Can You Add a Mezzanine or Loft to a Metal Shop in Spokane? Code Limits, Live Loads, Stairs and Permits (2026)

Want a mezzanine or loft in a new metal shop around Spokane? It's one of the best ways to get storage, an office or a parts room without a bigger footprint, but it's also one of the easiest things to get wrong. Washington's building codes cap how big a mezzanine can be and how much headroom it needs, the floor has to be designed for what you'll actually put on it, and the steel building itself has to know the mezzanine is coming. Here's what the codes and the industry say.

What counts as a mezzanine

In code terms, a mezzanine is an intermediate floor level inside a story, open to the room below. A storage loft over the back of a shop usually falls under the same rules. Two codes can apply:

• Shops and garages accessory to a house are often reviewed under the Washington State Residential Code (based on the IRC), which has its own mezzanine section, R325
• Commercial, business and other non-residential buildings fall under the Washington State Building Code (based on the IBC), Section 505

The building department decides which applies. The core rules are close.

The size and headroom limits

• One-third of the room: both codes limit the total area of all mezzanines in a room to one-third of the floor area of the room they sit in. Under the IBC, the mezzanine's own area isn't counted in the room area, and enclosed portions of the room are left out too
• Exceptions are narrow: the IBC allows up to one-half in Type I or II buildings with a full sprinkler system and an emergency voice/alarm system, and up to two-thirds for some special industrial occupancies. The residential code allows one-half inside a sprinklered dwelling unit. A typical metal shop doesn't qualify for either
• 7 feet clear above and below: both codes require at least 7 feet of clear height above and below the mezzanine floor construction. Floor framing and decking eat into that, so eave height matters
• It doesn't add a story: under IBC 505.2, a compliant mezzanine is treated as part of the story below and doesn't count toward building area or number of stories, though its area is included in the fire area

It has to stay open

• Commercial (IBC 505.2.3): a mezzanine has to be open and unobstructed to the room below, except for walls no more than 42 inches high, columns and posts. You can enclose it if the enclosed space has an occupant load of 10 or fewer, is no more than 10 percent of the mezzanine area, or the mezzanine has two or more exits
• Residential (R325.5): the open-side walls are limited to 36 inches, and the enclosed portion can be no more than 10 percent of the mezzanine area unless the building is sprinklered and no more than two stories

A fully walled upstairs office may not qualify as a mezzanine, so plan it before the building is ordered.

Live loads: design the floor for what goes on it

The floor's required capacity depends on how it's used:

• Residential code, Table R301.5: 20 psf for uninhabitable attics with limited storage, 30 psf for habitable attics and attics served by fixed stairs, 40 psf for rooms other than sleeping areas, and 40 psf for stairs
• Commercial code, Table 1607.1: 125 psf for light storage and 250 psf for heavy storage (the table notes warehouses must be designed for heavier loads if the anticipated storage requires it), 125 psf for light manufacturing and 250 psf for heavy, 50 psf for offices, and 20 psf for storage areas above ceilings
• Catwalks: 40 psf for maintenance and service access
• Guards and handrails: the residential table calls for a 200-pound concentrated load on guards and handrails

A loft for totes is a very different floor from one for tires, engine parts or pallets, so tell us the real use up front.

Stairs, guards and handrails

Residential code (R311.7 and R312):

• Risers: no more than 7-3/4 inches
• Treads: at least 10 inches
• Headroom: at least 6 feet 8 inches
• Width: at least 36 inches of clear width above the handrail
• Handrails: required on at least one side of any flight with four or more risers, 34 to 38 inches high
• Guards: required on open sides of mezzanines and lofts more than 30 inches above the floor below, at least 36 inches high

Commercial code (Chapter 10):

• Risers and treads: 7 inches maximum rise and 11 inches minimum tread. IBC 1011.5.2 allows 7-3/4 inch risers and 10 inch treads in Group U buildings accessory to a home, which covers many detached shops and garages
• Headroom: at least 80 inches (the same 6 feet 8 inches)
• Width: 44 inches, or 36 inches where the stair serves fewer than 50 occupants
• Guards: required where the open side is more than 30 inches above the floor below, and at least 42 inches high (with a 36-inch exception for some residential occupancies)
• Handrails: 34 to 38 inches above the tread nosings
• Alternating tread devices: allowed as egress only from a mezzanine of no more than 250 sq ft serving no more than five occupants, and only in Group F, H and S buildings

A ladder isn't a code stair, so ask the building department what they'll accept.

