What is the Proper Depth for Plywood Re-Floor? (5 Key Factors Explained)

Upgrading your floors can completely change the feel and value of your home. Over the years, I’ve worked on countless flooring projects, and one of the most important, yet often overlooked, parts of any floor upgrade is the subfloor — especially when it involves plywood re-flooring. Many people don’t realize that plywood thickness and installation method can make or break how long your floors last and how comfortable they feel underfoot.

I want to share everything I’ve learned about the proper depth for plywood re-floor — why it matters so much, how to figure out what you need, and tips from real projects that will help you avoid common pitfalls and get the best results.

What is Plywood Re-Floor and Why Does Depth Matter?

Plywood re-floor means installing a new layer (or sometimes multiple layers) of plywood over an existing subfloor or directly on the floor joists. The goal is to create a solid, flat base for whatever finish flooring you plan to install. This might be hardwood, tile, laminate, vinyl, or carpet.

You might wonder why you’d add plywood over an existing subfloor. Sometimes the original subfloor is damaged, warped, or too thin to support new flooring properly. Other times you’re upgrading to a heavier finish like tile that needs more support.

Here’s where plywood thickness comes in. It’s not just about stacking sheets — it’s about how thick those sheets are and how well they work with your home’s structure. Too thin, and you’ll have squeaky floors, flexing that can crack tile or damage hardwood, and an overall feeling of instability. Too thick, and you spend more money than needed and might run into height clearance issues.

From my experience, choosing the right plywood depth isn’t guesswork — it’s about balancing strength, cost, and the type of floor you want. So let’s look at the main factors that determine just how thick your plywood re-floor should be.

5 Key Factors That Determine the Proper Depth for Plywood Re-Floor

1. Type of Finish Flooring You Plan to Install

What finish flooring are you putting on top? This is the biggest factor in deciding your plywood thickness because different floor types have different support needs.

• Tile Flooring: Tile is rigid and heavy. It demands a strong, stable base to prevent cracking or grout failure. From my projects, I recommend at least 3/4″ (19 mm) tongue-and-groove plywood for tile subfloors when joists are spaced 16” o.c. If joists are spaced wider (like 24”), I prefer going up to 1″ thickness or adding a second layer of plywood.
• Hardwood Flooring: Hardwood is usually nailed down. For this, 3/4″ plywood works best because it holds nails securely and provides a solid feel underfoot. For engineered hardwood that will be glued down, you can sometimes go thinner (5/8″ or 1/2″ plywood), but thicker still adds durability.
• Laminate or Vinyl Flooring: These floors are lighter and more flexible. They can work over thinner plywood — often between 1/2″ and 5/8″ — but only if the subfloor beneath is already stable and flat.

In a kitchen remodel I worked on recently, the homeowner wanted large-format porcelain tile. We went with 3/4″ tongue-and-groove plywood over joists spaced 16” apart plus a cement backer board layer to make sure the tile wouldn’t crack years down the line.

2. Joist Spacing and Strength

The distance between your floor joists matters a lot for plywood thickness. Standard spacing is usually 16 inches on center (o.c.), but older homes or some designs have 24 inches o.c. or wider.

• With 16″ o.c. joists, many flooring types do fine with thinner plywood — as thin as 5/8” in some cases.
• With 24″ o.c. spacing, you need thicker plywood — generally 3/4” or more — because wider spacing means more flex when walking on the floor.

I once worked on a second-story renovation in an older home where the joist spacing was 24″. The original plywood was only 1/2″ thick, and there was noticeable bounce and creaking throughout the space. We tore up the floor and installed 3/4″ tongue-and-groove plywood, which eliminated all flex.

For safety and comfort, you want a subfloor that feels solid underfoot with no bounce, and thicker plywood helps achieve that when joists are spaced far apart.

3. Condition of Existing Subfloor

If you’re adding plywood over an existing subfloor instead of directly on joists, the condition of that base layer matters a lot.

• If the old subfloor is solid, flat, and mostly undamaged, you can often get away with a 1/2” or 5/8” overlay.
• If it’s warped, weak, saggy, or has water damage, you’ll want to replace damaged sections first and then add at least 3/4” plywood, sometimes even layering two sheets for extra rigidity.

One project I remember involved a basement floor where much of the original subfloor was nearly rotten near exterior walls due to moisture. Simply adding thin plywood would have been a waste; we replaced damaged areas with pressure-treated plywood and installed two layers totaling over an inch in thickness to get a truly solid floor.

4. Local Building Codes and Industry Standards

Building codes vary by location but often specify minimum requirements for subfloor thickness to keep floors safe and functional.

• For residential floors with 16″ o.c. joists, many codes require at least 3/4” plywood or equivalent structural panel.
• For commercial buildings or floors with wider joist spacing, codes often require thicker panels or engineered solutions like structural tongue-and-groove panels rated for higher loads.

I always double-check local codes before buying materials or starting work because inspectors may reject work that doesn’t meet standards—plus it protects your investment over time.

5. Waste Factor and Installation Method

You might not think about waste factor when choosing plywood thickness, but it’s practical for budgeting and installation.

• Thicker plywood sheets mean fewer layers are needed overall for strength.
• Tongue-and-groove edges on thicker panels help reduce movement between sheets.
• Including a waste factor of about 5-10% accounts for cuts, mistakes, and fitting odd spaces.

I’ve helped homeowners use online tools like FloorTally to calculate materials needed based on their room dimensions and waste factor. It’s saved them money by preventing overbuying while ensuring they always have enough material on hand.

What Thickness Do Experts Recommend? A Closer Look at Industry Advice

Here’s a quick summary of recommendations from industry standards combined with my personal experience:

I’ve found that going thinner than these recommendations almost always leads to issues like squeaks or floor bounce within six months to a year after installation.

Real Project Case Studies: How Plywood Depth Made a Difference

Case Study 1: Kitchen Remodel with Large Tile (3/4” Plywood)

A client wanted large-format porcelain tile in their kitchen on a second-floor remodel. The existing subfloor was uneven and damaged in places.

• We removed old plywood.
• Installed new 3/4” tongue-and-groove plywood over joists spaced 16”.
• Added cement backer board on top before tiling.

Result? No tile cracks or grout failures after two years despite heavy use. The solid subfloor eliminated flex underfoot.

Case Study 2: Old Home with Wide Joist Spacing (24” o.c.)

In an older farmhouse with joist spacing at 24”, the original 1/2” subfloor caused bouncing floors in bedrooms upstairs.

• We installed 1” tongue-and-groove plywood directly over joists.
• Finished with engineered hardwood flooring glued down.

Result? The bounce disappeared entirely; floors felt solid enough to dance on!

Case Study 3: Basement Re-flooring Over Damaged Subfloor

The basement had a mix of water damage and rotted floor panels near perimeter walls.

• Damaged sections replaced with pressure-treated plywood.
• Two layers installed totaling approximately 1-1/4” thickness.
• Laminate flooring installed on top.

Result? No sagging or creaks after three years; client was thrilled with stability.

What Happens If You Get Thickness Wrong?

I’ve seen plenty of projects where people tried saving money by using thinner plywood than recommended:

• Floors bowed or bounced noticeably.
• Tile cracked within months from flexing.
• Hardwood floors squeaked badly due to movement.
• Multiple callbacks for repairs increased overall costs.

Don’t let this be you! Spending a bit more upfront on proper plywood thickness avoids hassles later.

How to Choose the Right Plywood Thickness Step-by-Step

Here’s how I guide people through deciding what thickness they need:

1. Identify Your Finish Flooring
   What kind of flooring do you want? Tile? Hardwood? Laminate? Each has different needs.
2. Measure Joist Spacing
   Use a stud finder or look at floor plans; measure center-to-center distance between joists.
3. Inspect Existing Subfloor
   Is it flat? Sound? Damaged? This affects whether you can overlay thin plywood or need full replacement.
4. Check Local Codes
   Call your local building department or check online for minimum requirements.
5. Decide on Installation Method
   Will you install one thick layer or multiple thinner layers? Tongue-and-groove edges? Adhesive?
6. Calculate Materials & Waste
   Use tools like FloorTally to estimate sheets needed plus waste factor (~5-10%).
7. Budget Accordingly
   Remember thicker plywood costs more but saves money long term by reducing repairs.

Tips From My Experience For Better Plywood Re-Floor Installation

Thicker plywood alone isn’t enough without good installation technique:

• Always use construction adhesive between layers and under panels to reduce squeaks.
• Use screws rather than nails, spaced every 6–8 inches along joists.
• Stagger seams if installing multiple layers for strength.
• Leave a small gap (~1/8”) around edges for expansion.
• Acclimate plywood indoors for a few days before installation to minimize warping.

Following these tips will keep your floor quiet, stable, and durable.

Common Questions About Plywood Re-Floor Depth

Can I Use OSB Instead of Plywood?

OSB (Oriented Strand Board) is cheaper but less durable than plywood in some cases. For tile floors especially, I prefer tongue-and-groove plywood because it holds screws better and resists moisture longer.

Is Thicker Always Better?

Not always. Too thick can cause problems with door clearances or stairs height transitions. It also costs more unnecessarily if not required by load or finish type.

How Many Layers of Plywood Should I Use?

Usually one thick layer (3/4″) is enough if joists are close together and subfloor is sound. For damaged floors or wide joist spacing, two layers totaling over an inch can add rigidity.

Wrapping Up My Thoughts on Plywood Re-Floor Depth

Choosing the right depth for your plywood re-floor is one of the smartest moves you can make during a flooring upgrade.

By thinking through:

• What finish floor you want,
• How far apart your joists are,
• The condition of your existing subfloor,
• Local building codes,
• And practical installation details,

you’ll end up with floors that feel solid underfoot, last decades without squeaks or cracks, and protect your investment in beautiful flooring.

If you’re unsure about your home’s specifics or want help calculating materials and costs, I’m here to assist! Just ask — getting this right means fewer headaches and happier feet for years to come.

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