THERMAL BRIDGING VS AIR LEAKAGE — TWO-PATH READING RECORD
Use with the actual drawing or report reference. Original teaching cases, not an inspected building.

LOCATION RECORD 1
Location / drawing / report / revision:
Thermal path: insulation, conductive crossing, relevant geometry:
Air path: air-control boundary, opening, connection across enclosure:
Stated temperature conditions:
Stated pressure and mechanical/weather conditions:
Documented or observed evidence:
Unresolved hypothesis:
Additional detail, assessment or test scope needed:
One focused question:
What the answer changes:

LOCATION RECORD 2
Location / drawing / report / revision:
Thermal path: insulation, conductive crossing, relevant geometry:
Air path: air-control boundary, opening, connection across enclosure:
Stated temperature conditions:
Stated pressure and mechanical/weather conditions:
Documented or observed evidence:
Unresolved hypothesis:
Additional detail, assessment or test scope needed:
One focused question:
What the answer changes:

EVIDENCE COMPARISON
Observation | Possible mechanism | Evidence needed | Question | Scope limit
_____ | _____ | _____ | _____ | _____
_____ | _____ | _____ | _____ | _____
_____ | _____ | _____ | _____ | _____
_____ | _____ | _____ | _____ | _____
_____ | _____ | _____ | _____ | _____

THERMAL BRIDGING VS AIR LEAKAGE
Question | Thermal bridge | Air leakage
Mechanism | A locally easier heat-flow path through or around the thermal insulation. | Air travels through a connected path under a pressure difference.
What drives the illustrated flow | A temperature difference; the example concerns conduction through a solid. | A pressure difference, which can come from wind, buoyancy or mechanical systems.
Does air have to cross the enclosure? | No. A conductive connection can transfer heat while its air-control junction stays sealed. | Yes, for the enclosure-leakage case discussed here: the path connects across the enclosure.
Continuity to inspect | Insulation, conductive crossings and the geometry of the whole junction. | The air-control system, including joints, penetrations and connections.
What the other improvement leaves open | Reducing a conductive bridge does not establish airtightness. | Reducing leakage does not remove an unchanged conductive bridge.

EVIDENCE AND ITS SCOPE
Evidence | Supports | Leaves open | Question
A section or junction detail | Documents intended layers, geometry and connections at its cut. | Does not verify concealed installation or actual performance. | Which drawing and revision continue the thermal and air-control paths?
A thermal calculation | Estimates heat flow or surface conditions for a modeled assembly and assumptions. | Does not measure air leakage through the installed enclosure. | What geometry, material inputs and boundary conditions were used?
An infrared survey | Can help identify patterns for further investigation; consultants may use it during leakage diagnostics. | A pattern alone does not establish the mechanism or every hidden opening. | What conditions, location and additional investigation support the interpretation?
A whole-building airtightness test | Measures airflow and pressure across the enclosure under the stated preparation and method. | The total alone does not locate each leak or measure thermal bridging. | What boundary, openings, pressure/flow data and reporting method are included?
A component or local investigation | Describes the tested product, junction or location under its own scope. | Does not establish that every interface or the whole building behaves identically. | Which configuration was examined, and which adjacent connections remain outside the scope?

EIGHT PRACTICE QUESTIONS
Case 1: A conductive metal connection crosses the insulation. Its air-control junction is described as sealed. Must air leak through it for a thermal bridge to exist?
Your answer and reason:

Case 2: A gap is drawn in the air-control layer, but the sketch does not show whether it connects all the way to the occupied space. Has an enclosure leakage route been established?
Your answer and reason:

Case 3: Two spaces have different temperatures. No connected opening between them is shown. Does that temperature difference alone prove air leakage?
Your answer and reason:

Case 4: A survey shows a colder region near a floor edge. Can that pattern alone distinguish a conductive bridge from air leakage?
Your answer and reason:

Case 5: In a fictional comparison under matching test conditions, sealing a joint reduces measured airflow. A metal connection crossing the insulation is unchanged. Is the conductive path necessarily removed?
Your answer and reason:

Case 6: A whole-building airtightness report meets its stated project target. Does that result prove there are no thermal bridges at the facade?
Your answer and reason:

Case 7: An insulation product has a declared thermal resistance. Is that label enough to establish the airtightness of a wall assembled with it?
Your answer and reason:

Case 8: A rainscreen cavity is intentionally ventilated outside a documented air-control boundary. Is air movement in that cavity automatically leakage into the occupied building?
Your answer and reason:

ANSWERS AND EXPLANATIONS
Case 1: No. Heat can conduct through the solid connection while the air-control junction remains sealed.
The mechanisms have different prerequisites. A temperature difference can drive heat through a conductive solid; enclosure air leakage needs a pressure difference and a connected air path. The fictional description supports a possible thermal bridge without establishing leakage. Actual thermal significance and airtightness still need the assembly’s own evidence.

Case 2: Not yet. Trace the connected path and identify the relevant pressure difference.
An isolated gap is a clue to investigate, not a complete flow route. It may connect into another layer or an exterior cavity. Find the adjoining details and the intended air-control boundary. Airflow needs both connected points and a pressure difference; do not extend a blue arrow through unknown construction to finish the sketch.

Case 3: No. It can drive heat transfer without providing an air-flow path.
Temperature differences and buoyancy can contribute to pressure conditions, but an air-flow connection is still required. Heat may conduct through materials or transfer by other mechanisms without air crossing the enclosure. Keep the heat-flow question separate from the existence and continuity of a leakage route.

Case 4: No. Treat the pattern as evidence needing context and further investigation.
A cold region can guide a question about thermal geometry, air movement or other conditions. The image alone does not supply the whole assembly or a pressure/flow measurement. Review the matching detail and survey conditions. Where leakage is suspected, appropriate localized investigation and testing can supply additional evidence.

Case 5: No. The leakage improvement does not remove an unchanged solid thermal path.
The stated test result concerns air flow. A conductive crossing can remain even after its surrounding joint becomes tighter. Evaluate the thermal geometry separately rather than converting an airflow result into a thermal rating. The comparison is an invented learning case, not a report of tested construction or a promise of energy savings.

Case 6: No. An airtightness result is not a thermal-bridge assessment.
The test quantifies air leakage within its boundary and conditions. Thermal bridges concern heat-flow paths through materials and geometry. A building can have low measured leakage while conductive crossings remain. Read the thermal assessment and relevant interface details separately, keeping each result within its own scope.

Case 7: No. Check the actual air-control system and its connections.
A product’s thermal property does not describe every joint, penetration or adjacent layer. Some specified materials can perform more than one function, but the complete system still needs continuity and suitable evidence. Do not assign air-control performance from the insulation label alone or generalize one product’s properties to all insulation.

Case 8: No. Locate the flow relative to the occupied-space air-control boundary.
Deliberate exterior-cavity ventilation and uncontrolled enclosure leakage are different routes. Check whether a connected path crosses the air-control system into the conditioned space. The cavity’s drainage and ventilation have their own documented roles. A drawing-reading exercise should identify those roles rather than treating every visible opening as an instruction to seal it.

SOURCE REFERENCES
John Straube: BSD-011 — Thermal Control in Buildings, 2011
https://buildingscience.com/documents/digests/bsd-011-thermal-control-in-buildings
John Straube: BSD-014 — Air Flow Control in Buildings, 2007
https://buildingscience.com/documents/digests/bsd-014-air-flow-control-in-buildings
John Straube: BSD-040 — Airtightness Testing in Large Buildings, 2014
https://buildingscience.com/documents/digests/bsd-040-airtightness-testing-in-large-buildings