Counterflashing is the metal that caps the top of a roof base flashing and keeps water from getting behind it — and when its reglet termination fails, the roof-to-wall joint leaks no matter how good the membrane is.
At a roof-to-wall joint, the membrane turns up the wall as base flashing, and counterflashing caps it — lapping over the top so water runs down the outside rather than behind it. The counterflashing is held to the wall in a reglet, a cut or joint in the masonry. When the reglet termination or the counterflashing lap is wrong, water gets behind the base flashing and the joint leaks, regardless of how sound the roof membrane itself is.
The failures are predictable and repeat across roofs. The sections below cover the four that ACE sees most — loose or short counterflashing, failed reglet terminations, sealant-dependent details, and base flashing coordination — and how to detail the termination so it lasts.
These challenges rarely stay in one silo: the same discipline runs through the same playbook behind through-wall flashing failures, lessons from kickout flashing failures, and our guidance on insulating glass unit seal failures, and it all ladders up to ACE’s broader design peer review and value engineering.
Loose or short counterflashing is a leading failure, because counterflashing that does not lap far enough over the base flashing, or that has pulled loose from the wall, lets water run behind the base flashing at the top. Counterflashing sized to lap the base flashing generously and secured mechanically keeps that lap intact.
Wind and thermal movement work loose counterflashing further over time, so mechanical attachment rather than reliance on friction or sealant alone is what keeps it in place through the seasons.
Because the lap is what makes the whole termination shed water, verifying its depth and attachment is central to a durable roof-to-wall joint.
Representative of the roof-to-wall termination failures ACE finds in investigation and peer-review work. Illustrative distribution, not a published statistic.
Failed reglet terminations are the vulnerable heart of the detail, because the counterflashing is held in a reglet — a cut or joint in the wall — and a shallow, poorly cut, or unsealed reglet lets water in at the very top of the assembly. A properly cut reglet with the counterflashing mechanically locked and the reglet sealed keeps that termination watertight.
Surface-mounted terminations that rely only on a bead of sealant against the wall are especially prone to failure, since they have no mechanical engagement to fall back on when the sealant ages.
Getting the reglet cut, set, and sealed correctly is what separates a termination that lasts decades from one that leaks within a few years.
A roof-to-wall joint with failed counterflashing lets water behind the base flashing at the top, and the roof leaks despite a sound membrane.
Detail the termination mechanically: a proper reglet, generously lapped and secured counterflashing, sealant only as backup, and coordinated base flashing.
Water runs down the outside of the joint, the base flashing stays protected, and the termination lasts for decades.
Sealant-dependent details are a recurring root cause, because a termination that relies on sealant as its primary line of defense inherits the sealant’s limited service life and will leak when that sealant ages, cracks, or loses adhesion. Sealant belongs as a secondary measure over a detail that sheds water mechanically, not as the primary barrier.
The distinction matters because sealant is easy to apply and looks finished, so sealant-only terminations pass a casual glance while carrying a short, hidden clock to failure.
Designing the termination to shed water by geometry and lap first, with sealant as backup, is what gives it a long, maintainable life.
Get the counterflashing and reglet reviewed for lap, mechanical attachment, and base-flashing coordination.
Schedule a consultationCall (866) 389-8883Base flashing coordination ties the counterflashing to the roof system, because the counterflashing and the membrane base flashing are two halves of one joint and must be detailed together, with the counterflashing lapping over the base flashing by the right amount. When the two are designed by different trades without coordination, the lap is often wrong.
The height of the base flashing and the position of the reglet have to be set together so the lap is correct and the base flashing is tall enough above the roof surface.
The most valuable move overall is treating the roof-to-wall termination as one coordinated detail — base flashing, counterflashing, reglet, and sealant in their proper roles — and verifying it in the field.
In ACE’s field work, most counterflashing and reglet failures problems trace back to a few recurring locations — Failed / shallow reglet, Loose or short counterflashing, and Sealant-only terminations — rather than the open field of the wall or roof. The cost of resolving them climbs by roughly an order of magnitude at each stage: a detail corrected during design costs a fraction of the same fix during construction, which is itself far cheaper than a repair once the facility is operating. That economics is why we push envelope decisions as early in the project as possible.
Specify a proper reglet, counterflashing lapped and mechanically secured, sealant as backup only, and coordinated base-flashing height.
Confirm reglet cut and sealing, counterflashing lap and attachment, and base-flashing coordination while accessible.
Where a roof-to-wall joint leaks, check the reglet, lap, and attachment before assuming the membrane failed.
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