How to Repair a Rotted Roof Truss

Measure each part of the truss. A truss has a horizontal bottom chord, two or more vaulted top chords and supporting members that span the distance between the chords.

Diagram the truss measurements exactly so you can duplicate the truss twice.

Cut and label each piece of dimensional lumber you’ll use to duplicate the truss. You’ll have to build the two support trusses piece by piece in the attic, since there is no way to build them on the ground and then install them in one piece.

Start on one side and attach a new bottom truss chord tightly against the damaged truss, nailing it to the wall plates, and to the top of any load-bearing walls, if the original truss is so attached.

Construct the rest of the new truss in place,from the bottom up, cutting and fitting each piece and attaching it the same way the original truss is attached.

Repeat the procedure on the other side of the damaged truss. All three trusses should now sit side by side, with the rotted truss in the middle.

Insert carriage bolts from one side of the three trusses to the other side and tighten the bolts to secure the three trusses as a single weight-bearing unit.