Hambleside Danelaw Universal Slate Roof Vent - Airflow 10000mm2   Universal slate ventilator for man-made or natural slates, suitable for soil ventilation and mechanical extraction. Sizes to suit either 600 x 300mm or 500 x 250mm slates. Minimum rafter pitch: 22.5 degrees or 25 degrees depending on head lap. Actual ventilation area 10,000mm2 Available in Black as standard. Recycled content up to 50% (Black polypropylene)