Saturday, November 07, 2009

Economic and environmentally sustainability of modular buildings

Brendan Baxter commented on my review of the ANU shipping container apartment building. Brendan questions the economic and environmental sustainability of importing building modules manufactured in China. As he notes, an independent life cycle analysis would be useful. One preliminary analysis from the USA shows modular building reduces greenhouse gas emissions by 5%. Transporting modules from China would increase the CO2 emissions, but not by much, as they are sent by ship, which is relatively efficient.

The Michigan study is for a wooden frame single family dwelling, which is very different from ANU's steel frame 70 apartment block, but some factors are similar. A modular building requires more materials in each module, as they have to be strong enough to be transported. This applies particularly with shipping container modules, which are required to meet railway safety requirements for strength as well as being able to support the weight of five loaded containers on a ship. The result is that a building built from containers is very much stronger than required, with much more steel used than needed for a conventional building. This gives locally made building modules, made for transport by truck, an energy advantage.
A 1,456 ft2 modular home and conventional site built home in Benton Harbor, Michigan are analyzed to examine how the different construction and design methods of two types of housing influence environmental impact over their 50 year life span. The chosen modular home is fabricated by Redman Homes in Topeka, Indiana and transported to the building site. The conventional home is modeled after the modular home in collaboration with Douglas Construction Company. Many assumptions and simplification were made due to data gaps, so results represent preliminary estimates. The total amount of the materials placed in the conventional home is 9% less than the amount of the modular
home because the modular home is framed with larger 2X6 studs and requires additional structural components. The conventional home produces 2.5 times more construction wastes than the modular home. The lesser material consumption of the conventional home is offset by a larger amount of waste generation. The building use phase dominates more than 93% of the life cycle energy consumption and over 95% of the total greenhouse gas emissions for both homes. The total life cycle energy consumption for modular home is 5%
less than the conventional site home. The total global warming potential for the modular home is 5% less than the conventional site built home. The use phase energy consumption and greenhouse gas emission differences are attributed to the expected higher air tightness (0.194 ACH) of the modular home over the conventional home. The conventional home was modeled with 80% lower air tightness (0.35 ACH) than the modular home, which results in 7% more of the natural gas consumption over its service life. The modular home requires additional transportation energy compared to the conventional home for
delivering the fabricated modular home to the site. However, 4~5 days of the modular home’s short fabrication cycle time allows the modular home to significantly reduce the employee’s transportation energy compared to that of the conventional home.

From: Preliminary Life Cycle Analysis of Modular and Conventional Housing in Benton Harbor, Michigan, Doyoon Kim, University of Michigan, 2008
The road transport part of the energy budget for the modules is likely to be higher, where a truck is used. But If transported on land by rail, rather then by road, the energy use would also be low. Also the manufacture of modular buildings benefits from economies of scale. Large shipments of materials to a factory are more efficient than small deliveries to scattered building sites. Of course greater environmental efficiencies could be achieved by using local materials from the site for building, but this is not commonly done in Australia.

Buying imported buildings at the same time as the Government is attempting stimulate the local construction industry is an interesting issue. The building industry has previously not had to face overseas competition, but now has to with modular building. My view is that the government should support the development of an Australian modular building industry which can compete on price and environmental sustainability. Australians should be able to buy locally made modular buildings. Subsidising the building industry is not a viable long term strategy, as subsidies for the car industry have shown. When in Tasmania a few months ago I suggested development of hi-tech wood modular buildings.

No comments: