What is Subfloor, Underlayment, and Joists in Flooring and Differences?

What is Subfloor

Subfloor, underlayment, and joists are all important components of a flooring system. It is important to understand these three elements in order to choose the best option for your home. But how can you do that?

According to the report of the National Wood Flooring Association, a subfloor is defined as “the structural layer that provides the flat surface on which the finished flooring is installed.”

The subfloor is the foundation of your flooring system and is typically made of plywood or OSB (oriented strand board).

But underlayment is different. Underlayment is a layer of material that is placed between the subfloor and the finished flooring.

And joists are the horizontal support beams that make up the frame of your flooring system.

Throughout this article, we will learn about joists, subfloor and underlayments in detail and will also know how they are used step by step to make an impressive floor with all its strength and needed durability.

Also, I have shared differences between subfloor and underlayment and joists. If you want to know about these things in detail then must read this article till the end.

So, let’s get started.

Joists And Their Use In Flooring

Joists are used in the first place in the process of floor installation followed by subfloor and underlayment. These altogether create the platform upon which your floor is installed. These are the solid wood beams that make the foundation of your floor.

What Are The Joists And What Purpose Do They Fulfill In Flooring Systems?

Have you ever imagined what it would look like if there were no bones in a human body? It would become a stuff of flesh and blood with no proper shape or structure. 

Yes, Joists make the structure upon which a subfloor is installed. These are the beams that hold your lovely floor, like the bones that hold a human body in proper shape. 

Knowing Different Types Of Joists

Let me tell you that in house flooring, three types of joists are commonly used i.e  Solid Lumber Joists, Engineered Joists and Truss Joists, and the rest two i.e Steel Joists and Concrete  Joists are mainly used for commercial purposes or where generally the area is huge. Let’s know more.

  • Solid Lumber Joists: These are made of solid wood and therefore heavy and the strength level offered by these joists is medium.
  • Engineered Joits: If you are looking for joists that would be both lightweight and strong, then engineered joists are for you. These are a combination of wood and engineered materials which make these joists lightweight and strong. These are also known as I-Joists.
  • Truss Joists: Truss Joists or Open Web Strusses are made of wood members or metal. These are very strong and lightweight too.
  • Steel Joists: In Steel Joists, the main component that is used is steel which provides greater strength to hold a massive subfloor.
  • Concrete Joists: On the other hand, Concrete Joists are made of concrete with a T-shaped cross-section that hold a huge subfloor properly in place with enermous power.

Sizes And Load-Bearing Capacity Of The Joists

The Joists are available in various sizes, from the smallest to the largest. And with various sizes come variable load capacity. But, you have to choose the right one to suit your purpose.

What? Confused? Oh! No. No need to be worried. Seek suggestions from a structural engineer, and he will guide you properly.

Importance Of Properly Spaced And Supported Joists In Flooring System

After you choose the needed type of joists for your floor, now you have to place them properly leaving appropriate space in between the joists. You must not forget that the main purpose of installing the joists is to distribute the load equally all over your floor.

So, if the space is not measured accurately, you may end up messing things up. If you have zero experience in this matter, you are advised to take help from a team of floor installers to get the job done smoothly without any headache on your side.

Subfloor And Its Use In Flooring

After you install the joists properly, the second step is to work on the subfloor. Whether your floor will be rough or smooth, stable or unstable, it depends on the type of subfloor that you install and thus, it acts as the deciding factor. Your subfloor ensures the smoothness and stability of your flooring system.

What is a Subfloor And What Is The Purpose Of A Subfloor?

Subfloor acts as the base of the actual floor, which is directly installed upon the joists. If we compare the joists with the bones of the human body, then subfloors are the muscles.

In providing smoothness and durability to the actual surface, stability and weight distribution and finally, making your floor moisture free and soundproofed, we use a subfloor.

