What Is a Pre-Engineered Metal Building (PEMB)? Red Iron Frames, Purlins, Girts and Washington Code, Explained (2026)

A pre-engineered metal building (PEMB) is a steel building whose frame, purlins, girts, bracing and panels are designed together by one manufacturer for your exact site, then fabricated in a plant and bolted together on your foundation. You'll also hear it called a "red iron" building, after the red primer many manufacturers put on the main frames. For shops, machine sheds, RV storage and commercial buildings around Spokane, it's one of the most common ways to get a wide, column-free space that's engineered for our snow.

Here's what a PEMB actually is, how it differs from a metal "kit" or a pole barn, and what the code expects before one goes up in Washington.

Short answers

• What does "pre-engineered" mean? The manufacturer's engineers design the whole structural system for your building's size, use and site loads before anything is cut. The Metal Building Manufacturers Association (MBMA) describes these as integrated systems whose parts are "specifically designed to support and transfer loads"
• What is "red iron"? The primary frames: welded steel I-shaped columns and rafters. "Red iron" refers to the red-oxide primer common on them, not a different kind of steel
• Is a PEMB the same as a metal carport kit? No. A PEMB uses welded structural steel frames and comes with engineering for your parcel. Light-gauge tube kits are a different product
• Does it need a permit? In Washington, a shop or commercial building is built under the State Building Code. Since March 15, 2024, that's the 2021 International Building Code with state amendments, enforced by your city or county

The parts of a PEMB

MBMA and its education materials break a metal building system into a handful of parts that work together:

• Primary frames (the red iron): rigid frames of columns and rafters that carry the loads straight down to the foundation. They're usually welded I-shapes, often tapered so the steel is deepest where the forces are biggest, and they bolt together in the field with end plates
• Secondary framing: cold-formed C- or Z-shaped purlins on the roof and girts on the walls. MBMA's retrofit guide lists typical depths of 6 to 15 inches. They hold the panels and pass snow and wind loads to the frames
• Bracing: rod, cable or portal bracing that keeps the building from racking sideways in wind or an earthquake
• Cladding: the roof and wall panels, plus trim, doors, windows and insulation. Our metal panel guide compares PBR, R-panel and standing seam
• Connections: high-strength bolts at the frames and screws at the panels

Because every piece is designed as one system, MBMA cautions that the entire building should come from one accredited manufacturer as a single point of control.

How big can a PEMB be?

• Bay spacing: MBMA's retrofit guide says frames are commonly spaced 12 to 35 feet apart, and the spacing can vary along the building
• Clear spans: a single-span (clear span) frame can run up to several hundred feet with no interior columns
• Multi-span: with interior columns, the width is practically unlimited, which is how big warehouses are built
• Roof slope: typically from 1/4:12 up to 6:12
• Frame styles: gable clear span, single slope, lean-to and multi-span, and they can be combined at a frame line

For most shops around Spokane, that means a 40-, 50- or 60-foot-wide building with no posts in the middle, which is why PEMBs are popular for combines, RVs and lifts. Our shop sizing guide walks through common sizes.

PEMB vs. pole building vs. kit

• PEMB (red iron): welded steel frames on a concrete foundation with anchor bolts, engineered as one system. Wide clear spans and tall sidewalls are its strength
• Pole building (post-frame): wood posts set in the ground or on piers, with trusses and girts. We build both, and installed they run about the same in our market. See our red iron vs. pole barn comparison
• Metal building kit: sometimes a true PEMB package delivered for you to erect, sometimes a light-gauge carport-style building. A kit price leaves out the foundation, erection and site work. Our kit vs. installed guide explains the gap

What the code expects in Washington

• Which code: Washington adopted the 2021 International Building Code under WAC 51-50, effective in every county and city on March 15, 2024
• Engineering for your site: the manufacturer designs the building for the snow, wind and seismic loads your building department assigns to your parcel. Those vary a lot across Eastern Washington. For example, Lincoln County's design guidelines set a 50 psf ground snow load and a 30-inch frost depth. Our Spokane County snow load guide shows how to find yours
• Shop fabrication and special inspection: under IBC Section 1704.2.5.1, special inspection during fabrication isn't required when the work is done by a fabricator the building official has approved. Building officials can use the International Accreditation Service's AC472 accreditation for metal building manufacturers to make that call, and the approved fabricator submits a certificate of compliance at the end
• Field inspections still happen: IAS notes that AC472 doesn't eliminate inspections at the job site during assembly, and your permit still carries its normal footing, framing and final inspections
• Foundation: the manufacturer's drawings give the column reactions and anchor bolt layout, and the foundation is designed to carry them. Our PEMB foundations guide covers anchor bolts and hairpins
• Don't cut the frame: the ICC's guide to inspecting metal building systems says rigid frames shouldn't be modified in the field, for ductwork or anything else, without written approval from the design professional or the manufacturer's engineer

How a PEMB goes up

• Design and order: size, doors, framed openings, insulation and loads are set, and the manufacturer produces the engineered drawings
• Permit: the stamped drawings and foundation design go to your city or county
• Foundation: footings and the slab are poured with anchor bolts set exactly to the drawings
• Erection: frames are stood and bolted, then purlins, girts and bracing, then the panels, trim and doors
• Finish trades: your electrician, plumber and any interior work

Our PEMB lead time guide puts real timelines on each step. Raven isn't tied to one manufacturer, so we source each building from whichever manufacturer can deliver the engineered package fastest.

What an installed PEMB costs with Raven

Raven's going rate for an installed pre-engineered metal building is about $60 to $75 per sq ft. Electrical, plumbing and utility hookups are not included and are extra. Site conditions, grading, doors and size move the number, so we quote each building from your plans and parcel.

Get a PEMB quote

Raven Buildings handles the steel and the concrete under one contract across Spokane and Eastern Washington. Call 509-350-2016 or request a free quote with your size, door layout and address or parcel number. See our steel building services.

Sources

• Installed pricing: Raven Buildings' current going rate
• MBMA: Design Resources, The System
• MBMA Education: Metal Building Systems QuickStart Guide (PDF)
• MBMA: Retrofitting and Reinforcing Metal Building Systems (PDF)
• ICC: Guide for Inspecting Metal Building Systems, sample (PDF)
• IBC 1704.2.5.1 Fabricator Approval (UpCodes)
• IAS: AC472 Accredited Inspection Program FAQ (PDF)
• ICC Building Safety Journal: IAS AC472 and AC478 in Low-Rise Construction
• WAC 51-50-008: 2021 IBC effective March 15, 2024
• SBCC: Revised effective date for 2021 codes, March 15, 2024
• Lincoln County, WA: Design Guidelines