Plywood Subfloor Thickness? (9 Crucial Specs!)

Imagine this: You’re knee-deep in a home reno, staring at the bare bones of your floor.

What if the squeak-free future of your beautiful hardwood hinged entirely on the plywood beneath?

The strength, the longevity, the everything? Pretty wild, right?

Let’s dive into the nitty-gritty of plywood subfloors.

1. Understanding Plywood as a Subfloor Material

Okay, so what is plywood, exactly?

It’s not just one solid piece of wood. Think of it as layers of wood veneer, glued together with the grain running in alternating directions.

This cross-graining is what gives plywood its incredible strength and stability.

We’re talking about resisting warping, shrinking, and all those fun things that can ruin your flooring.

There’s a whole alphabet soup of plywood grades out there, but for subfloors, you’ll typically see these:

• CDX: This is your workhorse. “C” and “D” refer to the veneer quality (C being better than D), and “X” means it’s suitable for exterior use, though not designed for constant exposure.

• BC: A step up from CDX, with one face (the “B” side) being smoother and having fewer defects than the “C” side. Good for when you want a slightly nicer surface to work with.

• AC: Similar to BC, but with an even better-quality “A” face. You might use this if you’re planning to leave some of the subfloor exposed as a design element.

Why bother with plywood in the first place?

Well, it creates a stable, flat, and solid base for your finished flooring.

It’s like the foundation of a house, but for your feet! Without a good subfloor, you’re setting yourself up for problems down the road.

2. The Role of Subfloor Thickness

Now, let’s talk thickness. Why does it matter?

Think of it this way: a thicker subfloor is like a stronger bridge. It can handle more weight, resist flexing, and just generally hold up better over time.

Thickness affects a few key things:

• Structural Integrity: This is the big one. A thicker subfloor is simply stronger and less likely to sag or deflect under load.

• Sound Insulation: Thicker materials naturally dampen sound better. If you’re living in a multi-story building or just want to reduce noise, thickness helps.

• Moisture Resistance: While no plywood is waterproof, thicker sheets are generally more resistant to moisture penetration.

What’s “standard” thickness?

It depends on the application, but here are some common guidelines:

• Residential: For most residential applications, you’ll see 1/2 inch (12.5 mm), 5/8 inch (15.5 mm), or 3/4 inch (19 mm) plywood used.

• Commercial: Commercial spaces, with their higher traffic and heavier loads, often require 3/4 inch or even thicker subflooring.

3. Nine Crucial Specs to Consider

Alright, let’s get down to the nitty-gritty! Here are the nine things you need to think about when choosing plywood thickness:

3.1 Thickness Measurement

Okay, this sounds obvious, but let’s be clear.

Standard thicknesses you’ll find are:

• 1/2 inch (12.5 mm)
• 5/8 inch (15.5 mm)
• 3/4 inch (19 mm)
• even 1-1/8 inch (28 mm) for heavy-duty applications.

How do you measure accurately?

Don’t just eyeball it! Grab a reliable tape measure or even better, a digital caliper.

Measure in a few different spots on the sheet to make sure it’s consistent.

3.2 Load-Bearing Capacity

This is where things get interesting.

Thicker plywood can handle more weight. Period.

Imagine a sheet of 1/2 inch plywood vs. a sheet of 3/4 inch plywood.

Which one do you think will hold up better under a heavy bookshelf or a grand piano?

Exactly.

Here’s a simplified example:

Note: This is a simplified example. Actual load capacity depends on species, grade, joist spacing, and other factors. Always consult with a structural engineer or qualified contractor for specific load calculations.

Think about the weight of your furniture, appliances, and even the people who will be using the space.

Consider the type of flooring you’re installing.

Tile, for example, requires a very stiff subfloor to prevent cracking.

3.3 Span Rating

Span rating is a crucial spec often stamped directly on the plywood.

