What Is a Subfloor and How Does It Impact My Foundation

What is a subfloor, and why do you care about it? If you don't know what a subfloor is or why you should care read this article to learn why today.

You’re starting to think that your old flooring is wearing out. It squeaks when you walk, it shifts around as your feet move, and you’ve noticed a musty odor wafting through the place. Chances are, your problem isn’t only with your floors. 

Your subfloors are posing an issue as well. What is a subfloor? They exist underneath your regular floors to provide a stable foundation.

As long as they’re not exposed to a lot of moisture, they can last for a while, but there comes a time when you’ll have to look into a replacement. Check out this guide to learn more about subfloors and why your home can’t go without them.

What Is a Subfloor? 

Believe it or not, your floors are a complex system of layers. What is under a subfloor? The answer is joists. 

Joists are the lowest layer of flooring. Their purpose is to support everything above them. The only flooring that doesn’t have these helpful supports is concrete. 

The subfloor rests on top of these joists to provide a stable foundation to build your surface floor on. It also creates a smooth surface for you to walk on and keeps moisture at bay. 

Many people use the terms subfloor and underlayment interchangeably, but they’re a little different. The underlayment rests between the subfloor and surface floor. Not everyone has this installed, but it does keep moisture and noise at bay.

Do You Really Need a Subfloor? 

Is the subfloor as optional as the underlayment? Many flooring materials, such as carpet, can’t be placed on top of joists. You’ll have to have a subfloor installed first. 

If you don’t, the floor won’t be able to stand up to the weight of your furniture or regular foot traffic. Again, having a subfloor also protects your surface floor from water damage and mold. 

Types of Subfloors

So now that you know the answer to what is a subfloor in a house, it’s time to find out what your material options are. You can go with oriented strand board, plywood, concrete, or particleboard. They all have their own set of pros and cons. 

Oriented Strand Board

Oriented strand board is a bunch of wood chunks glued together to make a dense, compact surface. While the structure of this material is consistent and sturdy, it does have its cons. 

It doesn’t take in as much moisture as your other subfloor options. The moisture it does absorb takes forever to dry, which can pose a problem in the form of mold and mildew. 


Plywood is probably the most popular choice for subfloor because of its price point. It’s the cheapest material that you can get. Just because it’s cheap doesn’t mean that it’s not sturdy either. 

It’s comprised of several sheets of wood veneer that’s been glued together. This means that it can take plenty of punishment. It can absorb a lot of liquid, but it but dries fast. You won’t have to worry about mold or mildew. 


Most people use concrete as the subfloor in their basements or bathrooms. It’s stronger than any of the other materials that you can get. 

You will have to make sure that it’s clean before you put down your surface flooring. If there are any cracks or holes in the concrete, those will have to be repaired as well. 


Whereas oriented strand board is made up of large wood chunks, particleboard is made with smaller ones. Think almost sawdust sized. It’s for this reason why particleboard is the least used option. 

It can’t take as much punishment as the other subfloor materials. This is especially true when put in rooms that see a lot of moisture. You don’t want this material in your bathroom. 

Installing the Subfloor 

There’s a lot of subfloor preparation that you have to go through before you start the job. First, the joists have to be even. If they’re not, your surface flooring will be off. 

You might be able to use some construction adhesive to fix the problem. Lay down your plywood, particleboard, or oriented strand board. Attach the sheets to the joists with nails.

As you go along, make sure the nails remain at least 8 inches apart. When you have your subfloor down, check for any low points. If you see any, you can even things out by using a self-leveling underlayment.  


The lifespan of your subfloor is up to the material that you used and how much moisture you expose it to. If you keep it dry and chose a sturdy material, it might last for as long as the house remains standing. 

If you go with something that’s not quite as dependable, you may have to replace it after about 30 years or so. If you notice a musty smell or your floorboards begin to creak, it might be time for you to replace your subfloor. 

The cost to replace the subfloor can shoot anywhere between 500-700 dollars. It depends on rather or not you decide to replace it yourself or go with a professional. 

Schedule Your Flooring Installation 

Before you can have your surface floors replaced, you might have to get a contractor to look at your subfloor. What is a subfloor? It’s a slab of material that rests below your carpet or hardwood. 

It provides the top layer of flooring with the support it needs to handle large pieces of furniture and foot traffic. It also acts as a line of defense against moisture. Don’t try to go without it. 

Now that you have your subfloor down, it’s time to decide if you want to install tile, hardwood, or carpet. Check out the Household section of our blog to learn what’s best for your home. 

Recommended Articles