What Goes Under Hardwood Flooring?

Choosing hardwood flooring is one of the best flooring choices you will make. Hardwood is beautiful and practical, standing up to a lot of wear and tear. It is also one of the more expensive options, so making sure you take steps to make it last as long as possible will actually work out well in the long run.

To get the most out of your floors, you will need to understand what goes under hardwood flooring – which typically comprises underlayment which is placed on top of the subfloor.

Let’s take a look each what both of these mean, and how choosing the right underlayment can affect your hardwood floor.

What is a Subfloor?

A subfloor is the bottom structural layer to which the other layers of flooring are attached.

The subfloor is often attached with nails or screws to the floor joists. It is typically a layer of plywood or engineered wood panels that sit at the bottom layer of the flooring.

What is an Underlayment?

Floor underlayment is not going to be visible once the wood flooring is in place. However, this unseen layer can make a huge difference in how the hardwood floor looks, its comfort, and how long it lasts.

Floor underlayment is a layer of material that is installed between the subfloor and the hardwood flooring. It can be made of a variety of different materials to mitigate sound issues that wood flooring tends to generate and serves as a moisture barrier depending on the material used.

Underlayment provides a flat, smooth surface on which to lay the wood flooring.

The underlayment also provides a moisture barrier that helps keep the new hardwood floors from cupping, warping, or buckling from exposure to moisture that rises up from the subfloor.

An underlayment also provides insulation that can help to maintain a comfortable and more consistent temperature of the floor. This helps cut energy heating and air conditioning costs as well as provides comfort to walk across the floor with bare feet.

Choosing the Right Underlayment

Hardwood floors don’t need an underlay, but there are many benefits an underlay can provide. One main benefit is that it solves the unwanted sound issue that wood floors tend to generate with squeaks, creaks, and footsteps.

An underlay also serves as insulation to prevent moisture. When you first install an underlay, you could improve the quality and durability of your hardwood flooring investment.

Choosing the right underlayment will depend somewhat on the type of wood used in the flooring.

The type of wood should reflect the type of underlayment you choose. For instance, black walnut or white oak is a softer wood that requires additional support and stability between the wood floor and the subfloor. Cork or rubber underlayment works well with these softer types of wood.

On the other hand, harder wood such as maple or hickory will not need extra support. These types of wood will benefit from the insulation and the flexibility that foam or rubber provides.

Also, consider what the room is used for. If it is a high-traffic area, choose an underlayment that will stand up to a lot of use and wear and tear. If it is being used on a second-story level, get an underlayment with good sound absorption qualities. If it is a room with high humidity, choose an underlayment that will provide a good moisture barrier.

Choose from these types of underlay options:


A plastic underlay sheet works great in humid climates. In fact, plastic underlayment is a must in humid conditions.

The plastic can also be paired with other moisture barriers. A plastic underlayment will help keep condensation from warping the floors. It will also help to prevent mold and mildew from forming underneath the hardwood floors.


A foam underlayment layer will help to keep the flooring even.

When the foam is paired with a plastic sheet layer, it will provide added protection against moisture damage. The foam also serves as thermal insulation which may show up as huge savings in your energy bill costs.

Foam will also serve as a nice sound barrier which is very important underneath hardwood floors to muffle footsteps and other creaks and squeaks that tend to come hand-in-hand with wood flooring.

Foam will also provide a layer of cushioning between the wood and the subfloor.


Felt is a very popular choice for underlayment. Felt is cost-effective and is easy to work with to size appropriately and install. Felt offers a moisture barrier and serves as nice insulation and soundproofing.

When felt is used as an underlayment, it does not need to be glued down.

One possible downside to using felt as an underlayment is that it does not add extra softness to the floor unless you opt for a thick layer of black felt to provide extra cushioning.


Cork is a budget-friendly choice that is ideal to use on second-story floors where sounds from creaks and footsteps can otherwise be heard in the rooms below. It offers some great protection for a fraction of the cost.

Cork underlayment is very easy to work with.

Cork also has a natural antimicrobial benefit to help keep mold and mildew from becoming an issue. Cork is not, however, the best moisture barrier and will not do as well in high-humidity areas like kitchens, wet basements, or bathrooms.


Using rubber as an underlayment will provide some amount of a sound barrier. It is great to help prevent that hollow sound that wood floors tend to generate. Rubber can also serve well as a moisture barrier.

Rubber is easy to install and offers a lot of flexibility and pliability.

Rubber provides natural waterproofing to prevent moisture issues from developing on the wood floor above it. Rubber is, however, more expensive than other choices of underlayment.

Final Thoughts

Placing an underlayment between the subfloor and hardwood flooring is not required but does offer several benefits. Depending on what type of underlayment you choose, it could provide you with a great sound barrier, moisture barrier, and comfort.

Additionally, the right underlayment will smooth out the surface to keep the hardwood floors from buckling, warping, cupping, or otherwise becoming damaged before their time.