ASCE 7 · DESIGN WIND SPEED V
The basic wind speed is one mapped 3-second gust
V is the peak gust read straight off the ASCE 7 wind speed map for your building's Risk Category — a strength-level (ultimate) speed used directly in LRFD.
THE DEFINITION
Three conditions define V
Every mapped value assumes the same reference conditions — that is what makes V comparable nationwide.
Peak 3-second gust
V is averaged over a 3-second window — the short, intense burst structures actually feel, not a sustained or hourly mean.
3-SEC AVG33 ft in Exposure C
Measured at 33 ft (10 m) above flat, open terrain. Height and exposure adjustments are applied later through Kz.
33 FT · EXP CFrom the Risk-Category map
You read V off the ASCE 7 map that matches the building's Risk Category. The category picks the map; the map gives the mph.
MAP-BASEDASCE 7-16 / 7-22 · RETURN PERIODS
Risk Category selects which map you read
There is no importance-factor multiplier. A higher Risk Category points you to a map with a longer return period (MRI), which means higher design speeds.
Risk Category I
Low hazard to life — minor agricultural and storage structures.
300-YR MRIRisk Category II
Standard occupancy — homes, offices, retail, most buildings.
700-YR MRIRisk Category III
Substantial hazard — large assembly, schools, jails, power.
1,700-YR MRIRisk Category IV
Essential facilities — hospitals, fire / police / EOC, shelters.
3,000-YR MRIThese are mean recurrence intervals (return periods), not importance factors. ASCE 7-10, 7-16, and 7-22 eliminated the old wind importance factor — the category simply changes which speed map you read V from. Actual mph varies by location.
SINCE ASCE 7-10
Mapped V is ultimate, not nominal
The number on the map is a strength-level (ultimate) speed used directly in LRFD. For ASD, the wind load — not the speed — is multiplied by 0.6 in the load combination.
Vult — the mapped speed
Read straight off the map and plugged into LRFD load combinations. No conversion needed; the strength level is built in.
LRFD · DIRECTEquivalent Vnom = V × √0.6
Because load scales with speed squared, the 0.6 ASD load factor is equivalent to a nominal speed of about 0.78 V. Use the 0.6 on the load, not the speed.
ASD · ×0.6 LOADWORKFLOW
How to find your V
Four steps from building type to the mph you design with.
Set the Risk Category
Classify the building by occupancy and consequence using ASCE 7 Table 1.5-1.
Open the matching map
Each category maps to its own return period — 300, 700, 1,700, or 3,000-yr MRI.
Read V at your site
Find your location's mph contour. Special Wind Regions may require a site study.
Apply it as ultimate
Use V directly in LRFD; apply the 0.6 load factor for ASD combinations.
PUT V TO WORK
Let the calculator read V for you
WindLoadCalc.com applies the correct mapped basic wind speed for your location and Risk Category, with ASCE 7-compliant ultimate-level loads.
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