Session: Green Buildings I

Comparison of the Life Cycle Assessments of Three Houses: Masonry, Insulating Concrete Form, and Wood Frame
Medgar Marceau, CTLGroup
Martha VanGeem,^* CTLGroup

An environmental life cycle assessment (LCA) was conducted on three single-family houses. Houses were similar except they were modeled with three types of exterior walls: wood framed, masonry, and insulating concrete form (ICF). The LCA was carried out in accordance with ISO 14044, “Environmental management — Life cycle assessment — Requirements and guidelines.” The LCA includes the inputs and outputs of energy and materials from (i) extraction and manufacturing of materials, (ii) construction, (iii) occupancy, including heating and cooling energy use, and (iv) maintenance over a 100-year life. The houses were modeled in cities representing a range of U.S. climates. The ICF and wood frame houses were modeled in Miami, Phoenix, Seattle, Washington DC, and Chicago. The masonry and wood frame houses were modeled in Lake Charles, Tucson, St Louis, Denver, and Minneapolis.

The LCA was conducted by first assembling the relevant LCI data from published reports and commercially available databases. The LCA software tool, SimaPro, was then used to perform a life cycle impact assessment. The impact categories include land use, resource use, climate change, ozone layer depletion, human health effects, ecotoxicity, smog, acidification, eutrophication, and solid waste.

The house designs are based on typical houses currently built in the US and have 228 square meters (2450 square feet) of living space, which is close to the 2005 U.S. average of 226 square meters (2434 square feet). Each house is a two-story single-family unit with four bedrooms and an attached two-car garage. The same layout is assumed for the wood-frame, masonry, and ICF houses. The houses are designed to meet the requirements of the 2006 International Energy Conservation Code (2006 IECC) in all locations because the IECC is the most widely used residential energy code in the US. The energy saving features such as the windows and insulation are varied with climate to meet the requirements of the code. The HVAC equipment is sized for each location and for the peak heating and cooling loads of a particular house. Generally wood houses require larger HVAC equipment.

The paper compares, for a given climate, the environmental impacts for the wood, masonry, and ICF houses. The study is one of the most comprehensive available because it considers the same house construction for a wide range of climates and a complete range of impact categories. The most significant environmental impacts are not from building materials but from the production and household use of electricity and natural gas. Since the ICF walls are more highly insulating and energy efficient than the wood-frame and masonry walls (which are usually insulated to minimum code requirements) the ICF house has lower impacts.

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