Take these Five Steps to Solve Impact and Structural Noise Problems Once and for All
Footsteps and banging from neighbours is one of the most common complaints of residents and commercial tenants in multi-unit buildings, but it’s also one of the most difficult problems to solve.
Impact and structural noise is a leading complaint
Tapping, banging, thudding and other impact-driven sounds are among the leading annoyances that people complain about in residential and commercial settings. Whether it’s due to footsteps, pets and children running, people dropping weights in a gym, or appliances, these sounds tend to be pervasive and difficult to ignore. The problem is especially prevalent in stacked timber-framed townhomes, but steel and reinforced concrete structures can be just as problematic.
Impact noise is a serious pain point for property owners and managers. People living in condominium properties will sell and move to escape the noise. Leaseholders will issue multiple complaints and the amount of tenant conflict and turnover can escalate property management costs and reduce profits.
The Root Cause: the speed of sound is faster through solid materials
At the root of the problem is the physics of sound transmission. Sound travels much faster through solid materials than through gases or liquids. The general rule is that the denser the material is, the faster the speed of the sound traveling through it. That means sound transmission is more efficient through solid concrete than it is through the air, and noise will travel long distances through structural elements like wood beams, steel or concrete columns and beams, walls, and floor slabs. This simple fact makes impact noise both pervasive and difficult to solve — it can come from anywhere in the building, not just the floor above.
Solving impact noise takes thoughtful planning
On the surface (pun intended), reducing impact noise appears to be an easy task that is solved by putting underlayment beneath the floors. Gyms might specify one or two inch thick flooring, and the owner or manager may feel that the plan is good enough. Unfortunately, this approach can fail to resolve the problem adequately, and it’s helpful to consider the financial risk that this approach presents.
The installation cost of resilient underlayment and flooring can easily top $10 per square foot. If the project fails, the cost of removing and reinstalling the flooring will cost an additional $15 — $20 per square foot. In a project involving 10,000 to 20,000 square feet of flooring, such as a small multi-family building or a new gym, the unexpected budget increase could be a crushing blow to the business.
Like all noise control projects, careful planning is required to avoid failures and costly mistakes. A thoughtful, systematic, and rigorous approach using the following five key steps can yield great results. Be warned, however, that compromising or taking shortcuts on any one of them can lead to catastrophically expensive project failure.
1. Collect and analyze the existing building specifications
Taking the time needed to examine the existing building construction will be well worth the investment. Key items to investigate include the following:
- Construction type — is it timber, steel, or reinforced concrete?
- Specifics of the floor plate/assembly design. If it’s timber, how large are the joists, what is the spacing? Is it insulated? If it’s concrete, how thick is the slab — 6 inches or 8 inches?
- The location and size of columns — where are they and how are they connected floor to floor? Are they exposed to impact noise somehow?
- Are there any staircases within dwelling or commercial units and how are they mounted to the structure of the building?
- How are the walls constructed? Have any resilient layers been installed between the framing and the floor slab?
- Where are the plumbing, heating, and electrical runs from floor to floor? Are there shafts? Bulkheads? Ductwork? Pipes? Pumps?
- Have any previous renovations been performed on the property? Are there any details that might be relevant and have changed the structure or mechanical conditions?
- Will both the ceiling and floor be renovated or just one side of the assembly?
Gathering all these specifics will provide some of the key details needed to generate the final design specifications.
2. Gather data and interview occupants about current noise levels
If it’s possible, conducting an impact noise test with engineers will provide invaluable information about the current performance of the building structure. The data can be used to target the level of improvement and specifications needed with less guesswork, which can be risky.
How is impact noise measured?
Impact noise is measured through what’s called an Impact Insulation Class (or IIC) rating. It is an integer-number rating of how well a building floor attenuates impact sounds. A larger number means more attenuation. The scale, like the decibel scale for sound, is logarithmic.
The IIC is derived from ASTM method E989, which in turn uses a tapping machine specified in ASTM method E492. Like the STC rating scale, the IIC number is derived from sound attenuation values tested at 16 standard frequencies from 100 to 3150 Hz.
However, footsteps and other impact noises are also generated at frequencies below 100 Hz, so the IIC value may not accurately describe the complete noise attenuation performance of a floor.
