Impact noise will travel through a structure that does not have a resilient material as part of the construction assembly.

Floor soundproofing is a unique soundproofing scenario because our main focus is to reduce iminate impact noise. Typically, soundproofing efforts are directed at reducing sound traveling through the air, rather than the impact of foot traffic. That said, the solution to both is the same because the vibrations created are physically the same!

Considering the age ranges of buildings and homes and all of the types of construction methods and techniques that were or were not used over the years, most floors are not inherently soundproofed. In fact, it’s almost assumed in many older structures, especially multi-level residential structures, that “creaky floors” are just part of its charm.

Maybe in a horror movie, but for all of us who have lived somewhere with creaky floors, it’s a “feature” I’d like to eliminate. Thankfully, floor soundproofing is very effective and a relatively easy install compared to walls and ceilings. In this article, we’ll explore floor soundproofing, how it works, and the best products and installation techniques to eliminate impact noise and craft a serene sonic atmosphere.

How Sound Travels Through Floors

Sound travels through floors because of the sound of impact. Whenever anything, like a footstep or a dropped cup, hits the floor, the impact creates sound that vibrates through the floor as a mechanical wave. If you were to mount a speaker directed at the floor and play a loud sound, the process would be the same, except the speaker is creating the sound wave that enters the floor, rather than the impact.

The reason floors carry sound is because of the materials they are made from. The most common way to understand floor assemblies is to consider a typical two story residential home. Ever noticed how you can usually hear activity going on in the upper floor, like someone walking around or doors closing? And yet, on the main floor, someone walking around doesn’t make any sound at all. The simple reason is the main floor is sitting on a thick layer of concrete that sits on the earth, so it has an incredible mass that absorbs the impact energy. The upper floor, on the other hand, is an assembly of drywall underneath, beams, plywood, and a flooring finish on top. The materials and their mass isn’t enough to completely absorb the sound waves as they pass, which is why you can hear them.

Our mission then is to introduce soundproofing materials within the floor assembly in order to more effectively block the sounds so that they cannot pass through.

How to Soundproof Floors: Decoupling

Our main focus when soundproofing floors is to eliminate the sound wave as it passes through the assembly materials before reaching the other side. To do this, we need to decouple the flooring assembly. Decoupling essentially means providing space or a special soundproofing material between flooring components so that it makes it more difficult for the sound wave to keep passing through the stack of materials. Let’s think about an example.

Imagine a pool table and you have lined up 5 pool balls all touching one another. If you were to hit the first ball in the line with the pool stick just barely, that impact would vibrate through all of the balls because they are touching. Now imagine you lined up two balls touching one another, then left a space of 2 balls, then lined up another 2 balls touching one another. When you hit the first ball with the same exact amount of energy as the first time, the impact will transfer from the to the second ball and cause it to move forward across the gap. Because the gap is larger than the energy of the impact, the ball will stop before it hits the second set of balls.

What we did here is decouple the pool balls, and that allowed the impact energy to die off in the gap before the second set of balls were touched. This is exactly what we are doing when soundproofing floors, except instead of an air gap, we utilize specifically manufactured materials to sandwich between the floor assembly components to create layers that absorb sound wave energy.

The Ideal Floor Soundproofing Material: Iso-Step® Soundproofing Underlayment

Iso-Step® Soundproofing Underlayment, when installed correctly, is a double-duty acoustical underlayment. It improves IIC ratings (Impact Insulation Class) by providing an impact-resistant layer under flooring. This reduces the transmission of structure-borne sound. Additionally, Iso-step® will add to the STC (Sound transmission class) of the overall assembly.

Install Iso-Step® over wood or concrete sub-floor, beneath hardwood, engineered hardwood, vinyl, tile, and carpet flooring. Iso-Step® Soundproofing Underlayment is economically priced and available for quick shipment.

How to Install Iso-Step® Soundproofing Underlayment

Necessary Tools

  • Tape measure
  • Metal straight edge
  • White marker, chalk or chalk line
  • Utility knife
  • Duct tape (optional) 
  • Adhesive if required
  • Other tools may be required to install subsequent layers of flooring materials

Prep Work

Iso-Step® Soundproofing Underlayment and the flooring material to be installed must acclimatize, in their sealed packaging, in the room where they are installed for at least 48 hours, at a temperature of at least 65 degrees F. Before starting your installation of Iso-Step®, make sure the subfloor is permanently dry and free of dirt, dust, grease, and other foreign matter.

