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

Flooring is key factory of any house where you concern about the soundproofing, probably you have heard the wooden or tiles floor but do you know how any floor has been designed? It is a combination of subfloor, underlayment, and joist.

Flooring is the only place in the house which bears everything in the house no matter it is a machine or your own weight and also the major area which decide the decorative look of your house.

While you walking on a very smooth floor, have you ever tried to find out what makes that surface very strong and smooth and how it able to bear this much weight? It is because of it’s underneath layers.

That layers are made of subfloor, underlayment, and joist. Hence in this guide, we will discuss what is subfloor, underlayment, and joist in the flooring architecture and importance of each other.

what is subfloor,underlayment,joist in flooring

A general floor has four things to discuss one is the topmost layer which we call floor covering which every one of us can see then we have underlayment, subfloor, and joist one under another.

Let learn each one of them and make sure you learn everything by the end of this guide.

What is Floor Covering?

Floor covering is a general material applied on top of the subfloor for finish walking or good looking flat surface in the house.

If we talk about floor covering then the most materials used are carpet, tiles, laminated and vinyl. Selection of the floor covering materials is crucial for the soundproofing of any house.

It is the topmost layer from which sound or noise reflection happens, so make sure to buy such flooring materials which are having good Noise reduction coefficient (NRC), Sound Transmission Class(STC).

But in case of floor covering, better to check the impact insulation class (IIC) and find out the ability of any material to minimize or reduce the impact noise. floor covering above subfloor

Here are a few examples of floor Covering.


Carpet is widely used in every house due to its noise or sound-absorbing capacity it minimizes the echos and improves the sound quality in the house.

Denser and high-quality carpet really help to reduce the impact noise and the core soundproofing material as it is made of varieties of materials like wool, nylon, and polyester, etc.

Wood Flooring

This is the basic flooring, you have seen in almost every houses, it is either made of hardwood or softwood. Buying a wood could be expensive as compared to engineered wood.

Engineered wood has a thin top layer of wood with a very strong core base, if talking about the wood flooring than people also use Bamboo which is part of hardwood flooring.

Laminate Flooring

It is the best choice for those who are looking for an attractive look to the flooring as it is the man-made designed flooring material which front surface is decorated in varieties of colors.

Laminate flooring is designed of Flipboard which top up with multiple printed and protective layers and it is more durable than the hardwood.

It is designed in a way to durable in any environment, so no more shrinking or damage to the floor and will be a one-time setup and forgets for a longer duration.

Tiles flooring

This is the hard and tough flooring which includes the concrete and tiles flooring material. Tiles are available in different shapes and mainly made of marble and different natural stones.

After installation, it requires proper polishing to give decorative looks to the floor. These days people also started floating tiles flooring which is easy to install without any adhesive.

Till this point, you got an idea the very first top flooring component which we call finish flooring importance and use in floor soundproofing.

What is Underlayment?

Well, Underlayment is the first layer you will find under the floor covering, the use of an underlayment is not compulsory for every flooring but yes it is a must recommended in most of the cases.

Basically underlayment is placed in between the top floor covering and subfloor to provide a smooth base for the top floor covering.

It is under the floor covering and that is why hidden from the direct viewing but the most effective solution in soundproofing and moisture resistant.Floor underlayment above subfloor

It is made of plywood, Flipboard, hardwood, and cement board and many other favorite choices.

Importance of Underlayment

Let discuss the importance of underlayment and why this is a crucial part of floor construction.

  • It provides a smooth and flat surface for the top floor covering.
  • It helps to improve the adhesive nature of the tiles floor covering.
  • It helps to minimize the noise due to its noise-absorbing capacity, mainly effective in laminated flooring. 
  • Underlayment is resistive to moisture which in a result, no moisture rises from the foundation of the floor can pass through and spread across the floor covering.
  • Due to flatness, it also helps to eliminate the problem of fixing the top floor covering.
  • It also helps to keep the floor warms.
  • It also helps to create insulation under the floor and minimize the noise vibrations. 

I imagine the above points are good enough to explain the importance of Underlayment but is it compulsory for all types of flooring?

Is Underlayment compulsory?

Underlayment has much more important but the very best is to use in case when if you have subfloor which is not that much flat and unleveled throughout the room which causes an issue with top flooring.

