Manthorpe Telescopic Underfloor Vents with Extensions. Designed to provide a clear airflow passage to the void underneath a suspended floor. This telescopic vent (Part number: G960) provides 6,600mm² of airflow. The telescopic feature enables it to be adjusted between 3 and 7 brick courses. For optimal airflow, use with a Manthorpe G930 airbrick. Features a special grille to prevent vermin entry. Extension sleeves and other fittings for this product are available separately. Meets NHBC requirements for the control of condensation in buildings. This product is compatible with extension sleeves (G961) and remote void vents (G962) for additional depth and cavity span. Complies with BRE Digest 17, BRE Digest 262, Building Regulations C4, NHBC Standards 5.2, and BS 5250:2011 Control of Condensation in Building.