Manthorpe G630 Roof Felt Lap Ventilator

Manthorpe G630 Roof Felt Lap Ventilator

Product Code VNTMANFLV

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Manthorpe G630 Roof Felt Lap Ventilator The Manthorpe G630 Felt Lap Vent is a refurbishment product designed to increase the amount of ventilation into existing roof spaces. Usually fitted retrospectively to properties with additional loft insulation recently installed, however the Felt Lap Vent will help to combat the problem of condensation build up in any roof space with a lapped felt or membrane construction Note: The specifier should ensure that the opening of felt laps on the property will not adversely increase the wind uplift load on the tiles/slates or the driving rain resistance of the roof, for more information see BS 5534:2003, 5.8.1 &


Free Airflow + -

  • Equivalent to 3,000 m2 / mtr

Technical + -

  • Material: Polypropylene
  • Colour: White
  • Manufacturing Process: Injection Moulded
  • Size: 275mm x 193mm


  • Can be fitted at joist centres ranging from 400mm to 600mm
  • 3,000mm2/m airflow
  • Easy to fit, the tapered lead in helps to slot the product between the felt laps
  • The 3 integral felt clips help secure the product in place even if the edge of the felt is degraded
  • Manufacturers Part No: G630



  • Initially it is recommended that one ventilator be placed into the laps in every other rafter bay, down at low level (as near to the eaves as possible) and on both sides of the roof space to ensure a cross flow of ventilation
  • In extreme circumstances, additional ventilators can be positioned in the vacant felt laps to increase the overall amount of ventilation provided
  • Only one product should be positioned into a single felt lap
  • If additional vents are required, then more vents can be placed into the other felt laps within the same rafter spacing at higher intervals
  • The product can be installed in roof spaces with rafter spacings ranging from 400mm to 600mm
  • Each unit will provide 3,000m square metres; of free airflow into the batten void
  • For further information on the recommended ventilation requirements for roof spaces refer to BS 5250 Code of Practice for Control of Condensation in Buildings
  • Orientate the G630 so that flat face is facing upwards and the curved face with the felt clips is facing down
  • Push the tapered front edge of the vent into the lap of the felt, once the front edge is in; pivot the vent up flat against the felt forcing the lap apart
  • Push the vent down into the felt lap, ensuring the flat top is in line with the underside of the battens
  • When the vent is almost in position, the felt clips will slide over the lower lap of the felt
  • Ensure that all 3 clips are properly located before proceeding
  • Once correctly installed all that will be visible of the vent is the top edge with the stated airflow of 3,000m square metres; and the 3 felt clips
  • Working across the roof space, slot the vents into the appropriate felt laps between joist openings to give the required amount of ventilation