The Benefits Of A Flat, Even Subfloor – And How To Achieve It

The Benefits Of A Flat, Even Subfloor - And How To Achieve It

Installing hardwood floors is a complex process that should always be left in the hands of a trained professional. If hardwood flooring is not properly installed, it can lead to structural and aesthetic damage over time, including warping, bulging, cracking, and even irreparable moisture damage. 

Professionals know that the installation of hardwood flooring has to factor in multiple things, from floor prep and acclimating the wood planks, to using the right tools and machines and post-installation cleanup. Making sure the hardwood floors are placed over a flat, even, sound subfloor is a crucial step in the installation process, and one that should never be skipped. 

What is the purpose of a subfloor?

Most homes and buildings out there feature some kind of a subfloor, except perhaps very old homes. It’s an essential layer of protection that keeps moisture away from the hardwood planks, and provides support and a flat surface to ensure proper installation. The subfloor can directly impact the longevity of hardwood floors, so it’s crucial to choose the right type of subfloor and the right installation method. 

Subfloors should be installed beneath every type of flooring, be it hardwood, engineered wood, natural stone, ceramic tile, vinyl, laminate, or carpet. For hardwood flooring, plywood is the most common option. The subfloor is a sturdy structural layer placed right underneath the flooring on joists. It provides a stable surface that keeps the wood from creaking or squeaking underfoot, but also protects the hardwood planks from damage caused by heavy furniture or heavy traffic. Last but not least, the subfloor can also help with soundproofing hardwood floors.

Subfloors typically consist of 4×8 or 4×12-foot sheets of A/C-graded plywood, nailed or screwed onto the joist layer beneath the hardwood flooring. What the A/C grade represents is that one side of the subfloor has a smooth finish, while the other side is rougher, usually the bottom side. 

Subfloor vs underlayment 

The terms subfloor and underlayment should not be used interchangeably, because they are very different things. While the subfloor is the middle layer of the flooring system, providing a structurally-sound flat surface, the underlayment is different. 

The underlayment sits directly beneath the hardwood flooring, and it consists of a thin protective layer made of cork, felt, rubber, or foam. While the subfloor is required in every type of flooring system, the underlayment is optional. It’s always a floating-type of flooring and should not be glued down to the subfloor, in case repairs or replacements are necessary for either of the flooring layers. 

Why a flat subfloor is crucial for proper hardwood flooring installation

If hardwood flooring is installed over an unlevel subfloor, it can lead to creaking and squeaking whenever someone walks across it. It can also cause structural damage over time, leading to warping and denting of the hardwood planks, and affect the longevity of the floor. 

The subfloor has to be stiff and rigid to provide a flat base for the hardwood floors installed on top. It needs to be sturdy enough to withstand heavy foot traffic, heavy furniture, kitchen cabinets, or bathroom tubs, depending on the space. 

Another important aspect is that the subfloor must be moisture-resistant, to ensure it will maintain its stiffness and strength even after exposure to elements during construction work. If the subfloor doesn’t have good moisture-resistance, it can often swell and buckle over time, leading to the hardwood floors above to look uneven and even slope. 

Moisture is the biggest enemy of hardwood, so it must be avoided at all costs. This is why hardwood planks need to acclimate before installation, and the space they’re installed in should be properly ventilated and humidity levels stabilized prior to installation. 

How to achieve a flat, even subfloor 

Before you begin to install hardwood flooring, it’s important to take the time to properly ventilate the space you’re working in, and to acclimate the hardwood planks. Fix any structural issues and prep the surface for the subfloor. 

A/C-rated plywood with ½-inch or ¾-inch thickness is the most common type of subfloor used for hardwood flooring. Tongue-and-groove plywood can reduce squeaking and creaking and ensure the subfloor is properly fitted underneath the hardwood. 

Another popular option is oriented strand board, or OSB, because it’s slightly more affordable than plywood and offers more flexibility. The downside of OSB, however, is that moisture can lead to significant swelling and warping, and it’s not the best option for heavy flooring like tile or stone. 

To even out the subfloor prior to the hardwood flooring installation, it’s important to fix any issues, holes, using the right products for the job. You can use the Savogran Level-Best Floor Leveler to even out wood or concrete floors, or the Liquid Nails Subfloor & Deck Construction Adhesive. Also make sure to use the right tools for the proper installation of the hardwood planks, to ensure durability and, of course, client satisfaction. 

Find more tips on the First Atlanta Flooring blog, and contact us with questions about our products.