New timber is often supplied with a structural rating - also known as an F-rating - based on its ability to carry load in house framing. Hardwoods are often rated F8, F11, F14, F17 and F27 in residential one and two storey frames. An interim standard for recycled hardwoods has determined they will be rated lower than new timber for equivalent species. The rating is based on research and testing which indicates that timber under load for 40 years has a minor degree of loss in inherent strength over that time. •Interim Standard - Structural ProductsAs a rule of thumb, recycled hardwoods drop one strength group - for example - from F27 to F17 - and the interim standard describes this in more detail. The determination will affect horizontal load-bearing beams and rafters most of all and it means that the use of recycled beams should be either decorative, lightly-loaded, supported by steel in the design process - or used in unroofed pergolas. In most specifications for vertical supports or posts, however, recycled timbers can easily meet an F8 or F14 structural requirement. Usually there is scope for the dimensions used to exceed the specification and easily comply. Best use of big end-section recycled timbers such as bridge timbers will be as steps, as posts, as a free-standing landscape palisade, as seats, bollards, pergola posts and beams.Beyond the merely technical, your rule of thumb for structural use of recycled timbers should be as follows. When the structural components of a building are hidden by cladding - use steel, plantation pine or engineered products. When they can be seen, use timber - recycled timber preferably - when it can be readily sourced. Alternatively, used kiln-dried certified native hardwoods rather than imports.