Manthorpe Telescopic Underfloor Vents with Extensions. Designed to provide a clear airflow passage to the void underneath a suspended floor. Provides 6,600mm² of airflow. The telescopic feature enables it to be adjusted between 3 and 7 brick courses. Meets NHBC requirements for the control of condensation in buildings. The vent is suitable for use with a Manthorpe G930 airbrick and includes a special grille to prevent the entry of vermin. Extension sleeves and other fittings are available separately. Complies with BRE Digest 17, BRE Digest 262, Building Regulations C4, NHBC Standards 5.2, and BS 5250:2011 Control of Condensation in Building.