Explain heat flow and thermal bridging as drivers of comfort, energy, and condensation risk. Reframe insulation around thermal continuity and surface temperature control, not R-value alone.
Builds on: P6 (four control layers), P8 (air/vapor) · Leads to: P10 (assemblies), P11 (HVAC) · Cross-series: A9 Financing & Risk
P/A bridge: What evidence would let lenders/appraisers recognize verified thermal performance as lower payment risk or lower ownership cost?
Core Concepts
Thermal bridges undermine comfort and durability. Can identify and mitigate bridges in common details.
Condensation risk depends on temperature gradients. Can evaluate assemblies for cold-surface risk, not R-value alone.
Continuous thermal control simplifies the whole system. Can prioritize continuity across transitions and penetrations.
Three Common Thermal Bridges
1. Rim joist / band area
Symptom: cold band at floor line, musty odor, condensation or mold behind finishes
Why: thin or discontinuous insulation leaves framing exposed to exterior temps; minor air leaks supply moisture
Mitigation: continuous exterior insulation across the band, or spray-foam the cavity and air-seal the connection
2. Slab edge
Symptom: cold floors at perimeter, complaints of "drafts" (actually radiant asymmetry)
Why: concrete slab conducts heat directly to exterior; no thermal break
Mitigation: insulate slab edge (exterior preferred); detail to prevent thermal bypass at foundation-to-wall
3. Window opening
Symptom: condensation on frame or adjacent drywall; cold spots on thermal scan
Why: framing around opening creates concentrated bridge; installation gap may lack insulation
Mitigation: insulate jamb/head/sill gaps; return insulation to frame; use thermally broken frames where possible
Condensation Rule of Thumb
Cold surface + moisture source + time = damage. Keep interior-facing surfaces above ~55-60 °F during heating season and maintain reasonable indoor RH (30-50%). Failures happen where thermal bridges drop surface temps below that threshold.