.

The softness of the underlayment has several purposes.

The first is soundproofing; the underlayment prevents sounds from other floors of the building leaking through. It also softens the sounds of footsteps on the surface layer.

The underlayment can provide moisture resistance, which protects your floor covering. It can even consist of heating elements to provide warmth.

Finally, this layer acts as a barrier between the two hard layers of your surface flooring and your subfloor. Without the underlayment, your surface materials would meet directly with the tough material of the subfloor.

This would put unnecessary strain on your surface flooring, meaning it would need replacing much sooner and more often.

Floor Covering

Your floor covering, or surface flooring, is the most aesthetically important. There are so many options for flooring, each one bringing a different look to your room (and feel for your feet).

This last layer not only affects the entire look of your room, but also how you construct the layers beneath it. Using heavy materials such as ceramic or natural stone can require different layers of subflooring or even different materials altogether.

Why Is A Subfloor Important?

Since you attach it directly to the joists, the subfloor provides stability to the layers above it. It also provides a surface for the underlayment above.

Since the joists naturally have large gaps, it would be almost impossible to put soft underlayment down without it falling through. And since the floor covering needs the protection the underlayment provides, the whole system falls apart.

In the same vein, you have to choose a material and thickness for your subfloor that will protect the layers above it.

How Many Layers Of Plywood Do You Need For Your Subfloor?

Your first layer of plywood subfloor should have a thickness between 3/4” and 5/8”. While this is technically enough, it is clearly the bare minimum. Be sure to check the codes for your local area, as some may require more layers.

The number of layers you use also depends on what you use for your surface layer. Materials such as vinyl or wood don’t need as much support because they’re more lightweight.

If you’re using something heavy like natural stone or even ceramic tiles, however, you need at least a second layer. 

What Exactly Is Plywood?

Plywood is a form of engineered wood; it does not grow naturally but is instead processed from thin sheets of wood. The sheets are laid on top of each other in alternating directions with adhesive in between, and then pressed together to form a single, sturdy sheet.

Plywood is a very sturdy material and a cheaper alternative to natural solid wood. However, be careful to buy actual plywood instead of compressed or presswood; though similar, they are not the same material.

Alternatives To Plywood

Though plywood has become the standard in modern construction, there are a few alternatives for subflooring.

Wood planks are an old-fashioned material and can cause squeaks and uneven flooring over time. Concrete offers a smooth and very durable surface, and it doesn’t require the joist layer other floorings require.

However, concrete is not impervious to water, and it can be difficult to work with since you can’t use nails to attach your upper layers.

Finally, OSB, or oriented strand-board, is one of the most popular alternatives to plywood for subfloors. It’s a similar product, made of strands of wood between 3 and 4 inches thick that are glued and pressed together in a single sheet.

OSB has much denser layers than plywood, and some consider it a more durable material. It’s also cheaper, which is part of why it’s making a comeback as a leading subfloor option.

It doesn’t handle moisture quite as well as plywood, though, so be careful where you use it.

In Summary

Plywood is the leading material in subfloor construction today. It’s sturdy, smooth, and reasonably priced.

One layer of plywood subflooring is technically sufficient, but you may find that a second layer offers more support, especially for heavier floor coverings. You should also ensure your plywood layers are between 3/4″ and 5/8” thick, although the final thickness will depend on your other floor layers.

Use your local building codes and your choices for your other floor layers to determine the best layering of plywood for your project.

Katherine Ann

Katherine is a freelance writer who enjoys DIY home décor and refurbishing tired furniture. In addition to writing for PlumbJoe, she blogs about books and movies and writes creatively in her spare time.

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