What does GCp represent in C&C?

GCp is the external pressure coefficient for components and cladding, varying by roof/wall zone, effective wind area, and geometry per ASCE 7-22 Chapter 30 tables.

Do I need an importance factor I?

ASCE 7-22 uses risk-category-dependent wind speed maps (Vu). An explicit wind importance factor is not typically applied for Vu-based design.

Which wind speed should I enter?

Enter the ASCE ultimate design wind speed Vu for your site and risk category. Obtain this from official maps or jurisdictional tools.

How is Kz computed here?

This tool uses the ASCE power-law proxy Kz = 2.01·(z/zg)^(2/α), clamped near ground and at zg, with typical α and zg for Exposure B/C/D.

What enclosure class should I use?

Select Enclosed (±0.18), Partially Enclosed (±0.55), or Open (0.0) per ASCE enclosure definitions; internal pressure can control in some cases.

Are results suitable for permit drawings?

Use this as an engineering aid. Always verify against the official ASCE 7-22 provisions and your project’s governing code and authority.

ASCE 7-22 Wind Load Calculator (Components & Cladding)

Overview

This calculator implements the standard Components & Cladding (C&C) wind pressure equation from ASCE 7-22. It computes the velocity pressure at height \(z\), the internal velocity pressure at mean roof height \(h\), and combines them with user-specified \(G C_p\) and enclosure-based \(G C_{pi}\) to produce governing net design pressures.

Data Source & Methodology

Authoritative Data Source: ASCE 7-22, Chapter 30 – Components and Cladding. Also consult the Engineering Express – Wind Loads per ASCE 7 guide and your jurisdictional amendments.
All calculations strictly follow the formulas and data structures provided by this source.

The Formulas Explained

Velocity pressure (US customary): \\( q_z = 0.00256\\,K_z\\,K_{zt}\\,K_d\\,V^2 \\) [psf]

Velocity pressure (SI): \\( q_z = 0.613\\,K_z\\,K_{zt}\\,K_d\\,V^2 \\) [kPa]

Components & Cladding net pressure: \\( p = q_z\\,G C_p - q_i\\,G C_{pi} \\)

Internal velocity pressure: \\( q_i = q_{h} \\) (evaluated at mean roof height \(h\)).

Exposure profile proxy: \\( K_z = 2.01\\left(\\tfrac{z}{z_g}\\right)^{\\tfrac{2}{\\alpha}} \\) (bounded near ground and at \(z_g\)).

Glossary of Inputs & Outputs

\(V\): Ultimate design wind speed (mph or m/s).
Exposure: Terrain category (B/C/D) influencing \(K_z\).
\(z\): Height of interest for C&C (ft or m).
\(h\): Mean roof height for internal pressure (ft or m).
\(K_{zt}\): Topographic factor (≥ 1.0 when speed-up applies).
\(K_d\): Directionality factor (often 0.85).
Enclosure: Determines \(G C_{pi}\) (Enclosed ±0.18, Partially Enclosed ±0.55, Open 0.00).
\(G C_p\): External coefficient (from ASCE 7-22 C&C tables by zone/effective area).
\(q_z, q_i\): Velocity pressures at \(z\) and \(h\).
\(p_{net}\): Net design pressure, reported for both signs of \(G C_{pi}\) and governing case.

How It Works: A Step-By-Step Example

Given: Units US, \(V_u = 140\) mph, Exposure C, \(z=30\) ft, \(h=30\) ft, \(K_{zt}=1.0\), \(K_d=0.85\), Enclosed (\(G C_{pi} = \pm 0.18\)), \(G C_p = -1.3\).

Compute \(K_z\) with Exposure C proxy (\(\alpha=9.5\), \(z_g=900\) ft): \(K_z \approx 2.01(30/900)^{2/9.5}\).
Compute \(q_z = 0.00256 \cdot K_z \cdot 1.0 \cdot 0.85 \cdot 140^2\) psf.
Compute \(q_i = q_h\) (use \(h=30\) ft with same exposure).
Compute \(p = q_z(-1.3) - q_i(\pm 0.18)\). Report both signs and the governing absolute value.

Frequently Asked Questions

Where do I find \(G C_p\)?

In ASCE 7-22 Chapter 30 tables for C&C, by building geometry, zone (e.g., roof edges/corners), and effective wind area. Enter the appropriate value directly.

Does this output serviceability or strength-level pressures?

Pressures are computed from ultimate wind speeds \(V_u\); design combinations must follow your structural methodology. Refer to ASCE 7-22 load combos and local practice.

How accurate is the \(K_z\) proxy?

It follows the widely used power-law representation with typical \(\alpha\) and \(z_g\) by exposure. Always reconcile with official tabulated/standard values where required.

Should I input importance factor \(I\)?

For Vu-based design in ASCE 7-22, wind speed already reflects risk category; an explicit \(I\) is typically not applied.

Can I use SI units?

Yes. Switch to SI to use \(q_z = 0.613 K_z K_{zt} K_d V^2\) [kPa]. Ensure your inputs/interpretation match units.

Authorship & Review

Tool developed by Ugo Candido. Content verified by CalcDomain Engineering.
Last reviewed for accuracy on: September 22, 2025.