COMMUNITY NOISE LEVEL (CNEL) is the ambient sound level from outside sources that can be measured inside the building using specific methods that produce a weighted average over the day and night, keeping in mind an occupant's need for greater quiet at night. Residential codes require buildings to bring CNEL down to 45 db within a unit. If the measured outside CNEL is 70 db, then typically windows which achieve an STC (Sound transmission classification) of 25 would need to be used to reduce the CNEL to 45 inside. STC translates to the number of decibels by which the sound level is reduced by the assembly (door, window, wall, floor/ceiling, etc.) in question. Having said all that, live/work units in Oakland are recommended to consider, but not required to comply with , residential standards for CNEL attenuation. A word to the wise: if you are developing condominiums, do it. And pay close attention to sound (STC) and impact (IIC) transmission between units. Use an acoustical engineer-- it's relatively cheap insurance.