Prep For Wood Base

The subfloor should be properly leveled, structurally sound, and clean. Plywood sub-flooring should be of a good grade. Level any variations in floor level over 1/8″ within a three-foot span before installing underlayment. Remove or pound flat any nails or other protrusions. Repair holes and other surface variances prior to installation of Iso-Step®. To use IsoStep® with a nail-down hardwood floor, we recommend that you create a “raft” made of 2 layers of 1/2” plywood, glued and screwed together with the top layer turned 90 degrees in orientation and offset by 2 feet from the edge in order to cover the seams. Leave a 1/2″ gap between the wall and the raft to allow for expansion around the entire perimeter. Use 1-1/2″ nails applied at an angle to secure the hardwood flooring on top.

Prep For Concrete Base

Inspect the concrete subfloor for any open cracks and fill with high-grade epoxy filler. Remove any excess concrete lumps or residue that may interfere with the installation of Iso-Step®. If you use a vapor barrier, we recommend polyethylene sheeting. Install overlapping seams (6-8″ overlap) using tape to secure edges. Apply the vapor barrier directly over the concrete.

Floating Floor Systems

Under Laminate & Engineered Wood Flooring Or Tile

The laminate or engineered wood flooring is intended to float on top of the Iso-Step® Soundproofing Underlayment. In most cases, you can install acoustic underlayment in a few easy steps.

First, install a perimeter isolation strip to prevent the flooring from touching the walls or any protrusions in the floor. Make sure to prep all areas, and ensure they are level and free of dirt and debris. Then follow the installation guide as outlined in the documents section of the Iso-Step® Soundproofing Underlayment page and as instructed by the flooring manufacturer. If the engineered hardwood is required to be glued down you will also want to glue the floor underlayment to the subfloor.

Iso-Step Soundproofing Underlayment

Iso-Step® Soundproofing Underlayment

Under Tile

Iso-Step Soundproofing Underlayment - After installing a perimeter isolation strip, apply approved adhesive to the sub-floor using recommended trowel size.

After installing a perimeter isolation strip, apply approved adhesive to the sub-floor using recommended trowel size.

Iso-Step Soundproofing Underlayment - Roll out and lay the Iso-Step into the adhesive bond.

Roll out and lay the Iso-Step® into the adhesive bond.

Iso-Step Soundproofing Underlayment - Roll the Iso-Step with an approved flooring roller.

Roll the Iso-Step® with an approved flooring roller.

Iso-Step Soundproofing Underlayment - Apply adhesive to the Iso-Step using recommended trowel size.

Apply adhesive to the Iso-Step® using recommended trowel size.

Iso-Step Soundproofing Underlayment - Lay finish floor layer according to flooring manufacturer guidelines.

Lay finish floor layer according to flooring manufacturer’s guidelines.

Nail Down Hardwood Flooring

** Do not nail through Iso-Step® Soundproofing Underlayment**

Installation of solid nail-down hardwood flooring using a raft method: Install Iso-Step® from wall to wall — loose lay; lay ½” plywood on top leaving a ½” expansion/acoustic gap around all walls. Install a second ½” layer of plywood making sure to stagger the bottom seam from the top, glue and brad nail the top plywood to the bottom plywood. 

The plywood floats on top of the underlayment. You can fasten the nail-down hardwood into the plywood raft. Leave the expansion gap alone or fill it with acoustical caulk, and install baseboard slightly off the finished floor.

Cross-Section of Hardwood Floor Assembly

Cross-Section of Hardwood Floor Assembly

Soundproof Your Floors the Right Way with Acoustical Solutions

Soundproofing your floors is an extremely satisfying renovation and it doesn’t have to be a great challenge. The results, especially when impact noise is an annoyance, is well worth a bit of renovation, thanks to exceptional modern soundproofing materials and products. 

Give me a call today and we can discuss your specific situation and craft a plan to acoustically improve your floor with the best techniques and materials available.

To learn more about how Acoustical Solutions can solve your noise control problems, use our contact form, call one of our Acoustical Sales Consultants at (800) 782-5742, or visit us on the web at