A major reason for sound leakage through floors is caused by sound flanking. Sound can easily travel through solid materials like studs, joists, concrete, etc. with the help of vibrations. In many houses or even in flats there are joist systems installed under the floors.

As the space underneath it is interconnected even if there is no open-airpath, you can hear the transfer of sound waves from either end of such floor.

Same issues are seen where similar systems are used under ceilings. Sound leakage can also be caused due to common side walls, with no proper sound insulation.

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How to Soundproof floors between Joists

Sound leaks come from multiple areas that require basic soundproofing. But soundproofing noise coming from your floor is a very difficult task due to Impact Noise. Impact noise is caused when you drop something on your floor or a vibration caused by machinery. Controlling such noise is very challenging as it causes vibrations in the whole structure rather than a single point.

So, sound insulation under the floor always requires additional components that are specifically designed for preventing impact noise. But there is a catch here. You may be required to use more than one such product for better results.

Things to note before installation:

First of all, it’s not recommended to perform such tasks without the help of a professional.
Soundproofing materials differ based on your requirements.
It is not recommended to use costly predesigned products without a proper advisory. Not only because they are heavily priced. But also, because your problem might be solved by simple insulation using Green Glue or any other product.
Always use fresh products because changing faulty goods is very challenging in such cases.

Steps to Soundproof floors between Joists:

Under New Construction:

Floor Installation:
First off start by implementing Joist Gasket tape (available on Amazon) on all the available joists. By doing so, you will decrease the noise created by footsteps or any type of impact noise. It will also decrease the chances of additional squeaks caused due to the subfloor rubbing against the joists. In many cases, people might avoid using Joist tapes but experts say that using Joist Gasket tape is always beneficial in the long run.
Then install the sub-floor above Joist Gasket Tape on your Joist. After doing that, you have to apply Green Glue Noiseproofing Compound (link to Amazon) on your sub-floor. For every 4” x 8” sheet you have to use 2 tubes of Green Glue. It is a damping compound, used to reduce vibrations. This eventually decreases the chances of Sound leakage.
After this, all you have to do is apply another sub-floor above the applied green glue. Then fasten your 2^nd layer to the joists.
As an optional choice, you can also apply Rubber Underlayment above your sub-floor before applying the finished floor. This will greatly decrease the transmission of impact noise providing even better soundproofing.

It is recommended that you perform these installations before you form the walls. This will ensure that there is no sound seepage between the walls and provide a much better soundproofing experience.

Caulking: (Required only if the installation of the 2^nd layer is done after wall farming)

After installation of your 2^nd layer, you will have to seal the perimeter of the room using a high-quality Acoustical Caulk. This will ensure that the gaps are properly sealed.

Floor Covering:

After you have completed the floor installation and wall farming. All that is required is to install your final floor above the present sub-floor or the applied underlayment used.

Under Old Construction:

Many times, people are required to perform soundproofing of existing floors which can be very burdensome.

Although it is difficult to put sound insulation on a prebuilt floor, it is not that different from any other soundproofing job, all that is required is to be extra careful. There are many ways to soundproof between existing floors. We will be providing some of the most used options available.

Before we begin, if you’re living in a hostel or an apartment, it is best to be sure about the permissions required before performing any such activity. This is because in some apartments disturbing the prebuilt floors and ceilings is prohibited.

Options available for floor soundproofing under old construction:

Refurbishing old floor:

If you have to soundproof an old floor, the best option that you have is to refurbish the affected floor. But, make sure you’re ready for refurbishing before going forward because this might require more time and funds than you would have analyzed before. Below is a step-by-step guide that explains how to Soundproof the floor between joists under old construction.

First of all, the old floor surface should be removed. When this is done you will be able to see the old joists present under the floor. Take proper note of the required sizes so that you can move forward with proper measurements.
After that, if possible, you will be required to change your existing ceiling with an Acoustic Board which will dampen noise and provide excellent soundproofing. You can also use Resilient Channels along with boards if you’re facing major sound leaks.
If the ceiling is not replaceable you can either skip this or use a direct joist floorboard on the sub-deck. It will also provide similar results.
After that, the gap between joists must be filled with special wool designed for soundproofing. You can use Rockwool which is very good in quality and costs less than its counterparts. This will ensure that there is no gap in between joists. Rockwool has sound-absorbing capabilities that help it to dampen sound waves and stop them from passing through.
After you have filled the gaps, you have to cover this with a sub-board or another acoustic board if required.
After completing that you can apply sealants on the edges towards the wall to ensure no gaps are present.
Now all that’s required is to place your floor as it was and your good-to-go.

Conclusion

So, these were some of the widely used methods which are prominent in soundproofing floors between Joists. As mentioned earlier, it is not recommended to perform any of the above-mentioned tasks without expert supervision. Or if possible, we recommend you to appoint an expert for installation and refurbishment. This will also provide better finishing and guarantee safety.