When laying bradstone infilta concrete block permeable paving conventional mot type 1 is not used in the sub base as it is not free draining the bradstone 20mm open graded drainage is usedr r in free draining applications a suitable geotextile should be placed at formation level overlapping joints by 300mm below the drainage aggregate sub base when the sub base is designed to hold water an impermeable memebrane lining should be usedr r the depth of the sub base will be governed by the s