Wind coefficient

From ASHRAE, 1989

Shielding class Description

Wind coefficient aw,
(L/s)2 / [cm4 · (m/s)2]

Wind coefficient aw,
(ft3/min)2 / [in4 · (mi/h)2]

Number of stories

Number of stories

One

Two

Three

One

Two

Three

1

No obstructions or local shielding.

0.000319

0.000420

0.000494

0.0119

0.0157

0.0184

2

Light local shielding; few obstructions, a few trees or small shed

0.000246

0.000325

0.000382

0.0092

0.0121

0.0143

3

Moderate local shielding; some obstructions within two house heights, thick hedge, solid fence, or one neighboring house

0.000174

0.000231

0.000271

0.0065

0.0086

0.0101

4

Heavy shielding; obstructions around most of perimeter, buildings or trees within 10 m in most directions; typical suburban shielding

0.000104

0.000137

0.000161

0.0039

0.0051

0.0060

5

Very heavy shielding; large obstructions; typical downtown shielding

0.000032

0.000042

0.000049

0.0012

0.0016

0.0018