California Air Resources Board

Principal Investigator/Author: Mark Modera

Contractor: University of California, Davis

Contract Number: 19RD013

Project Status: Completed

Relevant CARB Programs: Health & Exposure

Topic Areas: Indoor Air Quality & Exposure

Research Summary:

Unlike single-family homes, multifamily units have many shared walls with neighboring units, which provide airflow connections between units and allow for unwanted transfers of air pollutants, odor, noise, and pests. Compartmentalization or increasing air tightness between units is a process to improve the sealing of each multifamily unit (i.e., apartment, condominium, etc.) from adjacent units, other interior spaces, and the exterior, such that each unit is effectively its own compartment. It can reduce air transfer between units and thus provide improved indoor air quality (IAQ), energy savings, and greenhouse gas (GHG) reduction benefits.

The purpose of this study was to investigate the impact of compartmentalization of multifamily units on IAQ, energy usage, and GHG emissions. Three newly constructed mid-rise multifamily buildings in California, including two buildings with compartmentalization targets and one without compartmentalization targets but rather using modular construction with a balanced ventilation system, were field tested for air leakages, air flow rates, air change rates, and inter-unit air pollutant transfers. Field measurements and data from literature were used in simulation models to extend the applicability of test results to multifamily buildings with different compartmentalization levels and different ventilation systems in other climate zones. The field measurements showed that all three buildings were tighter than current Building Code requirement (0.3 cfm₅₀/ft²), with an average unit leakage of 0.16 cfm₅₀/ft². Inter-unit transfer of pollutants in such tightness was found to be very small for gaseous pollutants and indiscernible for PM2.5. Modeling results showed that tightening up multifamily units increased concentrations of pollutants generated within a unit due to decreased infiltration from outdoors, but decreased inter-unit air pollutant transfer, suggesting that both types of pollutant generation need to be addressed. Annual energy savings and GHG reductions from compartmentalization were estimated to be 4-6%, depending on climate zone and ventilation strategy.

These results provide important information to support the update of California’s building codes, as the findings showed that multifamily units tighter than the current code requirement (0.3 cfm₅₀/ft²) are achievable, and enhanced compartmentalization could reduce inter-unit air pollutant transfer, energy use and GHG emissions in multifamily buildings. However, enhanced compartmentalization may increase air pollutants generated within a unit due to decreased infiltration from outdoors, therefore other complementary measures such as enhanced ventilation should be considered together with compartmentalization in future code updates.

Keywords: multi-family buildings (homes); indoor air quality; energy efficiency; greenhouse gas; ventilation; compartmentalization; air tightness; sealing; new construction; inter-unit transfer; building codes; balanced ventilation; exhaust ventilation; supply ventilation

Research Seminar

Dataset: Please email research@arb.ca.gov to request the dataset generated by this research contract.

Related links:

• Peer-reviewed publication