# Soundproofing Between Floors in Somerville Homes Page: https://magnoandco.com/blog-soundproofing-between-floors > Soundproofing between floors in Somerville and Cambridge multi-families: impact vs airborne noise, STC and IIC code numbers, methods and condo rules. Hiring & Planning ## Soundproofing between floors in two- and three-family homes: what actually works Soundproofing between floors in Somerville and Cambridge multi-families: impact vs airborne noise, STC and IIC code numbers, methods and condo rules. **Mateus Magno** Licensed Construction Supervisor · November 2, 2026 · 4 min read Quick answer Soundproofing between floors works best when you treat two kinds of noise: airborne sound like voices and TV, and impact noise like footsteps. The building code sets a minimum of STC 50 and IIC 50 for floor-ceiling assemblies between dwelling units in buildings under the base code, and the best upgrades combine a decoupled ceiling, mineral wool, extra drywall and a cushioned floor above. Owners of two-families, triple-deckers and condos in Somerville and Cambridge ask me about soundproofing between floors. Old wood-framed floors carry footsteps and voices straight down. The good news: with the right mix of fixes, you can make a big difference without tearing the whole building apart. The key is knowing which kind of noise you are fighting, because the fixes are different. ## Impact noise vs airborne noise - **Airborne noise** travels through the air first: voices, music, TV. It leaks through thin ceilings, gaps and holes. - **Impact noise** starts as a hit on the floor: footsteps, dropped objects, chairs sliding. It travels through the framing itself, which is why the thump from upstairs is so hard to stop. Most complaints I hear in Greater Boston multi-families are about impact noise, so a good plan treats both. ## STC and IIC: what the code numbers mean The [2021 International Building Code, Section 1206](https://codes.iccsafe.org/content/IBC2021P2/chapter-12-interior-environment) sets sound rules for walls and floor-ceiling assemblies between dwelling units: | Rating | What it measures | Code minimum | | --- | --- | --- | | STC (Sound Transmission Class) | Airborne sound, lab-tested to ASTM E90 | 50 (or NNIC 45 if field-tested) | | IIC (Impact Insulation Class) | Impact sound, lab-tested to ASTM E492 | 50 (or NISR 45 if field-tested) | Higher numbers mean better isolation. The same section says penetrations for pipes, electrical boxes, recessed fixtures and ducts must be **sealed, lined or insulated** to keep the rating. Massachusetts made [no amendments to this chapter](https://www.mass.gov/regulations/780-CMR-tenth-edition-chapter-12-interior-environment-amendments). Keep in mind that the state's [residential code](https://www.mass.gov/regulations/780-CMR-tenth-edition-residential-chapter-1-scope-and-application-amendments) covers detached one- and two-family homes, so the IBC numbers apply to buildings with three or more units, like most triple-deckers. On two-families, I still use STC 50 and IIC 50 as a good target. MAGNO & CO Planning a project in Somerville? Licensed builder & owner's rep · free walkthrough · written budget in about 48 hours. [Book a free consultation](https://calendar.google.com/calendar/appointments/schedules/AcZssZ3YJnElSsR4HsHaWVd6BsIBm7JOsDl2n-1EMy9trS9rj8PCyepopoQtl6O7um0eJcFcp5XXYk-Z)[978-397-5700](tel:+19783975700) ## Soundproofing between floors: methods that work These are the pieces I combine, from the ceiling below to the floor above: - **Mineral wool in the joist bays.** It absorbs sound inside the cavity. On its own it helps a little; combined with the next steps it helps a lot. - **Resilient channel or isolation clips.** They hang the new ceiling so it is not screwed tight to the joists. This breaks the path that carries footsteps. - **Double drywall with damping compound.** Two layers add mass, and a damping layer between them turns vibration into tiny amounts of heat. - **Sealing every gap.** Acoustic sealant at the edges and around lights and boxes. One open recessed light can undo a lot of work. - **A floating floor or acoustic underlayment upstairs.** A cushioned layer under hardwood or tile is one of the best fixes for impact noise. - **Rugs with thick pads.** The cheapest fix of all, and it works on footsteps right away. **Builder's tip:** Never screw through the resilient channel or clips into a joist. One stray screw can short-circuit the whole ceiling and send footsteps straight through. I mark every joist line on the wall before we hang drywall so the crew knows exactly where not to fasten. ## From the ceiling below or the floor above? - **Ceiling below** is usually easier when the upstairs unit is occupied or belongs to someone else. You control the work. - **Floor above** is where impact noise starts, so treating it there is very effective, especially during a kitchen or flooring project. - **Both** gives the best result when a gut renovation opens everything up. In a two-family, the residential code requires wall and floor assemblies between units with at least a **1-hour fire-resistance rating** ([IRC R302.3](https://codes.iccsafe.org/content/IRC2021P2/chapter-3-building-planning)). When I open a ceiling between units, I plan the new assembly so it keeps the fire separation while improving sound. ## Condo association rules If you own a condo in Somerville, Cambridge or Boston, read your master deed, bylaws and rules before you change flooring. Many associations set rules for underlayment under hard floors because of exactly this problem. On the permit side, Somerville's [building permit submittal checklist](https://www.somervillema.gov/sites/default/files/building-permit-submittal-requirements-checklist.pdf) includes an **approval letter from the condominium association** for the proposed work. My [condo renovation rules guide](https://magnoandco.com/blog-condo-renovation-rules-boston) covers what to ask your board. ## What drives the cost I don't quote soundproofing by the square foot without seeing the space. The price depends on: - Whether we remove old plaster ceilings or build below them (which costs headroom). - **Lead-safe work.