Why the steel building has to be designed for it

A pre-engineered metal building is designed by the manufacturer for the loads written on the order, and only those loads.

• MBMA's Common Industry Practices say the end customer or their design professional has to supply the design loads, including collateral and auxiliary loads, and that unless a load is specifically set out in the order documents, the manufacturer assumes it doesn't exist
• Mezzanine framing is an accessory: MBMA lists mezzanine or floor framing, joists and steel deck among the items a manufacturer provides only when expressly specified in the order
• Manufacturers don't design what they didn't supply: Vulcan Steel's published design practices, for example, say the manufacturer isn't responsible for components it didn't provide or their connection to the metal building unless that responsibility is in the order documents
• Unauthorized changes shift the risk: under MBMA's practices, the end customer indemnifies the manufacturer for modifications it didn't authorize in writing

So a mezzanine that bears on the building's columns has to be in the frame design from the start. Adding one later takes a structural engineer's review, and often a freestanding mezzanine on its own columns and footings or reinforcing the frame. If you might want one, put its size, location and use on the order now.

Mezzanine columns also bring concentrated loads to the slab, so footings are sized with the column layout. Our PEMB foundations guide explains how column reactions drive the concrete.

Permits around Spokane

• Spokane County: the County's BP-25 handout says permits are required to construct, enlarge, alter or repair a building or structure. A mezzanine isn't on its exempt list, and the list only exempts non-fixed, movable racks and partitions up to 5 feet 9 inches tall
• County permit types: the County lists Residential Alteration and Commercial Alteration permits, and its permit templates say a Minor Alteration doesn't involve structural work such as beams or new footings. For commercial alterations of spaces over 4,000 sq ft, plans have to be prepared by a design professional licensed in Washington
• City of Spokane: the City's residential permit application quotes IRC R105.1, requiring a permit to construct, enlarge or alter a building or structure
• New buildings: if the mezzanine is part of a new shop, it's reviewed with the building permit. That's the simplest path. Our shop and pole barn permit guide covers the rest

Questions to answer before you order

• What will the mezzanine hold? Light storage, heavy parts, an office or equipment, since that sets the live load
• How big, and where? Keep it within one-third of the room, and plan around overhead doors, lights and heaters
• How tall is the building? You need 7 feet clear under and over the floor framing
• Now or later? If later, design the frame and footings for it now. Our shop size guide helps with the footprint

Faster delivery on the building

Raven Buildings isn't tied to one PEMB manufacturer. We source from whichever manufacturer can deliver fastest for your building, and the mezzanine framing goes on the same order so it's engineered with the frame. Our lead times and permits guide explains the timeline.

What it costs

Mezzanines and lofts are quoted per project, since size, live load, framing, decking, stairs and guards all change the price. For the building itself, Raven's current installed rate for PEMB and pole buildings is about $60 to $75 per sq ft, and electrical, plumbing and utility hookups are extra.

Get a metal shop quote

Raven Buildings designs, pours and erects steel buildings and pole buildings across Spokane and Eastern Washington, foundation to finished shop. Call 509-350-2016 or request a free quote with your building size, how you'd use the mezzanine and your address.

Sources

• Building pricing: Raven Buildings' current installed rate for PEMB and pole buildings
• Washington State Building Code 2021, Chapter 5 (Section 505 Mezzanines, UpCodes)
• Washington State Building Code 2021, Chapter 16 (Table 1607.1 Live Loads, UpCodes)
• Washington State Building Code 2021, Chapter 10 Means of Egress (UpCodes)
• Washington State Residential Code 2021, Chapter 3 (R301.5, R311.7, R312, R325, UpCodes)
• MBMA Common Industry Practices, 2024 Edition (PDF)
• Vulcan Steel Structures, Design Practices (PDF)
• Spokane County BP-25, Permit Exemptions
• Spokane County, Apply for a Permit
• Spokane County, Building Permit Templates 2026 (PDF)
• City of Spokane, General Residential Permit Application (PDF)