For all materials, a process called life cycle assessment (LCA) can be used to quantify the amount of carbon dioxide which is emitted during manufacture. It includes other greenhouse gases as carbon dioxide equivalents.
In the case of timber, this CO2 would be associated with processes such as the forest management, harvesting, transport of logs, sawmilling, kiln drying etc. LCA studies allow comparison of the balance of carbon dioxide emitted in manufacture of one material with another, e.g. timber, PVC, steel, concrete, by comparing a functional unit of each material.
Timber compares favourably with many construction materials on carbon emissions. When timber is used in place of these other materials, a substitution effect is seen, reducing the total embodied carbon of the building. Recent studies by the BioComposites Centre, and by the NHBC, have shown that the combination of materials used in timber framed housing have lower carbon emissions than the materials used in masonry housing.