Is Spray Foam Insulation Good For Soundproofing?

Blocking or reducing sound transfer in existing or new construction has become increasingly more important as the distance between neighbors has decreased. Exterior walls are often better designed and built to insulate and decrease sound transfer while interior walls are often left hollow. If you’re contemplating filling the empty stud cores with spray foam for some peace and quiet, you’ll want to know, does spray foam insulation reduce noise?

Spray foam is not an effective soundproofing material. While open-cell is better than closed-cell, neither absorbs well nor decouples the wall layers. Spray foam can adhere to and couple wall layers together to make it easier for noise to move through, increasing sound transfer and disruptive resonance.

To help you determine the best option, we explain open and closed-cell foam insulation, the benefits and disadvantages, and which is better for soundproofing. Additionally, this article explores the use of spray foam in existing walls and ceilings, the costs, and looks at better options like rock wool, cellulose, and fiberglass.

Is Spray Foam Insulation Good For Soundproofing

Does Spray Foam Insulation Reduce Noise?

Polyurethane spray foam insulation is available in both open and closed-cell spray foams. It is made by blending methylene diphenyl diisocyanate (MDI) with a mix of polyol resins, surfactants, catalysts, and fire-retardants. The two components are combined as they are sprayed into wall cavities, onto walls or ceilings, and into crevasses where it expands and hardens to prevent airflow.

Stopping noise penetration through walls means damping, blocking, and absorbing sound waves so they can’t penetrate the wall barrier, which takes a lot of mass. It also requires decoupling of the wall layers or components to prevent sound vibration from transferring through. Think of low bass and drum noise and how the vibration it produces travels and makes objects vibrate. The same is true for higher frequencies too but is not as noticeable.

Open-cell spray foam works better than closed-cell spray foams at blocking sound transmission, unfortunately, neither is very good. The hardened, lightweight foam has good thermal insulation properties but lacks the mass to absorb or trap sound waves and be sound deadening.

It does reflect some noise and thus reduces noise transmission into or out of a room or building, however, the hard open or closed-cell foam will increase the resonance instead of dampening it – like hitting a drum skin vs a kitchen sponge. Additionally, the sticky foam attaches to all surfaces it touches and then expands and hardens, connecting or coupling the wall components together, making an easy path for sound vibration transfer.

A 2×4 interior wall with 1/2″ of drywall on both sides has a Sound Transmission Class (STC) of 34. Filling the cavity with closed-cell spray foam will improve that to 36 and open-cell to between 37 and 39.

However, the same thickness of stone wool, cellulose, or fiberglass can take the STC rating to between 39 and 52 depending on the insulation’s density.

The International Building Code (IBC) recommends a minimum STC of 50, so spray foam has a long way to go to match other sound-deadening materials.

Open Cell Spray Foam

Open-cell polyurethane spray foam uses water to deliver the two components that make the foam. The foam expands 150 times its compressed volume into an open-celled matrix that is semi-permeable to moisture. The hardened foam matrix stays slightly flexible and compressible, blocks and traps airflow, and thus some sound transmission. It has an R-value of 3.6/inch, a density of about 1/2 lb/ft³, and tensile strength of 4.0psi.

Closed Cell Insulation

Closed-cell polyurethane spray foam commonly uses hydrofluorocarbon to deliver its two components. The mixture expands 35 to 50 times its compressed volume to form a hard, solid barrier with more than 90% of the cells being close, making it more rigid and impermeable to moisture and air. The cured closed-cell foam has a density of 1-3/4 to 2 lb/ft³, an R-value of 6.1/inch, and tensile strength of 28psi.

Benefits of Spray Foam Insulation for Soundproofing

Soundproofing spray foam

  • Can be applied to walls, ceilings, and into wall cavities and crevasses
  • Some sound deadening benefit
  • Helps to keep sounds from traveling into or out of a room or building
  • Decreases utility bills
  • Great thermal insulator, plus moisture and air barrier

Disadvantages of Spray Foam Insulation

  • Spray foam insulation couples wall components together, increasing sound vibration transfer
  • Limited or no sound absorption
  • Increased reflective resonance, feedback, and sound distortion
  • Messy and can cause health issues
  • Expensive

Open Cell vs Closed Cell Foam: Which Is Better for Soundproofing?

Open-cell foam is a porous matrix of interconnected open cells. It is less rigid than closed-cell foam and allows some air and moisture penetration. The open structure is better for trapping sound, which is why it has better at noise reduction than closed-cell spray foam. However, the hard surfaces don’t absorb sound waves; they block, reflect, bounce, or resonate more.

Closed-cell foam is just that, the cells or bubbles form closed and solidify into a more durable and rigid mass. The air in the cells provides thermal voids, and the closed structure prevents moisture and airflow penetration. The hard surface can block or reflect some sound waves while others, unfortunately, resonate through it like a drum skin.

How Much Does Spray Foam Insulation Cost?

The cost of insulation materials depends on where you live, the size of the area to be insulated, the kind of foam insulation, and the R-value required. Open-cell is less expensive than closed-cell, and regular fiberglass costs less than both. DIY is also less expensive than hiring professionals but doesn’t carry any warranty.

Most spray foam insulation kits identify how many cubic feet they’ll cover. Whether hiring or DIY, a rough estimate is helpful. To determine the cubic feet of foam required, calculate the surface area to insulate and multiply it by the thickness desired.

