Water management and enclosure basics · Lesson 4 of 4

Water management and enclosure basics: defects, verification and case study

The recurring defects at roof-to-wall joints and edges, the number checks that catch them, the signs water leaves and why cladding can hide them, and a constructed case study worked through the trace-the-water method.

You will be able to: Diagnose common water-path defects such as a reverse lap, a missing kickout, sealant-only details and tight siding, explain corrective options, and document evidence for a reviewer.

11 min · 11 slides · 7 questions

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Slide 1 of 11

Defect: the reverse lap

The DOE and PNNL drainage-plane guide says flashings go on before the drainage plane so the wrap does not end up in a reverse lap.

The PNNL step flashing guide warns that a piece lapped under the piece beneath it can inject water into the wall rather than deflect it.

Fix: lap the wrap over the flashing, never tuck it behind.

Upper over lower in the first two details: a wrap tucked behind the flashing leads water in. The third shows siding held off the roof, as the DOE and PNNL guide expects. Blue arrows are water that stays out; red arrows are water going in. Not to scale.

Sources

Drainage Plane Behind Exterior Wall Cladding (last updated 2020-09-09) - U.S. Department of Energy / Pacific Northwest National Laboratory, Building America Solution Center
Step and Kick-Out Flashing at Roof-Wall Intersections (last updated 2020-09-14) - U.S. Department of Energy / Pacific Northwest National Laboratory, Building America Solution Center

Glossary

Reverse shingling: Laying a drainage-plane piece or wrap under the flashing it should lap over, so water running down is led behind the flashing and into the wall. The DOE and PNNL guide says to install flashings first to avoid it.
Integrated flashing: A flashing connected to the roof and wall drainage planes shingle-fashion so water passes from layer to layer without a break. The PNNL guide says a diverter that is not integrated with the water-resistive barrier can do more harm than good.
Sealant-only detail: A joint that keeps water out only because of a bead of sealant, with no lap or slope doing the work. AFS Division 07 notes say such a detail is not sound, because sealant backs up a lap rather than replacing it.
Wicking: Water drawn upward through tiny cracks and holes between close surfaces. EPA notes the closer together the surfaces are, the higher water wicks, so a gap or a drip at an edge breaks the path.