Our 18mm replacement fascias are so called because they need no backing board - they are a straight replacement for old timber fascias as they are nailed directly onto the rafter feet.The name is a little misleading as nowadays these boards are most commonly used on new build projects.Available in sizes from 150mm to 250mm, replacement fascias should be fixed using 2 x 65mm polytop nails at each rafter (maximum spacing 600mm for white and 400mm for all other colours).The return leg on the board is slightly rebated to accept a soffit board. The return leg measures 36mm overall from front to back as can be seen in the technical drawing tab.