The vocabulary, without the marketing.

A filtration medium processed to an extremely high internal surface area, which removes contaminants by adsorption rather than by straining. What a given product reduces depends on its specific certified claims.

Common measures · Certified reduction claims under NSF/ANSI 42 and 53; capacity in gallons

The layer or system that stops air moving through the enclosure. It only works where it is continuous, so its detailing at joints, transitions and penetrations matters more than the material chosen.

Common measures · Material air permeance in L/(s·m²) at 75 Pa; whole-building result as CFM50 or ACH50

The number of times a space's volume of air is replaced in one hour. The figure is only meaningful with its context attached, because ventilation, filtration, and enclosure leakage are all reported in air changes and none of them mean the same thing.

Common measures · air changes per hour (room volumes per hour)

A building's measured air leakage, expressed as the number of times its interior volume would be exchanged per hour while held at 50 pascals of pressure difference. A test condition, not a ventilation rate.

Common measures · Air changes per hour at 50 Pa; CFM50; CFM50 per sq ft of enclosure area. Test methods ASTM E779 and ISO 9972

Closing unintended openings in the building enclosure so air moves where it is designed to and not elsewhere. A separate function from insulation, which slows conducted heat but does little to stop air from moving through an assembly.

Common measures · CFM50 and ACH50 from a blower-door test, measured before and after

A design approach connecting occupants to natural systems through daylight, views, materials, water and spatial variation. Useful when tied to specific decisions, and empty when used as a synonym for adding plants.

Common measures · No standardized metric. Assessed against named pattern frameworks and against the underlying daylight and view metrics

A diagnostic that measures how leaky a building is by sealing a calibrated fan into an exterior doorway, holding the house at a set pressure difference, and recording the airflow required to maintain it.

Common measures · CFM50 and ACH50. Procedures per ASTM E779 or ISO 9972

The physical separation between conditioned interior and outdoor conditions — walls, roof, foundation, windows, and doors — understood as a set of continuous control layers for water, air, vapor, and heat rather than as a stack of materials.

Common measures · Assembly R-value and U-factor; ACH50 for airtightness

A gas exhaled by everyone in the room. Indoors, its concentration above the outdoor background is largely a function of how many people are present and how much outdoor air the space is getting, which makes it a usable proxy for ventilation.

Common measures · ppm

A colorless, odorless gas produced by incomplete combustion. It displaces oxygen on hemoglobin, and unlike other common indoor air pollutants it can reach concentrations in a house that are acutely dangerous.

Common measures · Parts per million (ppm). Residential alarms are listed to UL 2034

A marketing umbrella for lighting products and schemes claimed to support circadian rhythm. It has no single agreed technical definition, and the quantity it gestures at is melanopic EDI.

Common measures · No standardized definition. Where a claim is quantified it should be in melanopic EDI at the eye

A rating for portable air cleaners, in cubic feet per minute, combining how much air a machine moves with how efficiently it removes particles. Reported separately for smoke, dust and pollen.

Common measures · cfm, reported separately for smoke, dust and pollen (ANSI/AHAM AC-1)

A 0–100 score for how faithfully a light source renders colors against a reference. It averages eight pastel samples, which makes it a weak predictor of saturated-color performance — the gap TM-30 was created to close.

Common measures · Ra, 0 to 100; R9 for deep red; TM-30 Rf and Rg as the fuller replacement

The set of checks confirming that fuel-burning appliances receive the air they need and vent their exhaust outdoors under all operating conditions — including with every exhaust fan in the house running at once.

Common measures · Worst-case depressurization in pascals; draft and spillage testing; carbon monoxide in flue gas, ppm

A structured quality-assurance process that verifies a building's systems are installed, tested, and actually operating the way they were designed to. It is measurement and documentation, not a final walkthrough.

What happens when air contacts a surface colder than its dew point and water forms there. The mechanism behind window sweating, mold on exterior walls, and moisture accumulating inside assemblies.

