BPI Building Analyst key terms

The continuous layer of insulation and air barrier that separates conditioned space from unconditioned space. It must align with the pressure boundary to control heat flow and prevent condensation inside assemblies.

The continuous air barrier enclosing conditioned space, made of rigid materials, sealed sheathing, or membranes. Leaks here let outdoor air and moisture into the building and reduce the effectiveness of insulation.

Natural upward air movement caused by warm air rising and escaping near the top of a building while cooler air enters low. It intensifies infiltration in winter and drives moisture and pollutant transport.

The horizontal level in a building where indoor and outdoor pressures are equal. Above it air exfiltrates and below it air infiltrates, so its height shifts with temperature, wind, and mechanical system operation.

A path of relatively high heat conductance through an assembly, such as wood studs, steel framing, or concrete, that bypasses insulation. It lowers effective R-value and can create cold spots where condensation forms.

The installed performance of an insulation assembly after accounting for framing, gaps, compression, and convection. It is always lower than the labeled cavity R-value and is what energy models should use.

A measure of a material's resistance to conductive heat flow, expressed in square feet times degrees Fahrenheit hours per British thermal unit. Higher values mean better resistance; it does not describe air leakage performance.

The rate of heat transfer through an assembly, equal to the reciprocal of its total R-value. It is used for windows, doors, and whole assemblies, where lower numbers indicate better insulating performance.

The fraction of incident solar radiation admitted through a window as heat, ranging from zero to one. Lower values reduce cooling loads, while higher values can benefit heating-dominated climates.

A diagnostic test using a calibrated fan mounted in an exterior doorway to depressurize the house and measure air leakage. Results, usually in cubic feet per minute at 50 pascals, quantify envelope tightness.

The number of complete house air volume exchanges per hour during a blower door test at 50 pascals of pressure. It normalizes leakage to house size and is used for code and program thresholds.

A simple gauge placed over a register or opening during a blower door test to compare pressure differences. Higher readings suggest leakage paths connecting that zone to the outdoors or to unconditioned space.

A procedure that pressurizes the duct system with a calibrated fan while sealing registers, measuring leakage as a percentage of system airflow. It identifies losses to attics, crawlspaces, or garages that waste energy and endanger indoor air quality.

The portion of duct system leakage that connects to unconditioned or outdoor space rather than back into the conditioned envelope. Only this leakage drives real energy loss and pressure imbalances in the house.

The use of a thermal imaging camera to visualize surface temperature differences that reveal missing insulation, air leakage, moisture, or thermal bridging. Interpretation requires knowledge of conditions and confirmation with other tools.

An instrument that samples flue gases to measure oxygen, carbon monoxide, carbon dioxide, and stack temperature, then calculates efficiency and excess air. It verifies safe combustion and proper appliance performance.

A pressure measuring device used to read pressure differences across building assemblies, duct systems, and combustion appliance zones. Digital models report inches of water column or pascals for diagnostics and commissioning.

The practice of closing unintended holes in the pressure boundary with caulk, foam, gaskets, and rigid materials. It reduces infiltration, improves comfort, and helps control moisture and pollutant entry.

Unintentional outdoor air entering a building through cracks and penetrations, driven by wind, stack effect, and mechanical pressure. It carries moisture and pollutants and increases heating and cooling loads.

A short vertical wall separating conditioned space from an attic or roof cavity. It is a common air leakage and insulation failure site because the thermal boundary is often discontinuous there.

A projecting floor section, such as a bay window or second-story overhang, that often lacks proper insulation and air sealing underneath. Its floor cavity frequently connects conditioned space to the outdoors.

A material that limits the diffusion of water vapor through an assembly. Its correct placement depends on climate, and installing it on the wrong side can trap moisture and cause decay.

The coordinated control of bulk water, vapor, and condensation in a building through drainage, air sealing, and appropriate material selection. It protects durability and indoor air quality and prevents mold growth.

An industry method for sizing heating and cooling equipment by calculating room-by-room heat loss and gain from envelope, window, and internal loads. It ensures equipment matches the actual building load.

An industry procedure for designing duct systems, including sizing, routing, and calculating friction rates, so that each room receives its required airflow. Proper design supports comfort and efficient equipment operation.

The resistance to airflow within a duct system, measured in inches of water column. Excessive static pressure reduces airflow, raises energy use, and can shorten equipment life.

Determining the volume of air moving through ducts or at registers, typically in cubic feet per minute, using flow hoods, anemometers, or pressure-based methods. It verifies that equipment delivers design airflow.

The quantity of refrigerant in a heat pump or air conditioner, which must match manufacturer specifications for efficient operation. Incorrect charge reduces capacity and efficiency and can damage the compressor.

The temperature of refrigerant vapor above its saturation point at a given pressure, used to verify charge in fixed-orifice systems. Excessive superheat suggests undercharge; too little suggests overcharge.

The temperature of liquid refrigerant below its saturation point at a given pressure, used to verify charge in systems with a thermostatic expansion valve. It confirms adequate liquid is reaching the metering device.

A procedure that depressurizes the area around combustion appliances with a blower door and fan to check whether flue gases spill or backdraft. It confirms the appliances can vent safely under worst-case conditions.

Flue gases escaping from a combustion appliance into the living space instead of venting outdoors. It is a serious safety hazard detected during worst-case depressurization testing and requires immediate correction.

A reading of the pressure or flow drawing flue gases up a vent, typically taken in the vent connector. Adequate draft confirms safe venting, while weak or reversed draft signals a hazard.

A colorless, odorless gas produced by incomplete combustion that is toxic at low concentrations. Testing appliances and installing alarms are essential safeguards in homes with fuel-burning equipment.

The amount of air supplied to a burner beyond what is theoretically needed for complete combustion, expressed as a percentage. It is measured with a combustion analyzer to balance safety and efficiency.

A balanced ventilation system that transfers heat from exhaust air to incoming fresh air through a core. It provides controlled ventilation in tight homes without excessive energy penalty.

The process of adjusting a simulation's inputs so its predicted energy use matches metered utility data within an acceptable tolerance. It increases confidence in savings estimates for proposed improvements.

The modeled or measured condition of a building before improvements, used as the reference for calculating savings. A credible base case is essential for accurate savings projections and financing.

Adjusting energy consumption data to remove the effect of weather variation so that different periods can be compared fairly. It uses degree-day data and supports accurate savings verification.

A written description of the specific improvements to be performed, including materials, quantities, locations, and sequencing. It aligns contractor work with the audit findings and the client's budget.

A ranked sequence of recommended improvements ordered by safety, cost-effectiveness, and dependency. It guides clients to address health and safety items first and to combine related shell and HVAC measures.

The estimated lifetime energy savings divided by the installed cost of a measure. A ratio above one suggests the improvement pays back within its useful life and helps compare competing options.