Guided evidence worksheet
Attic frost: source opening versus frost field
Map frost before thaw, then compare the frost field with ceiling penetrations, exhaust routes and the coldest roof surfaces.
Reasoning guardrail
Separate the routes before choosing a repair.
The thickest frost is not automatically located directly above the air leak.
- Trigger
- Cold snaps after high indoor humidity produce the clearest evidence.
- Area
- Attic
- Provenance
- Original explanatory diagram, not a site photograph.
1. Freeze the evidence
What happened first?
2. Competing hypotheses
Record evidence for and against each route.
Interior air leakage through a ceiling bypass
Warm moist indoor air enters the attic through a penetration and spreads before freezing.
Evidence that raises fit
Evidence that lowers fit
Notes
Bathroom or dryer exhaust discharging into the attic
A fan or duct releases concentrated moisture directly into the roof space.
Evidence that raises fit
Evidence that lowers fit
Notes
Roof-space ventilation imbalance
Poor air distribution keeps some roof surfaces colder or wetter and amplifies another moisture source.
Evidence that raises fit
Evidence that lowers fit
Notes
3. Decision points
Change one condition at a time.
Is there a concentrated frost plume at an exhaust duct or fan route?
Yes: Treat the exhaust connection as a priority defect.
No: Map ceiling bypasses and pressure-driven air leakage.
Observed answer and evidence
Does the frost field align with one cold or poorly ventilated roof zone?
Yes: Assess ventilation distribution as an amplifier, not automatically the original source.
No: Focus on the moisture entry route and indoor humidity load.
Observed answer and evidence
Safety boundary
Stop rather than create a better clue.
- Do not enter an attic with unsafe access, damaged framing or exposed electrical hazards.
- Do not disturb suspect insulation or vermiculite without material identification.
5. Current conclusion
