Heat Flow, Thermal Bridging & Condensation Management
Thermal control is not just “energy.” It’s also comfort and moisture risk control. This session focuses on thermal bridges, surface temperatures, and how condensation risk shows up in real buildings.
Potential agenda
- Intro (2 min): “Cold surfaces create moisture problems—and complaints.”
- Desired outcome (6–8 min): Warmer surfaces, fewer bridges, predictable condensation control
- Common failures (6–8 min): Bridges, bypasses, and the “condensation plane” moving to the wrong place
- Core concepts (6–8 min): Effective vs nominal R, surface temps, and safe assemblies
- Takeaways (2–3 min): High-payoff bridge fixes and “red flags”
- Discussion (30–45 min): Prompts embedded below
Desired outcome
- Comfortable interior surfaces (floors, walls, window perimeters) in winter.
- Reduced thermal bridging at common bridge locations (rim joists, slab edges, balconies, headers, fasteners).
- Condensation control by keeping vulnerable layers warm enough and/or able to dry.
- Performance that matches expectations (avoid “I paid for R-XX but it doesn’t feel like it”).
Discussion prompt
- Worst bridge: In your experience, what detail causes the biggest comfort complaints?
Common failures
Thermal/condensation failure patterns Often misdiagnosed as “HVAC problems”
- Cold corners / cold bands: thermal bridges or missing insulation continuity.
- Condensation at window perimeters: cold surfaces + interior humidity + airflow patterns.
- Roof/ceiling moisture: thermal bypass + air leakage + cold sheathing.
- Ice dams: heat loss + roof temperature gradients + snow melt/refreeze cycle.
Examples (worked into failures)
Example — Rim joist cold band and odor/musty spots
A thin or discontinuous thermal layer at the rim creates cold surfaces; minor air leakage supplies moisture; mold risk increases locally.
Example — “We insulated more and now the sheathing is wet”
Changing insulation configuration moves the condensing surface. If the assembly can’t dry, moisture accumulates.
Discussion prompt
- Condensation stories: Where have you seen condensation show up (windows, roofs, walls, basements)? What was the root cause?
Core concepts
Effective R beats nominal R
Real comfort and energy performance depend on continuity. Thermal bridges can dominate the “effective” result.
Surface temperature is the “felt” metric
Occupants feel radiant imbalance and cold surfaces. This is often misattributed to furnace sizing.
Condensation control is geometry + materials
Where is the cold surface, and can it dry? Build the assembly so the answer stays safe over time.
Bridges concentrate risk
Even if the average wall is “fine,” localized cold spots can create localized failures.
Takeaways
- Thermal control improves comfort, reduces condensation risk, and saves energy.
- Thermal bridges are often the hidden reason assemblies underperform.
- Think in surfaces: “What will be the coldest surface, and is it safe?”
- Next (P10): we apply this to real assemblies and transitions—walls, roofs, windows, and doors.
Further reading
Optional links will be added here (short, high-credibility readings that match the session focus).