Occupant experiences are key data points
Gathering information about current and past performance from the occupants’ viewpoints are also key inputs into designing an appropriate solution. Ultimately, noise control is about the people using the space, and their experience is a primary factor in success or failure. Whatever the tests show, if the neighbours report that they can hear certain sounds very easily, or if a previous commercial tenant was evicted or cancelled a lease due to noise problems, the information will help you to set the target performance you need. It also can help you to understand if there’s a difficult-to-solve problem lurking in the existing structure that will not be rectified with a standard solution.
3. Walls, doors, cabinets, and appliances matter, too
The sound of footsteps (especially hard soled-shoes) is often cited as a complaint-inducing issue, but other sources of impact noises can be just as problematic. Structural sound can be transmitted through the walls, doors, cabinetry, machinery, appliances, and unexpected items like garbage disposals, compressors, and circulation pumps that are in a residential or commercial building.
The energy from a bathroom door slamming can easily transmit into the floor plate via the surrounding wall that is sitting directly on the concrete slab supporting the unit. A large switching mechanism that turns on a boiler in a mechanical room can reverberate into a penthouse unit below. Cabinets can act like like drums and amplify the sound of a drawer closing, especially if it happens when there is very little ambient sound in the building, such as late at night, when someone is getting a midnight snack.
4. Finalize the performance and installation requirements
Getting the design right will involve setting the final requirements, including:
- The target IIC performance (IIC 55, 60 or 72?)
- The need for low frequency attenuation needed
- Locations where it is needed (everywhere or just selected areas?)
- The area of construction (e.g., will the ceiling below be part of the project or only the floor?)
- How long does the material need to maintain its performance (10 years? 50 years?)
- The installation requirements of the flooring (Nails? Glue?)
- Any additional conditions and requirements such as exposure to dampness, mechanical and electrical conduit, low-VOC, LEED credits, or others.
5. Design with resilience in mind and perform quality control inspections during installation
Separating solid layers by applying damping, or “resilient” layers is the key design technique used by engineers and architects to prevent impact noise transmission. Clearly, underlayment is a resilient layer of material that separates hardwood floors from the floor plate structure below. But as we mentioned at the beginning, it’s a little more complicated than just installing underlayment to truly solve an impact noise problem.
For resilient layers to do the job of damping impact noise effectively, the final specifications and construction details may include one or more of the following:
Flooring and underlayment specifications:
Fully detailed design components and installation details that include the following:
- Underlayment materials selected and quality (e.g., cork, rubber, or vinyl)
- Number of underlayment layers
- Hardness rating of the materials selected (there are many grades of cork, for example)
- Thickness of the material — 6mm, 10mm, etc.
- Overall density of the material, expressed as pounds per cubic foot or kilograms per cubic meter
- Requirements for a raised floor system or concrete topping if required
- Floor preparation including slab penetrations due to pipes and ducts.
- Final conditions needed to install the flooring layer
- Specifications for areas where the flooring meets walls, thresholds, columns, and doorways, etc.
Ceiling specifications (if in scope):
Detailed ceiling partition specifications that include the following:
- Framing materials and installation specifications
- Resilient hangars if required
- Insulation quality, density, amount, and installation method
- A sound barrier if specified, and it’s quality, density, and installation
- Drywall specifications
- Specifications for dealing with openings in the ceiling such as lights, fire and smoke alarms, fans, ductwork, etc.
- Acoustic putties and sealants for all seams, gaps, and openings
Doors and cabinets:
Specifications for the following should be included to prevent the use of doors and cabinets from being a source of impact noise:
- Door closers that prevent door slamming
- Soft close hinges and drawer pulls
- Resilient layers between cabinets, floors plates, and walls and any other resilient layers
Appliances and HVAC components
Preventing mechanical devices from causing impact and structural noise may involve the following items:
- Resilient hangars including spring loaded models
- Resilient pads, shock mounts, and resilient mounts designed to
- Concrete pads or plinths
- Damping compounds
- Insulation layers, if needed
Perform quality control at every step
Once the specifications have been set, a rigorous quality control plan will be needed to ensure that they are installed correctly. Like all other acoustics and noise control projects, 100% of the specifications need to be followed for the solutions to work. Every layer and step in the process must be inspected to ensure the performance meets expectations and that the investment pays off as planned.
