We remove the existing felt and decking boards and check the structure for any water damage. Depending on the type of structure, this could be a good time to add additional insulation to your roof space. We then install new 18mm OSB3 decking boards, then fit the relevant trims to the edges and tape the joints. When installing a fibreglass roof we only use 600g matting as standard for a stronger roof. We then apply a dark grey top coat.