PEMB Foundations Explained: Anchor Bolts, Column Reactions and Hairpins (What to Ask Before You Pour in Spokane)

A pre-engineered metal building (PEMB) has a design advantage: the manufacturer engineers the steel frame for your exact size, snow load and wind speed. But the foundation isn't part of the steel package. It's designed separately, and that's where many shop and commercial projects go wrong. Here's how a PEMB foundation works, what paperwork it depends on, and what to ask your contractor before any concrete gets poured.

Who designs what

• Steel frame, purlins, girts, bracing: PEMB manufacturer's engineer
• Anchor bolt layout and column reactions (the forces at each column base): PEMB manufacturer provides these
• Footing size, anchor-rod embedment, slab, and how outward column thrust is resisted: Your foundation engineer (the project's registered design professional)
• Building the foundation to that design: Concrete contractor

Industry guidance is consistent on this. A structural engineer writing about PEMB foundations put it this way: foundation design "is rarely done by the PEMB supplier," but the supplier should provide a complete "Anchor Bolts and Reactions" package (1). STRUCTURE magazine's review of metal-building foundations covers the design choices the engineer of record makes, including tie rods, hairpins and moment-resisting footings, and notes the ACI 318 issues involved (2).

What a complete "anchor bolts and reactions" package includes

Before your foundation is designed, the steel supplier should give you (1):

1. A footprint drawing with overall dimensions, column locations, grid lines and anchor-bolt detail callouts
2. A reaction table showing the loads at every column and brace connection, listed by load case and by grid line
3. Anchor bolt details: diameter, projection and pattern

If a bidder offers to "just pour a slab" before this package exists, that's a red flag. A general guide on metal building prices makes the same point: the anchor-bolt pattern, column reactions and foundation design all have to agree with the building package before concrete is placed (3).

The three forces your foundation has to handle

1. Uplift (usually controls footing size)

Wind tries to lift a metal building off its foundation. One engineer notes that footing size is "most likely governed by wind uplift", not by the building's weight. He also warns against suppliers who say you only need to design for 70% of wind uplift (1). Spokane County and the City of Spokane use a 110 mph design wind speed (4).

2. Outward thrust ("column kick")

A rigid steel frame pushes outward at its base under roof load, and in the Inland Northwest that roof load includes heavy snow. There are a few ways to resist that push (2):

• Hairpins + slab ties: How it works: U-shaped bars at each column carry the force into the slab reinforcement; Trade-off: Cheapest, but it depends on the slab. Saw cuts, trenches or joints near columns can weaken it
• Tie rods / grade beams: How it works: Opposite columns are tied together under the slab; Trade-off: More reliable. Grade beams survive future slab cuts
• Moment-resisting foundation: How it works: The footing's mass resists sliding and overturning; Trade-off: Very reliable and works with pits, trenches or no slab, but costs more
• Trench footing: How it works: A deep concrete-filled trench resists uplift and thrust; Trade-off: Depends on the soil and the site

Practical tip: If you might add a floor drain, a trench drain or a vehicle lift pit later, tell your engineer now. Hairpin systems make the slab part of the structure, so later cuts near columns can weaken it (2).

3. Frost

Footings must sit below frost depth: 24 inches in Spokane, Spokane Valley and unincorporated Spokane County, 30 inches in Lincoln County (Davenport), and 36 inches in Deer Park (5, 6, 7). Spokane's joint policy allows frost-protected shallow foundations. Ask whether that design makes sense for your building.

Snow load gets into the foundation too

A higher roof snow load increases both the downward load and the outward kick at every column. Ground snow loads vary a lot around here: 39 psf for much of Spokane County (30 psf minimum roof), 50 psf in Lincoln County, and 56–65 psf in Deer Park. Some parts of Spokane County reach 150 psf (4, 6, 7). Order your building with your parcel's actual snow load. The reactions in your foundation design come from that number.

Seven questions to ask before the pour

1. Do we have the final anchor-bolt plan and reaction table, not the preliminary one?
2. Who is the foundation engineer, and are the plans stamped?
3. How is column thrust resisted: hairpins, tie rods or grade beams?
4. What's the footing depth for my jurisdiction's frost line?
5. Are anchor bolt templates being used, and who checks bolt location and projection before the pour?
6. Where are the slab control joints, and do they cross any hairpin zones?
7. What inspections does my building department require before the pour?

Typical cost context

Most published installed prices for metal buildings include a slab. BuildingsGuide budgets $4–$8 per sq ft for the slab foundation (3), and HomeGuide lists installed 4-inch slabs at $6–$8 per sq ft and 6-inch slabs at $8–$10 (8). Engineered footings with deeper frost lines, grade beams or moment-resisting footings add to that. That's why two "40x60 with slab" quotes can be far apart. Compare foundation designs, not just square-foot prices.

FAQ

Does the metal building company design my foundation? Usually not. The supplier provides the anchor-bolt plan and column reactions, and your engineer designs the foundation (1).

What are hairpins in a metal building foundation? U-shaped bars at each column that transfer outward thrust into the slab reinforcement. They're the cheapest method, but they make the slab structural (2).

How deep do PEMB footings need to be in Spokane? At least to the 24-inch frost depth in Spokane and Spokane Valley, and deeper in Deer Park (36") and Lincoln County (30"). The engineered depth may be greater because of uplift (5, 6, 7).

Can I pour the slab before the steel arrives? Yes, if you have the final anchor-bolt plan and an engineered foundation design. Without those, don't.

One contractor for the foundation and the frame

Raven Buildings builds PEMB foundations and erects the steel, so the people setting the anchor bolts are the people who'll set the columns. We're manufacturer-neutral: we source each building from whichever supplier can deliver fastest for your size and load, then design the foundation around that supplier's anchor-bolt package. Call 509-350-2016 or request a quote. See steel buildings and concrete slabs and flatwork.

Sources

1. "Pre-Engineered Metal Buildings" (structural engineer's notes)
2. STRUCTURE magazine, "Foundations for Metal Building Systems"
3. BuildingsGuide, "Metal Building Prices"; ArchitectureCourses.org, "Prefab Metal Building Prices"
4. Spokane County BP-06 / Building FAQ; and
5. City of Spokane / Spokane County Joint Policy BUILD-07 Frost Depth
6. Lincoln County, WA, Design Guidelines
7. City of Deer Park Municipal Code 15.04.010
8. HomeGuide, "How Much Does a Concrete Slab Cost? (2026)"