Under-appreciated Inefficiency

by Don Friedman on May 5, 2011

Efficiency is ordinarily a goal in any technological undertaking. We want our vehicles to be energy-efficient, our computers to be time-efficient, and our building designs to be simply “efficient.”

But what does efficiency actually mean? Any design is a response to multiple criteria including the physical properties of materials, code requirements, costs, clients’ stated desires, aesthetics, and conservation philosophy. When we pursue efficiency, we optimize our design to favor one or two – or on rare occasions three – of the optional criteria. We cannot negotiate code requirements or physical constraints, but we can reduce cost by reducing complexity at the expense of preserving less historic fabric. We can preserve the maximum amount of historic fabric at the expense of greater cost and slower construction. We can minimize disruption of occupied spaces within buildings at the expense of slower construction and greater loss of original material. We can provide maximum flexibility of use at the expense of greater intervention and cost.

Much of our work in conservation benefits from past inefficiency. Structural inefficiency, in the form of under-stressed materials from the over-conservative nature of old codes and design techniques, allows old buildings to survive damage that reduces their load-carrying capacity. Architectural inefficiency, in the form of thick masonry bearing walls and partitions[link or pix from HABS], provides locations for installing modern mechanical systems and provides thermal mass for modern energy analyses. Conservation inefficiency, in the form of old partial repairs and alterations, preserves a physical record of work performed and of the previous versions of a building.

There is an obvious place for efficiency in new-building design and construction, but the standards of efficiency change with technology. For example, a steel-frame design that was efficient in the past may now seem wasteful in a pure structural analysis, but usefully wasteful when deterioration and overloads are taken into account. Or a design that was structurally redundant may show a benefit that the builders did not expect when a poorly-designed alteration removes part of the main load path. In addition, new-design efficiency loses meaning when we consider one of the most basic trade-offs in building life-cycles: first cost versus maintenance. A design that is physically efficient but expensive is useless to a client with a small capital budget, while a design that is cost-efficient but will require periodic re-work or extra maintenance will be an annoyance to a client with occupied spaces that cannot easily be emptied.

There are obvious places for efficiency in restoration and alteration work. For example, space for new structural or mechanical systems may be limited by existing finished surfaces and only an efficient design can fit in the space available. However, we must not make the mistake of thinking that the aging processes and interior use of a building are frozen at the time of our restoration. Weathering will continue, accidental overloads will continue, and the need to change mechanical systems will continue. A restoration design that is too efficient may rapidly become obsolete while one that is “wasteful” remains serviceable. Worse, such a design is self-defeating. If the purpose of conservation is to preserve the built environment, the work must be performed in such a way that allows for future conservation. Based on our experience of the past, this requires inefficiency – which we must be careful to not eliminate from our work.

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