Package room requirements split into two systems that the drawings routinely confuse: the USPS 4C mailbox unit the postal carrier services, and the carrier-agnostic package room or smart locker bank that handles Amazon, UPS, and FedEx deliveries. The postal service governs the first through USPS-STD-4C. Nobody governs the second, which is exactly why it gets underbuilt. Get both wrong and you delay mail service, strand residents without a place to receive parcels, and hand your Division 10 sub a set of rough openings that no longer fit the unit you ordered.
This guide separates the two, gives you a verified USPS-STD-4C spec table for the mailbox, walks the sizing and access decisions on the package room, and connects each spec back to the interiors buildout you have to coordinate before drywall closes. If you take one thing from it: the mailbox is a code item with hard numbers, and the package room is a design item with none, so the package room is where most of your judgment goes.
Two systems, two sets of rules
The 4C mailbox is the equipment the letter carrier opens with a USPS arrow lock to distribute mail and small parcels. USPS requires it on new multifamily construction receiving mail delivery, and the postal service will not start service to a building without an approved installation. Its dimensions, mounting heights, and parcel-locker count come from USPS-STD-4C, and the local postmaster confirms the installation before delivery begins.
The package room is a different animal. It holds the boxes that private carriers drop, the ones too large for a 4C parcel locker or delivered by a carrier that does not have an arrow key. No federal standard sets its size, shelving, or access. That freedom is the trap. Teams copy a room off a prior set of plans, size it for a 2015 delivery volume, and open a building where packages stack on the floor by the second week of leasing. Treat the package room as a real program element with a throughput target, not a leftover closet near the mailroom.
USPS 4C mailbox requirements
Every number below comes from USPS-STD-4C, the postal standard that replaced the older 4B system for new construction. Confirm each against the specific unit on your submittal, because compartment counts and parcel-locker inclusion change the overall size.
| Requirement | USPS-STD-4C spec | Coordination note |
|---|---|---|
| Approved product | Unit must be a USPS-approved 4C model from an approved manufacturer | A generic “4C-style” box will not pass postal approval. Confirm the model on the product data sheet. |
| Highest tenant lock | No tenant lock higher than 67 in. above finished floor | Caps the number of tiers in the unit and drives overall height. |
| Lowest tenant compartment | Interior bottom shelf no lower than 28 in. above finished floor | Sets the floor line of the tenant bank. |
| Parcel locker height | Interior bottom shelf no lower than 15 in. above finished floor | Parcel lockers sit below the tenant tiers, which is why they anchor the unit’s bottom. |
| Arrow (carrier) lock | Master arrow lock mounted 36 to 48 in. above finished floor | The carrier’s access point. The installer coordinates keying with USPS. |
| Parcel locker ratio | One parcel locker per five tenant compartments | Updated from the older 1:10 ratio. Many guides still print 1:10. Confirm the current count with the local postmaster. |
| Minimum tenant compartment | Interior form factor at least 12 in. W by 15 in. D by 3 in. H | The 15 in. interior depth is why 4C units need a deep wall recess, not a standard partition. |
| Accessibility | At least one compartment within the 15 to 48 in. reach range, with clear floor space for a forward approach | Aligns the 4C install with the ADA Standards for Accessible Design. |
The two lines that cost the most money when missed are the compartment depth and the parcel-locker ratio. A 4C unit built around a 15-inch interior compartment does not fit a standard 3.5-inch metal stud partition with drywall on each side. It needs a framed alcove or a recessed niche sized to the unit’s overall depth, which commonly runs 15 to 19 inches depending on the model and whether parcel lockers are included. Put that recess on the framing drawings before the first stud is set, and confirm the exact depth against the ordered unit rather than a catalog default.
The parcel locker ratio drives the unit size
The parcel-locker count is not a detail you settle at installation. It sizes the whole unit. USPS-STD-4C now requires one parcel locker for every five tenant compartments, a change from the older one-per-ten rule that many spec sheets and older articles still repeat. A 60-unit building that needed six lockers under the old ratio needs roughly twelve under the current one, and those extra lockers add modules, width, and rough-opening dimensions.
Confirm the count two ways. First, apply the 1:5 ratio to your tenant compartment count as a baseline. Second, verify it with the local postmaster, who has the final say on the required number and can call for more based on the building’s expected volume. Lock this down during the Division 10 scope review, before procurement, so the unit you order matches the opening you frame.
Sizing the package room
Size the package room to parcel throughput, not to unit count alone. The drivers are the number of homes, the resident profile, and how much of your delivery volume the 4C parcel lockers already absorb. A building of young renters who order heavily online moves far more boxes per door than an age-restricted community, and a building with generous 4C parcel lockers needs less overflow room than one with the minimum.
