The following paragraphs provide guidance on how to provide the necessary fire resistance in an existing timber floor (see Para 7.3.2, Para 7.3.3).

The techniques generally adopted to upgrade the fire resistance of timber floors are as are as follows:

(a) The provision of a fire-resisting layer, or layers, beneath the existing floor joists. There are many techniques and materials available for such purposes. In some cases, it is also necessary to provide a protective layer on top of the existing floor- boards or between the floor joists.

(b) The provision of a suitable fire-resisting material in the voids between the existing floor surface and the ceiling below, or where there is no ceiling, between the floor joists. There are a number of proprietary systems available which are based on this method. These are often more appropriate than the method outlined at

(a) above in buildings of historic or architectural interest, where existing plasterwork is to be retained.

Many of the techniques employed in upgrading timber floors involve the use of proprietary materials and systems. These must be capable of achieving the required performance in the situations for which they are adopted. Particular care and attention to detail in the execution of any such upgrading works is necessary to ensure the required performance.

Table 14 of the Building Research Establishment report - Guidelines for the Construction of Fire-Resisting Structural Elements (BR 128) provides guidance in relation to the construction of fire-resisting timber floors.

Guidance on upgrading the fire resistance of existing timber floors is provided in Building Research Digest, number 208, and BS 5268 - Part 4 - Structural use of timber - Fire resistance of timber structures - Recommendations for calculating fire resistance of timber stud walls and joisted floor constructions.

7.3.4 Fire Resistance of Timber Floors in Existing Buildings

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