Common measures · Compared as surface temperature versus dew point, both in °F or °C

Insulation installed as an uninterrupted layer outside the structural framing, so studs and joists do not penetrate it. Its purpose is addressing thermal bridging, not simply adding R-value.

Common measures · Continuous R-value outboard of framing; ratio of exterior to cavity R-value

The temperature, in kelvin, of the blackbody radiator whose color most closely matches a light source. It describes appearance only: two sources at identical CCT can render colors very differently.

Common measures · Kelvin (K); Duv as the distance from the blackbody locus

Natural light admitted into a building, and the design decisions governing how much arrives, from which direction, and at what times of day. Distinct from a view, and distinct from the solar heat that travels with it.

Common measures · Illuminance in lux; daylight factor as a percentage; spatial daylight autonomy (sDA) per IES LM-83

Removing moisture from indoor air, either by condensing it on a surface below the dew point or adsorbing it onto a desiccant. Air conditioning does this as a side effect — which means it stops when cooling stops.

Common measures · Pints or litres per day at a stated test condition; energy factor in L/kWh

The temperature at which air becomes saturated and water vapor starts condensing into liquid. Unlike relative humidity, it describes the absolute amount of moisture in the air and does not change when that air is heated or cooled.

Common measures · °F or °C

A European classification for wood-based panels whose formaldehyde emission is at or below 0.124 mg/m³ when tested to the EN 717-1 chamber method referenced by EN 13986.

Common measures · ≤ 0.124 mg/m³ formaldehyde by EN 717-1 under EN 13986 classification

The greenhouse gas emissions from producing, transporting, installing and eventually disposing of building materials, as distinct from the emissions from operating the finished building.

Common measures · kg CO₂e, by life-cycle stage (A1–A3 upfront, A–C whole life)

Laboratory measurement of chemicals released from a product or material into air under controlled temperature, humidity, loading, and air-exchange conditions.

Common measures · mg/m³ (or ppm) under named chamber / reference conditions; loading factor and air exchange as specified by the method

A balanced ventilation system that exhausts stale indoor air and supplies outdoor air through a core that transfers both heat and a portion of moisture between the two air streams.

Common measures · CFM (airflow); sensible and latent recovery efficiency, %

A standardized, third-party-verified report of a product's life-cycle impacts. Two EPDs are only comparable if they were produced under the same product category rules.

Common measures · Impacts per declared unit per ISO 14025 and EN 15804; global warming potential in kg CO₂e

Removing particles from air by passing it through a medium that captures them. A recirculating process: it cleans air already inside the house, and by itself neither introduces outdoor air nor removes gases.

Common measures · MERV under ASHRAE 52.2; CADR in cfm under ANSI/AHAM AC-1; capture efficiency by particle size in µm

Any route by which sound bypasses the assembly meant to block it — through shared framing, ductwork, outlets, or a floor that runs continuously beneath a wall. It sets the ceiling on real-world performance.

Common measures · Identified by field testing; caps achievable ASTC regardless of the assembly's lab rating

A simple organic gas used in many adhesives and resins for wood-based panels and furniture. It can off-gas into indoor air after manufacture and installation.

Common measures · mg/m³ or ppm in air; product emission under chamber methods such as EN 717-1 and REACH Appendix 14 reference conditions

Chemicals and resins that are not formaldehyde itself but can liberate formaldehyde during manufacture, curing, or the life of a finished article.

Common measures · Article emission as formaldehyde concentration under chamber / REACH Appendix 14 conditions

The transparent portion of a window or door assembly, and the properties that come with it: thermal transmittance, solar heat gain, visible light transmittance, acoustic performance and any coatings or laminations.

Common measures · U-factor, SHGC, visible transmittance (VT) and STC or OITC, typically per NFRC ratings

Equipment that moves heat rather than generating it, using a refrigerant cycle that can run in either direction. A single machine for heating and cooling, and not a combustion appliance.

Common measures · COP and HSPF2 for heating; EER2 and SEER2 for cooling; capacity in Btu/h at a stated outdoor temperature

A balanced ventilation system that exhausts indoor air and supplies outdoor air through a core that transfers heat between the two streams without meaningfully transferring moisture between them.

