10 min read · Updated 2026-07-14
What Are Wind Loads, Snow Loads, and Live Loads? A Steel Building Owner's Guide
Learn how wind loads, snow loads, seismic design, and live loads affect metal building engineering, pricing, permitting, and long-term performance. Understand why every steel building must be engineered for its specific location.
Key takeaways
- ▸Every steel building is engineered for its specific location.
- ▸Wind loads are one of the biggest factors affecting structural design.
- ▸Snow loads vary dramatically by region and roof type.
- ▸Sealed engineering is required for most permitted commercial buildings.
- ▸Lower-priced buildings may not include the same engineering requirements.
Introduction
If you've requested quotes from multiple metal building companies, you've probably noticed that prices can vary even when the buildings are the same size.
One of the biggest reasons is engineering. Every pre-engineered metal building must be designed for the exact environmental conditions where it will be built. Wind speeds, snow accumulation, seismic activity, occupancy, and local building codes all influence how a building is engineered.
Understanding these requirements helps you compare quotes more accurately and ensures your investment is designed for long-term performance — not just the lowest price.
What Is a Design Load?
A design load is any force a building must safely resist over its lifetime. Engineers combine multiple load types — dead, live, wind, snow, and seismic — using code-mandated formulas to size every column, rafter, purlin, and anchor bolt in the structure.
Building codes such as the International Building Code (IBC) and ASCE 7 set minimum design loads and safety factors. Safety factors intentionally over-design the structure so it can absorb unexpected events without failure.
Engineering matters because a metal building is only as strong as the loads it was designed for. A building engineered for 90 mph winds installed in a 140 mph coastal zone is a liability — not a bargain.
Understanding Wind Loads
Wind load is the horizontal and uplift pressure the wind exerts on a building. Design wind speeds come from ASCE 7 wind speed maps and are set by ZIP code — a coastal Florida site might require 170 mph design speed, while central Kansas is typically 115 mph.
Exposure category also drives the calculation. Exposure B covers urban and suburban environments with buildings and trees that slow wind down. Exposure C is open terrain — farmland, coastlines, and rural lots — where wind hits the building at full speed. Exposure D is unobstructed water frontage.
Wind creates three main forces on a steel building: uplift on the roof (wind flowing over the roof creates suction that tries to lift it off), inward pressure on the windward wall, and outward suction on the leeward and side walls. Corners and edges see the highest local pressures, which is why anchor bolt patterns often concentrate at the endwalls.
What Are Snow Loads?
Snow load is the downward weight of accumulated snow on the roof, measured in pounds per square foot (psf). Ground snow load for your county comes from ASCE 7 maps and is then adjusted for roof slope, exposure, thermal factor, and importance factor to get the roof snow load the building must carry.
Regional differences are dramatic. Gulf Coast counties may design for 5 psf, while mountain regions in Colorado, Utah, or Vermont routinely exceed 100 psf. A 60x100 building at 100 psf is carrying 600,000 lb of design snow load — that drives significantly heavier primary framing.
Drifting and unbalanced loading are also critical. Snow drifts against parapets, taller adjacent structures, and roof steps can multiply local loads. Steep or asymmetric roofs must also be designed for unbalanced load cases where snow accumulates more heavily on one slope.
What Is a Live Load?
Live load is any temporary, movable load the building must support — occupants, furniture, vehicles, inventory, forklifts, and equipment. It excludes wind, snow, and seismic (those are separate load cases) and excludes the permanent weight of the structure itself (that's dead load).
Roof live load typically covers workers and equipment during maintenance — usually 20 psf minimum for low-slope roofs. Mezzanine and floor live loads depend on use: 40 psf for residential, 50 psf for offices, 100 psf for retail and light storage, and 125–250 psf for heavy storage or industrial.
If you plan to hang cranes, conveyors, HVAC, or heavy racking from the frame, tell your building supplier up front. Adding these loads after engineering is complete usually means a full redesign.
Understanding Dead Loads
Dead load is the permanent, unchanging weight of the building itself — primary steel frame, secondary framing (purlins and girts), roof and wall sheeting, insulation, and any permanently attached equipment.
Additions like HVAC units, sprinkler systems, solar panels, ductwork, ceiling grids, and interior partitions all add to the dead load. A 40 kW rooftop solar array can easily add 3–4 psf across the roof — well worth designing for at the outset if solar is on the roadmap.
Dead load is small compared to wind or snow, but it never goes away, so it directly influences long-term deflection, foundation sizing, and anchor bolt design.
What About Seismic Loads?
Seismic load is the lateral force an earthquake exerts on a building. Seismic Design Categories (SDC A–F) are assigned by ZIP code based on soil type and expected ground motion, and they drive bracing, connection details, and anchor bolt design.
It's not just California. Parts of Washington, Oregon, Alaska, Utah, Missouri (the New Madrid zone), South Carolina, and Tennessee all have significant seismic requirements. Ignoring seismic engineering in these regions can make a building unpermittable and uninsurable.
Seismic design is often invisible in the final building but shows up in heavier bracing, moment connections, and larger anchor bolts. A metal building engineered for a high SDC costs more up front but survives events that flatten under-engineered structures.
What Does Sealed Engineering Include?
Sealed engineering is the package of structural calculations and drawings stamped by a professional engineer (PE) licensed in the state where the building will be erected. It is what your building department requires to issue a permit.
A complete sealed engineering package includes: structural calculations for all applicable load cases, sealed anchor bolt and reaction drawings for the foundation engineer, sealed erection drawings for the crew, and a letter of certification that the design meets the specified code and loads.
Iron Forge Buildings works with manufacturers who provide state-specific sealed engineering with every building — designed for your ZIP code, your exposure category, your snow and wind loads, and your local building code. That's the documentation package your permit reviewer will ask for.
Why Engineering Affects Price
Two buildings with identical footprints and eave heights can be priced very differently because the engineering under them is different. A 40x60 building designed for 115 mph wind and 20 psf snow uses meaningfully less steel than the same 40x60 designed for 170 mph coastal wind and 60 psf mountain snow.
Factors that drive engineering cost include design wind speed, ground snow load, seismic design category, exposure category, roof live load, occupancy classification, and building use (a public assembly building carries a higher importance factor than a private garage).
When you're comparing quotes, always compare the engineering assumptions — not just the price. A cheaper building that ignores your actual site loads is not the same product.