When I set about to repair an old trellis, I found that the rafters had developed dry rot around the toenails that affixed them to the support beam. To prevent this from happening again, I devised the combination flashing/anchor shown in the drawing. First I had a metal shop make up a standard parapet-type flashing out of 18-ga. galvanized sheet metal. The legs and drip edge of the flashing are about 1 in. wide. After laying out the positions of my rafters on the flashing, I used a sabersaw to cut 1-in. wide tabs in the flashing legs to correspond with the rafter layout. Bent upward, these tabs lie flat against the underside of the rafters. At each tab, I ran a 1-in. #10 sheet-metal screw into the bottom of the rafter. Now the trellis beam is protected by a flashing, and the rafters are anchored to it with fasteners that aren’t exposed to the weather.
Les Watts, Herndon, VA