How it works

The 3-2-10 rule prevents wind eddies from driving exhaust gases back down the chimney and ensures the flue rises above turbulent air at the roof line. Vertical termination components include a Class A or masonry chimney section, a storm collar that seals the pipe-to-flashing interface, a flashing assembly, and a rain cap or termination cap rated for the chimney type. The cap also keeps animals, debris, and water from entering the flue.

Improperly terminated chimneys exhibit chronic draft problems and downdrafts during high-wind conditions. Sweeps measure termination height during CSIA Level 2 inspections and document any non-conformance. Common findings include chimneys originally compliant with the 3-2-10 rule that became non-compliant after a roof addition raised the surrounding roof line.

DFW context

DFW two-story tract homes with chimneys on a lower roof section often violate the 3-2-10 rule when measured against the upper roof line, producing draft complaints from owners. North Texas wind regimes during spring storms exacerbate the problem. TSE evaluates roof geometry during Level 2 inspections and recommends extension when termination height fails to meet code, using Class A pipe extensions for prefab chimneys and brick courses for masonry.

Related terms

• [Horizontal termination](/glossary/horizontal-termination/)
• [Storm collar](/glossary/storm-collar/)
• [Single-flue cap](/glossary/single-flue-cap/)
• [Crown](/glossary/crown/)

Sources

• IRC 2021, Section R1003.9
• NFPA 211 (2024), Section 9.6
• IFGC 2021