Failure simulations
Step through the physical route from trigger to symptom, then see what evidence would support or weaken the pathway.
Warm indoor air becomes attic frost
Air leakage carries indoor moisture into a cold attic where it freezes on roof sheathing and later melts.
- Warm humid room air reaches ceiling penetrations.
- Pressure and buoyancy move air into the attic.
- Cold roof sheathing drops below freezing.
Wind-driven rain passes a flashing interface
Rain pressure and direction expose a roof or wall junction that remains dry during calm vertical rain.
- Wind redirects rain upslope or sideways.
- Water reaches a vulnerable flashing edge.
- It follows underlayment, framing or fasteners.
Bathroom exhaust discharged into the attic
A disconnected or intentionally terminated duct delivers concentrated warm moisture to cold attic materials.
- Shower raises indoor moisture.
- Fan moves moisture into the duct.
- The duct ends or leaks inside the attic.
Chimney flashing admits side-driven rain
Step flashing, counterflashing or masonry interfaces allow water to enter during particular wind directions.
- Rain strikes the upslope or side face.
- Water reaches a flashing or mortar defect.
- The chimney chase redirects the path.
Ice dam backs meltwater under roofing
Snowmelt flows to a cold eave, refreezes and creates a reservoir that can move under roof coverings.
- Heat loss melts snow upslope.
- Meltwater reaches a cold eave.
- Ice accumulates and blocks drainage.
Wet insulation hides a roof leak after rain stops
Insulation stores water and releases it slowly, separating the visible drip from the weather event.
- Rain enters the roof assembly.
- Insulation absorbs and spreads water.
- The storm ends.
Wind washing reduces insulation performance at the eave
Outdoor air moves through or over low-density insulation, cooling the ceiling edge and altering attic moisture patterns.
- Wind enters near the eave.
- Air passes through exposed insulation.
- Effective thermal resistance falls.
