What is Allowable Stress Design (ASD) for wind loads?

Allowable Stress Design is a service-level method where the wind load W is multiplied by 0.6 in the load combinations and the result is checked against allowable stresses rather than member strength. Because the wind speed maps in ASCE 7 are ultimate (strength-level), the ASD pressure equals 0.6 times the ultimate pressure.

Why is the wind load multiplied by 0.6 in ASD load combinations?

Since ASCE 7-10, mapped wind speeds are ultimate (strength-level). The 0.6 factor converts that strength-level wind pressure down to a service-level pressure suitable for ASD. So every governing ASD combination, such as D + 0.6W or the 0.6D + 0.6W uplift case, applies 0.6 directly to the wind load.

Does the 0.6 factor apply to the wind speed or the pressure?

It applies to the pressure, not the speed. Velocity pressure scales with speed squared (qz = 0.00256 Kz Kzt Kd Ke V squared), so a 0.6 factor on pressure equals only a square-root-of-0.6 factor on speed, roughly 0.78V. In practice you apply 0.6 to the wind load and leave the mapped ultimate speed unchanged.

What are the main ASD load combinations that include wind?

Wind enters at 0.6W in each governing ASCE 7 Section 2.4 combination: D + 0.6W is the baseline check, D + 0.6W + 0.75(L + S) and D + 0.6W + 0.75(L + R) add companion live, snow, and roof loads, and 0.6D + 0.6W is the uplift case that often governs lightweight roofs, canopies, overhangs, and components.

When should I use ASD instead of LRFD for wind loads?

ASD is preferred or required for many building types: pre-engineered metal buildings, post-frame and agricultural structures, residential and low-rise wood framing, and components and cladding rated by Design Pressure (DP). It also keeps retrofits consistent with existing ASD-designed structures. Some plan reviewers favor ASD, so confirm local jurisdictional preference before starting.

ASCE 7 · SECTION 2.4 · DESIGN METHODS

Allowable Stress Design puts 0.6 on the wind load

In ASD load combinations the wind load W is multiplied by 0.6 and checked against allowable stresses — a service-level approach, not a strength one.

0.6WWIND LOAD FACTOR

ServiceLEVEL CHECK

√0.6≈ 0.78 ON SPEED

FROM ULTIMATE TO SERVICE LEVEL

One factor turns ultimate pressure into an ASD pressure

Mapped wind speeds are ultimate (strength-level) since ASCE 7-10, so the ASD-level pressure is simply 0.6 times the ultimate pressure.

Ultimate pressure

Computed from the mapped ultimate wind speed — the same ASCE 7 velocity-pressure equation used for LRFD.

STRENGTH LEVEL

ASD pressure = 0.6 × ultimate

Apply the 0.6 wind load factor and the result is the service-level pressure you check against allowable stresses.

SERVICE LEVEL

ASCE 7 · SECTION 2.4

Key ASD load combinations that include wind

Wind enters every governing ASD combination at 0.6W. The uplift case pairs it with 0.6D, the check that often governs lightweight roofs and components.

D + 0.6W

Dead load with wind — the baseline lateral and pressure check.

WIND + DEAD

D + 0.6W + 0.75(L + S)

Wind acting together with companion live and snow loads.

WIND + SNOW

D + 0.6W + 0.75(L + R)

Wind with companion live and roof live loads acting at once.

WIND + ROOF

0.6D + 0.6W

The uplift case — reduced dead load resists wind suction. Governs canopies, overhangs, and roof components.

UPLIFT

THE COMMON CONFUSION

0.6 belongs on the pressure, √0.6 on the speed

Because pressure is proportional to speed squared, the 0.6 load factor is not a 0.6 speed factor. Mixing the two double-counts or undercounts the wind.

On the load: × 0.6

Apply 0.6 directly to the wind load W in the load combination. The ASD pressure is 0.6 of the ultimate pressure.

PRESSURE × 0.6

On the speed: × √0.6 ≈ 0.78

If you ever express ASD as an equivalent speed, multiply V by √0.6, roughly 0.78 V — never 0.6 V.

SPEED × 0.78

Pressure scales with the square of speed, so a 0.6 factor on pressure equals only a √0.6 ≈ 0.78 factor on speed. In practice you apply 0.6 to the wind load and leave the mapped ultimate speed alone — ASD then compares the result against allowable stresses.

WHERE ASD STILL LEADS

When to reach for Allowable Stress Design

ASD remains the preferred or required method across several building types and product standards.

Metal building systems

Pre-engineered metal buildings and their MBMA design manuals are built around ASD.

PEMB

Post-frame & agricultural

Pole barns and ag buildings use ASD almost exclusively, following NFBA standards.

POST-FRAME

Components & cladding

Windows, doors, and cladding carry Design Pressure (DP) ratings expressed as ASD pressures.

DP RATINGS

Residential construction

Low-rise and wood-framed homes commonly design to ASD, as do many prescriptive codes.

LOW-RISE

Retrofits & additions

Existing ASD-designed structures are simpler to extend by staying with ASD for consistency.

EXISTING

Jurisdictional preference

Some plan reviewers and building departments favor ASD — confirm local preference before you start.

CODE REVIEW

RUN THE NUMBERS

Generate ASD pressures with the 0.6 factor applied

WindLoadCalc.com produces ASCE 7 ASD and LRFD wind pressures, Component & Cladding results with DP ratings, and complete calculation reports.

Open the Calculators ASD ↔ LRFD Conversion

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