choose between ceramic and vinyl floor tiles by comparing their relative environmental impacts per pound or kilogram. One would have to use something like impacts per square metre of flooring. In fact, in most cases, it would be better to consider the whole flooring assembly per metre, since the adhesives and underlayment required for each product could have major impacts. In comparing building materials it is often very difficult to avoid comparing apples and oranges in order to determine the most appropriate measures of functional equivalence. How comparisons are made also depend on the overall goals and audiences of the evaluation systems. All systemshowever simple or complexare usually some combination of evaluation and encouragement. They are all intended to create conditions for improvement. No evaluation system, no matter how scientifically based, is absolutely objective; some advocacy is implicit. But all systems express a different mix of evaluation and encouragement. Whereas life-cycle assessment (or LCA) is a more formalized quantitative procedure, eco-labelling and green product directories are more explicitly concerned with promoting the use of environmentally-benign products to consumers. But the subjective and objective elements of encouragement and evaluation are involved in all these systems. The different audiences affect the level of simplicity and aggregation in the systems (Jonsson, 2000). Some evaluation tools are software programmes for LCA specialists; they do much less interpretation and aggregation, and more raw data processing. Other evaluation tools are services for decision-makers. For example, the results of Hollands EPM ranking system, and many other forms of life-cycle assessment, are intended for use by manufacturers, designers or policy-makers, in order to improve