How to Install Curb Flashing for Leak-Free HVAC Ductwork
Properly installed curb flashing is essential for preventing leaks around HVAC ductwork penetrations. At SF Industries, we understand the importance of a watertight seal. In this guide, we’ll walk you through the steps to properly install curb flashing for HVAC ductwork to ensure long-term durability and performance.
What is Curb Flashing?
Curb flashing is a metal or waterproof barrier that protects the edges of a curb-mounted duct from water infiltration. It directs water away from the ductwork and integrates with the existing roofing system to ensure a weatherproof seal.
Tools and Materials Needed:
- HVAC duct and curb
- Roofing nails
- Roofing sealant
- Flashing kit (includes head flashing)
- Utility knife
- Roofing underlayment
- Measuring tape
- Hammer
- Screw gun
- Mastic sealant
Step-by-Step Installation Guide:

1. Prepare the Roof Opening
Ensure the roof opening is the correct size for the HVAC duct. Install the pre-built curb (typically made from wood or metal) securely to the roof deck. Apply a waterproof underlayment around the curb to add an extra layer of protection.
2. Secure the Head Flashing
The head flashing, or back pan, is placed at the top of the curb (the highest point on the slope). It should extend beyond the width of the HVAC duct to divert water away effectively. Apply roofing sealant along the edges before securing it with nails.
3. Apply Mastic for a Watertight Seal
At the rear of the duct where it meets the curb, apply a layer of mastic sealant. This will create a waterproof barrier, preventing moisture infiltration and ensuring a durable installation.
4. Inspect and Seal
Once all flashing components are installed, inspect the seams and fasteners for any gaps. Apply additional sealant where necessary to reinforce the waterproof barrier. Ensure the roofing material overlaps the flashing for proper water drainage.
Final Checks and Maintenance
After installation, conduct a water test by gently spraying the area with a hose to check for leaks. Regular maintenance, such as clearing debris and inspecting seals, will help prolong the life of your HVAC ductwork installation.
Trust SF Industries for Your Roofing and HVAC Needs
Proper curb flashing installation is essential for a leak-free HVAC ductwork penetration. At SF Industries, we provide high-quality materials and expert advice to ensure your projects meet the highest standards. Contact us today for more information on ductwork and roofing solutions!
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