TL;DR
Counterflashing is the upper flashing layer, let into a mortar joint reglet or surface-mounted on masonry and sealed, that laps down over the base flashing so water running down a chimney or wall sheds past the joint instead of behind it. The two-piece system exists because a roof and a chimney move independently; rigidly tying one flashing to both guarantees an eventual tear.
What it means
Counterflashing is the upper flashing layer, let into a mortar joint reglet or surface-mounted on masonry and sealed, that laps down over the base flashing so water running down a chimney or wall sheds past the joint instead of behind it. The two-piece system exists because a roof and a chimney move independently; rigidly tying one flashing to both guarantees an eventual tear. Loose, caulk-smeared, or missing pieces around chimneys are among the most common findings in roof inspections and the source of many mystery ceiling stains.
Where it sits in the glossary
Counterflashing is part of the Trade jargon group inside the ProFix Directory glossary. Browse every term in this category from the glossary index.
Why Ohio homeowners should know it
This is a term Ohio homeowners encounter when reading contractor quotes, hiring paperwork, or inspection reports. Understanding it well enough to ask one good follow-up question is usually all the protection a homeowner needs.
ProFix Directory keeps definitions short on the index page and saves the longer context — Ohio-specific rules, where the term comes from, and which ProFix tools touch it — for these per-term pages so the term is easy to cite and easy to share.
ProFix tools that touch this term
See also
License: CC-BY-4.0 — quote freely with attribution to ProFix Editorial Team / ProFix Directory.