Domain 4
Indoor Air Quality
Measured ventilation rates, filtration, and source control at the point of specification.
What this domain covers
Indoor Air Quality works in a fixed order: control the source first, ventilate second, filter third. A pollutant that is never released does not have to be diluted or captured.
The domain covers whole-house outdoor-air ventilation and the measurement that proves it is actually delivering; filtration and the equipment built to carry it; where mechanical equipment and ductwork are allowed to sit; exhaust at the cooktop and the handling of combustion; the attached garage and the air that moves between it and the house; the deep clean before handover; and the ongoing care programme after the family moves in.
Why it matters in Central Texas
In this climate the outdoor air brought into a house is also a moisture load, so ventilation cannot be designed without designing for the water that comes with it. Filtration interacts with the same problem: a filter that restricts airflow reduces how much moisture the cooling equipment can remove, which in a hot-humid summer is the thing most worth protecting.
Attached garages are close to universal here, and the air in one is hot, humid and carries whatever is stored in it. Because a Sage Co. house is deliberately airtight, incidental leakage is no longer diluting anything indoors — so the garage, the kitchen and the equipment room are treated as design problems rather than afterthoughts.
How depth is chosen
This domain carries all three rungs. Essential is the floor present in every Sage Co. house: balanced whole-house ventilation with its delivered airflow measured, equipment kept inside conditioned space and out of the garage, an air handler built so that higher-efficiency filtration can be dropped in later without redesign, the garage treated as an exterior wall and held under continuous exhaust, a ducted hood covering the full cooking surface, and a fine-particle clean before handover.
Enhanced raises installed filtration and sizes bedroom airflow against a calculated occupancy target. Comprehensive tightens that target, adds supplemental filtration with no ultraviolet or ion-generating stage, and adds an independent indoor air test before occupancy — recorded as a condition, not used as a pass or a gate.
What we document
The Record holds design airflow against measured airflow with the instrument and date; measured pressure relationships; equipment and filter data with photographs; the calculation behind bedroom airflow and its assumptions; the dated photographs and catalogued cleaning agents from the pre-handover clean; and, where elected, the pre-occupancy air test.
Measurement is made by an independent party at commissioning and handover.
Findings in this domain are recorded in the Sage Co. Record. Sage Co. may mark a requirement specified and installed. Only an independent third party can mark it verified, and verification is elected domain by domain — how verification works.
Reviewed by Jake Rangel, September 19, 2026
Related reading
- Understanding Ventilation in Hot-Humid Climates
- LBNL Indoor Environment Group — IAQ Science
- NIST Indoor Air Quality and Ventilation Group
- ANSI/ASHRAE Standard 62.2 — Ventilation and Acceptable Indoor Air Quality in Residential Buildings
- ANSI/ASHRAE Standard 241 — Control of Infectious Aerosols
- EPA Indoor airPLUS Construction Specifications
Build this into your house
Sage Co. builds and consults across Austin, San Antonio and the Hill Country. Start with a call and we will walk this domain — and the other ten — against your project.