Cluster Box Units (CBUs)

Comprehensive Cluster Box Units (CBUs) Buyer’s Guide

Cluster Box Units (CBUs) have become an increasingly popular mail delivery solution for multi-tenant properties such as apartment complexes, condominiums, and office buildings. These centralized mailbox systems provide a secure, convenient way for residents to receive both USPS and private deliveries. In this comprehensive buyer’s guide, we’ll explore the key features, benefits, and considerations when selecting and installing CBUs.

Table of Contents:

Types of CBUs

CBU MailboxesCBUs are available in four main types (Type I, II, III, and IV) to accommodate different capacities and parcel locker configurations. All units are constructed with heavy gauge aluminum and stainless steel hardware, ensuring a weather-tight and durable mailbox system.

Key Features and Benefits

  • Individually-locked customer compartments to keep mail private and secure
  • Outgoing mail collection compartment for convenient mail pickup by USPS
  • Parcel lockers of varying sizes (depending on CBU type) for secure delivery of small to medium packages on a first-come, first-served basis
  • Large master loading door with arrow lock for easy access by USPS
  • Durable powder coat finish in postal-approved colors like dark bronze or postal gray
  • Units pre-numbered with USPS-approved identification decals and placards

What is a CBU Mailbox?Cluster Box Unit (CBU) Overview Video

Choosing the Right CBU Type

When choosing the right CBU type for your property, consider the number of residents and the expected package volume.

  • Type I: Best for small multi-family properties with up to 8 residents, offering 8 standard locked customer compartments and 2 parcel lockers (one small and one large).
  • Type II: Accommodates up to 12 residents with 12 standard compartments and 1 large parcel locker.
  • Type III: Ideal for larger properties with up to 16 residents, providing 16 standard compartments and 2 small parcel lockers.
  • Type IV: Suitable for properties with fewer residents but higher package volume, offering 13 large customer compartments and 1 large parcel locker.

High-Security Features of CBUs

Cluster Box Units (CBUs) are designed with high-security features to ensure the safety and protection of residents’ mail and packages. These features provide a significant advantage over traditional mailboxes, making CBUs an ideal choice for multi-tenant properties. Let’s explore the key security features that make CBUs stand out.

  1. Robust Construction

CBUs are constructed using heavy-gauge aluminum or stainless steel, which provides exceptional strength and durability. The robust construction ensures that the units can withstand attempted break-ins, vandalism, and harsh weather conditions. The use of high-quality materials also prevents rust, corrosion, and general wear and tear, maintaining the unit’s structural integrity over time.

  1. Individual Compartment Locks

Cluster Box Unit LocksEach customer compartment in a CBU is equipped with a high-quality, individual lock. These locks are designed to be pick-resistant and drill-resistant, deterring potential thieves from accessing the contents of the compartments. The locks are also corrosion-resistant, ensuring reliable operation even in humid or wet conditions. Customers are provided with keys unique to their compartment, ensuring that only they have access to their mail.

  1. Master Loading Door with Arrow Lock

The master loading door, used by USPS carriers to deliver mail, is secured with a special arrow lock. This lock is exclusive to the USPS and can only be opened by authorized postal service personnel using a special key. The arrow lock is highly resistant to tampering and picking, preventing unauthorized access to the master compartment and adding an extra layer of security to the entire unit.

  1. Anti-Fishing Devices

CBUs incorporate anti-fishing devices, such as metal plates or baffles, which prevent someone from inserting an object through the outgoing mail slot to “fish out” mail from the customer compartments. These devices ensure that mail can only be retrieved through the designated customer compartment doors, maintaining the security and privacy of each resident’s mail.

  1. Parcel Locker Security

In addition to the standard customer compartments, CBUs often feature parcel lockers for the secure delivery of packages. These lockers are designed with similar high-security features, including robust construction and reliable locking mechanisms. When a package is placed in a parcel locker, the recipient is provided with a key or access code to retrieve their item, ensuring that only the intended recipient can access the package.

  1. Tamper-Evident Design

CBUs are designed with tamper-evident features that make it easy to detect attempted break-ins or tampering. For example, if someone attempts to pry open a customer compartment door, the damage will be clearly visible, alerting the property manager and the affected resident to the issue. This allows for swift action to be taken to repair the damage and ensure the ongoing security of the unit.

  1. USPS Approval

USPS ApprovedAll CBUs must be approved by the United States Postal Service before they can be installed and used for mail delivery. The USPS has strict standards for the security, durability, and design of CBUs, ensuring that only high-quality, secure units are approved for use. When choosing a CBU, look for models that have been approved by the USPS to ensure that you are getting a product that meets their rigorous security standards.

The high-security features of Cluster Box Units provide property managers and residents with peace of mind, knowing that their mail and packages are well-protected. By investing in a CBU with robust construction, individual compartment locks, a secure master loading door, anti-fishing devices, and tamper-evident design, you can significantly reduce the risk of mail theft and tampering. When combined with proper installation and regular maintenance, these high-security features make CBUs an excellent choice for ensuring the safety and security of your residents’ mail and packages.

Installation and Mounting Options

Proper installation of your Cluster Box Unit is crucial for ensuring its longevity, security, and compliance with USPS regulations. CBUs can be installed either as freestanding units using the included pedestal or wall-mounted, depending on your site’s specific requirements and layout.

Pedestal Mounting

Pedestal mounting is the most common installation method for CBUs. The units come with a pedestal that allows for freestanding installation on a concrete pad. When installing a pedestal-mounted CBU, consider the following:

  • Choose a level, well-drained area that is easily accessible to residents and USPS carriers.
  • Prepare a concrete pad that is at least 4 inches thick and extends 6 inches beyond the edges of the CBU on all sides.
  • Ensure the concrete pad is level and flat to prevent the unit from tilting or rocking.
  • Securely anchor the pedestal to the concrete pad using the provided bolts and follow the manufacturer’s instructions for proper installation.
  • Maintain a minimum of 12 inches of clearance from the nearest obstruction to the front of the CBU for easy access.

USPS and Local Requirements

When installing a CBU, it is essential to adhere to USPS and local requirements to ensure compliance and avoid potential issues. Some key considerations include:

  • Height: The bottom of the lowest customer compartment must be at least 28 inches above the finished floor, while the bottom of the outgoing mail compartment must be at least 30 inches above the finished floor.
  • Distance from the curb: For curbside installations, the front of the CBU must be 6 to 8 inches from the front of the curb.
  • Pedestrian access: Ensure that there is a clear, unobstructed path to the CBU from the nearest sidewalk or pedestrian walkway.
  • Lighting: Adequate lighting should be provided around the CBU to enhance safety and security.
  • Local regulations: Check with your local building department and zoning board for any additional requirements or permits needed for CBU installation.

Hiring a Professional Installer

While CBU installation can be a DIY project, it is often recommended to hire a professional installer, especially for wall-mounted units or complex installations. A professional installer can:

  • Ensure proper installation techniques are followed to maintain the unit’s warranty and longevity.
  • Navigate local building codes and permitting requirements.
  • Provide guidance on the best location and mounting method for your specific site.
  • Complete the installation efficiently and safely.

When hiring a professional installer, look for a contractor with experience in installing CBUs and a thorough understanding of USPS regulations. Request references and verify their licensing and insurance before proceeding with the installation.

By carefully considering your mounting options, adhering to USPS and local requirements, and following the manufacturer’s installation instructions or hiring a professional installer, you can ensure that your Cluster Box Unit is installed correctly and ready to provide secure, convenient mail delivery for years to come.

How to install a CBU Mailbox:Cluster Box Unit (CBU) installation video

CBU Mailbox Style Options

Standard and decorative Cluster Box Unit (CBU) mailboxes differ primarily in their aesthetic design and styling, while maintaining the same core functionality and USPS approval.

Standard CBU Mailboxes

  • Have a basic, utilitarian design with a sleek, modern form.
  • Typically come in a range of standard colors like sandstone, bronze, white, green, black, and gray with a durable powder-coated finish.
  • Include all necessary components like the pedestal, mailbox compartments, parcel lockers, hardware, number plates, locks, and keys.
  • Provide the essential security and mail distribution features required by the USPS.

Decorative CBU Mailboxes

  • Feature more ornate and visually appealing designs compared to standard models.
  • Come in various styles like Classic, Traditional, and Stucco Column Enclosure, each with distinct decorative elements like crown molding, pillar bases, column pedestals, and appealing tops.
  • Offer the same functionality as standard CBUs, with mailbox compartments, parcel lockers, and necessary accessories.
  • Provide an elevated aesthetic appeal suitable for tasteful residential developments and communities.

While standard CBUs prioritize a functional and utilitarian design, decorative CBUs incorporate additional decorative elements and styling to enhance the visual appeal, while still meeting all USPS requirements for secure mail delivery and distribution.

Traditional decorative style and classic decorative style are two distinct options for the decorative Cluster Box Unit (CBU) mailbox line. Here are the key differences between these two styles:

Traditional Decorative Style CBUsTraditional Decorative Style CBUs

  • Features a more ornate and vintage-inspired design.
  • Includes column pedestals and appealing tops, from which the mailbox body appears to hang.
  • Offers a mid-mod vintage flair suitable for modern housing developments.
  • Available in various configurations, such as 12-door and 13-door models.
  • Typically includes all necessary components like mailbox compartments, parcel lockers, hardware, number plates, locks, and keys.

