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Preventing Sound Intrusion in Wood-Framed Multifamily Projects

July 31, 2023


Sound intrusion can be detrimental to a project and be very costly to resolve after the completion of the project. As is often the case, planning ahead and investing in smart practices upfront, such as retaining consultants and making sure construction documents are followed, can save a project from major cost overruns, re-work, and insurance claims.  

In this post, we will discuss the following sound intrusion in a wood framed Multifamily Project: 

  • Discuss sound intrusion and define acceptable Sound Levels in Multifamily Projects. 
  • When an acoustical consultant should be retained. 
  • Services VERTEX offers to help identify, evaluate, and document sound intrusion. 


Because of its stiffness, wood framing readily transmits low-frequency sounds and impact noises through wood-frame projects. This is particularly a problem in floors and walls separating units. Sound can travel through both air (airborne sound) and solid materials (structure-borne sound). Structure-borne sound can be directly imparted to the building structure by a vibration, such as a humming compressor, or by direct impact, such as a boot stepping on a hardwood floor. Sound Intrusion is similar to water Intrusion, regardless of what you think, sound and water intrusion will negatively affect the project if not properly designed for.  

As sound energy travels through a building, it changes from one type of transmission to the other and back, losing energy in each transition. Because of its rigidity, wood framing is a very good transmitter of low-frequency sound. Hollow wall cavities, and thin doors do little to reduce sound transmission. Living spaces between floors can also require special treatment to reduce impact noises from above. This is another kind of noise control that is important to consider when a project is located by a major highway or near an arena or airport. The goal here is to keep outdoor noises from entering the unit/project by reducing sound transmission through windows, doors, and exterior walls and ceilings. Special acoustical windows rated for low sound transmission are often required for substantial reductions from outside noise. 

Sound levels are measured in decibels (dB), which are on a logarithmic scale. A sound increase of just 10 dB indicates an increase of ten times the intensity, although our subjective experience is that the sound is twice as loud. Continuous exposure to sounds above about 85 dB can cause hearing loss in most people. Wall and floor assemblies are rated per standards established by ASTM International Standard Organizations and are indicated in Manufacturer’s literature as Sound Transmission Class (STC). The higher the rating, the greater the ability of the assembly to contain sound transmission. Minimum STC ratings in bedrooms is 44 and living rooms is 46. 

Sounds in an acoustically “live” room with all hard surfaces will seem loud and harsh due to the sound reverberating off the hard surfaces. Adding sound-absorptive materials, such as carpeting and soft furniture, will make sound softer and more pleasant within the room but will do little to reduce the transmission of sound to adjacent rooms. To reduce transmission requires sound isolation strategies, typically using high- mass materials, double-framed walls, or resilient connections between the drywall and framing. 

There are four main strategies to keep sound from passing through walls and floors. 

  • Add Mass:
    Increase the mass of the wall or floor. Examples may include additional layers of drywall and lightweight concrete over soundproofing floor mat over the subfloor. Doors are often overlooked and the STC rating of the door assembly should match the wall rating. 
  • Decoupling:
    Break the path of vibration with a break in the framing or a resilient connection to the drywall. A properly installed resilient channel can raise the STC rating by 10. 
  • Absorption:
    Provide sound-absorptive material, such as fiberglass batts, in the wall or floor cavity.  
  • Sealing:
    Block airborne sound from leaking through gaps and cracks. The drywall should be caulked at the floor and ceiling to seal any gaps. Electrical boxes should be sealed and not installed in the small wall cavity between units. 


Acoustical Consultants assist the Owner/Developer and Architect in providing the best practices in controlling sound intrusion. Depending on the project location, the Consultant can suggest design features, products, and materials to control sound Intrusion within the project and especially if the project is by a highway or other noise source. The consultant can review the construction documents and provide field observations on conformance to the documents. The consultant can investigate work in place to determine compliance with the design documents and solutions to contain the sound intrusion, if required. 


Determining the cost responsibility for sound intrusion can be difficult depending on the circumstance. If such was caused by negligence of the general contractor, the general contractor should be responsible for additional costs related to re-work and schedule delay. If caused by a subcontractor’s negligence, then re-work should be back charged to the responsible subcontractor. If it is believed to be due to faulty equipment or material, the subcontractor should reach out to the appropriate supplier or manufacturer to investigate the cause. 


As a lender’s representative, if these sound intrusion incidents are mentioned by the project team or observed during a construction site observation, VERTEX recommends that the appropriate third party be brought out to the site to inspect the areas of sound intrusion to identify if the work in place was constructed correctly and if construction materials need to be removed and replaced. We will also apprise our clients accordingly of any such incidents and how the general contractor plans to proceed. Ensuring that remediation reports are received is critical for identifying the issues, incident areas, and action items that need to be adhered to.  

Other preventative measures can include having a 3rd party sound consultants and manufacturers verify that work has been completed appropriately with components installed correctly throughout construction. These consultants can also test areas at buildings for sound intrusion to help solve the problem before an issue ever occurs. 

In addition to lender’s representation, VERTEX also provides in-house Building Envelope consulting and Residential Quality Assurance services. For more information on any of the services VERTEX has to offer, please visit our services.

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