Flooring subfloor product optimum for home insulation

What Is the Best Subfloor Thickness for Optimum Insulation?

If you are in the market for new flooring, you may already be overwhelmed by the number of choices you have to make. But the decision-making does not end once you settle on mahogany hardwoods or contemporary porcelain tiles. There are subflooring aspects to consider that can significantly impact the comfort and longevity of your flooring.

The good news is that there are many added advantages to getting the right subflooring, including energy savings. Installing adequate insulation in a roof space or walls is a common construction practice, but flooring is often overlooked. By conduction or through leaks, air can seep through your floor, reducing your home's energy efficiency.

How can subflooring help mitigate these issues? Keep reading to find out. You will be able to select subflooring that makes the floors in your home sturdier and more comfortable while helping save on your energy bill as well.

Subfloor Basics

Renovating flooring is one of the smartest return-on-investment decisions you can make for your home. For this reason, it is important to understand the complexity of this undertaking. Flooring structure is much more than some boards laid atop your foundation.

Every floor is made of two or three layers. There is the outer, visible layer of carpet, vinyl, tile, hardwood, or other material. This is what most people consider when they think of "floors." But there are sublayers that are as important, if not more so.


Underneath the top flooring layer is often (though not always) an underlayment. It comprises padding materials and is typically about 1/4 to 1/2 inch in thickness.

The purpose of the underlayment is to provide a sturdy yet comfortable layer for your outer flooring to sit on. Underlayment can be made of wood or even cement, but most often is some type of foam padding.


Beneath the underlayment is a subfloor that is the foundation for the entire flooring structure. It secures to the baseboard joists to form a base structure for the flooring.

The subfloor layer is usually made of plywood, particleboard, or oriented strand board (OSB). OSB is compressed layers of wood flakes held together by some type of adhesive. It was invented in the 1960s and, since that time, has become common in various load-bearing applications.

In addition to providing structure, subflooring can be the first line of defense against air and moisture coming up from underneath the home. For this reason, subflooring is usually coated in a layer of resin that helps stave off rot and corrosion.

If not protected, subflooring can swell when exposed to moisture or dampness. If you have ever walked on a squeaky or unstable wooden floor, it is most likely due to an uneven, misshaped, or otherwise damaged subflooring.

What Determines Subfloor Thickness

The minimum thickness of plywood for subflooring is about 5/8 inch. Since it does not hold fasteners as well as plywood, OSB must be a little thicker, or at least 23/32 inch.

There are several factors that determine what subfloor thickness is optimal for added benefits like insulation. Note that all these variables should be taken into account collectively since each one can be a limiting factor in subfloor thickness.

Joist Spacing

The spacing of the joists that the subfloor sits on is a huge factor in determining thickness. For structural purposes, the farther apart the joists are, the greater thickness of subflooring required.

For instance, if the joists are 16 inches or less apart, a 1/2 inch of subflooring may be enough. In older homes, where the joists may be farther apart, you will need thicker subflooring for stability. This will require at least 7/8 inch plywood and 1 inch thick of OSB.

The stiffness of subflooring has a lot to do with how your floor feels underfoot. It also plays a major role in ensuring that your flooring stays flat and even. So, it is imperative to select the appropriate thickness of subflooring relevant to your home’s structure.

The reason this is relevant is that, while thicker subflooring may be better for insulation, it could limit the vertical space remaining for underlayment options.

Vertical Spacing

Flooring material thickness also should take into account a product’s insulating capacity or "R-value." Building materials with a higher R-value have the ability to keep heat from escaping the flooring during the winter and keep it out during the summer. For a basic example, wool carpeting will have one of the highest R-values, while thin, engineered wood will have one of the lowest.

The same goes for subflooring. Plywood has a lower R-value (1.1 per inch) than OSB (1.4 per inch). So, while structurally you may be able to get away with thinner plywood, it will have a lower insulating quality than OSB of the same thickness.

This is important to consider, especially if the space between your flooring and the crawlspace or slab is limited. In short, for tighter vertical spaces, you would want to go with a higher R-value product to ensure you are getting the desired amount of insulation.

Underlayment Options

And this brings us to underlayment options. You can make up for sacrifices in subflooring insulating quality with greater R-value underlayment products. For example, if the underlayment membrane you choose is highly insulating, you may be able to get away with a thinner subfloor.

And vice versa. If you choose an underlayment product that optimizes comfort but to the detriment of insulation, a thicker and/or higher R-value subflooring may be a smart option.

Select the Right Subflooring

Now that you have a basic understanding of subfloor thickness and how it can contribute to better insulation for your home, you are ready to take the next step in your flooring installation or replacement. An experienced technician can discuss what options you have in more detail to ensure you are selecting the product that is right for your home.

We provide the top flooring brands with a variety of options available to you, so you have a wide selection to choose from. Our direct-to-customer model allows us to offer some of the lowest prices in the market. And our certified technicians have decades of industry knowledge, so you can have the peace of mind that your flooring will be installed correctly.

We offer free in-home estimates, so you have nothing to lose by contacting us. Your floor will look and feel great and, with the proper subflooring, will help you save money on your energy bill as well.