Different Types Of Subfloors

Like the joists, different materials are used to make a subfloor. Some commonly used materials are-

  • Plywood: Plywood subfloors are the first choice to many because of their strength, durability and affordable price range. It is made with multiple layers of thin wood veneer that are glued together.
  • OSB: OSB or Oriented Standard Board is another popular material, often available with a variety of thicknesses. People prefer to use it as a replacement for plywood as it is less expensive.
  • Concrete: If you are living in an area that is prone to moisture or flood, then choosing concrete as the material for your subfloor is a wise choice. It much durable and can last for many years.
  • GFB: GFB or Gypsum Fibre Boards are made with a combination of wood fibers and gypsum. If you are looking for fire resistance and sound insulation, it’s a great choice.
  • Particleboard: Compressed wood particles are bonded together with the help of adhesive in making a particle board. Yes, it is a cost-effective option. But you must know that it is less durable too.
  • Advan Tech subfloor: It’s an engineered product, specially designed to resist moisture, swelling and wrapping. You may consider this. It’s kind of an all-in-one solution.

Importance Of A Sturdy Subfloor While You Install Your Floor

You must know that the quality of an actual floor depends a lot on the subfloor you use; whether in terms of stability or enhanced appearance. So, it is always advised to install a sturdy subfloor. 

You shouldn’t solely give importance to the amount to be spent while choosing your subfloor type. You may end up picking up the cheap quality. And in the case of a subfloor, quality ofcourse matters. Choose one that will be good in quality as well as budget-friendly.

Some Common Issues With Subfloors And How To Deal With Them

Though we take proper care while installing our subfloor, but with the advancement of time we may face some issues. Some common issues are- sagging, squeaking, cracking, tearing, moisture damage, pest damage etc.

However, the issues are common but not the outcomes. If you don’t give proper attention to the issues (even if you have any of them) or just pass a don’t care attitude, your subfloor will be ruined with the actual floor. 

So, you better call a professional, show him the condition and act as per his instruction if you face any of the issues.

Underlayment And Its Use In Flooring 

By installing joists and subfloor, you have proceeded one step closer to your floor installation process. Now, it’s time to work on the underlayment. The outside beauty and the charmness of your floor depends a lot on the type of underlayment that you use.

What Is Underlayment In Flooring And What Role Does It Play?

Underlayment is a kind of layer that is used between the subfloor and the furnished floor or the top surface. It is generally made of plywood, cement board, foam etc.

The role of underlayment is to provide smoothness, comfort and insulation. To enhance the comfort level while walking or to make your floor durable, it plays a very important role.

Different Types Of Underlayment Materials Used In Flooring

Different types of underlayment materials are used in flooring for different purposes. I am going to mention a few of them that are commonly used. They are-

  • Foam Underlayment: It is typically made of foam rubber, a soft cushioning material mainly used to reduce vibration and noise.
  • Rubber Underlayment: If you want to make your floor waterproof and moisture free, then it’s a great choice for you. The rubber used in this fulfils the purpose well.
  • Cork Underlayment: If you have played badminton, you know about cork. Yes, the bottom round part of the shuttle cock is made of cork. In flooring, it’s an excellent choice for sound insulation.
  • Plywood Underlayment: If you are living in a heavy-traffic area, you may consider using plywood underlayment which is sturdy and stable. It is also known as Rigid Underlayment.
  • Vapour Barrier Underlayment: This is another type of underlayment, used to prevent moisture. It is generally made of polyethylene or other materials to serve the purpose.
  • Felt Underlayment: It is also known as tar paper, is mainly used to protect the floor from moisture. It is generally made of organic fibers or fiberglass saturated with asphalt.

The Common Functions Of Underlayment

If you have gone through the different types of underlayments that are discussed above, you already know the answer. Is it not? 

Okay, let me tell you again that underlayments are used for various purposes such as to provide comfort, sound insulation, thermal insulation, moisture reduction, subfloor preparation, ensuring the protection of the subfloor and so on.

