BPI Multifamily key terms

The portion of a building's energy use that stays roughly constant regardless of weather, driven by plug loads, lighting, and domestic hot water. Separating it from weather-driven use sharpens savings estimates.

A diagnostic test that mounts a calibrated fan in a doorway to pressurize or depressurize a unit, measuring air leakage. In multifamily work, guarded or single-unit setups reveal envelope and compartmentalization defects.

The boundary separating conditioned interior space from unconditioned or outdoor space, including walls, roofs, windows, doors, and foundations. Its continuity governs heat, air, and moisture movement.

The continuous layer that resists uncontrolled air movement through the enclosure. In multifamily buildings it must connect across unit partitions, floor assemblies, and penetrations to prevent stack-driven leakage.

The line defining where insulation is installed and where conditioned space ends. Misalignment with the air barrier creates thermal bypasses and condensation risk.

A path of high heat conductance through the envelope, such as a steel stud, balcony slab, or shelf angle. Bridging lowers effective R-value and can cause cold interior surfaces and condensation.

Buoyancy-driven air movement caused by indoor-outdoor temperature differences, producing upward flow in tall buildings. In multifamily towers it drives infiltration at lower floors and exfiltration at upper floors.

The practice of sealing unit boundaries so each apartment behaves as its own pressure zone. It limits odor and pollutant transfer, reduces stack-driven leakage, and improves heating and cooling control.

The surface across which a pressure difference is measured or maintained, such as a unit's walls, ceiling, and floor. Identifying it correctly is essential for valid diagnostic testing.

A test using multiple reference tubes and gauges to measure pressure differences between zones, such as a unit and a common hallway. It reveals leakage pathways that a single blower door test cannot localize.

A calibrated fan and pressure gauge assembly used to measure duct system leakage at a specified test pressure. Results are reported as leakage per unit of conditioned floor area or as a percentage of fan flow.

Air lost from or drawn into ductwork through joints, seams, and disconnected runs. In multifamily buildings, ducts in unconditioned attics or crawlspaces can leak large fractions of delivered airflow.

A procedure measuring draft, spillage, and carbon monoxide around combustion appliances under worst-case conditions. It confirms that pressure changes from exhaust fans or envelope work will not backdraft equipment.

A test setup that operates all exhaust fans and closes doors to create the strongest negative pressure a unit can experience. Combustion appliances are then checked for spillage and draft failure.

Combustion gases escaping from an appliance's flue into indoor air rather than venting outdoors. It is a health hazard and a red flag when planning air sealing or exhaust upgrades.

Outdoor air supplied to replace air exhausted by fans, dryers, or combustion appliances. Without adequate makeup air, units depressurize and may backdraft combustion equipment.

The quantity of outdoor air delivered to a space per unit time, often expressed per occupant or per floor area. Multifamily standards set minimum rates to control moisture, odors, and pollutants.

The residential ventilation and indoor air quality standard specifying minimum whole-building and local exhaust rates. Multifamily programs commonly cite it when defining scope for ventilation corrections.

A strategy that removes stale air with fans and relies on envelope leakage for replacement air. It is inexpensive but can depressurize units and pull in pollutants from adjacent spaces.

A system supplying and exhausting roughly equal air quantities, often with heat or energy recovery. It controls pressure better than exhaust-only designs and reduces heating and cooling penalties.

A balanced ventilation device that transfers sensible heat between outgoing and incoming airstreams. In cold climates it preconditions outdoor air and limits frost and comfort problems.

A balanced ventilation device that transfers both heat and moisture between airstreams. It suits humid climates where limiting latent load from outdoor air matters.

The energy needed to remove moisture from air to reach a target humidity. In multifamily buildings, infiltration, ventilation, and internal moisture sources all contribute to it.

The heat gained or lost that changes air temperature without changing moisture content. It is the portion of load addressed by conventional heating and cooling equipment.

A weather metric summing the daily difference between a reference temperature and outdoor temperature over a period. Heating and cooling degree days support normalization and savings estimates.

Adjusting measured energy use to remove the influence of actual weather so performance can be compared across periods or buildings. Regression models against degree days are a common method.

A statistical fit relating energy consumption to drivers such as weather, occupancy, or production. Analysts use it to establish a baseline and estimate savings from efficiency measures.

Annual energy consumption divided by floor area, expressed in site or source energy units. It allows comparison of multifamily properties of different sizes and supports benchmarking.

Comparing a building's energy performance with similar buildings or its own history, often using a normalized score. It helps prioritize properties and justify deeper assessments.

Reviewing historical gas and electric bills to identify consumption patterns, seasonal trends, and anomalies. It establishes the baseline needed before modeling or scoping savings measures.

A structured process for quantifying savings actually achieved after an upgrade, using agreed methods and baseline adjustments. It protects both owners and contractors from disputed savings claims.

A systematic evaluation of a building's energy use, envelope, systems, and operations that identifies improvement opportunities. Multifamily audits often combine unit sampling with whole-building analysis.

A brief site visit identifying obvious efficiency issues and candidate measures without detailed measurement. It is a screening step that precedes a full audit or modeling effort.

Selecting a subset of units or buildings to represent a larger population during assessment. Sound sampling design determines how confidently findings can be extrapolated to the whole property.

A written description of the measures, quantities, specifications, and responsibilities for a project. Clear scopes prevent change orders and align contractor bids with program requirements.

The technical detail within a scope describing materials, installation methods, and quality standards for a measure. It gives contractors and inspectors an objective basis for acceptance.

A written modification to an agreed scope, price, or schedule after work begins. Documenting the cause and cost protects the project budget and the contractor relationship.

A post-installation check verifying that work matches the approved scope and specifications. Findings feed back into contractor coaching and program compliance decisions.

A pre-approved savings value per measure, based on prior research, used instead of site-specific measurement. It simplifies program administration but requires careful documentation of assumptions.

An analysis comparing the present value of a measure's benefits with its costs, using methods such as simple payback or total resource cost. Results guide measure selection and program design.

Closing unintended gaps in the envelope and interior boundaries with caulk, foam, gaskets, or sheathing. It reduces infiltration and stack-driven leakage but must be paired with combustion safety checks.