Rules of Thumb are general principles derived from practice and experience rather than precise theory. The 5th edition of Rules of Thumb has been created by referencing various contemporary sources in the building services industry and can reasonably be held to reflect current design practices. As with our previous guide, it will be useful for approximately calculating values, setting outline targets and rapidly comparing different options to inform the early stages of the design process. This popular publication has been updated and expanded to include more detailed information and now comes in a more user-friendly spiral-bound format.