The Lateral Bracing Required for Roof Trusses

Temporary End Bracing

• Trusses need both temporary and permanent lateral bracing. That starts with setting the first truss at the end of a roof. Once it is raised to the roof, set it upright and plumbed to be perfectly vertical and then fasten it to the wall caps on each side through the truss ends. It must be braced to keep it plumb and secure. This is done with 2-by-4-inch boards nailed to the outside of the truss rafters and to stakes in the ground outside. These are removed once framing is complete.

Purlins

• Once the third truss is set, temporary lateral bracing needs to be added with 1-by-4-inch boards cakked purlins, nailed across the outsides of the truss rafters. This will hold all three trusses plumb. Add purlins every third truss as they are erected down the wall. Some truss designs use a center ridge board for lateral support. This runs between the angled rafter tops and the length of the roof to hold trusses laterally. Many truss designs omit the ridge board.

Purlins and End Braces

• There are some options for lateral bracing, depending on roof style, snow load, wind and other factors. One style uses purling along the outsides of the truss rafters from end to end, with angled braces in three-truss clusters. These braces run from the top of internal braces to the bottom chord of the third truss, usually arranged in a triangle so the lateral braces meet at the bottom chord.

Maximum Bracing

• Maximum strength lateral bracing uses three-truss clusters with both top and bottom braces. Bottom braces run across the bottom chords, or horizontal members of the truss alongside the bottoms of internal braces; they are staggered so braces on one cluster are on the outside edge of the internal support, along the inside edge on the next. Diagonal braces run from the bottom of the first truss to the top of the third, one in the center and one on each side.

Decking

• Roof decking also provides lateral support. Either plywood or oriented strand board nailed to the truss rafters will support them laterally. This may be all the lateral bracing needed for a shed or other small building, unless there are strong snow or wind loads to contend with. The decking will add lateral support also with other types of lateral bracing.