Layers of a Floor – Anatomy, and Parts (Illustrated)

A good floor system for your home is as good as its structural composition. Squeaks and sags can be avoided if you understand the anatomy of a floor. Other major problems can be avoided when all the layers of your floor interact properly with each other.

Your floor’s anatomy has many parts that add to the stability, comfort, and beauty of your home. The different layers of a floor include; joists, underlayment, subfloor (beams and adhesives), and coverings. When they are blended together they form a durable and stronger floor system.

Floors in your residential home or commercial space consist of four layers. We’ll go into detail about each layer below.

Layers of a Floor

The four layers that make up the wood floor system consist of; the Joists, Subfloor, Underlayment, and Floor Covering. Discussed below are the four layers of a floor with their purpose on the top-down technique.

1. Floor Covering

Floor covering—also popularly known as the finish floor or flooring—is the visible upper finished layer of a flooring system surface. It may include materials like hardwood planks, carpets, cork, linoleum, concrete, ceramic tile, and vinyl floorings. This is the layer you see daily, walk on, and place your furniture on. It’s the upper surface of a floor system structure that covers the other structural layers of flooring beneath.

The flooring materials can be installed differently depending on the needs and requirements of a room. When selecting the flooring, you need to consider the area’s moisture content, cleaning and maintenance methods, durability, quality, and the feel and comfort it provides when walking on it.

For high-traffic areas or areas where spills often occur (like the kitchen), you’ll want to select and install durable floor coverings, like tile, concrete, hardwood, vinyl, and laminate. To protect hardwood in family rooms, dining rooms, and bedrooms, consider picking a soft and invitingly textured covering like an area rug or carpet to go over top.

Purpose of Floor Covering

The purpose of the floor covering is to provide a smooth, durable, clean, impervious, hard, and attractive surface. The floor covering provides a strong durable base that’s easy to clean and maintain, with a wide range of designs and styles to choose from. In general, it provides a finished material for us to walk on.

Here’s how to install floor covering and some tips to help you along the way.

2. Underlayment

What is an underlayment? This is a thin layer of material installed between other materials. Floor underlayment is mostly made from sponge rubber, foam, felt, crumb rubber, and recycled plastic.

The underlayment material is installed below the floor covering and placed on top of a subfloor. Under the visible covering, there is a layer made of soft or foam-like materials with a thickness of between 1/4  – 1/2-inch.

The underlayments are available in different materials to choose from depending on the flooring needs and the type of floor covering to be installed. Some common choices include; foam, hardboard, cork, plywood, and cement board. In case you’re considering installing engineered flooring or hardwood flooring, the best underlayment may be foam or cork; however, cork may offer some added advantages to your flooring.

Purpose of Floor Underlayment

The purpose of floor underlayment is to provide comfort underfoot as well as reduce wear on the covering. Its purpose is to provide a smooth, flat surface for the floor covering. It also serves additional functions like deadening the sound of footsteps, softening the feeling underfoot, or even acting as a moisture barrier.

It also provides sound insulation, improves moisture resistance, retains warmth, heat, and even retards fire outbreaks. Underlayment, in many cases, helps to rectify subfloor imperfections. Always pick the best underlayment for laminate, vinyl, and hardwood floors.

Here’s a video on how to underlay your floor.

3. Subfloor

What is a subfloor? A subfloor is a layer between the floor underlayment and the joists. Its sturdy structural part rests on top of the floor joists and acts as a foundation for the underlayment and the floor covering.

Subflooring helps to make the floor smoother and more comfortable to walk on, while being structurally sound to support the underlayment, floor covering, and people, furniture, pets, and everything in the house.

The subfloor can be made from particleboard, OSB (Oriented Strand Board), plywood, or concrete. It is part of a home’s floor system construction, installed between the underlayment and floor covering. The OSB or plywood are commonly used as an integral material for the subflooring structure of a home’s flooring. Subfloor increases the strength and rigidity of the floor system since it’s attached to the joists.

Purpose of Subfloor

What is the purpose of the subfloor? Subfloor provides the foundation of the floor. It levels the surface and makes it easier to install the upper covering, hardwood, vinyl, linoleum tile, or even carpets. Subfloor provides support and ultimately makes the floor look more aesthetically pleasing.

