Unprotected areas in external walls

Any part of an external wall which has less fire resistance than that required by Section 4 should be considered to be an unprotected area. Where an external wall has the appropriate fire resistance but has a combustible material more than 1 mm thick as its external surface, that wall should be considered to be an unprotected area amounting to half the actual area of the combustible material as shown in Diagram 5.3. However, where such a combustible material has a Class 0 (National class) or Class B-s3,d2 or higher (European class) classification it need not be considered to be such an unprotected area. Any part of the external wall of a protected stairway should be discounted when calculating unprotected areas. (However, Section 2 and Section 6 contain provisions relating to the relationship between the external walls of protected stairways and the unprotected areas of other parts of the building.) Small unprotected areas may be discounted where they occur in an otherwise protected area of wall, provided that they do not exceed the areas and comply with the minimum spacing shown in Diagram 5.4.