How to Prepare Your Subfloor Before You Install Hardwood Flooring

So, you’re getting ready for hardwood floor installation. Great choice. Nothing beats the warm, solid feel of real wood underfoot. But before you even think about laying those planks, there’s one step you really can’t skip: prepping the subfloor.

Yeah, it’s not the glamorous part. It’s the behind-the-scenes work that nobody sees once the floor is done—but trust me, if you ignore it, you’ll feel it. Literally. Creaks, gaps, and uneven boards will all come back to haunt you if you rush this step.

Let’s walk through how to properly prepare your subfloor before installing hardwood floors. No fluff, just real, practical advice. Because if your subfloor’s not right, your whole floor’s going to feel off.

First—What Exactly Is a Subfloor?

You’d be surprised how many people skip this basic question. A subfloor is the layer beneath your finished flooring. Think of it like the foundation for your floors. It might be plywood, OSB (oriented strand board), concrete, or even an old wood floor in some cases. Whatever it is, it’s got one job: hold your new hardwood in place without shifting, squeaking, or throwing it out of alignment.

So yeah, it matters. A lot.

Step One: Clean It Like You Mean It

Sounds obvious, but you’d be shocked at what people try to install hardwood over—dust, paint chips, drywall scraps, even nails. If it’s not firmly attached or completely clean, it’s going to interfere with how your hardwood lays.

Grab a shop vac. Sweep first, then vacuum every corner. You want that surface spotless. Not just “looks fine” clean—actually clean.

Oh, and if you're working on a concrete subfloor? Make sure it’s completely dry. Moisture is your floor's worst enemy. That leads us to…

Step Two: Moisture Check—Seriously, Don’t Skip This

Whether you're laying hardwood floor over wood or concrete, moisture can ruin everything. Wood expands and contracts. That’s normal. But if the subfloor’s got hidden moisture issues, your new floor’s going to buckle, warp, or gap over time.

Buy a moisture meter. They're not that expensive, and they're worth every penny. For wood subfloors, you're aiming for moisture content within 2-4% of your hardwood flooring. If it’s way off, give it time to acclimate before you install. For concrete, a simple calcium chloride test or relative humidity test will tell you if it's dry enough.

Think of this like checking your tires before a road trip. Not exciting, but kind of critical.

Step Three: Level Things Out

Run your hand across the floor. Feel any dips? High spots? Even slight unevenness can mess up the installation.

Grab a straightedge or a level and start checking. You want your subfloor to be flat within 1/8 inch over 6 feet. If it’s worse than that, you’ve got two options: sand down the high spots or use a leveling compound to build up the low ones.

If you're working with an old home, prepare yourself. There’s a good chance the floor’s going to need some serious work here. But skipping this part will cause all sorts of headaches later—boards that don’t lock in right, hollow sounds underfoot, or worse, actual damage over time.

Step Four: Tighten Things Up

If your subfloor is plywood or OSB, listen closely—literally. Walk across it. Hear any squeaks? That’s a problem.

Squeaks come from movement. Movement comes from loose nails or gaps between the joists and the subfloor. Drive some screws in to tighten it all up. Nails might’ve worked when the house was first built, but screws give a tighter hold now. It's a little extra time, sure, but you’ll be glad you did it.

And while you're at it, check for loose boards or panels. Replace anything that’s damaged. No point laying a flawless hardwood floor over something that’s already falling apart underneath.

Step Five: Check for Underlayment Requirements

This part depends on your hardwood floor installation method. Are you nailing it down? Gluing it? Floating it?

If you’re installing hardwood floors using a floating method, you'll need an underlayment—something to cushion the floor and block moisture. If you're gluing down planks, you might need a vapor barrier or adhesive-approved underlayment.

Pay attention to the manufacturer’s instructions here. They’re not just throwing suggestions around. Ignoring them can void warranties, and nobody wants that surprise down the road.

Step Six: Mind the Transitions and Edges

Ever noticed how pro installs just feel... polished? That’s not magic. It’s because the prep work was dialed in—especially around edges and transitions between rooms.

Check doorways, trims, and thresholds. Make sure there’s enough space to install the boards cleanly. You may need to trim door casings or adjust thresholds so everything fits together properly when you install hardwood flooring.

If you’re working in multiple rooms, take time to plan how the boards will run across transitions. It’s one of those little details that make a huge difference in the final look.

A Quick Word on Old Subfloors

If you're dealing with a really old subfloor—think squeaky, brittle, patched-together planks—you might need to replace it entirely. Sometimes, trying to patch a failing base just isn’t worth it.

You can lay new plywood over the old one, or tear everything out and start fresh. It’s more work, obviously, but sometimes that’s the only way to get a solid, long-lasting hardwood floor installation.

One Last Thing: Let Your Hardwood Acclimate

This isn’t technically subfloor prep, but it goes hand in hand. Before you install hardwood flooring, bring those planks into the room and let them sit for a few days. Hardwood needs to adjust to the room's humidity before it’s nailed or glued down. Otherwise, you risk warping later.

Let them breathe. Let the wood get used to its new home before you start laying hardwood floor.

Wrapping It All Up (Without a Bow)

Prepping your subfloor isn't glamorous, but it's everything. This is where the real success of your hardwood floor installation begins—not with the first plank, but with the hidden layer underneath it all.

Skip the prep and you’ll feel it—creaks, gaps, and maybe a regret or two. Do it right, and your floors won’t just look great—they’ll feel rock solid, year after year.

So take your time. Scrape, sand, level, test, fix, and tighten. It’s not about perfection—it’s about getting the bones of your floor ready to support everything above it.

Now, you’re ready to install hardwood flooring the right way. Let the fun part begin.

See for further details at Where Not to Install Hardwood Floors? | Robar Flooring