There are some major problems that affect the subfloor. In case you didn’t pay a lot of attention during the construction of your floor, you are bound to come across one or more of the subfloor issues listed below.

• Foul smell: This signifies moisture buildup formed from mold and mildew on the subfloor.  It may come from below or from the floor covering. Water moisture is one of the worst enemies of the subfloor so be sure to take necessary precautions.
• Sagging: This is a sign that the subfloor is getting worn out or there is a structural weakness.
• Squeak sound as you walk on the floor: A new sound will always signify a damaged subfloor and need to be fixed.

How to Install a Subfloor?

To build a good structural sound subfloor, you need to know the number of layers you expect to build on top. Here is a video on how to install subfloor and prevent subfloor squeaks.

Tips for Subfloor

• Ensure you determine the subfloor material and thickness carefully. Depending on your area, you may also consider things like heating vents, the area of installations, basement or crawlspace, and stairs above as well as the joist below.

• The floor is as great as its foundation. If you want to keep enjoying your floor’s aesthetic look, consider investing in its subfloor. It plays a very important part in your home and makes sure your floors stay beautiful for  longer. Hire a flooring professional; subfloor issues can’t be diagnosed by you alone or are not recommended as a DIY project.

How Many Layers of Plywood for Subfloor?

If you are using plywood for your subfloor, you should use a minimum of one layer that is between ¾” and ⅝” thick. This thickness will suffice for most floors; however, codes will vary and a second layer is a good idea if your floor covering is going to be a heavy material like ceramic tiles or natural stone. 

4. Joists

What is a joist? A joist—also known as band sill—is a structural form of a beam that spans horizontally between the foundation of a building, walls, or two beams. They are lateral wooden framing members that rest on foundation walls and beams to provide the structural support for the entire framing system.  Sometimes they’re noisy, squeak, or bounce.

Purpose of Floor Joists

Floor joists provide the structural support of the entire floor, and, at times, may not be considered as part of the floor layers. They’rean essential part of the floor layer matrix, although you won’t find them in concrete slab floors.

Floor joists are the pillars of the structure that support all the other parts of the floor, except on concrete slabs. They support a subfloor that spans over an open area. 

When joined with a floor framing system, the joists provide and enhance the stiffness of the subfloor sheathing. This allows the joists to function as a horizontal diaphragm of the floor.

The joists are mostly made from laminated wood, engineered wood, and dimensional lumber. The joist also has its challenges, especially after the subfloor has been installed.

The joist span is determined by floor strength, wood species, joist spacing, depth of joist,, and engineering. These will help determine the distance between support joists below the subfloor. When the subfloor is nailed on top of the floor joists, it forms the flooring system.

Joists are built to support the load on which the floor is built to bear. They are typically made from lumber or engineered microbial members. In combination with other joists, it provides support to the floor or even at times, the ceiling.

Here is a video on how to install a floor joist:

How do I Find the Joist Under the Subfloor?

To find the joist under the subfloor (from the floor covering like carpet or hardwood floor) requires the use of a hammer. Tap the floor from one edge or corner and listen for a thud sound. Generally, most areas will have a hollow sound, but a thud sound signifies the presence of a joist. You can continue until you determine the area where the next joist is. Hopefully they were installed with the same distance from one another, in which case you can quicken the process by measuring the distance of the identified joists to locate others.

What is the Difference Between a Beam and a Joist?

Joists and beams are structural flooring elements made for similar and related functions. They are the primary structural component for a floor and roof. Beams are large in size while joists are smaller. Beams are used to support the joists by providing support to the horizontal structure of the floor. Joists and beams can be made from solid and engineered wood or even steel; however, joists are commonly made from solid lumber.

Take Care of Your Floor So It Can Take Care of You

Understanding the different layers of your home’s floors will help you identify when repairs are needed, what is required during renovations, and best practices when it comes to flooring. When possible, enlist the help of a flooring specialist—especially when it comes to the subflooring. 

If you take care of your floor and all of its layers, you will have a floor that will last a long time, for years to come.

Sources and References

Wikipedia: What is the flooring?

Britannica: What is floor covering?