Common measures · CFM (airflow); sensible recovery efficiency, %

High-Efficiency Particulate Air filtration. Under the U.S. definition, a HEPA filter captures at least 99.97 percent of particles at 0.3 micrometers, a size near the range these filters find hardest to capture, which is why the test uses it.

Common measures · 99.97% at 0.3 µm under the U.S. DOE test convention; EN 1822 classes H13–H14 classify on a different basis

Adding moisture to indoor air. Useful in cold-climate winters, and capable of causing condensation and material damage when the added moisture exceeds what the enclosure and outdoor temperature will tolerate.

Common measures · Gallons or litres per day; resulting relative humidity at a stated indoor and outdoor temperature

Heating, ventilation and air conditioning — the umbrella term for the equipment conditioning a building's air. Its three functions are separable, and a system can heat and cool well while ventilating and filtering badly.

Common measures · Varies by function: Btu/h and SEER2 for cooling, CFM for airflow, cfm of outdoor air for ventilation

Heating that distributes energy through water rather than air. A distribution medium rather than a heat source: the water can be heated by a boiler, a heat pump, or something else entirely.

Common measures · Supply and return water temperature in °F or °C; flow in GPM; output in Btu/h

A single-number rating of how well a floor-ceiling assembly limits impact noise, measured with a standardized tapping machine. The test source is far lighter than footfall or a dropped weight.

Common measures · Dimensionless rating per ASTM E989; field-measured equivalent is AIIC

The condition of the air inside a building, described by the pollutants present in it — particles, gases, moisture, and biological material — and by how effectively ventilation and filtration keep those concentrations down.

The combined condition of everything inside a building that occupants experience — air, temperature, humidity, light, sound, and the surfaces around them — treated as one system rather than a set of independent problems.

Material that slows heat transfer through an assembly. It is not by itself an air barrier, a vapor control layer or a sound isolator, though products are frequently marketed as though one layer did all four.

Common measures · R-value per inch and total assembly R-value; air permeance where claimed

A treatment process that swaps unwanted ions in water for others held on a resin. Conventional softening exchanges calcium and magnesium for sodium; other resins target different ions entirely.

Common measures · Grains per gallon of hardness removed; resin capacity; regeneration frequency

The portion of a cooling load that comes from removing moisture rather than lowering temperature. In humid climates it can rival the sensible load, and equipment sized only for temperature will not meet it.

Common measures · Btu/h or kW of latent capacity; sensible heat ratio (SHR) as the split

A standardized method for tallying a product's environmental impacts across defined stages of its life. Results depend entirely on the system boundary and assumptions declared, which is why two studies can disagree.

Common measures · Impact categories per ISO 14040 and 14044; global warming potential in kg CO₂e

A material certified to emit below defined thresholds for specified compounds under a specified test. A disclosure about tested emissions rather than a verdict that a product is safe or chemically simple.

Common measures · Certification thresholds under CDPH Standard Method v1.2, GREENGUARD Gold, or equivalent

Outdoor air supplied deliberately to replace air removed by an exhaust device. Needed when a fan removes more air than the enclosure will passively admit, which would otherwise leave the house at negative pressure.

Common measures · Exhaust cfm versus makeup cfm; house pressure relative to outdoors, in pascals

The average time since air at a location entered the space as outdoor or supply air. It describes how long that air has been indoors — not how much air the ventilation system is moving.

Common measures · time (seconds or hours); local or zone mean age; tracer-gas methods (ISO 16000-8, ASHRAE 129)

The area-weighted average temperature of the surfaces around a person, which governs how much heat the body exchanges by radiation. It is not what a thermostat measures.

Common measures · °F or °C, area-weighted by view factor; measured with a globe thermometer

Light weighted by the response of the retinal cells that drive circadian signalling, expressed in lux. The measurable quantity underneath most claims about circadian lighting, standardized in CIE S 026.

