Acoustic joist tape is a thin, pressure-sensitive, plastic strip with an adhesive backing. It is commonly used to reduce transmission of airborne sound such as footsteps and voices (when used as a sound barrier) through floor and roof assemblies.
The function of the tape is to dampen vibrations between two parallel surfaces – either within a single joist or between two joists. The sound vibrations are attenuated by the tape because it effectively dampens the primary vibration mode of the joist. The tape is installed within a gap between two parallel surfaces, typically in a floor or roof assembly.
Where to use acoustic joist tape
- Floor joist assemblies
Here, the tape is installed underneath floor coverings (such as carpet, vinyl flooring or ceramic tiles) to reduce transmission of airborne sound through the floor. The tape can also be used between two joists if required. This reduces impact sound transmitted through the subfloor and to adjoining rooms below.
- Wall assemblies
Wherever cross-bridging occurs in wall assemblies (i.e., at top plates, studs or trimmer studs), you can install acoustic foam products on either side of these elements. Cross-bridging is one reason walls are not efficient structures for containing sound within a room; it causes noise to “flap” back and forth across these elements, resulting in an echo effect that allows sound leakage into adjacent spaces.
- In a drop ceiling assembly
The tape is applied beneath the metal support members where they meet with the cross-slats, creating a gap for sound to be conducted through. This distributes impact sound away from its source and prevents it from being transmitted back into the space below – where it might interfere with activities taking place directly above. Acoustic foam products can also be applied to surfaces of a drop ceiling facing down toward a space below to prevent leakage of noise vertically out of the slotted areas, as well as horizontally from one slotted area to another.
- Underlay under carpeting or floor coverings
This application reduces transmission of airborne sounds such as voices and footsteps by dampening vibrations between two joists. This application differs from others because the tape is installed underneath the floor covering, which sits on it without any gap.
How to install acoustic joist tape
- Start by installing solid blocking at wall and floor perimeters. The solid blocking must be screwed or nailed securely into place before you take up the flooring that would have otherwise covered it. Solid blockings should also be placed beneath door casings, if possible. Blocking creates a “solid core” for your walls and floors to rest upon – an essential factor required for this particular product’s success.
- On top of this, install 1st layer (or course) of subflooring (usually plywood) over solid blockings ensuring that joists are visible.
- Install 2nd layer (or course) of subflooring on top of the 1st layer. The second layer of flooring will also cover the joists.
- Trim back any excess acoustical foam product to fit between the two layers of flooring and lay it over both your joists, ensuring an even application along its length.
- Take up your floor covering or carpet and apply tape underneath it where needed, at each perimeter and wherever cross bridging occurs in wall assemblies (i.e., at top plates). Ensure that no gaps exist between the tape and other components (such as door casings), which would allow sound to “short circuit” through these areas without being reduced by acoustic insulation first.