The environmental performance of construction is of increasing importance to building designers, owners and occupiers. Building impacts arise mainly from operation, but also from environmental impacts 'embodied' in the fabric of the building. Using Life Cycle Assessment (LCA), environmental impacts of construction products can be compared and the impacts of extraction, manufacture, use and disposal can be measured. LCA of timber products shows that in many applications timber has a low environmental impact, when one takes into account the impact of replacement, maintenance and disposal. This Digest contains guidance to help construction professionals take advantage of the excellent performance of timber products. It gives typical environmental impacts from the various stages in preparing sawn, treated UK-grown softwood. Data from the BRE Environmental Profiles Database show that building elements containing timber often perform better than their alternatives. Different types of ground floors, external walls and flooring are compared for their environmental impacts. 8 pages.