** Under the [EPA's RRP rule](https://www.epa.gov/lead/renovation-repair-and-painting-program), anyone paid to disturb paint in a pre-1978 home must be certified and use lead-safe practices. My [lead paint guide](https://magnoandco.com/blog-lead-paint-older-homes-renovation) explains what that adds. - Lights, sprinkler heads, ducts and pipes in the ceiling that need to be moved or sealed. - Flooring removal and replacement upstairs. - Access, parking and stair carries on tight Somerville streets. Every building is different, so I give a written line-item budget after a free walkthrough. ## Need a hand? I quiet down floors in two-families, triple-deckers and condos across Somerville, Cambridge and Greater Boston. [Book a free walkthrough](https://magnoandco.com/contact) and I will look at your ceiling and floor build-up, then send a written line-item budget, usually within 48 hours. ## Frequently asked questions What is the best way to soundproof between floors? Combine a decoupled ceiling on resilient channel or isolation clips, mineral wool in the joist bays and extra drywall with damping, then add a cushioned underlayment or rugs upstairs. Treating both sides works best. What STC and IIC rating is required between apartments? The 2021 International Building Code requires floor-ceiling assemblies between dwelling units to reach STC 50 and IIC 50 in lab tests, or NNIC 45 and NISR 45 if field-tested. How do I reduce footstep noise from upstairs? Footsteps are impact noise, so the best fix is at the source: an acoustic underlayment under the flooring or thick rugs with pads. From below, a decoupled ceiling helps most. Do I need condo approval to soundproof my floor? Usually, yes. Check your master deed and rules, and in Somerville the building permit checklist includes an approval letter from the condominium association. **Want someone on your side?** See [what I do as an owner's representative](https://magnoandco.com/owners-representative-somerville) and [how I price work](https://magnoandco.com/pricing). **Good to know:** this article is general information, not legal or engineering advice. Rules change and every property is different — confirm the details for your home with your city's building department, or [ask me](https://magnoandco.com/contact). See our [Terms & Disclaimers](https://magnoandco.com/terms). **About the author** Mateus Magno founded Magno & Co in 2020. He is a licensed Massachusetts Construction Supervisor (CS-123658), registered Home Improvement Contractor (HIC #220484) and certified Lead-Safe Renovator Supervisor who has renovated and managed over $5 million in projects across Greater Boston. [More about Mateus →](https://magnoandco.com/about) Keep reading ## More from the blog [Hiring & Planning ### Load bearing wall removal cost: opening up an old Somerville house the right way Load bearing wall removal cost in Somerville and Greater Boston: engineer, LVL or steel beam, posts to the foundation, permits and what hides in old walls. 4 min read · Read article →](https://magnoandco.com/blog-load-bearing-wall-removal-cost) [Hiring & Planning ### Aging in place home modifications for Greater Boston homes Aging in place home modifications for Somerville and Greater Boston homes: curbless showers, grab bars, first-floor suites and Massachusetts loans. 4 min read · Read article →](https://magnoandco.com/blog-aging-in-place-remodel-massachusetts) [Hiring & Planning ### Change orders in construction: what they are and how to handle them in an old house Change order construction basics for Somerville and Cambridge homeowners: why change orders happen in old houses, what to put in writing and the red flags. 4 min read · Read article →](https://magnoandco.com/blog-construction-change-order) ## Have a question about your project? Plans, a sketch or just an idea — talk to me. You'll get honest advice and a clear written budget and schedule. [Book a free consultation](https://calendar.google.com/calendar/appointments/schedules/AcZssZ3YJnElSsR4HsHaWVd6BsIBm7JOsDl2n-1EMy9trS9rj8PCyepopoQtl6O7um0eJcFcp5XXYk-Z) [Call 978-397-5700](tel:+19783975700) ## Worked with Magno & Co? A 1-minute Google review helps Somerville neighbors find a builder they can trust, and it means a lot to a small local business. [Leave a Google review](https://g.page/r/CW23iOz7D9gnEAE/review) [Read our reviews on Google →](https://maps.google.com/?cid=2871062337128281965) --- Magno & Co · licensed owner's representative and builder · 55 Davis Square, Fl 3, Somerville, MA 02145 · 978-397-5700 · info.magnoandco@gmail.com · MA CSL CS-123658 · MA HIC #220484 · https://magnoandco.com/