Classic Decorative Style CBUsClassic Decorative Style CBUs

  • Elevates the functionality of standard cluster units with added decorative elements.
  • Features crown molding and a sturdy pillar base.
  • Provides a more refined appearance compared to standard models while maintaining a sleek look.
  • Includes all the standard features such as hardware, number plates for tenant doors, and individual locks and keys.

Both traditional and classic decorative styles offer enhanced aesthetic appeal compared to standard CBUs while maintaining USPS approval and meeting all necessary security and functionality requirements. The choice between these styles often depends on the architectural theme of the development and personal preference for visual aesthetics.

Ordering and Customization

When ordering CBUs, it’s essential to purchase from USPS-approved manufacturers. While units come in pre-configured types, some minor customization may be available, such as engraving customer compartments with apartment or unit numbers for a small fee. Matching stand-alone parcel lockers can also be added to increase package delivery capacity. Replacement parts, including locks, keys, doors, and hardware, are readily available from manufacturers.

Maintenance and Upkeep

Regular maintenance and upkeep of your Cluster Box Unit (CBU) are essential for ensuring its longevity, appearance, and proper functioning. By following a consistent maintenance schedule and addressing issues promptly, you can keep your CBU in top condition and provide a secure and reliable mail delivery system for your residents.


Regularly cleaning both the interior and exterior surfaces of your CBU helps maintain its appearance and prevents the buildup of dirt, grime, and potential corrosion. Follow these cleaning guidelines:

  • Interior: Sweep or vacuum the inside of the compartments to remove any debris, dust, or cobwebs. Use a mild detergent solution and a soft cloth to wipe down the interior surfaces, ensuring they are completely dry before closing the compartments.
  • Exterior: Use a soft cloth or sponge with a mild detergent solution to clean the exterior of the CBU, including the doors, hinges, and pedestal (if applicable). Rinse the unit thoroughly with clean water and dry with a soft cloth to prevent water spots.
  • Avoid using abrasive cleaners or harsh chemicals, as these may damage the finish or cause discoloration.


To ensure smooth operation of the CBU’s moving parts, annually lubricate the hinges, locks, and latches. Use a dry, graphite-based lubricant or a silicone spray designed for locks and hinges. Avoid using oil-based lubricants, as they can attract dirt and grime, potentially clogging the mechanisms.

  • Hinges: Apply a small amount of lubricant to the hinge pins and move the doors back and forth to distribute the lubricant evenly.
  • Locks: Spray a small amount of lubricant into the keyway of each lock and insert the key to work the lubricant into the mechanism. Wipe away any excess lubricant with a soft cloth.
  • Latches: Apply a small amount of lubricant to the latch mechanism and operate the latch several times to distribute the lubricant evenly.

Touch-Up Paint

Over time, the powder coat finish on your CBU may develop minor scratches or chips. To prevent corrosion and maintain the unit’s appearance, touch up these areas using manufacturer-provided paint. Clean the damaged area with a mild detergent solution, rinse, and dry thoroughly. Apply the touch-up paint according to the manufacturer’s instructions, using a small brush or applicator.

Lock Replacement

If a customer compartment lock becomes damaged or fails to operate correctly, it should be replaced immediately to maintain security. Contact the manufacturer or a licensed locksmith to obtain a replacement lock. In most cases, the lock can be easily replaced by removing the interior locking mechanism and installing the new lock following the manufacturer’s instructions.

Arrow Lock Maintenance

The master loading door arrow lock is maintained by the United States Postal Service (USPS). If you experience any issues with the arrow lock, such as difficulty opening or closing the master door, contact your local Post Office for assistance. Do not attempt to repair or replace the arrow lock yourself, as this may violate USPS regulations.


To protect your CBU from the elements and prevent water infiltration, inspect the unit regularly for any gaps, cracks, or damage to the weatherproofing seals. If you notice any issues, contact the manufacturer for guidance on the appropriate weatherproofing materials and application methods.

Reporting Damage or Vandalism

If your CBU is damaged due to vandalism, accident, or natural causes, report the issue to your local Post Office and the manufacturer immediately. They will provide guidance on the necessary repairs or replacement parts to restore the unit to its proper functioning state.

By implementing a regular maintenance and upkeep schedule, you can ensure that your Cluster Box Unit remains a secure, attractive, and functional mail delivery solution for your residents. Promptly addressing any issues and working closely with the manufacturer and USPS will help extend the life of your CBU and minimize potential disruptions to mail service.

Additional Care and Cleaning Information

In Summary

Cluster Box Units provide an efficient and secure solution for multifamily mail and package delivery needs. By understanding the different types available and their capacities, property managers can select the optimal configuration for their building. Proper installation and regular upkeep will ensure the CBU remains an attractive and functional amenity for residents for years to come. To streamline the purchasing and installation process, work closely with your local Post Office and an approved CBU supplier.

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