The Noise Insulation Regulations 1975

Specification for Windows

4.—(1) The existing window shall either be retained and converted to a double window by the installation of a new inner window, or replaced by a new double window if this is essential, and the following conditions shall be complied with—

(a) subject to the requirements of sub-paragraph (c) below, any gaps in the outer window shall be effectively sealed if this is possible by compressible resilient strip or other means;

(b) the inner window may be framed in wood, metal or plastic, shall be well fitted into the existing window reveal or planted on the wall face round the reveal, with the junction between wall and 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;

(c) both the outer and inner windows shall be adequately openable for direct ventilation when required, and the inner window shall be adequately openable for cleaning purposes, but the opening lights of the inner window shall be well sealed round their edges either by compressible resilient strip or other equally effective means;

(d) 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;

(e) at least two reveals of the window opening between the outer and inner window shall be lined with sound absorbent material;

(f) the shortest 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 not be less than the distance specified in the second column of Table 1 below in relation to the thickness of glass of the inner window specified in the first column of that Table:

TABLE 1

Less than 4 mm and not less than 3 mm thick	200 mm
Less than 6 mm and not less than 4 mm thick	150 mm
6 mm thick or more	100 mm

(2) Where it is not practicable to comply with any of the specifications in this paragraph the most practicable alternative specification may be used, provided that in every case the windows shall be adequately openable for direct ventilation.