Saving Energy versus Saving Materials

To reduce energy consumption and carbon dioxide (CO2) emissions in housing construction, the energy‐intensive processes and life‐cycle stages should be identified and integrated. The environmental impact of vertically integrated factory‐built homes (VIHs) constructed with increased material inputs in Japan's northern island of Hokkaido was assessed using life‐cycle inventory (LCI) analysis methods. Manufacturing process energy and CO2 intensities of the homes were evaluated based on the material inputs. They were compared with those of a counterpart home hypothetically built using the vertically integrated construction methods, but in accordance with the specifications of a less material‐intensive conventional home (CH) in Hokkaido today. Cumulative household energy consumption and CO2 emissions were evaluated and compared with those of the production stages. The annual household energy consumption was compared among a VIH, a CH, and an average home in Hokkaido. The energy intensity of the VIH was 3.9 GJ production energy per m2 of floor area, 59% higher than that of the CH. Net CO2 emissions during VIH manufacturing processes were 293 kg/m2, after discounting the carbon fixation during tree growth. The cumulative use‐phase household energy consumption and CO2 emissions of a VIH will exceed energy consumption and CO2 emissions during the initial production stage in less than six years. Although VIHs housed 21% more residents on average, the energy consumption per m2 was 17% lower than that of a CH. This may indicate that using more materials initially can lead to better energy efficiency.