It tells you the maximum distance (in inches) that the plywood can span between supports (like joists) without excessive deflection.

You’ll usually see two numbers, like “32/16”.

The first number (32) is the maximum span when the plywood is used as roof sheathing.

The second number (16) is the maximum span when used as a subfloor.

So, “32/16” means you can space your floor joists up to 16 inches apart if you’re using that plywood as a subfloor.

Thickness directly impacts span rating. Thicker plywood can span greater distances.

If your joists are spaced further apart, you’ll need thicker plywood with a higher span rating.

3.4 Moisture Resistance

Plywood and water aren’t exactly best friends.

While CDX plywood is designed for some exposure to the elements, it’s not waterproof.

Moisture can cause plywood to swell, warp, and even delaminate (where the layers separate).

Thicker plywood generally holds up better to moisture because it takes longer for the water to penetrate all the way through.

If you’re installing a subfloor in a bathroom, kitchen, or laundry room (areas prone to moisture), consider using a thicker grade of plywood.

Also, make sure to properly seal the edges and seams of the plywood to prevent water from seeping in.

3.5 Sound Dampening

Want to create a quieter space?

Plywood thickness can help!

Thicker, denser materials naturally block and absorb sound waves more effectively than thinner, lighter materials.

If you’re building a home theater, a recording studio, or just want to minimize noise between floors, consider using a thicker subfloor.

You can also combine thicker plywood with soundproofing underlayment for even better results.

3.6 Compatibility with Floor Coverings

Not all flooring is created equal.

Some types of flooring require a stiffer, more stable subfloor than others.

• Tile: Tile is rigid and unforgiving. It needs a very stiff subfloor to prevent cracking. I usually recommend at least 3/4 inch plywood for tile installations, and sometimes even thicker.

• Carpet: Carpet is more forgiving, but you still need a solid subfloor to prevent dips and bumps. 1/2 inch or 5/8 inch plywood is often sufficient for carpet.

• Hardwood: Hardwood flooring needs a flat, stable subfloor to prevent squeaks and movement. 5/8 inch or 3/4 inch plywood is generally recommended for hardwood installations.

3.7 Installation Techniques

Proper installation is just as important as choosing the right thickness.

Here are a few key tips:

• Stagger the seams: Don’t line up all the seams of your plywood sheets in a row. Stagger them like bricks in a wall to create a stronger, more stable surface.

• Use construction adhesive: Apply a bead of construction adhesive to the floor joists before laying down the plywood. This will help to bond the plywood to the joists and prevent squeaks.

• Fasten securely: Use screws, not nails, to fasten the plywood to the joists. Screws provide a stronger, more reliable hold.

• Leave a gap: Leave a small gap (about 1/8 inch) between the plywood sheets to allow for expansion and contraction.

3.8 Cost vs. Performance

Let’s be real: cost is always a factor.

Thicker plywood costs more than thinner plywood.

But, it’s important to weigh the cost against the performance benefits.

Skimping on subfloor thickness to save a few bucks can end up costing you more in the long run if you have to repair or replace your flooring due to a weak subfloor.

Think of it as an investment in the long-term stability and durability of your flooring.

3.9 Building Codes and Regulations

Don’t forget about the rules!

Local building codes often dictate minimum thickness requirements for subflooring.

These codes are in place to ensure the safety and structural integrity of your home.

Check with your local building department to find out what the specific requirements are in your area.

Ignoring building codes can lead to fines, delays, and even having to tear out and re-do your work.

4. Conclusion

So, there you have it!

Choosing the right plywood subfloor thickness isn’t rocket science, but it does require some careful consideration.

By understanding the nine crucial specs we’ve discussed, you can make informed decisions that will lead to a successful and long-lasting flooring project.

Don’t just grab the cheapest plywood you can find.

Take the time to assess your specific needs and conditions, and choose a thickness that will provide the strength, stability, and performance you need.

Your floors (and your feet!) will thank you.

Learn more