Paragraph 6 Specifications for windows
An existing window shall either be retained and converted to a double window by the installation of an additional window or, if this is not practicable in the opinion of the responsible authority, be replaced by a new double window, as follows-
any gaps in the outer window shall be effectively sealed by a compressible resilient strip or other means;
the inner window shall be framed in wood, metal or plastic, and shall be well fitted into the existing window reveal or planted on the wall around the reveal, with the junction between the wall and the window frame fully sealed by means of mastic packing, cover strips or other equally effective means, and shall be glazed with glass having a thickness of not less than 3 millimetres, except for those windows which reach to less than 800 millimetres from the floor, and those windows within 300 millimetres of a door which reach to less than 1,500 millimetres from the floor, which corresponding to the width of such windows specified in the first column of Table 1 below shall be glazed with glass of a thickness specified in the second column of that Table:
TABLE 1
| Width of window | Thickness of glass |
|---|---|
| Not more than 250 millimetres wide | 6 millimetres |
| More than 250 millimetres, but not more than 1,100 millimetres | 8 millimetres |
| More than 1,100 millimetres, but not more than 2,250 millimetres | 10 millimetres |
| More than 2,250 millimetres | 12 millimetres |
both the outer and inner windows shall be capable of being opened sufficiently for means of escape in case of fire to the extent that the existing outer window allows for this, and for direct ventilation when required; the inner window shall be capable of being opened sufficiently for cleaning purposes but the opening lights of the inner window shall be well sealed around their edges either by compressible resilient strip or by other equally effective means;
if the window is a bay window or bow window, the inner window shall either follow the shape of the outer window or shall be taken straight across the bay or bow, and any projecting surround or window board required to close off the window cavity shall have a weight of not less than 10 kilogrammes per square metre;
the shortest horizontal distance or, in the case of a bay window or bow window where the inner window is taken straight across the bay or bow, the mean horizontal distance, between the glass of the outer window and the glass of the inner window shall be not less than the distance specified in the second column of Table 2 below in relation to the thickness of glass of the inner window specified in the first column of that Table:
TABLE 2
| Thickness of glass of inner window | Distance between inner and outer windows |
|---|---|
| At least 3 millimetres, but less than 4 millimetres | 200 millimetres |
| At least 4 millimetres, but less than 6 millimetres | 150 millimetres |
| At least 6 millimetres | 100 millimetres |
two or more reveals of the window opening between the outer and inner windows shall be lined with sound absorbent material;
if desired by the claimant, the works specified in this paragraph in relation to an inner window may include materials other than glass, whether or not the standard of acoustic performance provided by such material is comparable to that provided by the use of glass as specified in sub-paragraph (b), but grant shall be payable only up to a maximum of the cost of the work specified in sub-paragraph (b);
balanced vertical sliders shall be provided where appropriate.