The spread of fire within a building and from one building to another can most effectively be restricted by the identification and isolation of potential hazards. Therefore, the first defence involves siting. Having established that potential fire risks exist by the nature of the functions accommodated, it is necessary to select the appropriate siting for a building relative to safety of nearby properties. An extreme example might be that of a building accommodating particularly dangerous fire hazards (e.g. manufacture and/or storage of highly flammable chemicals).
This should be located in a remote part of the countryside, away from properties likely to be damaged by heat radiation caused as a result of the fire.

Building legislation exists (Building Regulations, Approved Document B: Fire safety) to restrict fire spread by stipulating periods of fire resistance and construction methods appropriate to the function of a building, as discussed earlier. It also limits the use of certain construction methods according to their distance from other properties and/or boundaries. For example, only a nominal amount (0.1 m2) of unprotected combustible material (such as timber cladding) is permitted on an external wall of a small residential building if this is within 1 m of its boundary.
The unprotected area can increase relatively between distances of 1 m and 6 m; over 6 m the amount is unrestricted. Windows, doors and other openings in external walls are also carefully controlled since, unless special forms are used, they do little in stopping the spread of fire from inside or into a building. Regulations restrict the positioning, size and amount of these openings according to function (fire risk of a building as well as location of the external wall relative to other properties and /or boundaries).