BPI Multifamily cheat sheet

Stack effect: warm air rises through a building's central core, drawing in outdoor air at the bottom and forcing air out at the top; pressure difference scales with height and indoor-outdoor temperature difference.

Pressure boundaries separate conditioned from unconditioned space; air barriers control unintentional flow, while vapor retarders control diffusion. A single material can serve both functions only if continuous and properly placed.

In multifamily buildings, the compartmentalization boundary typically includes the unit's exterior walls, roof/ceiling, floor over unconditioned space, and unit-to-corridor or unit-to-unit demising walls.

Typical U-values: single-pane clear window ~1.0 Btu/h·ft²·°F; double-pane low-e ~0.35; insulated 2x4 wall ~0.07-0.10; uninsulated brick wall ~0.30. Lower U means better insulation.

Infiltration loads are estimated with Q = ACH × volume / 60 (CFM) and sensible load = 1.08 × CFM × ΔT; latent load = 0.68 × CFM × Δgrains.

Common multifamily heat-loss pathways: uninsulated slab edges, cantilevered floors, recessed lights, duct leakage in unconditioned attics, and fireplaces with open dampers.

Required ventilation: ASHRAE 62.2 whole-dwelling rate Q = 0.03A + 7.5(N+1) CFM, where A is conditioned floor area and N is bedrooms; local exhaust (kitchen 100 CFM intermittent, bath 50 CFM intermittent) is separate.

Duct leakage in multifamily central systems often exceeds 20% of system airflow; sealing and testing to a target (e.g., 10% or less) is a common scope item.

Blower door test: pressurize/depressurize to 50 Pa, record CFM50; convert to natural infiltration using ACHnat ≈ ACH50 / N, where N is typically 15-20 for multifamily (higher N for leakier, low-rise buildings).

Compartmentalization testing: measure leakage from the unit to outside and to adjacent units; target often ≤ 0.30 CFM50 per ft² of enclosure area for new construction.

Zone pressure diagnostics: use a second gauge to measure pressure across interior doors or between zones; a pressure difference that changes when a known hole is opened helps locate the dominant leakage path.

Infrared thermography requires a steady indoor-outdoor temperature difference of at least 10°F (preferably 15-20°F) and low solar gain; scan in early morning or on an overcast day.

Duct leakage testing: pressurize the duct system to 25 Pa and measure leakage; total leakage is reported as CFM25 and compared with system airflow (e.g., ≤ 10% of design airflow).

Combustion safety: test for ambient CO (threshold 35 ppm), draft pressure in the flue (should be negative, typically -2 to -5 Pa), and spillage at the draft hood; a worst-case depressurization test depressurizes the house with all exhaust fans running.

Moisture assessment: use a pin or pinless moisture meter; readings above 20% wood moisture content indicate active or recent wetting; confirm with a thermo-hygrometer (indoor RH target 30-50%).

Data collection: record building orientation, unit mix, HVAC type and age, envelope assembly, and utility data (12 months of gas/electric bills) to establish baseline EUI (kBtu/ft²/yr).

Whole-building energy use intensity (EUI) = annual site energy (kBtu) / conditioned floor area (ft²); typical multifamily EUI ranges from 40-80 kBtu/ft²·yr depending on climate and systems.

Degree-day method: annual heating energy ≈ (UA × HDD × 24) / (η × fuel content), where UA is the sum of assembly U × area, HDD is heating degree days (base 65°F), and η is system efficiency.

Savings from envelope improvements: ΔE = (UA_before - UA_after) × HDD × 24 / η; for cooling, use CDD and the cooling system's SEER/EER.

Interactive effects: air sealing reduces both infiltration load and duct leakage; savings from one measure can be offset by another (e.g., added insulation reduces the benefit of further air sealing).

Baseline calibration: compare modeled annual consumption with 12 months of utility bills; a calibrated model typically matches within ±10% for annual energy and monthly shape.

Simple payback = installed cost / annual savings; measure life and discount rate determine lifecycle cost; use net present value (NPV) for comparing measures with different lifetimes.

Utility rate structures (tiered, time-of-use, demand charges) affect savings value; a measure that reduces peak demand can yield demand-charge savings beyond energy savings.

Common modeling tools: EnergyPlus, eQUEST, and TREAT/REM-Rate for residential; report both source and site energy and state the weather file (TMY3) used.

A scope of work (SOW) must specify location, quantity, material, installation method, and acceptance criteria for each measure; avoid ambiguous terms like 'as needed' without a defined trigger.

Air sealing SOW: identify specific leakage sites (top plates, rim joists, penetrations, chases, fireplaces) and specify sealant type (caulk, foam, gaskets) and thickness.

Insulation SOW: state R-value, product type (fiberglass batt, blown cellulose, spray foam), coverage area, and required clearances (e.g., 3 inches around recessed lights, 1 inch from chimneys).

HVAC SOW: include equipment sizing (Manual J or equivalent), duct sealing and insulation R-value, refrigerant charge verification, and combustion safety testing before and after.

Ventilation SOW: specify fan model, CFM, control strategy (continuous or intermittent), and commissioning with a flow hood or pressure pan.

Change orders: any deviation from the SOW must be documented with a written change order approved by the program or owner before work proceeds.

Quality control: define inspection points (pre-work, rough-in, final) and sample size (e.g., 10% of units) for verification testing.

Health and safety: SOW must address asbestos/lead testing before disturbing materials in pre-1978 buildings, and proper PPE and containment.

ASHRAE 62.2 sets residential ventilation and acceptable indoor air quality requirements; ASHRAE 90.1 and IECC set envelope and equipment efficiency minimums for commercial and residential buildings respectively.

BPI standards: the Building Performance Institute publishes technical standards for envelope, heating, cooling, and air conditioning; certification requires written and field exams.

ENERGY STAR Multifamily High-Rise and DOE Zero Energy Ready Home programs specify performance targets (e.g., 15% above ASHRAE 90.1) and third-party verification.

Reporting must include: building and unit identifiers, test conditions (indoor/outdoor temperature, wind), instrument calibration dates, measured values, and pass/fail against the program threshold.

Test report example: blower door result reported as CFM50, ACH50, and ELA (effective leakage area) in in²; compartmentalization reported as CFM50 per ft² of enclosure.

Combustion safety reports: record ambient CO, flue CO, draft pressure, and spillage observations for each appliance; note pass/fail against BPI or program limits.

Data retention: keep raw test data, photos, and calibration records for the program-required period (often 3-5 years) and make them available for QA audits.

Standard references: ASTM E779 (blower door), ASTM E1827 (airtightness), and RESNET/BPI test protocols; cite the edition and method in the report.