If you are thinking about remodeling your home and want to educate yourself on some of the terms you may come across during the process; you are at the right place. Or maybe you want to change your floors, and you’re asked what subfloor you have and if you have underlayment. So what is underlayment? What is a subfloor? And what are the differences between the two? Are there similarities? If yes, what are they?
Unless you have concrete slab floors, there are heavy-duty beams under the floors of every room in your house. These beams, which are known as joists, support everything above. The subfloor is usually nailed to the joists to ensure it stays in place. The subfloor remains on the joists; after joists, it is the bottom-most layer of your flooring.
You can install finished flooring (for example, vinyl tiles, ceramic tiles, carpets, etc.) or underlayment on a subfloor. If you install underlayment, you can install your finished flooring on top of the underlayment.
Underlayment is an optional layer that goes between a subfloor and finished flooring. It serves many purposes, the most prominent of which is to improve the soundproofing of floors. The subfloor is the structural layer upon which underlayment and finished flooring are placed, and it stabilizes the flooring of your home.
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| Underlayment | Subfloor | |
| Materials | Underlayment is made of a wide range of materials which determine the rooms in which these underlayments should be used. Underlayment is often made with the more common materials such as cork, rubber, foam, etc., but it is also made with lesser used materials such as cement backer boards and plywood. | Subfloors are often made of plywood because of how sturdy and strong they are. Plywood is flat enough and capable of maintaining its quality through changes in humidity. Other materials used in subfloors include Oriented Strand Board (OSB), cement, etc. |
| Cost | The cost of underlayment depends on the type of underlayment, the density of the material, its thickness, and its features (for example, a built-in vapor barrier). | Similar to underlayment, the cost of a subfloor is determined by the material of the subfloor. |
Differences Between Underlayment and Subfloor
Subfloor and underlayment are two different flooring parts with entirely different functions. Their distinct similarity lies in the fact that they are both used in flooring. The significant differences between underlayment and subfloor are the materials from which they are made and the functions and purposes they serve.
Materials
Subfloor
The subfloor can be made of different materials, but it is typically made of plywood or oriented strand board (OSB). Plywood is made by gluing or cementing sheets of wood together. It is a good choice for the subfloor because it is flat and relatively strong to hold up entire structures. It is also affordable, durable, and easy to use. Although plywood is not waterproof, it can withstand sudden changes in humidity. Plywood can become water-resistant with a moisture barrier.
Oriented Strand Board (OSB) is made of compressed layers of wood strands glued together in specific orientations. Hardboard is another material used in making subfloors. Hardboard is a very dense fiberboard formed from tightly packed wood fibers. It usually has a smooth surface.
Subfloor does not have to be made of wood or wood-related materials. Concrete is a common subfloor in basements.
Underlayment
Underlayment can be made of different materials; some of the more popular materials used for underlayment include rubber, cork, foam, felt, plywood, etc. Whatever underlayment you use should depend on the flooring you want to install. For example, it is not advisable to use rubber underlayment with vinyl tiles because rubber reacts with vinyl chemicals, which causes staining. With hardwood flooring, your options for underlayment include foam, rubber, cork, and felt.
Function
Subfloor
The subfloor is a structural component of your home that works alongside other structural parts such as joists, headers, rafters, etc., to maintain the stability of the building. The subfloor provides strength and stability to your home’s flooring and serves as a foundation for your finished flooring.
Underlayment
Underlayment adds comfort and softness to your flooring, so your feet are protected when you walk across or stand on your flooring. It provides a smooth surface for flooring, especially if your subfloor is bumpy and uneven. On the other hand, underlayment does not serve a structural purpose. An underlayment performs many functions aside from smoothening imperfections in a subfloor.
Underlayment can be moisture resistant or waterproof and protect your flooring from moisture moving up from the subfloor. Alongside your subfloor, underlayment provides more support and stability for your flooring. The most notable function of underlayment is that it absorbs and minimizes the sound caused by foot traffic and other levels of impact, so it is helpful in hotels and apartments. All these functions ensure a long lifespan of your flooring.
Frequently Asked Questions (FAQs)
What underlayment should I use for my subfloor?
In most cases, your flooring should determine the type of underlayment you use because you cannot use certain kinds of underlayment with certain types of flooring. It would be best to consider using cork underlayment with laminate flooring rather than rubber underlayment with vinyl tiles.
But sometimes, your choice of underlayment depends on the subfloor material. For example, if your subfloor is wood or wood-related and your flooring is tile, you will need an underlayment known as a cement backer board.
How much do subfloor and underlayment cost?
The prices of both subfloor and underlayment are determined by various factors: materials used, size of the room (or building), the labor cost of installation, and many others. Rubber underlayment is one of the most expensive types of underlayment, surpassing cork and foam underlayment in terms of price. Also, OSB costs significantly less than plywood subflooring.
Generally, the cost of subfloor material range from $1.50 to $7 per square foot. On the other hand, underlayment can be as low as $0.50 per square foot or as pricey as $6 per square foot
| Material | Thickness | Cost |
| Plywood Subfloor | 15mm (⅝”) | $1.50 per squad foot |
| Cork Underlayment | 12mm (½”) | $1.30 per square foot |
How is flooring layered?
Joists are not precisely a layer of flooring, but they play an essential role in the flooring layers and the stability of a building’s floors. They are made of lumber or engineered wood. All houses, except those with concrete slabs, have joists. The next layer is the subfloor which is above the joists and provides structural support for the underlayment or finished flooring.
The underlayment is the next layer, and it is installed on the subfloor. The underlayment is an optional layer, but it is incredibly beneficial to your house. The last layer is the finished flooring; it is the layer that is visible most times (exceptions being during renovation or something similar). The finished flooring plays no structural role, so you should choose it based on the room and its use. For example, you should not use carpet in a bathroom or kitchen.
Conclusion
Underlayment and subfloor are two different elements of flooring with different functionalities. The subfloor provides a stable and level surface to your floor. On the other hand, underlayment is the layer between the subfloor and the floor.