Multiplier Effect: High Performance Construction Assemblies and Urban Density in US Housing

Abstract

The suburban house—an emblem of the 20th century American Dream—has come to symbolize unsustainable excess in the new millennium. For the homeowner, the single family home is increasingly burdensome to finance and maintain; for planners and policy makers, suburban sprawl has undermined efforts to limit land consumption and mitigate anthropogenic greenhouse gas (GHG) emissions. While the link between sprawl and transportation emissions is well-established, the atmospheric impacts in the construction and operation of single-family houses are acknowledged but not as well understood. Using a readily available lifecycle assessment tool and building modeling software, this study compares the carbon emissions of low- and high-density housing morphologies and weighs the lifecycle embodied energy costs against the operational energy benefits of increasing thermal performance in the building envelopes of each housing type. The assessment shows that in spite of increasing energy demands embedded in the materially and technically intensive construction of high performance assemblies, the adoption of these techniques in both the house and multi-unit apartment dramatically reduces lifetime GHG emissions. However, the initial toll of building high performance houses—measured in emissions and extrapolated as construction costs—is burdensome to the environment and homeowner alike. As an alternative, high performance apartments can be built at a carbon and dollar cost only marginally higher than that of conventionally-constructed multi-unit dwellings, with a per-unit lifetime GHG footprint that is one quarter of that of a standard house. The economic and land-use efficiencies of enhanced construction assemblies deployed in dense urban residential development create a multiplier effect in potential GHG reduction; a critical factor for contemporary environmental planning and policy.