For example: A wall 8’ high and 20’ long has an area of 8 x 20 = 160ft²

Multiply by 1 ÷ 12 (the thickness) or 0.083 = 160 x 0.083 = 13.3ft³/inch of foam

So, if you want 3” of foam, you’ll need 3 x 13.3ft³ or 39.9 ft³

The professional cost (sound insulation material and installation) of open-cell polyurethane foam is around $20 a cubic foot, while the closed-cell cost is about $40 per cubic foot. The cost of purchasing a kit depends on the size of the kit with prices ranging from $12 to $22 a cubic foot – the unit price often goes down the larger the volume selected.

By comparison, 3-1/2” thick R-13 fiberglass battens will cost a DIYer about $2.00 a cubic foot, with the cost going up the greater the sound attenuation the insulation possesses, and if installed by a pro.

Soundproofing With Spray Foam

Sound deadening spray foam The main purpose of spray foam is to provide a thermal insulation barrier and in the case of closed-cell spray foam, a vapor barrier too. If using it for soundproofing, it should be used with other materials that have greater mass, decoupling, and sound absorption properties. Open-cell spray foam has better sound control properties than closed-cell, so consider using it – it’s also cheaper and lighter.

Existing Walls

Spray foam is ideal for sealing gaps where air and noise can slip through. Closing leaks around electrical outlets and fixtures, between drywall sheets, and around doors and windows will reduce noise transfer through existing walls. The hardened foam can be trimmed if necessary, sealed, and painted to finish the wall.

Filling wall cavities through holes drilled between studs is a costly process as it will require more spray foam than the two or three inches commonly sprayed on unfinished open walls. The expanding foam can also cause wall panels to bulge if not done properly.

Additionally, the hardened foam will couple both surfaces of the wall together and increase sound transfer. An alternative is to frame a new wall against the existing one, foam it, and apply a layer of drywall. This process will further decouple the wall, add mass, and reduce noise.

Ceiling

Unfinished ceilings can have spray foam applied directly between the floor or ceiling joists to seal cracks and crevasses where sound can leak through. Unfortunately, the hardened surface lacks the mass, decoupling ability, and sound absorbency to block impact noise from feet, chairs, or dropped items.

Open-cell foams will prevent more sound movement than closed cells, but both need to be used with other materials like mass-loaded vinyl, acoustic calking, and an extra layer of drywall to better control sound transfer.

Ceilings that are already closed up and finished can have holes drilled between the joists or rafters to permit the insertion of the spray nozzle for foam injection. Once the foam insulation has been injected, the holes are plugged, mudded, sanded, sealed and the ceiling repainted.

Most attic ceilings are already insulated, so either remove the old insulation, apply the foam, and then relay the old insulation on top of the cured foam. This will improve the sound barrier and block more outside noise penetration. Alternatively, consider foaming the underside of the roof deck – ensuring vents and soffit openings are maintained. This will improve the thermal barrier and possibly provide sound deadening properties.

What Type of Insulation Is Better for Soundproofing?

There are different types of thermal insulation that have greater mass, decoupling, and sound absorbency properties than those possessed by spray foam insulation. Most brands toot the sound attenuation properties of their different products, so it may be difficult to cut through all the advertising and jargon to find the noise reduction coefficient (NRC) or sound transmission class (STC) and what those ratings mean.

Rockwool Insulation

Roxul 1' x 48' x 24' Mineral Wool/Foil Backing High Temperature Insulation, Density 8#, Green - 40260 Pack of 2Mineral or stone wool is dense multi-directional insulation material made from molten stone or slag that has been spun into fibers. The rigid panels don’t slump and are friction-fitted between studs, joists, and rafters to absorb and trap sound and air, making them the best option for a sound and thermal barrier.

Rockwool 60 or 80 and Owens Corning Thermafiber have excellent sound ratings with NRC values between 0.95 and 1.2 and STC’s of 52 to 65 depending on thickness and wall construction. Plus, they’re resistant to fire, mold, and mildew.

Blown in Cellulose

U.S. GREENFIBER LLC INS541LD Fiber Insul 40FT Cocoon LW DUSBlown-in cellulose insulation is an excellent interior retrofit option for soundproofing existing walls.

Available in loose and dense fill options, it mutes echo, absorbs sound, and reduces noise transfer.

With an STC ranging from 44 to 68 and NRC of 0.8 to 0.9, depending on density, cellulose provides more sound deadening than spray foam.

Fiberglass Insulation

Owens Corning R-19 Faced Fiberglass InsulationThe thickness and density of fiberglass insulation affect its sound deadening properties. The fiberglass will absorb sound and decrease some noise movement through walls. The denser material tends to block more sound and is more rigid, so it doesn’t slump and produce gaps in the sound barrier.

Based on wall construction, density, and thickness, NRC values range from 0.5 to 1.10, and STC ratings between 39 to 52.

Conclusion

Spray foam insulation provides a good thermal insulation barrier but isn’t very effective at absorbing sound or preventing sound movement through existing walls. The hardened foam reflects some sound waves but can couple wall surfaces together which increases sound movement through the wall. It also acts like a drum skinned resonating chamber, amplifying mid-range frequencies, and adding to the disharmony.

Hopefully, you have a better understanding of the soundproofing value of spray foam insulation and find the peace and quiet you’re looking for.

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