BPI BA-T cheat sheet

Heat flows from warmer to colder across all three modes: conduction (solid), convection (fluid/air), radiation (electromagnetic); total envelope load is the sum of parallel paths.

Conduction formula: Q = U x A x ΔT, where U is assembly conductance (1/R), A is area, and ΔT is indoor-outdoor temperature difference.

Assembly R-value is the sum of layer resistances plus surface films; adding a low-permeance layer inside the insulation moves the dew point and raises condensation risk.

Psychrometrics: relative humidity = (vapor pressure / saturation vapor pressure) x 100; dew point is the temperature at which air reaches saturation at constant moisture content.

Air leakage carries both sensible and latent load; a 1-inch hole can move more moisture than a large diffusion area, so air sealing precedes insulation decisions.

Stack effect drives upward air movement in winter (warm air buoyant) and downward in summer; neutral pressure level shifts with envelope leakage distribution.

Thermal bridging through studs, slabs, and balcony penetrations lowers effective R-value; parallel-path method: U_eff = f_frame x U_frame + f_cavity x U_cavity.

Moisture balance: wetting (rain, vapor diffusion, air leakage, ground moisture) versus drying (ventilation, diffusion, drainage); a durable assembly keeps drying capacity greater than wetting.

Pre-assessment scope defines building type, vintage, occupancy, HVAC systems, and known complaints; scope drives which instruments and sampling plan are used.

Site walk sequence: exterior (drainage, envelope, penetrations) then interior (moisture, air leakage, HVAC, occupant patterns) to avoid missing systemic causes.

Moisture meters: pin-type reads surface conductivity; pinless reads relative moisture via capacitance; both require material-specific calibration and confirmation with a second method.

Blower door test setup requires all exterior openings closed, interior doors open or pressure-balanced, combustion appliances off, and baseline pressure recorded before the test.

Sampling plan should record location, time, instrument, method, and calibration status; chain of custody matters for any data used in a report or dispute.

Visual inspection hierarchy: water entry points first, then storage and distribution (HVAC, plumbing), then occupant-generated moisture sources.

Occupant interviews capture complaint timing, weather correlation, and recent changes (renovations, new appliances) that explain data patterns.

Data quality checks: repeat readings, compare instruments, flag outliers, and note environmental conditions (temperature, wind, stack effect) that bias results.

Blower door: CFM50 divided by conditioned volume gives ACH50; divide by 60 for ACH natural estimate only with a documented leakage curve, not a fixed factor.

Pressure diagnostics use a manometer referenced to outside; a zone reading near the house pressure indicates a connected zone, while near zero indicates isolation.

Infrared thermography requires a minimum ΔT (typically 10°F or more) between inside and outside to resolve thermal anomalies; solar gain and wind create false positives.

Duct leakage testing (Delta Q or duct blaster) measures system leakage at 25 Pa; results are reported as CFM25 and as a percentage of system airflow.

Combustion safety: measure CO in flue and ambient air, draft pressure, and spillage; a draft reading that reverses under worst-case conditions indicates a hazard.

Pressure pan testing: measure pressure difference across a register with the house depressurized; higher readings indicate greater duct leakage to outside.

Tracer gas and zone pressure testing isolate pathways; a door or hatch that changes zone pressure when opened confirms a connection.

Instrument calibration: manometers zeroed before each test, anemometers checked against known flow, and all readings recorded with units and conditions.

Field notes should record date, time, weather, instrument model and serial, calibration date, test conditions, and exact measurement locations.

Photos require scale references and orientation notes; label each image with location, direction, and what it documents.

Report structure: objective and scope, methods, findings with data, limitations, conclusions, and recommended actions with priority.

Distinguish measured facts from interpretation; label estimates as estimates and cite the instrument and method behind every number.

Record negative results (tests that found nothing) because absence of evidence informs the conclusion and protects against later disputes.

Units and conversions must be explicit: Pa, CFM, ACH, °F/°C, and moisture content percentages; mixing units is a common documentation error.

Limitations section should state inaccessible areas, weather constraints, and any test conditions that reduce confidence in results.

Recommendations should be actionable and prioritized by risk, cost, and verification method so the client can act and confirm the fix.