Because no standard sets a square-footage figure, work from throughput. Estimate daily package volume, decide how long a box can sit before pickup, and size shelving to hold that peak without floor stacking. Smart-locker vendors publish sizing tools that convert door count and delivery assumptions into a recommended locker bank, and those numbers are a better starting point than a guessed room size. Whatever total you land on, put the room near the leasing office or a staffed lobby so it stays inside the access-controlled envelope and under a camera.
Shelving and layout
Shelving is where a package room succeeds or fails day to day. Adjustable wire or laminate shelving on a French cleat or standard-and-bracket system lets staff retune shelf spacing as package sizes shift, which they will. Anchor brackets to studs or to blocking, not to drywall alone, and set the layout against actual stud locations. That is the same blocking discipline the rest of the Division 10 scope runs on, and it belongs on the pre-drywall coordination list.
Leave a clear aisle wide enough for a hand truck and a landing surface near the door for oversized boxes that will not shelve. If the room doubles as a smart-locker location, plan the wall the lockers mount to for the unit’s depth and weight, and confirm blocking behind it. A room laid out for boxes on the floor is a room that fills with boxes on the floor.
Access control and carrier access
Access control decides who reaches the parcels, and it has to serve two different populations. Residents need self-service entry on the building credential they already carry, the fob, mobile key, or code that opens the amenity doors. Carriers need a way in to drop, which is the harder half. Some properties issue carriers a controlled credential, some route deliveries through a video intercom to a staffed desk, and some rely on smart lockers that give the carrier a one-time code tied to a specific compartment.
Keep the 4C mailbox out of this conversation. The letter carrier opens the 4C bank with the USPS arrow lock, a postal-controlled key you do not manage and cannot substitute. The access-control design applies only to the package room and any private smart lockers. Coordinate that design with the low-voltage and door-hardware scopes early, because a package-room door that needs an electric strike, a reader, a power supply, and a camera drop is a multi-division item, not a hardware afterthought.
Smart locker options
Smart lockers replace or supplement the open package room with a bank of electronically controlled compartments. A carrier scans the resident, drops the box in an assigned locker, and the system texts the resident a pickup code. The appeal is accountability: the system logs each parcel to a compartment and a person, which cuts the front-desk labor and the “my package is missing” calls that an open room generates.
Lockers cost more than shelving and carry real buildout requirements. They need dedicated power, a data or cellular connection, and a wall or floor structure rated for a loaded bank. Mixed configurations, a smaller locker bank for accountability plus an overflow room for peak volume and oversized items, are common because pure locker banks rarely hold a holiday surge. Whichever way you go, treat the locker vendor’s rough-in drawing the same as the 4C submittal: confirm power, data, mounting depth, and blocking before framing.
How these decisions hit the Division 10 buildout
Every choice above lands on the interiors scope, most of it under Division 10. The 4C unit needs a framed recess at the confirmed depth, blocking behind the mounting points, and the accessible clearance in front. The package room needs anchored shelving, blocking for lockers, and a door coordinated across hardware and low-voltage. None of it is expensive at pre-construction. All of it is expensive after drywall and paint, when a shallow alcove means reframing and a missing power drop means opening a finished wall.
Two timelines run alongside the buildout. The USPS approval process, which the owner or property manager initiates, runs about four to six weeks and has to start well before occupancy or residents move in without mail service. The smart-locker activation runs on the vendor’s install and commissioning schedule. Put both on the pre-construction coordination log next to the rough-opening dimensions, so the mailbox recess, the package-room shelving, and the locker rough-in all get resolved before the framing crew closes the wall. Reading the Division 10 submittal closely is how you catch a mismatch between the ordered unit and the drawn opening. See how to read a Division 10 submittal and what a Division 10 package includes for the wider scope this sits inside, and the wire shelving guide for the anchoring detail the package room shares with unit closets.
How Innergy coordinates the mailroom and package room
At Innergy Interiors, the 4C mailbox and the package-room specialties fall under our Division 10 scope. Before we bid, we confirm the 4C unit size against the tenant compartment count and the current 1:5 parcel-locker ratio, and we flag the count for postmaster confirmation. We give the GC the exact rough-opening depth for the ordered unit before the framing crew starts the alcove, specify blocking for the mailbox, package-room shelving, and any locker bank, and coordinate the package-room door across the hardware and low-voltage scopes. We do not treat the mailroom as a last-minute delivery, and we make sure the postal approval conversation starts on a timeline that clears before your projected occupancy date.
Innergy covers Division 10 specialties for multifamily construction under a single subcontract. If you are running a multifamily project in Texas, Washington, Oregon, Colorado, Utah, New Mexico, or Arizona and need Division 10 scope with the mailroom and package room coordinated, send us the project details and we will respond within one business day.