How level does subfloor need to be for hardwood?

Author: Shyann Erdman  |  Last update: Friday, March 28, 2025

A subfloor needs to be clean, dry, level and structurally sound. Use a level to determine if the floor is level within 3/16-inch change per 10 feet. Mark any high or low spots with a pencil or marker. If you're gluing the new floor to the subfloor, use a sander to remove oil, wax, paint, adhesives or other materials.

How flat should a subfloor be for hardwood?

Please follow these requirements:
  • Subfloor unevenness cannot be greater than 3/16 of an inch over a 10-foot span or 1/8 inch over a 6-foot span.
  • Subfloors must not slope more than ½ inch per 6 feet (25 mm per 1.8 m)
  • Subfloors must be structurally sound.

Can you install hardwood on an uneven floor?

Can You Install Hardwood on Uneven Floors? In order to properly install hardwood on uneven flooring, the floor itself has to be smoothed out. This can be done through the use of underlays and re-surfacing. For concrete surfaces, sanding and polishing may be required.

How to level a subfloor before hardwood?

The high spots should be cut down with an electric planer, setting nails first with a quarter inch punch and hammer so the blades don't get chipped or an edger with coarse sand paper. The low spots can be marked for filling using the straight-edge after this step. Underlayment mix can be used for the low areas.

What is the flatness tolerance of a subfloor?

The Standard simply defines the required flatness of a concrete subfloor. The subfloor, or 'underfloor' as I like to call it, “shall not deviate more than 3/16 of an inch in ten feet.” Photo 1 shows a ten straight edge being used to gauge the undulation of the floor.

How to Prep Subfloor for Hardwood

Can you lay hardwood directly on a subfloor?

Most engineered flooring can be installed using staples, full spread adhesive or a floating method over an approved subfloor. Make sure you have a sturdy subfloor: 3/4-inch CDX plywood is preferred and 3/4-inch OSB is acceptable.

Do I need underlayment for a 3/4 hardwood floor?

It is beneficial to install hardwood floors with an underlayment. Despite the slight increase in cost and time, the added protection will benefit your floor long-term by reducing moisture. Additionally, increasing noise and evening out minor subfloor flaws without requiring substantial rework.

Is it OK if my floors aren't level?

Though floor sloping is a common problem, it isn't purely a cosmetic problem. Floor sloping can indicate that there's a much more severe issue at hand. Sloping floors can signify that there is significant structural damage to a home's foundation, warped floor joists, or water damage requiring foundation repair.

What goes between subfloor and hardwood?

Simply put, underlayment is a layer of material between your subfloor and your floor. While some flooring comes with the underlayment attached, others will require you to install a separate underlayment. Most of the time, underlayment consists of rubber, cork, foam, or felt.

What if my subfloor is not level?

Depending on the situation, you can either sand down areas of the subfloor that are too high, or install shims beneath the subfloor so that the entire floor is brought up to the same level.

Can you install hardwood flooring below grade?

Most manufacturers will recommend you to not install solid hardwood flooring below grade.

Can you lay hardwood on uneven floors?

If you install hardwood flooring directly over an uneven subfloor, your new floor will also be uneven. But when you first cover this subfloor with a self-levelling compound, then your new floor will be level and smooth.

What is the tolerance for uneven subfloor?

The acceptable tolerance for subfloor unevenness for laminate flooring is typically 3/16 inch over a 10-foot span. If any areas exceed this tolerance, they will need to be addressed before proceeding with the installation.

How do you prep a subfloor for hardwood floors?

Preparing the subfloor is a critical step, especially for the glue down or nail down methods. Sand down the surface to remove any materials. Vacuum up the remnants, and then dispose of them. If there are any squeaky spots, securely screw the subfloor into the floor joists.

How much uneven floor is acceptable?

In general, if a floor slopes ½ inch to 1 inch for every 20 feet of the floor, it may require you to watch the situation, but it may not be a big concern. Sloping or sagging floors of more than 2 inches will indicate a problem. Sometimes, original builders slope the floor to allow for drainage.

What is the cheapest way to level an uneven floor?

The Cheapest Ways to Fix and Level Your Uneven Wooden Floors
  1. Why You Shouldn't Ignore a Wonky Floor.
  2. Option 1: Self-Levelling Compound (When Quick and Easy is King)
  3. Option 2: Shims and Plywood (for the Dedicated Cheapskate)
  4. Option 3: Sander and Patience (A Quick Fix for Light Unevenness)

Are floors supposed to be perfectly level?

Most flooring manufacturers specify a flatness tolerance, typically 1/8” over a 6-foot span, or 3/16” over 10 feet. However, tolerances can be much tighter especially for industrial and healthcare applications. In the level areas, we needed to achieve a near-zero deviation—less than 1/8” over 10 feet.

Do hardwood floors need a vapor barrier?

Conclusion. Choosing the right underlayment or vapor barrier is essential for ensuring the longevity and performance of your hardwood floors.

How many times can you sand a 3 4 hardwood floor?

Refinishing these floors more than once poses a risk of wear-through. Solid boards that have a 1/4- to 5/16-inch covering over the nails and a 3/4-inch-thick body can sustain, on average, up to 10 minor sanding jobs that mostly affect the finish or four major reworks that remove more substantial amounts of material.

Why put paper under hardwood flooring?

But it's still commonly used and if you speak with builders or wood flooring installers or architects, you hear all sorts of reasons for the purpose of this paper: It prevents floor squeaks. It's a vapor barrier. It cuts down on dust.

How flat does the subfloor need to be for hardwood?

Most experts agree that the maximum tolerance for a subfloor is 3/16” over a ten-foot span. Any dips or mounds exceeding this measurement need to be addressed before installation.

How to level a subfloor for hardwood?

Thoroughly vacuum the existing floor, and use a long floor leveler and tape measure to ensure the subfloor is level within 3/16 inch for every 10 feet. You'll need to know how to level a floor: Just sand any high spots and fill the low spots with leveling compound.

When should you not install hardwood floors?

Rooms with high humidity are generally not suitable for hardwood flooring. This is almost always solved by installing engineered flooring and/or using a finish and sealer.

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