In July, there was a change to the Postal Operations Manual that may affect you. In the past you needed 1 parcel locker for every 10 mail compartments, now you need a parcel locker for every 5. This does not apply to current CBU’s but will be required for all new installs or remodels. You can read the new regulation here:

632.622 Location and Arrangement

Regulations for the location and arrangement of receptacles are subject to Postal Service approval as follows:

1. All new or remodeled apartment houses can only install USPS-approved 4C equipment. When installing this equipment, a requirement is to have at least one parcel locker for every five customer mail compartments. For those buildings with a minimum of five mail compartments, there must be at least one parcel locker installed.
2. Receptacles and parcel lockers in apartment houses should be located reasonably close to the entrance in vestibules, halls, or lobbies. The carriers must be able to serve the boxes without interference from swinging or open doors. The area must be adequately lighted to afford the best protection to the mail and to let carriers read addresses on mail and names on boxes without difficulty.