This document is based on BSRIA "Technical Note" TN5/88.1, "Rules of Thumb 2nd Edition". Its aim is to compare the rules of thumb values listed in the note with the practical rules followed by professionals in the French building services industry. A comparison of values reveals that the majority of data is similar, particularly those values which are closely connected with physics or unitary equipment. However, the document highlights some areas where French practice is substantially different from that in the UK. This difference is probably related to economic or legal situations, for example, town planning rules or decision-making patterns. In particular, the major differences are: the French allow considerably smaller dimensions for plant room sizes; building services costs per square metre of building area appear to be lower in France compared to the UK when related to total building costs. In the case of offices the difference amounts to 20 to 30 per cent. This difference seems mainly to be the cost of air conditioning. This may be due to lower air change rates generally applied in France. Air change rates imposed by regulations are usually lower in France than in the UK.
These lower rates are generally offset by a systemic application of the "cross-flow" principle, whereby polluted rooms are ventilated by air coming from less-polluted ones rather than from outdoors.