Common measures · Melanopic EDI in lux, at the eye and in the direction of gaze; melanopic-to-photopic (M/P) ratio

A rating from ASHRAE Standard 52.2 describing how effectively an HVAC filter captures particles across three size ranges. Higher numbers indicate better capture of smaller particles under defined laboratory conditions.

Common measures · MERV 1–16 (ASHRAE 52.2); MERV-A for the same test after conditioning

Lighting conditions with different spectral power distributions that produce the same or very similar perceived color for a standard observer.

Common measures · Matched chromaticity / CCT with divergent SPD; often evaluated with melanopic EDI or melanopic daylight efficacy ratio at fixed illuminance

A single number describing how much sound a surface absorbs, averaged across four octave bands from 250 to 2000 Hz. An absorption rating, which is a different property from isolation.

Common measures · 0 to 1, occasionally above 1 for deep absorbers; per ASTM C423

The release of volatile compounds from a material into the air after installation. Emission rates generally decline over time, but the curve differs by compound and material and can extend well past a move-in date.

Common measures · Emission factor in µg/m²·h; chamber test concentrations at 24 h, 72 h and 14 days

A single temperature combining air temperature and mean radiant temperature to describe what an occupant actually experiences. At low air speeds it can often be approximated as the average of the two.

Common measures · °F or °C; defined in ASHRAE Standard 55

A performance standard for very low heating and cooling demand, reached through airtightness, continuous insulation, heat-recovery ventilation and controlled glazing. Two certifying bodies publish different criteria.

Common measures · Annual heating and cooling demand in kWh/m²·yr; 0.6 ACH50 airtightness under the PHI criteria

A large family of synthetic fluorinated compounds used for water, grease and stain resistance. They resist environmental breakdown, which is why they are widely detected in water supplies and why regulation is still developing.

Common measures · Parts per trillion (ppt) or nanograms per litre

Airborne particles 2.5 micrometers in diameter or smaller. The size fraction is small enough to stay suspended for hours and to reach deep into the lungs, which is why it is tracked separately from larger dust.

Common measures · µg/m³

A measure of resistance to conducted heat, per unit area. Product R-value describes a material in isolation; the assembly containing it almost always performs worse, because framing and gaps conduct around it.

Common measures · ft²·°F·h/Btu in the U.S.; RSI in m²·K/W

A hydronic or electric system that warms a floor so its surface heats the room largely by radiation. Output is capped by the maximum floor surface temperature that is comfortable and safe underfoot.

Common measures · Btu/h per sq ft of floor; floor surface temperature in °F or °C; floor covering R-value

A radioactive gas produced by the decay of uranium in soil and rock, which enters buildings through the foundation. EPA identifies it as the second leading cause of lung cancer in the United States.

Common measures · Picocuries per litre (pCi/L) or becquerels per cubic metre (Bq/m³). EPA action level 4 pCi/L

The list of substance restrictions under the EU REACH regulation. Each entry can limit manufacture, use, or placing on the market of substances, mixtures, or articles.

Common measures · Entry-specific concentration or content limits; for entry 77, mg/m³ formaldehyde under Appendix 14 test conditions

The amount of water vapor in air expressed as a percentage of the maximum that air could hold at its current temperature. Because the denominator moves with temperature, the same quantity of moisture reads differently in different rooms.

Common measures · % RH

How long sound persists in a space after the source stops, conventionally the time for the level to fall by 60 decibels. Defined for rooms large enough to sustain a diffuse sound field.

Common measures · Seconds, by octave or third-octave band

A treatment process that forces water through a semi-permeable membrane under pressure, leaving most dissolved substances behind. It produces a reject stream, so some water is discharged for every volume treated.

Common measures · Percent rejection by contaminant; gallons per day; recovery ratio

The fraction of solar radiation striking a window that ends up as heat inside, from 0 to 1. Whether a low number is desirable depends on climate, orientation and shading.

Common measures · 0 to 1, dimensionless; g-value is the European equivalent

A single-number rating of how much airborne sound an assembly blocks, derived from laboratory measurements between 125 and 4000 Hz. It describes nothing below 125 Hz, where most complaints originate.

