Soundproofing your basement is a great idea. It’s remarkable how loud it can be when someone walking across the floor above. It’s also unnerving to have the floor you’re standing on start vibrating because of loud sounds in the basement! We’ve included several things to consider below.
It’s also helpful to talk about sound transmission in a measurable way. There are IIC ratings, which measure impact-related sound and STC ratings, which measures sound transmitted through the air. In a wood-framed single-family home which is typical in the USA, a 2×4 wall with standard drywall on each side has an STC rating of 34 db. A typical floor system with drywall on the ceiling side has a rating of 40-45 db. The higher the number, the better it is at blocking sound. For an in-depth look at this topic you can check out HUD’s Sound Transmission Class Guideline here. https://www.hud.gov/sites/documents/DOC_16419.PDF For reference, a home theater is usually expected to generate 75 decibels of sound.
Upper level floor coverings
If you have or are installing carpet you’re already doing a great deal to reduce sound transmission. Carpet results in an IIC rating of around 70-75 and an STC rating close to 60. The more dense the padding and the thicker the pile, the better for sound absorption. However, carpet is going out of favor in main living areas in favor of hard flooring.
TriMaxTraditional hardwood can be installed over sound-absorbing underlayment systems to help reduce sound transmission. One such product is Proflex-90. This product can be used under a number of finished floors, but we prefer it for under hardwood and laminates instead of tile. The density of the wood will also make a difference. Hardwood is more dense than softwood, which means it won’t transmit sound as much. Our domestic hardwoods in North America aren’t as dense as some other options like Brazilian walnut or pecan.
Floating floors, whether laminate, engineered hardwood or luxury vinyl plank (LVP) can be installed with underlayments that help, although many of these floors now come with attached underlayments that limit sound transmission. You can determine the effectiveness of their sound dampening qualities through a product specification sheet available from the manufacturer. For example, COREtec Plus XL Enhanced is an LVP product we installed in a condo building recently. It has an attached cork underlayment and has an IIC and STC rating of 62 db. Some underlayment and flooring products may be able to be combined for added benefit.
Tile will provide more challenges due to the complexity of installation requirements. Natural stone floors require 2 layers of sheathing on the floor system, plus a proper bonding layer. Large format ceramic and porcelain tile have different requirements, as does mosaic tile and other less-common materials like cement tile, sliced thin brick, etc. that must be taken into account. Our preferred tile installation materials come from Laticrete, a pioneer of modern tile installation methods and materials. They have multiple products available (125 TRI MAX, for one) that can help limit sound transmission.
Floor system options
Various floor systems will transmit sound differently. A traditionally-framed, dimensional lumber floor system with joists at 16” on-center (o.c) and 3/4” tongue-and-groove subfloor materials should be quite rigid. The continuous solid lumber provides a lot of material for impact vibration to travel through, transmitting the sound to the space below. Engineered joists, or I-joists (also known as TJIs) have a narrow center web that reduces some vibration. The irregular TJI shape will also limit some air transmission. These floors are often built with the joists on 19.2″ centers, so there’s fewer joists to transmit vibration through. Floor trusses, or “open-web” floor trusses are even better. They’re typically installed at 24” o.c. and are built with multiple 2x members at different angles to support long continuous spans. This helps reduce impact transmission.
In order to limit air transmission, it’s common to fill a floor system of any type with blown-in, loose-fill fiberglass insulaton. Other materials like fiberglass batts or recycled cotton batts can be used as well. TJI and truss floor systems are often deeper than traditional lumber floor systems so they can accommodate more filler. Depending on how seriously you want to block sound, it may be necessary to cover HVAC ducts and drainpipes with specialty materials.
Ceiling finish options
A common method of reducing sound transmission is by installing 25-gauge sound channel on the underside of joists. We can apply sound-absorbing foam tape to the sound channel. While high-strength 1/2” drywall is usually supportive enough for ceilings, installing 5/8” material is better for sound reduction due to it’s added thickness. Sound-absorbing gypsum is even better. While acoustic “pop-corn” texture has become less popular, it does function better than a smooth ceiling for sound absorption.
Walls and finishes
Other considerations include how the basement is constructed and the finished materials. Installing a rigid rubber padding between the ceiling and wall framing will prevent some direct transmission from the upper floor into the basement walls. Building walls with foam padding or silicone between the framing and wallboard, installing sound-dampening drywall, or building double-layer walls filled with insulation, with limit sound between rooms. Installing solid-core doors and finishing walls with a texture can help. Breaking up the space into individual rooms instead of maintaining a large open area can also help.
It’s probably obvious, but there are many options for sound-proofing your basement. I hope this overview of different factors and options has been helpful. A cost-effective combination for reducing day-to-day noises could be as simple as installing blown-in fiberglass insulation to fill the floor system, sound channel, and 5/8” standard drywall on the ceiling if the basement also has carpeting. Make sure your approach to sound-proofing matches your goals. If you’re in the Minneapolis, MN area and looking for basement finishing services, feel free to contact us.
