When you take a step onto a floor there is a lot that goes into making the floor sturdy, resilient, and safe. There are multiple layers that make up your floors. You have the top layer that is your floor covering (Hardwood, Laminate, Vinyl, Carpet, etc.), next you have the underlayment (usually a thin layer of fiber, foam, rubber), below that you have your subfloor (plywood, OSB, concrete), and lastly you have the joists which are the foundation to your floors. So, what does all of this mean?

The floor covering is pretty simple. It is the top layer that you directly walk on, and see. As an example this would be your Vinyls, Ceramics, Laminates, Hardwoods, etc. This will all depend on your tastes, budget, and design.

The underlayment is what the floor covering lays on. It can dampen sound, and it can protect your flooring from moisture and heat. Note that for carpeting the underlayment is padding for added comfort and it helps if anything is spilled on the carpet to not seep through to the subfloor. The purpose of an underlayment is to provide a smooth, flat surface for the floor covering. It can be made of many different materials. It’s chosen depending on the needs of the floor covering. Now let’s throw a curveball here – laminate is the only floor covering that uses an underlayment. And most other floor covers, besides hardwood and ceramic, have padding glued on the underside of the planks or tiles.

Speaking of the subfloor – The subfloor is next. The subfloor sits on top of the joists. This allows your floors to have a continuous structural surface over the floor joists. There are different materials that can be used for the subflooring. Those are wood planks, plywood, OSB (Oriented Strand Board) and concrete.

Wood planks are rarely used anymore. Why may you ask? Money. It is more labor intensive to use wood planks vs plywood, OSB, etc. Cutting and nailing the subfloor is very labor intensive as well as the waste that results from the angle end cuts. With wood planks they must be run at a 45 degree angle to minimize the effects of cupping of the subfloor planks when tongue and groove finish flooring is used (Which is most flooring coverings). At the angle, the finish flooring rests on the high spots of the subfloor.

Now, Plywood and OSB are most commonly used for subflooring. We will be discussing both of these together. Plywood is made by gluing together multiple thin layers of solid wood at 90-degree angles and pressing them tightly as the glue dries to form a very strong structural sheet. This took over solid wood planking as a subfloor in the 1950’s in homes. OSB or Oriented Strand Board, is made by using large, flat wood chips arranged in dozens and dozens of layers, which are glued together and pressed into sheets. It is usually cheaper than plywood, because it uses leftover wood material. OSB came into use as a subfloor material in the 1970s.

Plywood is more resilient in most ways compared to OSB. Plywood is stronger and more rigid. Plywood doesn’t swell when it gets wet, where OSB can swell on the edges. You can use plywood for all types of floor covering. Whereas OSB should not be used for ceramics and tiles. Plywood has more holding strength when it comes to being nailed down than OSB.

Concrete is normally used for the subfloor in highrises, and in basements. Concrete is very dense, and very hard. It is extremely difficult to nail into. In addition, concrete can also allow moisture to seep through. Usually a moisture resistant underlayment/barrier is required when working with a concrete subfloor. However, even with that barrier it is not recommended to install hardwood floor coverings on a concrete subfloor. Concrete is also very susceptible to changes and shifts within the ground, and outside forces – such as tree roots pushing up against the concrete and eventually cracking it. All in all, installing a floor covering on a concrete subfloor can be very difficult. The subfloor needs to be smooth as possible, there’s a lot of prep work that needs to be done, and as it was mentioned before – it is very difficult to nail into. So there usually needs to be a floating subfloor installed which is made with special tongue-and-groove panels of OSB adhered to a base layer of plastic or rigid foam insulation.

With the exception of concrete, all other of the subfloor materials and other flooring layers rest on the floor joists. The floor joists are the foundation to your floors. Floor joists are structural and support everything above. Joists are made of engineered, laminated wood or dimensional lumber. Except for those that have concrete slabs, all houses have joists.

While there are some instances where you could have less layers to your flooring, that would be the exception to the rule. In almost every instance there is the floor covering, the underlayment, the subfloor, and the floor joists. This is what makes up your floors, and gives them structural integrity to keep you and yours on solid ground.