Common measures · Dimensionless rating per ASTM E413; field-measured equivalent is ASTC

The distribution of optical power a light source emits across wavelengths. The spectral fingerprint underneath color appearance metrics such as CCT.

Common measures · Relative or absolute power versus wavelength (nm); derived quantities include CCT, chromaticity, color-rendition metrics, and melanopic EDI

A lighting system that can deliberately alter its spectral power distribution, not only its intensity or correlated color temperature appearance.

Common measures · Multi-channel SPD control; often specified with channel counts, chromaticity gamut, and derived metrics (CCT, melanopic EDI) at stated setpoints

Sound carried as vibration through solid building elements rather than through air. It re-radiates from surfaces far from the source, which is why adding mass to one wall often fails to stop it.

Common measures · Vibration velocity or acceleration; re-radiated sound pressure level in dB

A path through an assembly that conducts heat more readily than its surroundings, such as a steel stud or a cantilevered slab. It lowers whole-assembly performance and creates cold interior surfaces.

Common measures · Whole-assembly U-factor including bridging; linear transmittance (psi-value) in W/(m·K)

The condition in which a person is satisfied with the thermal environment. It is a perceptual state rather than a temperature, governed by six factors of which air temperature is only one.

Common measures · Operative temperature in °F or °C; PMV and PPD indices (ASHRAE 55)

The combined concentration of dissolved substances in water, usually inferred from electrical conductivity. A bulk figure that says nothing about which substances are present or whether any of them matter.

Common measures · Milligrams per litre (mg/L) or parts per million, usually estimated from conductivity in µS/cm

A lighting control capability that varies correlated color temperature, usually alongside intensity, across the day. A control feature — it does not by itself establish any particular effect on an occupant.

Common measures · CCT range in kelvin; dimming range and curve; control protocol such as DALI Type 8 or 0–10V

The rate of heat transfer through an assembly per unit area per degree of temperature difference — the reciprocal of total R-value. A window's rated U-factor includes frame and edge effects, not just the glass.

Common measures · Btu/(h·ft²·°F) in the U.S.; W/(m²·K) elsewhere. NFRC rates whole-window U-factor

A material layer that limits how readily water vapor diffuses through an assembly. The appropriate permeability depends on climate and assembly, and the wrong choice can trap moisture rather than exclude it.

Common measures · Water vapor permeance in perms; Class I, II and III vapor retarder designations

The deliberate replacement of indoor air with outdoor air at a controlled rate. Distinct from filtration, which cleans and recirculates the air already inside, and from air conditioning, which changes its temperature.

Common measures · CFM or L/s of outdoor air; air changes per hour; the whole-house rate calculated under ASHRAE 62.2

A measure of how well supplied outdoor air reaches the occupied zone, relative to perfect mixing. Air-change rate describes how much air is moved; ventilation effectiveness describes whether that air arrives where people breathe.

Common measures · dimensionless ratio (zone air distribution effectiveness Ez; air-change effectiveness); 1.0 denotes perfect mixing

Interrupting the path that carries vibration from equipment into the structure, using resilient mounts, pads or breaks. Performance depends on matching the isolator to the load and the frequency involved.

Common measures · Static deflection in inches or mm; natural frequency in Hz; percent isolation efficiency

Carbon-based chemicals that evaporate readily at room temperature, entering indoor air from paints, adhesives, sealants, flooring, furnishings, and cleaning products. The category spans thousands of compounds with very different toxicity.

Common measures · µg/m³ or ppb, per compound; TVOC as a combined index

The concentration of dissolved calcium and magnesium in water. Primarily a scaling and soap-performance issue rather than a health one, and separate from whether the water contains anything harmful.

Common measures · Grains per gallon (gpg) or mg/L as calcium carbonate

A certification framework scoring buildings against requirements in categories including air, water, light and thermal comfort. Meeting a framework requirement is not the same as demonstrating a health outcome.

Common measures · Points across concepts, to Bronze, Silver, Gold or Platinum certification levels