*Approximate sizes, for exact quantity required please measure the area to be covered in m² and then divide by 4.08 to give you the number of rolls needed. Quantities indicated above are estimates based on insulating the attic floor with one top up layer only, if rafters are being insulated this is not included, if a double layer of insulation is used on the floor this is not included. Dormer quantities are based on half the area of the roof area being a sloping section and this area is not included in the quantity of rolls required. Factors influencing this area are angle of roof pitch, knee wall height and attic space available, please contact our tech department for further assistance.