The Noise Insulation Regulations 1975

Specifications for Permanent Vents

7.—(1) Every permanent vent shall consist of a sound attenuating purpose-made opening or duct which is designed to allow the passage of air between the room and the external air at all times, and shall have an external cowl (or grille) for protection against the passage of snow, rain and vermin. It shall be so constructed that when installed in a cavity wall exposed to the weather, the weather resistance of the cavity is retained and the acoustic performance of the vent is not impaired.

(2) The effective area of the air path through the permanent vent shall be ascertained by the method described in paragraph 6(g) above, save that for the words “ventilator system” in that paragraph there shall be substituted “permanent vent”.

(3) When installed the permanent vent shall be securely fixed to the wall and the junction between the vent and the face of the wall shall be fully sealed by means of compressible strip, mastic packing, cover strips or other equally effective means and where the vent has an air supply duct traversing a cavity wall the junction between the supply duct and the internal leaf shall be fully sealed by suitable means to prevent the passage of air to or from the cavity.

(4) Permanent vents shall be so constructed and installed as not to present a fire hazard.

(5) Every permanent vent shall either

(a) Vent type A

(i) have an effective area, ascertained in accordance with sub-paragraph (2) above, of not less than 3250 square millimetres and not more than 6500 square millimetres; and

(ii) be so constructed that the sound pressure level difference, ascertained by the method described in paragraph 6(h)(ii) above, complies with the requirements of that paragraph, save that for the words “ventilator unit” in that paragraph there shall be substituted “permanent vent”; or

(b) Vent type B

(i) have an effective area, ascertained in accordance with sub-paragraph (2) above, of not less than 3250 square millimetres; and

(ii) be so constructed that the sound pressure level difference, ascertained by the method described in paragraph 6(h)(ii) above, complies with the requirements of that paragraph, save that for the words “ventilator unit” in that paragraph there shall be substituted “permanent vent” and after the words “(where A is the measured sound absorption in the receiving room in square metre units at each ⅓ octave frequency)” there shall be added “and the addition of

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(where S is the measured effective area of the permanent vent type B in square millimetres)”.