Bulk Water & Light Control: WRBs, Cladding, Roofing
Bulk water is the most common driver of costly failures. This session is about keeping liquid water out, managing drainage and drying, and respecting the long-term stress of sun/UV.
Potential agenda
- Intro (2 min): “Gravity never sleeps.” Bulk water wins when details are ambiguous.
- Desired outcome (6–8 min): Drainage-first thinking: shed, drain, dry
- Common failures (6–8 min): Flashing, transitions, and water that gets behind claddings
- Core concepts (6–8 min): Shingle-lap logic, capillarity, and durability under UV
- Takeaways (2–3 min): “Red flag” details you can spot in minutes
- Discussion (30–45 min): Prompts embedded below
Desired outcome
- Primary water-shedding surface that reliably sheds rain and snow.
- Secondary drainage plane (WRB/underlayment) that still works when the primary surface leaks.
- Clear drainage paths that let water out quickly (no “dead ends”).
- Drying strategy that matches climate, cladding type, and exposure.
- UV awareness: protect materials that degrade in sun during construction and over the long term.
Discussion prompt
- Reality check: Where does water go when (not if) it gets behind the siding or roofing?
Common failures
Recurring bulk-water failure patterns Often concentrated at transitions
- Bad shingle-lap logic: reverse laps that route water inward.
- Missing kick-out / diverters: roof runoff driven into walls.
- End dams and pan flashing gaps: windows/doors become funnels.
- Capillary wicking: materials in contact stay wet (no break).
- Trapped water: no drainage gap, no weeps, no exit route.
Examples (worked into failures)
Example — Roof-to-wall “dump zone”
High-volume runoff concentrates at one spot; without a kick-out or diverter, the wall sees chronic wetting.
Example — “Looks sealed” window install
Lots of sealant but no deliberate drainage path; when water gets in, it has nowhere to go except into framing.
Discussion prompt
- Most common miss: What flashing/detail mistake do you see most often (and why does it keep happening)?
Core concepts
Shed, drain, dry (in that order)
The WRB is not a magic membrane—its job is to direct water to daylight, repeatedly, for decades.
Transitions are the real assembly
If your detail set doesn’t make transitions explicit, the building will “choose” a pathway—usually the wrong one.
Capillarity is sneaky
Small gaps can wick water upward and inward. Provide capillary breaks and drainage gaps where needed.
UV is a durability load
Sun exposure during construction can matter. Specify and protect materials with clear exposure limits.
Takeaways
- Bulk water problems are usually detail logic problems, not “material” problems.
- Every cladding/roof system needs a clear drainage path to daylight.
- Assume water will get behind things—design for safe failure.
- Next (P08): we tackle the next biggest driver: air leakage and vapor control logic.
Further reading
Optional links will be added here (short, high-credibility readings that match the session focus).