A house requires energy for its operation. Keeping warm in winter or reading a book at bedtime takes oil from the tank or electricity through the meter. During the past 15 years, a lot of effort has been allotted to reducing this operational energy demand. It has been the focus of energy conservation programs worldwide. But there is another type of energy investment in buildings. It is the energy required for their construction: for the manufacture of components, their transportation to, and erection at, the chosen site. This has been called the embodied energy of a building, and it amounts to roughly the one quarter (25%) of the operational energy requirement over the life of the structure. This is quite a bundle, and the bundle gets proportionally bigger if the building is designed, constructed, and managed efficiently. Such an operationally efficient building may see more than half of its total lifetime energy requirement committed before the occupants even move in. The embodied energy therefore is a significant part of the lifetime total.

Let's look more closely at this energy vested in construction. Firstly, do not confuse embodied energy of a building component, as we are considering it here, with its potential value as fuel. Take a 2x4 stud, for example. Energy has been "embodied" in the stud through the felling of the tree, the milling, the shipping from the mill to the lumber yard and from the lumber yard to the construction site, and finally with its transformation from a stick on a pile to a functioning component of a framed structure. It also has a prorated share of the capital energy in the sawmill equipment used to mill it, and the transport system used to ship it. Furthermore, it has its share of the energy required to sustain the workers who have contributed to its evolution along the way. It is all part of the cost -the energy cost- of production which, in the case of our humble 8'0" length of 2x4, is about 40,000 Btu's. If, on the other hand, we were to burn the stud - that is to convert the biomass store of solar energy of the spruce/pine to heat - it would yield about 10,000 Btu's. Now that might be all you can do with some sticks off the lumber pile these days, but by burning them you are not retrieving their embodied energy. You are releasing a store of sunshine that was in the tree. The energy embodied in the manufacture of a building component is essentially a measure of non-renewable fossil fuel consumed.

During the 1970's a major study was undertaken using data gathered and reported by the Bureau of Economic Analysis of the U.S. Dept. of Commerce. The study identified the embodied energy requirements for over 400 different building materials and products

It is a particularly valuable store of information and has been largely neglected in the years since its publication.

To show the value of this storehouse of data, I have prepared some representative residential construction wall sections. There are six of them. Each diagram shows a typical one square foot "core sample" through the wall and below it ... Click here to download entire PDF.

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