Layers of a Floor: Anatomy and Parts

I can install toilets. I know about the wax ring. I can tile floors. I’m learning how to basic wiring – Sandra Bullock

A veteran builder with more than four decades of experience once told us “The more you know about something, the better you understand it”.

The point that he was gently making was that everything seems complicated until you take the time to sit down, figure it out, and learn all that you can about it.

And if you do that, the things that previously seemed like rocket science slowly, but surely, start to make sense. experts are here to delve deeper.

Layers of a Floor

While most of us take the floor under our feet for granted and just accept it as an everyday part of life, it’s actually an incredibly vital part of any home or building’s structure.

As well as providing something comfortable for you to walk on, it helps to provide stability to your home and ensures that it stays warm and retains heat that might otherwise be lost through, and to the ground.

Good flooring is vital to any home, but like everything else, even the best floors can end up suffering from a number of problems that usually manifest as squeaks or areas in which it begins to sag and feels weaker underfoot.

If this does or has happened to your home, don’t worry and don’t panic, it can be easily fixed.

And the best way to fix your floor is by understanding how floors and flooring work, how they’re put together, what each part of the flooring system does and why they’re a necessary component of a floor’s structure.

In other words, we’re about to explore and guide you through the anatomy of floors and modern flooring.

The Four Layers Of Flooring

All modern flooring systems are composed of four distinct and different layers, each of which we’ll look at in detail.

The layers are, in order, floor joists, a subfloor, underlay or underlayment, and the floors covering surface.

Each plays a vital part in helping your floor to remain structurally sound and strong and makes sure that it acts as an insulating barrier between you and the ground that your home rests upon.

Starting At The Bottom – Joists

Joists are structural members that serve to join beams together in a framework pattern to provide the support and structure that a subfloor rests on.

While they are usually made from wood or engineered wood (which is more commonly known as composite wood), in rare cases where additional structural support is needed, steel beams can be used as joists to ensure that there is a rigid, structurally sound frame onto which a subfloor can be fitted.

The joists are the load-bearing part of the flooring system and are fitted in a framework pattern to ensure that they can bear not only the weight of the flooring that is going to be mounted on to them but can also help said flooring to support the weight of any, and all, household furniture and cope with the everyday stresses and strains that family life places on the flooring.

Like every component of a modern flooring system, joists can fail and when they do, they can often be a root cause of areas of your flooring beginning to sag or feel soft.

If this does happen, don’t panic, as floor joists are relatively easy to replace. But to replace them, you need to be able to locate them.

Finding A Joist

Remember when the heroes in those old television shows would try to find a secret door or a hidden room by tapping on a wall in order to ascertain if it was hollow or solid? Well, the same principle applies to finding a joist.

Gently tap your floor with a hammer around the area where the damage has occurred, and listen carefully.

If there’s a little echo and give in the floor when the hammer hits it, then that’s strictly subfloor, but if it feels and sounds solid, then you’ve just hit the joist payload.

While you might be tempted to replace the joist yourself, and even though it’s a relatively straightforward procedure for anyone with some rudimentary carpentry skills, we’d always recommend that you call in a professional to do the job for you.

A lot of insurance companies balk at the idea of homeowners carrying out these sorts of fundamental, structural repairs and prefer to use their own contractors to do the work.

So if you don’t want to get caught up in, and want to avoid (and who doesn’t) all kinds of legal red-tape and run the risk of your policy being canceled, then leave the work up to the professionals.

That said if you’ve already located the potential problem area, you can point it out to your contractor, which can help to shorten the duration of the time that they’ll take to fix the problem.

What If I Don’t Have Any Joists?

Again, don’t worry.

Some homes don’t have joists and instead of using a wooden framework system to provide the strength and integrity that the subfloor, and indeed the rest of the floor needs to rest on in order to work effectively, they have a solid concrete base.

While concrete based flooring isn’t anywhere near as popular here as it is in Europe, it is an effective way to ensure that there is a solid, strong foundation on which the other components of a flooring system can be fitted.

Concrete is also a surprisingly effective insulator and can help to minimize any potential heat loss through the floor.

Some contractors swear by it, while others hate it. The best way to find out if your floor has a concrete base?

Use the same hammer test that you would to locate a joist, and if every tap is met with a resounding, and reassuring solid thud, then in all likelihood, your floor has been laid on a concrete foundation.

And the main advantage of having concrete as your flooring base? Your flooring will never sag or feel soft underneath your feet.


This is the layer of your flooring that gives it the majority of its everyday strength and makes sure that the floors of your home are level.

It’s the foundation that your flooring surface (and its underlayer) is built on and needs to be tough, strong, and durable.

Usually constructed from plywood or OSB (oriented strand board), a subfloor needs to be fitted accurately and correctly if it’s going to be strong enough to hold your flooring of choice, and last for the lifetime of your home.

As we’ve already mentioned though, nothing lasts forever, and subfloors, just like every other flooring component can fail.

And if it does, there are three definitive telltale signs that your subfloor could be in imminent danger of collapse.

Subfloor Warning Signs

The three major signals that indicate that the subfloor of your home has started to fail are all fairly obvious, and if we’re honest, shouldn’t be ignored and need to be dealt with immediately. They are:

A Musty Odor

If there’s a general musty smell in any room of your home that you can’t get rid of no matter how hard, or how many times, you clean the room the smell is in, there’s a good chance that it’s coming from underneath your feet.

In all likelihood, the smell is being caused by moisture that’s become trapped underneath your subfloor that has led to mold developing underneath it, which is almost certainly the cause of the smell that you can’t get rid of.

As mold is a serious health hazard, it needs to treated immediately and the only way to effectively do so is by calling an environmental specialist who is licensed to not only remove and clean the affected area of your subfloor but can also locate the problem area and recommend a contractor who can replace it when the mold has been effectively dealt with.

Sagging and Softness

Is there’s a soft area of your subfloor, which you’ll be able to feel when walking across your floor, or you can see your floor visibly sagging, then it means that your subfloor has almost certainly developed a structural problem, which has probably been caused by a build-up of moisture that has weakened the boards that make up the subfloor.

Again, it’s imperative that you deal with this issue as soon as possible before you’re faced with the inevitable mold problem that will follow.

It isn’t a colossal life-changing job, and most contractors will be able to easily replace the affected boards in a day and make sure that your subfloor is as good as new again.

What’s That Noise?

Squeaking floorboards and floors are usually a pretty good warning sign that your subfloor has started to fail.

So if your floor begins to squeak while you’re strolling from one side of the room to the other, then you should really have your floor looked at as soon as possible.

The good news though is that you won’t have to pay for an investigation, as, thanks to the squeaking, you’ll know exactly where the problem is.

Between the Subfloor and the Floor – The Underlay

The insulating layer between the subfloor and floor covering that also serves as a moisture barrier, helps to deaden and absorb the impact of any and all footfalls on the floor covering and also helps to keep heat where it should be, that’s in your home and not in the ground, is called the underlay.

Depending on the type of floor covering that your home has fitted, the material used in the underlay can be anything from foam rubber to cork, or hardboard to cement board.

It should be between a quarter and half an inch thick and should be fitted accurately ensuring that every part of the subfloor is completely covered and that there are no visible or even unseen gaps.

And Last But By No Means Least, There’s The Floor Covering

Thanks in no small part to the explosion in popularity of interior designers, the choice of covering for your floors is now nearly limitless.

If there’s a material that you think would look good on your floor, the chances are, some clever designer has already developed a patented floor covering system that uses it.

However, the more conventional and traditional floor coverings and the ones that have been purpose made to put a shiny and aesthetically pleasing ribbon on top of the other three layers of your flooring system and have been designed to feel good underfoot and insulate your home are carpets, tile, vinyl, laminate, and hardwood.

Each of them has its own inherent advantages and should be chosen and fitted according to your needs and what you value and cherish above everything else.

And, if we’re honest when it comes to choosing your final floor covering, the most important factor and the one that should help you to determine what floor covering you want, is your heart.

Always listen to your heart, because that’s where your home is.

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