Four ways to write down a design wind, and what each means for a roof

Europe: EN 1991-1-4 and the National Annex

The EN Eurocodes are a series of 10 European Standards, EN 1990 to EN 1999, and EU Member States must accept designs made to them. Wind sits in Eurocode 1, Part 1-4, and the JRC's training material gives that part a scope of buildings and civil engineering works up to 200 m tall.

The starting number is a characteristic 10-minute mean wind velocity at 10 m above open ground with low vegetation, with an annual probability of exceedance of 0.02, a 50-year return period. The standard itself does not print one European wind map. Each country sets its values in a National Annex, because the Eurocodes leave climate-dependent choices such as wind to Nationally Determined Parameters, and the level of safety stays a national decision. That 50-year value is then factored up for design; the worked examples in the JRC-hosted handbook apply a partial factor of 1.5 to wind.

A second-generation Eurocode 1 is on the way, and the JRC lists a technical webinar on the second-generation EN 1991 for October 23, 2026.

Australia: wind regions, wind classes and a 1-in-500 target

Australia's National Construction Code (NCC) tells house designers to take wind actions from AS/NZS 1170.2 or AS 4055. A house is Importance Level 2, and for that level the design event has an annual probability of exceedance of 1 in 500 whether the wind is cyclonic or not.

The NCC defines design wind speed as the design gust wind speed for the site and sorts houses into wind classes: N1 to N6 in the non-cyclonic Regions A and B, and C1 to C4 in the cyclonic Regions C and D. Western Australia's variation treats Region B as cyclonic too.

For cyclonic areas, the NCC's explanatory text says the roof must be tied through the walls to the footings by a continuous chain of connections, with every connector able to carry the uplift, because the building's resistance depends on its weakest link. Garage doors and other large access doors in Regions C and D must meet AS/NZS 4505. The prescriptive tile-fixing table in the housing provisions covers only wind classes N1, N2 and N3; at N3, every second full tile in every course in the field of the roof must be fixed.

Canada: hourly wind and 50-year pressures

Canada's National Building Code takes a third route. A Government of Canada climate assessment explains that NBCC design wind pressures for 10- and 50-year return periods come from hourly wind speeds recorded at a standard anemometer height of 10 m.

United States: ASCE 7, the IRC and Florida's HVHZ

U.S. codes draw on ASCE 7. A NIST-authored paper explains that ASCE 7-10 introduced maps of 3-second gust wind speeds tied to return periods of 300, 700 and 1,700 years by Risk Category, while cutting the wind load factor from 1.6 to 1.0; ASCE 7-16 added a 3,000-year map for Risk Category IV. Florida's home wind mitigation form, for example, reads its wind regions off the ASCE 7-22 700-year map for Risk Category 2.

ASCE 7-22 added the country's first tornado load maps, but NIST notes they apply only to Risk Category III and IV buildings in the tornado-prone region, such as schools and hospitals, not to houses.

For houses, the International Residential Code maps a "wind design required" region, and Louisiana's Legislative Auditor lists eight Southeastern states, Alabama and Mississippi among them, inside that region in the 2021 IRC.

Florida adds a further tier. Its High-Velocity Hurricane Zone covers Miami-Dade and Broward counties, and the state's product approval search separates products approved for use in the HVHZ from those approved only outside it.

Hail: tested product by product

The parts of Eurocode 1 listed by the JRC cover self-weight and imposed loads, fire, snow, wind, thermal actions, execution and accidental actions; hail is not among them. In the U.S., the hail resistance a homeowner can ask for is spelled out in product tests. IBHS's voluntary FORTIFIED program uses UL 2218 Class 4 for metal and FM 4473 Class 4 for tile in its optional Hail Supplement, which also requires shingles to rate Good or Excellent in IBHS's own hail ratings. Mississippi's new state grant goes further and requires the FORTIFIED Roof High Wind designation with the Hail Supplement.

The four systems side by side

How the Alabama and Mississippi coast has tested these ideas is on the Mobile and Baldwin and Mississippi coast pages. Trade readers can find code and standards papers in the National Roofing Directory's document library and get storm alerts through The Roofing Wire.

Frequently asked questions

Why can't I compare a Eurocode wind speed with an ASCE 7 number directly?

They measure different things. Eurocode starts from a 10-minute mean with a 50-year return period and then applies safety factors, while ASCE 7 maps a 3-second gust at a 700-year return period for ordinary buildings with a load factor of 1.0.

What do Australia's N and C wind classes mean?

The NCC uses N for non-cyclonic and C for cyclonic winds: N1 to N6 apply in Regions A and B, and C1 to C4 in the cyclonic Regions C and D.

Does ASCE 7 require houses to be designed for tornadoes?

No. The tornado provisions in ASCE 7-22 apply to Risk Category III and IV buildings in the tornado-prone region.

Is FORTIFIED a building code?

No. IBHS describes FORTIFIED as a voluntary construction and re-roofing program, and the National Roofing Directory's FORTIFIED roof explainer covers what it adds.