Julien Schwartz, M.Eng. 2014
Supervisor: Dr. Rodrigo Mora
Historically, the wood-frame construction has been the predominant choice for new residential construction in the United States and Canada. The motivation has been the lower cost and ease of acquiring materials, with less consideration for the operational energy cost over the lifetime of the building or the environmental impact of the building [1]. In a typical residential building, a large portion of the energy is transferred through walls, ceilings, and air infiltration. Therefore, although it may cost more initially, selecting high performance walls and ceilings can significantly reduce the energy consumption tied to space heating and cooling, which would lower utility bills and eventually offset the higher initial cost within a number of years. One high performance alternative to traditional wood-frame construction is the Insulated Concrete Forms (ICF) construction. ICF constructions provide continuous layers of concrete and expanded polystyrene (EPS) surrounding the building.
This report presents the results of the first phase in a study of comparative life cycle performance of ICF construction and wood-frame construction for residential buidlings, which focuses on energy performance. The measures adopted to evaluate and compare the energy performance are mechanical system capacity and annual energy consumption. The annual energy consumption is in turn used in conjuntion with the embedded energy of materials, construction processes, maintenance, operational energy, and disposal, in a preliminary Life-Cycle Assessment (LCA) to predict the life-cycle performance of the sample houses. Another measure in terms of Global Warming Potential (GWP) is also determined from this preliminary LCA.
Energy performance of a hypothetical 3600 sq.ft. house in five geographical locations in the US and three geographic locations in Canada, in difference climate zones, was estimated for a wood-frame variation and an ICF variation of the house, respectively. The wood-frame house was modeled according to the local code requirements for each city, while the ICF house was modeled using standard ICF construction specifications for houses in each city. Given limitations in the Life-Cycle Inventory (LCI) database from the LCA software, the preliminary LCA was conducted in two US cities and three Canadian cities.
For an assumed building life of 70 years, the data show overall lower impacts for the ICF variation in all locations, both in terms of total primary energy and global warming potential. Depending on climate, when compared to the wood-frame varation, the total primary energy use reduction of the ICF variation ranges from 4.8% to 12.7%, while in terms of GWP, the decrease ranges from 3.4% to 12.5%. The impact of operational energy use accounts for most of the impacts (about 90%) throughout the house life cycle, which is in agreement with previous studies. Superior performance of the ICF house can be attributed to the higher thermal resistance, higher thermal mass, and tighter construction inherent to ICF construction. Further work is still required to compare the life-cycle performance of high-performance wood-frame construction versus ICF construction.
[1] M.A. Sherman, A Life Cycle Comparison of Light-Frame Wood and Insulated Concrete Form Building Enveloeps: Energy Use and Green House Gases, Thesis, Universityof Tennessee, 2011.