Bulk Water Control

Rain, snow, and ice are the source. Climate, exposure, and site orientation determine how much water the building sees and how often. A sheltered single-storey in a dry climate and a three-storey windward wall in a wet climate face fundamentally different water loads.

💡 Design starts with the exposure, not the product. The same detail that works in one exposure can fail in another.

⚠️ Ignoring wind-driven rain exposure leads to under-designed walls that rely on sealant instead of drainage.

Explore in PF: Precipitation (B2b)

Precipitation becomes a load when it reaches the building surface. Roof geometry, wall height, and runoff concentration turn rain into specific volumes at specific locations. The load is not uniform — valleys, roof-to-wall intersections, and kickout locations see far more water than flat field areas.

💡 Loads concentrate at geometry changes. The most dangerous spots are where water from a large area is funneled to a small one.

⚠️ Treating all wall areas as equal exposure ignores the reality that 80% of water problems occur at 20% of the surface — transitions and concentration points.

Explore in PF: Bulk water load (C3a)

Water enters through gravity drainage failures, capillary action, wind-driven pressure differentials, and kinetic energy. Most bulk water intrusion is gravity-driven at transitions: laps that face the wrong way, flashing that doesn't extend far enough, or sealant joints that have opened. The mechanism matters because it determines what actually stops the water.

💡 Sealant is not a mechanism — it is a temporary gap-filler. The mechanism that stops water is overlap, drainage, and pressure management.

💡 Understanding the entry mechanism tells you whether the fix is a material, a detail, or a sequence change.

⚠️ "It leaked" is not a diagnosis. Was it gravity? Capillary? Wind-driven? The answer changes the fix entirely.

Explore in PF: Moisture mechanisms (E2c)

When water passes the control layers, it causes visible failure modes: rot, mold, staining, structural damage, and coating failures. These are the symptoms. They appear at transitions (roof-to-wall, window heads/sills, penetrations, deck ledgers) because that's where continuity is hardest to achieve and where multiple trades overlap.

💡 Failures are predictable. They cluster at transitions, not in field areas. Designing transitions explicitly is higher leverage than upgrading field materials.

⚠️ Callbacks from water intrusion are among the most expensive in residential construction — often discovered late and requiring extensive tearback.

Explore in PF: Envelope failures (F3)

The control layer strategy for bulk water: primary shedding surface (roofing, cladding), secondary drainage plane (WRB, underlayment), flashings at transitions, and a drying path for water that does get in. Control must be continuous from roof to foundation. The control is only as good as its weakest transition.

💡 Good water control is a drainage system, not a seal. Design for "water will get in somewhere" and give it a path out.

💡 Sequencing is part of the control. Shingle-lap logic and install order determine whether the drainage plane actually works.

⚠️ A perfect WRB with one bad lap at a roof-to-wall transition can cause more damage than a mediocre WRB with correct laps everywhere.

Explore in PF: Water Control (G4)

1) Roof-to-wall runoff management

• Kick-out / diverter at roof-to-wall ends where runoff would otherwise dump into siding.
• Shingle-lap continuity from roof underlayment to wall WRB so water always overlaps outward.
• Drainage gap + exit: if water gets behind cladding, it has a clear path out.
• Clear scope: roofer vs siding vs WRB installer — who installs the diverter and who verifies it?

2) Window/door opening with safe drainage

• Sill pan logic: end dams and slope to daylight (or to a deliberate drainage path).
• WRB integration: head flashing and WRB shingled correctly (no reverse laps).
• Air barrier continuity: opening-to-air-barrier connection is specified and buildable.
• Thermal bridge awareness: plan exterior insulation returns/reveals where applicable.

Bulk water control is incomplete without addressing ground moisture and soil gas. Even in dry climates, intermittent wetting and capillary movement can drive chronic moisture problems.

• Capillary breaks: between footing/foundation and framing; under slabs (vapor retarder + granular layer as appropriate).
• Drainage & grading: keep water away from foundations and provide a path for it to leave.
• Radon strategy: sub-slab collection + vent path; seal obvious openings as part of the air control strategy.
• Continuity mindset: connect below-grade water/air strategies to above-grade control layers.

• Shingle-lap audit: follow water from roof to wall to opening — are there any reverse laps?
• Kick-outs present: any roof-to-wall "dump zones" without diverters?
• Drainage exits: where does water leave the wall system (weeps, gaps, flashings)?
• Window sills: is there an end dam / pan strategy, or is sealant doing all the work?
• Penetrations: are they flashed to shed and drain, or just caulked?
• Construction sequencing: are WRBs/tapes protected from overexposure to UV and weather?

Tip: assign each interface an owner (install) and an owner (verify). If both are "everyone," it's no one.