Goal: To create a comfortable and relaxing living environment for residents, minimizing the distractions from noise impact.
- There are several issues that must be addressed concerning acoustics in a multi-family project. These issues stem from the two types of sound that must be controlled: airborne sound and impact sound. A typical airborne sound is music or talking. A typical impact sound is the footfall sound of an upstairs neighbor.
- · Many builders seek to increase the marketability of a development by promoting "luxury" acoustic conditions. While potential residents will certainly appreciate the effort, you can expect construction costs to increase as a result. There must be a balance between the acoustics and the budget while, at the same time, the expectations of the residents should be met. It should be noted, however, that even when the acoustical issues in multi-family housing are addressed, some noise transfer between units is inevitable. Describing the units as "sound proof" or making statements such as, "you'll never hear your neighbors" creates unreasonable expectations and should be avoided.
- · Factors that contribute to noise transmitting into a neighboring unit include residents' living habits, background noise and the isolation quality of the partitions. Obviously, the amount of transmitted noise will be highly dependent on the amount of noise created in the adjacent spaces. Additionally, if a room has a relatively high background noise level, this will help to mask the transmitted noise. However, if a room has a relatively quiet background noise level, the transmitted noise will be more noticeable.
- There are two rating systems (STC and IIC) that compare the acoustic quality of various building assemblies. Both classify acoustical performance with a single number. In both cases, the higher the number, the better the sound isolation performance. Sound Transmission Class (STC) rates a partition's resistance to airborne sound transfer. Impact Insulation Class rates a floor/ceiling assembly's resistance to structure borne noise transfer.
- The Uniform Building Code (UBC) contains requirements for sound isolation between dwelling units in Group R occupancy projects (including apartments and condominiums). However, these criteria are not universally enforced. UBC requires walls and floor/ceiling assemblies to have an STC rating of 50 (if tested in a laboratory) or 45 (if tested in the field). The code also requires that floor/ceiling assemblies have an Impact Insulation Class rating of 50 (if tested in a laboratory) or 45 (if tested in the field). The field test evaluates the dwelling's actual construction and includes all sound paths. *NOTE: Even if a particular municipality has not adopted this part of the code, it is still recognized as an industry standard minimum.
- All air-gaps and penetrations must be carefully controlled and sealed. Even a small air-gap can degrade the isolation integrity of an assembly.
- The perimeter of the wall and any penetration must be sealed air-tight with a non-hardening acoustic sealant.
- Avoid the installation of back-to-back penetrations (outlets, light switches, and phone jacks). Consider installing a putty pad to the back of all outlets in party walls.
- Ideally, elevator shaft footings, floor pads, masonry shaft walls, elevator equipment mountings, etc. should be totally isolated from the building structure. Structure borne noise/vibration from elevator operation may be extremely annoying. Additionally, any penetration or air gap in or around the wall must be sealed airtight with a non-hardening acoustic sealant.
- The building code (UBC) specifies that the entrance doors from interior corridors shall have an STC rating of 26 or higher. Obviously, the higher the STC rating of the doors, the better the isolation. However, if the seal around and under the door is not maintained, selecting a high rated door is meaningless. Ideally, drop seals that seal to a threshold (not carpet) can be installed. An acoustically absorptive ceiling and carpet in the corridor will help to control the noise levels within the corridor.
- The majority of noise concerns can be alleviated through proper space planning. Sensitive areas should not be located near potentially noisy areas. Potentially annoying sound transmission from floor to floor (for example, from a restroom or kitchen above a bedroom) can be mitigated through the vertical mirror of spaces. Horizontally, potentially noisy areas (such as elevators, vending rooms and laundry facilities) should not be adjacent to bedrooms.
- Although the building code does not address plumbing noise, this issue can be a major source of noise complaints. Plumbing noise can be both airborne and structure borne. To reduce plumbing noise, pipes should be resiliently mounted, that is, adequately insulated from their supports. To further reduce plumbing noise, the pipes should be wrapped with pipe lagging material.
- Any roof-mounted equipment should be analyzed for potential noise/vibration impact.
- Be concerned about exterior noise impacting the interior rooms (such as a nearby airport or freeway). The majority of this noise is transmitted through the windows. Upgrading the window assemblies might be necessary.
- Noise Criteria (NC) ratings can be used to specify the allowable background noise levels (not activity noise from the occupants) within a given space. Recommended NC levels vary depending on the type of space and the listening requirements. The recommended NC level for a bedroom is NC 20-30. Most multifamily air-conditioning systems produce noise levels well in excess of the recommendation. Additionally, HVAC noise can act as a masking system in multifamily projects, raising the background noise level and thus reducing the awareness of transmitted noise. (NOTE: Obviously, this benefit only occurs when the system is on.) The equipment noise should not exceed NC 25-30 and the air noise of the HVAC system should not exceed NC 35.