Learn how proper HVAC curb installation protects commercial roofing systems in Colorado and Georgia. Get step-by-step tips and code insights from experts.

How to Install HVAC Curbs on Commercial Roofs the Right Way

Commercial Roofing
June 01, 2025•3 min read

Commercial Roofing HVAC Curb Installation: What Every Property Owner Should Know

Installing HVAC equipment on a commercial roof isn’t just about setting a unit and sealing around it. The real success of this job depends on the proper installation of HVAC curbs—the structural framing that supports rooftop units and keeps the roof watertight.

Here’s a breakdown of what you need to know if you're managing a commercial building in Colorado or Georgia.

What Is an HVAC Curb?

An HVAC curb is a raised frame—usually steel or aluminum—mounted on a commercial roof. It supports HVAC units and creates a stable, level base that protects the roofing system from leaks and structural stress.

Why it matters:

  • Prevents water intrusion

  • Provides structural support

  • Ensures correct airflow and duct alignment

  • Maintains roofing system warranties

Key Factors in HVAC Curb Installation

1. Curb Type and Sizing

The HVAC curb must be designed to match the size, weight, and layout of your HVAC unit. It also needs to fit your roof type—whether it's a TPO, modified bitumen, or metal system.

  • For metal roofs, curbs often require custom fabrication and built-in cricket details for drainage.

  • On flat roofs, the curb should be insulated and flashed into the roofing membrane per manufacturer guidelines.

2. Structural Reinforcement

HVAC curbs must transfer the load to structural members—like joists or purlins—not just deck panels. Reinforcement may be required beneath the curb, especially for heavier units.

According to the MCA and IBC 2021 codes, roof decks must support both dead loads (like equipment weight) and live loads (snow, maintenance traffic).

3. Waterproofing and Flashing

This is the most critical part. Poor flashing around the curb is one of the top sources of roof leaks.

Best practice:

  • Install a base sheet or membrane up the sides of the curb at least 8"

  • Use counterflashing or a curb cap to protect the top

  • Ensure full tie-in to the existing roofing system

Use high-temp ice and water shield in cold climates like Colorado for extra protection.

4. Slope and Drainage

HVAC curbs must be installed level, but the roof needs slope to drain water. A curb cricket is often added behind the curb to divert water around it.

Colorado and Georgia Code Considerations

Both states follow the International Building Code (IBC), which requires:

  • Mechanical units to be supported to prevent vibration and uplift

  • Roof penetrations to be properly sealed and flashed

  • Compliance with wind uplift and snow load requirements (especially in Colorado)

Always check with your local building department. In Denver, for example, additional snow load reinforcement may be required.

FAQs

How high should an HVAC curb be on a commercial roof?
Minimum height is usually 8", but 12" or more is recommended in snowy areas like Colorado.

Can HVAC curbs be installed on metal roofs?
Yes, but they must be reinforced and sealed properly to prevent leaks. Custom crickets are often required.

What’s the most common reason for HVAC curb leaks?
Improper or missing flashing and poor membrane tie-in are the top causes.

Need HVAC Curb Work on Your Commercial Roof?

If you're in Colorado or Georgia, trust the team at Roof Nuts. We install and flash HVAC curbs to code—no shortcuts, no leaks.

Call us today:

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