# The Heathrow Airport–London Noise Insulation Grants Scheme 1989, Paragraph 5: Specification for Windows


The existing window shall either be retained and converted to a double window by the installation of a new inner window or be replaced by a new double window, if this is essential, and the following conditions shall be complied with:
(1) any gaps in the outer window shall be effectively sealed by compressible resilient strip or other means;
(2) the inner window may be framed in wood, metal or plastics, and shall be well fitted into the existing window reveal or planted on the wall face around the reveal, with the junction between the 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;
(3) both the outer and inner windows shall be adequately openable for means of escape in case of fire to the extent that existing outer window allows for this, and for direct ventilation when required; 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 by other equally effective means;
(4) 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;
(5) at least two reveals of the window opening between the outer and inner window shall be lined with sound absorbent material provided that the works specified in this paragraph in relation to an inner window may include materials other than glass if the standards of acoustic performance provided by such materials are not less than those which would have been provided by the use of glass as specified in paragraph (2) of this Article;
(6) 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 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 thick 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

---
Source: https://www.legislation.gov.uk/uksi/1989/247/schedule/paragraph/5 (the official version)
Page: https://openlegislation.uk/heathrow-airportlondon-noise-insulation-grants-scheme-1989/schedule/paragraph-5
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.