A metal building withstands the design wind speed its engineer set for that site and that building’s use, taken from the code wind map for its risk category. What wind speed a metal building can withstand is therefore a question about the site and the design, not a fixed rating that comes with the product. The speeds in the building code are 3-second gusts measured 33 feet above open ground, not sustained winds. Two identical buildings in different places, or with different uses, are designed for different wind speeds. For wind-resistant steel buildings, the design wind speed is one of the loads the whole structure is engineered around, from the roof panels to the anchor bolts.
Why “rated to X mph” is the wrong question
Buyers often ask what wind speed a building is rated to. For an engineered metal building, the answer comes from the site and the design, not a catalog.
“It’s based on the exact location, the local building department, and the design of the building. The wind rating is also based on the surrounding geographical area.”
Stephen Tanco, owner, Universal Steel
Fixed ratings such as 140, 170 or 180 mph, tied to the gauge of the frame, describe a product chosen from a table. An engineered building isn’t chosen from a table. It is designed for the wind its site and its use call for, and the frame, bracing, panels and connections are sized to match.
The metal building industry’s own guide specification, published by the Metal Building Manufacturers Association, makes the same point. Its wind load clause leaves the basic design wind speed blank, to be filled in for each project from the wind map for that building’s risk category.
How the design wind speed for a building is set
Three things set the design wind speed for a building: where it is, what it is used for, and what surrounds it.
Location. The starting point is the basic wind speed for the site, read from the maps in ASCE 7, the national loading standard the building code refers to. The local building department decides which edition of the code applies, and the design follows the department’s requirement, not a figure from a brochure or an old quote.
Use. The risk category reflects what the building is for and what a failure would mean for the people in and around it. Risk Category I covers buildings that pose little risk to people. Risk Category II covers most ordinary buildings. Risk Categories III and IV cover buildings with large numbers of occupants and essential facilities that need to keep working after a storm. ASCE 7 has a separate wind map for each risk category, so a school and an equipment shed on neighboring lots start from different wind speeds.
Surroundings. The exposure category describes the ground upwind of the site. Exposure B is towns, suburbs and woodland, which slow the wind down. Exposure C is open country with scattered obstructions. Exposure D is flat, open ground facing open water, where the wind arrives at full strength. On coastal sites in states such as South Carolina, North Carolina and Louisiana, the exposure category matters as much as the map.
The engineer then turns the design wind speed into the pressures each part of the building must resist, using the building’s height, roof shape and size. Corners and roof edges take higher pressures than the middle of a wall, which is why panel fastening is closer together around the edges of the building.
Large doors and open walls change the design
Large doors and open walls change the wind design of a metal building, and the engineer needs to know about them before the design starts.
“It changes the engineering design. We would need to know if the open wall will remain open, or what it will be used for.”
Stephen Tanco, owner, Universal Steel
Wind that enters a building pushes outward on the walls and up on the roof from the inside, while the wind outside pulls on the same surfaces. ASCE 7 classes every building as enclosed, partially enclosed or open, and the class sets the internal pressure the frame and roof are designed for. A wide opening on the windward wall can turn an enclosed building into a partially enclosed one, which raises the uplift on the roof.
Overhead doors, windows and louvers are designed to the building’s wind load like any other component. Large doors also add their own weight to the framing around them, which the engineer calculates separately. Buyers should say up front where the large doors go, how big they are, and whether any wall will stay open.
What changed with the 2024 code
The 2024 International Building Code adopted ASCE 7-22, and the wind maps changed with it.
“We have seen wind loads increase in many areas due to the wind code change.”
Stephen Tanco, owner, Universal Steel
The changes go in both directions. According to FEMA’s summary of the ASCE 7-22 wind changes, basic wind speeds for Risk Category II buildings rose by about 10 mph along the south Texas coast, and in Destin, Florida, from 142 to 152 mph. They fell along the North Atlantic coast and around Mobile, Alabama, from 154 to 146 mph.
A new map only applies once the state or city adopts it. Florida’s current building code, the 2023 edition, already uses ASCE 7-22, so the higher Panhandle speeds apply to buildings designed there today, as the Florida page explains. Other states adopt new editions years apart. A design wind speed on an older quote or drawing, prepared to an earlier edition, may not match what the building department requires now.
Tornado loads for schools, hospitals and other critical buildings
For the first time, the 2024 International Building Code requires tornado loads in building design. Section 1609.5 brings in Chapter 32 of ASCE 7-22 for Risk Category III and IV buildings in the tornado-prone region, which STRUCTURE magazine describes as roughly the part of the United States east of the Continental Divide. Those buildings are designed for whichever is greater, the tornado load or the ordinary wind load. Where the mapped tornado speed is under 60 mph, tornado design isn’t required.
The rule catches buildings where a failure would put many people at risk, or would take out a service a community needs after a storm. Schools above a set number of occupants fall in Risk Category III, and hospitals in Risk Category IV.
Oklahoma’s statewide code moved to the 2024 International Building Code on September 14, 2026, tornado provisions included, as the Oklahoma page covers.
The tornado rules have a clear limit. According to the FEMA and NIST design guide for the new tornado requirements, design tornado speeds range from 60 to 138 mph, roughly the EF0 to EF2 range on the Enhanced Fujita Scale. A building designed to Chapter 32 is not a storm shelter or safe room. Storm shelters and safe rooms follow separate standards, ICC 500 and FEMA P-361, at far higher design speeds, such as 250 mph in the central United States.
Frequently asked questions
Can a metal building withstand a hurricane?
A metal building is engineered for the design wind speed at its site, and the hurricane coasts carry some of the highest wind speeds on the code maps. Near those coasts the code also maps a wind-borne debris region, where the design has to account for flying debris striking windows and doors. Our page on hurricane-resistant steel buildings covers coastal design in more detail.
Is a 3-second gust the same as a sustained wind speed?
No. Code wind speeds are 3-second gusts measured 33 feet above open ground. A sustained wind speed is averaged over a longer period and is lower than the gust for the same storm, so the two numbers can’t be compared directly.
Where do I find the design wind speed for my building?
The design wind speed appears on the building’s construction documents, along with the exposure category and the risk category it was designed for. Our guide to PEMB drawings explains where the design loads sit in the drawing set.
Can a building be designed for more wind than the code requires?
Yes. ASCE 7 sets minimum design loads, so an owner can ask for a higher design wind speed than the code requires, for example on a building that needs to stay in use after a storm. The engineer designs to whichever value is higher.
Engineered for the wind at your site
Every Universal Steel building is engineered to the wind load at its site and for its use, under the code the local building department enforces. The same applies to the other loads a roof carries, including snow. To start with the wind speed and the risk category for your site, see how we engineer storm-resistant steel buildings or request a quote.
