Indoor air quality in 24 California residences designed as high-performance homes

Today's high-performance homes are reaching previously unheard of levels of airtightness and are using new materials, technologies, and strategies for which impacts on indoor air quality cannot be fully anticipated from prior studies. This research study used pollutant measurements, home inspections, diagnostic testing, and occupant surveys to assess indoor air quality in a heterogeneous sample of 24 new or deeply retrofitted homes designed to be high-performance homes in California; homes were not all built or certified to the same performance standard (e.g., California Title 24). Although the mechanically vented homes were six times as airtight as non-mechanically ventilated homes (medians of 1.1 and 6.1 ACH50, n = 11 and n = 8, respectively), their use of mechanical ventilation systems and possibly window operation meant their median air exchange rates were almost the same (0.30 versus 0.32 hr—1, n = 8 and n = 8, respectively). Pollutant levels were also similar in vented and unvented homes. Numerous faults were observed in complex mechanical ventilation systems, and they were not corrected as part of this study. More rigorous commissioning is recommended to avoid or correct these faults. Cooking exhaust systems were used inconsistently, and several suffered from design flaws. Failure to follow best practices led to indoor air quality problems in some cases. Ambient nitrogen dioxide benchmarks were exceeded or nearly so in four homes that either used gas ranges with standing pilots or in passive house-style homes that used gas cooking burners without venting range hoods. Homes without active particle filtration had particle count concentrations approximately double those in homes with enhanced filtration, though the effects could not be controlled for outside particle levels and mixing in forced-air homes. The majority of homes reported using low-emitting materials; consistent with this, formaldehyde levels were approximately half those previously measured by another study in conventional, new California homes built before 2008. Emissions of ultrafine particles (with diameters <100 nm) were about 40 times lower on induction electric cooktops compared with either gas or resistance electric models. These results indicate that high-performance homes can achieve acceptable and even enhanced indoor air quality by providing adequate general mechanical ventilation, using low-emitting materials, providing mechanical particle filtration, incorporating well-designed exhaust ventilation for kitchens and bathrooms, educating occupants to use the kitchen and bath ventilation, and possibly by installing induction cooktops.