What is a Subfloor? The Foundation Beneath the Beauty

If someone asks you “What kind of flooring do you want?” the first thing that may come to mind is wood look vs. carpet. Instead, you should be asking yourself, “What’s beneath the surface?” Hardwood, vinyl, tile, and carpet may be the only thing your family and guests see, but where there’s beauty, there’s a subfloor providing support. What is a subfloor? Let’s find out.

Layers of Flooring

Flooring is made up of several layers, beginning with the joists below, the subfloor and underlayment in the middle, and the surface at the top.


Joists are the first, lowest layer of flooring and support everything above. Every floor has joists, except for concrete. Joists are typically made of engineered wood, laminated wood, or dimensional lumber.


The subfloor is the next layer above the joists and acts as a foundation for both the underlayment and surface levels of flooring. A subfloor provides a stable, level surface that new flooring can be easily installed on. Subfloor not only makes it easier for installers to lay new carpeting, laminate, hardwood, vinyl or tile, but it also makes your floors smoother to walk on.


Underlayment is the third layer, residing just above the subfloor. While a subfloor provides structural support, the underlayment serves as a sound barrier and can protect your flooring from moisture and heat. For carpet, underlayment is used as the extra layer of comfort and can be used as a barrier for topical moisture. The only hard surface floor requiring underlayment is laminate. Underlayment can help protect laminate from moisture that may rise from below.


This is the top layer that is visible. It doesn’t hold a structural purpose, but should still be chosen wisely based on your lifestyle and how the room is used. If you are expecting high-traffic or have pets and/or kids, it’s best to get flooring that is highly durable.

what is a subfloor

Different Types of Subfloors

Subfloors vary in material, which often determines what type of flooring is ultimately installed in your home.


Plywood consists of sheets of wood veneer that are glued together with an adhesive. In addition to being flat and strong, it’s generally affordable, making it a popular choice for subfloors in residential homes.

Oriented Strand Board

Competing in popularity with plywood is oriented strand board (OSB). OSB is fabricated with large pieces of chipped wood that are glued and pressed together.  Although both can make great subfloors, they both have pros and cons. OSB compacts several layers into one sheet, providing a denser and more consistent structure than plywood. And, while OSB may not absorb as much moisture as plywood, plywood often dries out faster. That means moisture lingers longer in OSB and can cause damage. It’s best to weigh your options and do the proper research to see if OSB subfloor is right for your home.


Particleboard subfloor isn’t as strong as plywood or OSB. Instead, particleboard is made from smaller chips that can be compared to sawdust. Because of its weak structure, particleboard isn’t used as subfloors as much, especially in moisture-prone rooms.


Concrete is mostly found in high rises and condos, but is commonly found in basements and bathrooms of houses as well. Concrete subfloors are much stronger than particleboard, but should still be inspected for cracks and other imperfections to ensure a smooth installation of your surface flooring.

How to Identify a Damaged Subfloor

Years of wear and tear, especially from moisture, can have unintended effects on your subfloors. How can you tell a subfloor is damaged? Some signs include:

  • Squeaking sound when you walk on your floors. This sound may be common if you have older wood floors. The problem arises when you haven’t heard this noise before. This means the noise may be beyond the surface and may be a sign of a damaged subfloor.
  • Sagging floors. If sagging is visible, or you feel it when you walk across your floors, this is a sure sign that your subfloor has worn out its welcome.
  • Foul Smell. Not every subfloor has visible signs of damage. Sometimes, you can detect subfloor problems by strange, unpleasant smells (often from mold accumulating in damaged areas).

If any of your subfloors are damaged, you may need to have another layer of subfloor installed on top of it. This can be the same material as the original, or maybe even something with a better structure. For instance, if you have a damaged particleboard, adding a layer of plywood above may be an option to consider before choosing new flooring.

How Subfloors Can Make a Difference

Knowing the state of subfloor is a necessity. Providing a smooth, stable surface, subfloors are the structural base for your flooring. After all, a floor is only as nice as its foundation. The aesthetics play an important part of completing your home’s décor, but the subfloor is the most important factor in making sure your floors stay beautiful for a long time.

Subfloor issues can’t be diagnosed by you alone. An inspection or conversation with a flooring professional is highly recommended. Once again, you really can’t make an informed decision on a new flooring style until you know the status of the subfloors beneath.  Schedule a FREE In-Home Estimate today and ask a flooring professional about your options.

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