In some cases, you don’t even need underlayment, you can directly lay down your floor covering on top of the subfloor but most recommended underlayment for laminated flooring.

As discussed, underlayment can be plywood, cement board or OSB but you can also use soft underlayment which will not sticky to the subfloor.

Foam and cork are part of soft underlayment where they provide proper insulation for the noise and also help to cover the small holes and gaps of the subfloor to provide more levelness for the floor covering.

As far as my learning, you should not replace your hard underlayment with the soft as hard underlayment will be more effective in case you are laying down a new floor covering on top of the existing.

It is advisable to have your underlayment as thin as possible to avoid any unnecessary issues.

Must use underlayment,in case of soundproofing between the existing floors if you are living in an apartment which has noisy neighbors upside and down to the apartment.

What is Subfloor?

The subfloor is the hardest and flat surface above the joist and below the underlayment or maybe in case of no underlayment just below the floor covering.

Floor covering is not that much efficient enough to bear a whole lot of weight on the floor hence a strong base set below that to handle the weight of machinery and everything on top of the floor covering.

The subfloor is must for every floor to create strong support and provide a level surface for the floor covering,it actually stabilizes the foundation of the floor.

It is the foundation of the flooring on top of which many activities carried out so these are strong, rigid and durable enough to face every worst condition happening on the top flooring.

Subfloor could be a wooden plank, plywood Oriented standard board (OSB) or concrete material but mainly in the house basement, people use the concrete subfloor.

Subfloor for soundproofing

Never confused subfloor with the underlayment as the subfloor is the mandatory component for any flooring construction however underlayment is optional.

These days in Europe, most of the newly constructed houses are sold without a floor covering as there will be the last layer of subfloor only, the reason is later on top of that people can lay their own choice of floor covering.

Here are different materials used in Subflooring

Wooden Plank Subfloor

It is the oldest material people use in the 1950s which are usually the size of 1*6 and made of pine fir or kind of same softwood.

These were easy to fix with the joist using the flooring glue or standard nail boxes but this has been replaced with the plywood subflooring.

Plywood or OSB Subfloor

It is the most favorite subfloor material used these days which comes into the thickness of 1/2 inch and 5/8 inch thickness.

It is also easy to install by gluing with the joist using the adhesive material and can be available in thinner or thicker size.

The thinner one is effective for vinyl or any such flooring and for tiles flooring better to have thick subfloor.

Concrete Subfloor

It is most recommended in case of ground floor or basement as it allows easy fixing of tiles floor covering.

Concrete subfloor has an issue with the moisture release to the top floor covering so ideally it is recommended to have an underlayment for the concrete subflooring.

It has an issue with coldness and hardness, which be eliminated by setting up soft underlayment like foam in between the top floor covering and the subfloor base.

Well, till this point you are clear with what is a subfloor and which materials are very famous for subflooring.

What is Joist?

Joist is the fundamental of the flooring architecture and the mandatory for any flooring architecture except concrete flooring.

Every other layer of flooring is built on top of the joist, which means it is the bottom-most layer in flooring construction.

Joist is a horizontal structure placed between the beams to provide strong support for the subfloor created on top of the joist.

what is jost in flooring

The joist is made of wood, engineer wood or steel the quality of the joist material will decide the weight-bearing capacity of the floor. The closer the joists are will improve the strength and can carry more load.

If there is a wider spacing in between the joist can cause deflection under heavy load and that is why people have started joist products such as i-Joist which has high strength and more weight-bearing capacity.

I-Jost are made of engineer wood which is no likely to bow, twist, crack or split even in very heavy load condition.

Make sure below two-points while referring to the joist

Size of Joist

The ideal joist dimension should be in the range of 2*6 inches where 2 inch is in width and 6 inch is in verticle length.

Spacing of Joist

The ideal spacing of the joist from the top layer should be in between 16 inches, which improve the ability to handle enough weight.

To improve the joist ability to bear the weight more than common weight than make sure all joist should put closer with around 10-12 inch spacing.

Great, you got almost every idea what is joise, what is subfloor, what is floor covering and what is underlayment let me compare in brief.

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 than that there will be an optional layer we call underlayment.

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

Which means joist is the base and made of thick wood ideally in the range of 2 inches 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 an optional however subfloor is basic need of any flooring and if struggling with the soundproofing than better to check how to soundproof a flooring.

what is subloor,underlayment,joist in flooring

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

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