Guide To Choose The Right Underlayment For Different Flooring Types

Choosing the right underlayment for your floor is crucial. And for that, before you plan to purchase any of the underlayments mentioned above, you must have sufficient knowledge about your floor type. For example, if you install hardwood flooring, carpet underlayment is unsuitable.

Again, you have to think of the climate of your area also. For example, if you live in an area where the temperature is too low, the underlayment that provides insulation would be your first choice. You should consult with a professional to help you to decide this.

A Comparative Study: Joists, Subfloor And Underlayment

A table is provided below for the purpose of a comparative study so that you can understand things without any confusion in your mind.

PurposeTo prepare a solid and stout base by distributing the load equallyTo provide additional support by keeping the floor moisture- free and insulationTo provide an acceptable base for the floor cover
Materials UsedWood, Steel or ConcretePlywood, OSB, Concrete etc.Foam, Rubber, Cork, Plywood etc.
Thickness2 to 4 inches¾ to 1 inch¼ to ¾ inch
PlacementIt’s the structural base, placed to support the subfloorBetween the subfloor and underlaymentJust below the floor covering and above the subfloor
CostAt the current market price, $1 to $2 per linear footAt the current market price, $1 to $2 per square footAt the current market price, $0.50 to $1 per square foot
LifespanGenerally, 50 to 75 yearsGenerally, 20 to 30 yearsGenerally, 10 to 20 years

Choosing the Right Combination for Flooring And The Factors Behind It

With the installation of joists followed by subfloor and underlayment, 80% of your work is done. Now you have to work with floor-covering materials to give your floor a finishing touch with a nice and sturdy look.

Types of Floor Covering: The common types of floor covering that people use are- Hardwood Flooring, Carpet Floor, Vinyl Flooring, Laminate Flooring, Tile Flooring, etc., and each type of floor covering requires a particular type of underlayment, subfloor, and joists according to the needs and situations.

Considerable Factors: Based on your requirement and budget, you have to make a combination that will be long-lasting as well as praiseworthy. But don’t forget to seek suggestions from professionals to get the job done correctly and smoothly.

Wrap Up On Subfloor vs Joist vs Underlayment vs Floor Covering

Well till now you got a good idea on what individuals are all about so let me summarize for you so you will get a conclusion on your learning.

Starting from the top, then the topmost layer is the floor covering which you can view from the top and you walk upon that below that there will be an optional layer we call underlayment.

Beneath the underlayment, there will be a subfloor that will provide flat support for the floor covering and subfloor is laid on top of the joist.

This means joist is the base and made of thick wood ideally in the range of 2 inches in width and 6 inches in verticle length and all this joist has lied on the beam which is more than 4-6 inch in thickness.

It is not always mandatory to have underlayment but well recommended in case of concrete flooring to avoid moisture pass to the top flooring.

Never confuse in between underlayment vs subfloor as the underlayment is optional however subfloor is the basic need of any flooring and if struggling with the soundproofing than better to check how to soundproof a flooring.

FAQ: What are Subfloor, Underlayment, and Joists

Many people have many questions related to Subfloor, Underlayment, and Joists. So here I am answering some important questions.

Q1. How do you know which type of flooring to choose for your home?

Ans: There are many factors to consider when choosing to floor for your home, including the type of activity that will take place in each room, your budget, and the overall look and feel you want to create.

Q2. Why is it important to have a solid subfloor?

Ans: It is important to have a solid subfloor because it provides support and stability for the flooring material. It also helps to protect the flooring material from moisture and other elements that can cause damage.

Q3. How do you know if your flooring needs joists or beams?

Ans: You can determine if your flooring needs joists or beams by checking the manufacturer’s specifications. If the manufacturer recommends using joists, then you’ll need to install them before your new flooring can be installed.

Hey, I am Kirtish Vyas a YouTuber and believer in making life peaceful, a couple of years back I started soundproofing my house, bedroom, studio, and Car to reduce the unwanted noise, and the same experience I am sharing on SoundProofidea. Read More