This detail illustrates the installation of sag blocks on roof purlins for single slope (lean-to) roofs with a slope less than 2:12. Sag blocks provide lateral bracing to prevent purlins from rolling under load.
Different sag block types are used at different locations: SE- at the low eave strut, SI- at intermediate purlins, and SH- at the high side. Sag block clips (BC-42, L 2 x 4 x 16 ga.) are attached to each purlin.
At both the low eave and high side, sag blocks are secured using (2) 1/2" x 1" A307 fin head bolts with (2) washers per clip. At intermediate purlins, clips are secured using (2) 1/2" x 1-1/4" A307 bolts with (4) washers per clip, plus (2) member screws per clip in roof color. Maximum purlin spacing is 5'-0" O.C.
