What is the value of Kd for buildings?

For buildings, Kd is 0.85 for both the main wind force resisting system (MWFRS) and components and cladding (C&C), read directly from ASCE 7 Table 26.6-1. Round and axisymmetric shapes such as round chimneys, tanks, and circular domes use Kd of 1.0, because their loading is direction-independent and no reduction applies.

Why is the Kd factor less than 1.0?

Kd is below 1.0 because two peaks seldom coincide. The design wind speed assumes the peak gust can arrive from any direction, but the worst pressure coefficient occurs only over a narrow band of approach angles. Requiring both extremes together would over-design the structure, so ASCE 7 applies Kd to reflect that reduced joint probability.

How is Kd used in the velocity pressure equation?

Kd is one factor in the velocity pressure that drives every wind load: qz = 0.00256 times Kz times Kzt times Kd times Ke times V squared. You apply Kd as a given multiplier rather than re-deriving it, since it is already calibrated into the ASCE 7 load combinations. For buildings you simply insert 0.85.

Do I always apply Kd of 0.85 to wind loads?

Not always. Kd is 0.85 for buildings (MWFRS and C&C), arched roofs, freestanding walls, signs, and most trussed towers, but it varies by structure type in ASCE 7 Table 26.6-1. Square chimneys and tanks use 0.90, hexagonal use 0.95, and round or octagonal shapes and circular domes use 1.0. Always read the value for your specific structure.

ASCE 7-22 · TABLE 26.6-1 · DESIGN METHODS

The Wind Directionality Factor Kd

Q: What is the Kd factor in ASCE 7?

Kd is the wind directionality factor in ASCE 7. It is a code-built reduction that accounts for the low probability that the worst wind direction lines up with a structure's worst aerodynamic loading at the same instant. For buildings it equals 0.85, so it lowers the calculated wind load rather than increasing it.

A code-built reduction that accounts for the slim chance the worst wind direction lines up with a structure's worst aerodynamic loading.

0.85BUILDINGS MWFRS & C&C

26.6-1ASCE 7 TABLE

< 1.0WHY IT REDUCES LOAD

THE CORE IDEA

Direction rarely aligns with worst-case

Peak gusts can blow from any heading. The orientation that produces a structure's peak pressure coefficient is only one of many.

Kd captures that mismatch in probability with a single multiplier — for buildings, 0.85.

WHY Kd IS LESS THAN 1.0

Two peaks seldom coincide

The design wind speed assumes the peak gust can come from any direction. The peak pressure coefficient (worst Cp) occurs only for a narrow band of approach angles. Requiring both extremes at once would over-design the structure, so ASCE 7 applies Kd to reflect the reduced joint probability that the peak wind direction coincides with the peak aerodynamic loading.

Kd is already calibrated into the load combinations — you apply it; you do not re-derive it.

TABLE 26.6-1 · VERIFIED VALUES

Kd by structure type

Read the directionality factor straight from the table for your structure and cross-section.

Structure type	Cross-section / detail	Kd
Buildings — MWFRS	Main wind force resisting system	0.85
Buildings — C&C	Components & cladding	0.85
Arched roofs	—	0.85
Chimneys, tanks & similar	Square	0.90
Chimneys, tanks & similar	Hexagonal	0.95
Chimneys, tanks & similar	Octagonal	1.0
Chimneys, tanks & similar	Round	1.0
Solid freestanding walls, signs & rooftop equipment	—	0.85
Open signs & single-plane open frames	—	0.85
Trussed towers	Triangular, square, rectangular	0.85
Trussed towers	All other cross-sections	0.95
Circular domes	—	1.0

Round and axisymmetric shapes reach 1.0 — their loading is direction-independent, so no reduction applies.

THE EQUATION

Where Kd fits in velocity pressure

Kd is one factor in the velocity pressure that drives every wind load.

q_z = 0.00256 · K_z · K_zt · K_d · K_e · V²

K_z

Velocity pressure exposure coefficient (height & terrain).

EXPOSURE

K_zt

Topographic factor for hills, ridges & escarpments.

TERRAIN

K_d

Wind directionality factor — 0.85 for buildings.

THIS PAGE

K_e

Ground elevation factor for air density.

ELEVATION

V²

Basic design wind speed, squared.

WIND SPEED

0.00256

Unit constant for q_z in psf with V in mph.

CONSTANT

KEEP GOING

Apply Kd in a full calculation

See how directionality flows through directional procedures and the complete ASCE 7 method.

Run it in the calculator More on Kd

The Wind Directionality Factor Kd

Direction rarely aligns with worst-case

Two peaks seldom coincide

Kd by structure type

Where Kd fits in velocity pressure

K_z

K_zt

K_d

K_e

V²

0.00256

Apply Kd in a full calculation

Wind Directionality Factor Guide

Design Methods (ASCE 7)

Complete Wind Load Guide