Install Backer block tight to top flange. Attach with 10 no. 3.75 x 75mm nails, clenched where possible. Backer block to be a minimum of 250mm wide.

Install filler block tight to top flange. Nail using 4.0 x 75mm nails as per Filler block table.

Use 4.0 x 90mm nails for 89mm wide flanges.