Two methods are given in this document for calculating the acceptable amount of unprotected area in an external wall that is at least 1 m from any point on the relevant boundary (For walls within 1m of the boundary, see Para 4.4.4 and Para 4.4.5 above).

Method 1 (See Para 4.4.6.2) is only suitable for small residential buildings which do not belong to Purpose Group 2(a): Residential (care facility).

Method 2 (see Para 4.4.6.3) may be used for buildings or compartments for which Method 1 is not appropriate.

For the buildings outlined above, either Methods 1 or 2 as appropriate, or the enclosing rectangle (geometric) method, or protractor method specified in BR 187 External Fire Spread: Building Separation and Boundary Distances may be used.

For buildings or compartments not meeting the criteria as specified in Methods 1 or 2 (including buildings higher than 10 m or compartments more than 10 m in height,) the enclosing rectangle (geometric) method specified in BR 187 External Fire Spread: Building Separation and Boundary Distances should be used.

For buildings or compartments which are fitted throughout with an appropriate automatic sprinkler system (see Section 8), the values in columns (a) or (b) of Table 21 may be halved. Similarly, where BR 187 is used, the provisions of Para 2.1.7 of that document are appropriate where buildings or compartments are fitted throughout with an appropriate automatic sprinkler system (see Section 8).

4.4.6.1 Methods for Calculating Acceptable Unprotected Area

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