Hygrothermal Performance of Energy Retrofits in Buildings: An Assessment of the Residential Building Stock in the U.S.

Thesis (Ph.D.)--University of Washington, 2023Improving buildings’ energy efficiency has been widely recognized as one of the most versatile and effective means of reducing energy consumption in existing buildings. However, recent investigations of retrofits in residential buildings have raised concerns about unintended impacts correlated with negative effects on a building's life span, indoor environment, and occupant wellness. One of these unintended impacts is excess moisture in the building's envelope, potentially caused by inadequate air infiltration, lack of ventilation, and thermal insulation malfunction. The problem with damp building materials is that they can generate humidity that encourages the development of mold in the envelope’s cavity, affecting overall hygrothermal behavior (i.e., combined movement of heat, air, and moisture), and potentially degrading both the envelope and structure of the building. Hygrothermal behavior of buildings, in turn, is influenced by a range of building conditions (i.e., air and water permeability, thermal insulation, ventilation rates, occupant behavior, climate, and location). This dissertation examines the unintended effects arising from implementation of energy efficiency measures on wall assemblies, affecting the hygrothermal performance of building envelopes. The hygrothermal performance of an existing building envelope is assessed through dynamic transient simulations. Case studies for this assessment included three retrofit approaches defined by the location of the intervention (exterior, core, and interior). Since the implementation of energy retrofits in buildings is tied to local code policy, we drew on the International Energy Conservation Code (IECC) as an input in the design of the retrofit assemblies, applying its prescriptive component method. Moreover, since hygrothermal performance is sensitive to climate, we examined different climate zones, including hot and humid, marine, cool, cold, and arctic climates. Findings suggest that the implementation of energy retrofits can impact the hygrothermal performance of existing envelopes, and that those impacts are closely linked to the climate context. Specifically, EEMs installed in the exterior side of the thermal envelope led to the least hygrothermal consequences across six climate contexts studied. The use of strategies such as air layers in timber frame assemblies has been found to minimize undesired outcomes such as excess moisture, and mold growth. The study further indicates that the prescriptive framework provided by the current local codes for energy retrofits is inadequate in several climate zones studied, particularly in hot and humid regions