The GRSV30/25R Refurbishment Slate Vent is designed to be retro fitted without the need to cut slate battens. It is manufactured as standard for 600 x 300 slates but can be easily trimmed to fit 500 x 250 slates using the pre marked cut lines. It can be used for both high and low level roof ventilation requirements. Allows 10000mm2 airflow per vent UV Stablised Polypropylene The hood of the GRSV30/25 features a 4mm fly screen to prevent blockage from falling debris and entry of large insects into the roof space. Not suitable for extraction The GRSV30/25 has been extensively independently wind tunnel tested to the following standards:- BS 6367 Deluge test 225mm/hour rainfall. Driving rain test down to a roof pitch of 15 degrees with an up roof wind speed of 13m/s. Rainfall rate of 200mm / hour to generate a fine penetrative spray.