Why Office and Meeting Room Designs have Acoustics Issues and How to Improve Them
Common Causes of Noise and Privacy Issues in Offices and How to Fix Them
Acoustics are a major issue in offices and almost anyone who has worked in one has experienced noise and privacy disturbances. However, many offices and meeting rooms are inexpensively built and fail to deliver on the level of privacy and noise control that most people expect to have.
One of the main reasons we build offices and meeting rooms is to give people privacy from prying ears nearby. Noise control issues affect office staff productivity, and can create legal risks when the lack of privacy affects sensitive conversations in human resources, legal affairs, mergers and acquisitions, and executive offices. In medical and psychology offices, a lack of privacy can make offices unusable.
In this issue of Acoustics Insights, we review four design and construction issues that are the root cause of many acoustics problems in offices and meeting rooms.
1. The rooms were designed with lightweight ceilings concealing open plenums
A common design in office buildings involves a lightweight ceiling system that spans the entire office, with walls that stop at the ceiling tile. In this design, the open area above the ceiling tile is used for air transfer, and air return grilles are simply open holes into the ceiling cavity.
The first and most obvious issue is that the walls don’t provide a complete separation between rooms. Above those walls, the ceiling cavity is wide open from room to room, and the area is known as the “plenum.” The ceiling tile will provide some sound attenuation, but not nearly enough to match the performance of the surrounding walls or of a drywall ceiling, and provide privacy to the occupants.
The second issue with this design is that the plenum is used to transfer air back to a circulation fan unit, without any ducts. Every system will include air supply ducts, but the air flow will return to the fan unit through the plenum without any additional ductwork. This design provides great cost savings in office construction, but the acoustics are negatively impacted, since the air return grilles are simply open into the plenum and allow sound to carry from room to room.
New construction designs improvements
In new construction the design can be altered to include:
- Walls that are built from floor deck to ceiling.
- Ducted air returns.
- A drywall ceiling.
Further improvements can be made with:
- Resilient layers at the top and bottom plates of the walls.
- Acoustic sealant installed along at the perimeter of all wall framing.
- Acoustic batt insulation in walls and pinned to ceilings.
- A sound barrier such as mass loaded vinyl or rubber.
- Resilient channel included in the framing (or resilient clips and drywall furring channel).
- Acoustic putty on all outlets and switches.
- Surface mounted light fixtures.
- Soundproofing drywall such as QuietRock ES or SilentFX (installed according to the manufacturer’s specifications).
- Acoustic sealant in all gaps, seams, and around the perimeter of the drywall.
- Air supply and air return ducts with premium acoustic lining.
- Acoustic panels in the room to prevent high reverb and echo.
Retrofit fixes to improve privacy and noise transfer
Several retrofit options are available to owners and tenants of existing office spaces with acoustics issues.
- Close off the gaps at the tops of the walls by installing drywall all the way to the ceiling or floor deck above, or use something called “privacy board” for a faster and less expensive retrofit solution. The installation should include 100% blockage of the plenum separation between rooms with no gaps or weak areas.
- Install high performing ceiling tile. These should have a high CAC rating as well as a good NRC rating to keep the sound from leaving the room and prevent echo. Rockfon and Armstrong both manufacture ceiling tiles with high specifications.
- Install a “hush box” over the air return grilles to prevent sound from transferring into the plenum. A hush box is a short sound absorbing duct that is lined with acoustic duct liner, and ideally includes a baffle or a turn so that sound is absorbed inside the box and very little sound pressure makes its way into the plenum. When installed over each vent opening, this approach can be quite effective.
- Replace sections of air supply ducts with ones that include acoustic liner.
2. Ductwork spans across offices and carries sound from room to room
When the walls and ceilings are properly built but sound transfer issues persist, ductwork is often the cause of sound transmission between rooms. The ducts by necessity span across the ceilings of many offices, with vent openings in each office and sound will transmit through the ducts, allowing conversations to be heard in the next room and often even further away.
Noise control problems can also be caused by the installation work itself. Air supply and/or return ducts are often installed without considering the impact on acoustics. When new ducts are retrofitted into a building, the crew will cut holes in the walls to run the ducts, leaving openings in walls in the plenum that create sound flanking paths and allow sound to transfer.
Retrofit fixes to reduce sound transfer through ductwork
Methods to prevent ductwork from causing sound transfer issues include the following:
- Install acoustic duct liner with a high NRC rating at the duct openings.
- Install additional runs of duct with duct liner and at least one ninety degree bend in the duct.
- Remove sections of duct and install new duct runs with 6 feet (2 meters) of duct that is lined with acoustic duct liner, ideally with one or two additional ninety-degree bends in the duct.
- Repair areas around the perimeter of ducts where they penetrate the walls between rooms with insulation and acoustic sealant to provide a complete seal around the opening.
3. The walls are weakly built or improperly sealed
Poorly built walls with lightweight drywall and no insulation will transmit a lot of sound into adjacent areas. A standard steel framed wall with ½” drywall will have an STC rating of around 30–35. In most cases this will allow conversations to be easily overheard.
Another common issue with walls is sound transmitting through switches and outlets. Often these are placed close to one another on opposite sides of the wall, and have gaps around the perimeter of the openings. This causes them to easily transmit sound as well.
A third issue is gaps around the perimeter due to the wall intersecting with window escutcheons and other uneven surfaces. These also allow sound to transmit into adjacent areas.
Retrofit fixes to poorly built walls
There are several options available to improve the performance of walls that are already built in offices and meeting rooms.
If possible, remove drywall on one side of the wall to rebuild it to a specification that will yield a much higher STC rating. Several options exist (read our article on soundproofing drywall to review your options).
- If the wall already includes some form of insulation, adding drywall layers to the existing wall will have a positive impact.
- Seal outlets and switches with acoustic putty and sealant.
- Inspect the wall for gaps and weak points, and seal these with caulking and acoustic sealant.
- If the room tends to be highly reverberant and have high volumes when meetings are underway, consider installing acoustic panels to help reduce sound pressure.
4. Conversations can be heard through the office or meeting room door
The quality of an office or meeting room door and its installation can have a major impact on sound transmission into an open area nearby or hallway, and even the next room.
A lightweight or hollow core door will provide little in the way of noise control, and the problem can be made worse by a poor installation that leaves gaps around the perimeter and at the bottom of the door.
Retrofit options for improving noise control through doors
Several options should be considered to improve the acoustic performance of the doors.
- Replace hollow core or inexpensive solid core doors with high-quality solid core door, fire-rated doors or even soundproofing doors.
- Be wary of inexpensive solid core doors, as these are often built with inexpensive filler and have poor performance. Insulated steel doors are also highly effective at sound control when properly installed. Installing a soundproofing door is always an option (these cost between $3,000 and $10,000).
- Ensure that the installation includes a solid perimeter around the door jamb. Carpenters will often use shims and leave gaps around the jamb, which creates flanking paths around the door.
- If using a steel “knock down” door frame, insulate the frame with spray foam or batt insulation.
- Install acoustic perimeter seals on the door frame to close off all gaps between the door and the frame.
- Install an automatic door bottom to prevent sound from transmitting below the door.
- An inspection during installation and before trim is installed is mandatory to ensure that there are no gaps between the wall framing and the door jamb, and that all weak points are closed off with acoustic sealant.
If your carpenter resists any of these options, we recommend finding another carpenter for the installation, because doing it twice is always more expensive that getting it right the first time.
