Deck Ledger, Joist Drilling, and Field-Cut Roof Truss
A 16-foot by 20-foot deck is attached to a house with a 2x10 rim joist. The builder fastened the ledger with 16d common nails at 12 inches on center; there are no lag screws or through-bolts, and the ledger is installed over 1/2-inch foam sheathing with vinyl siding. The deck joists are 2x10 at 16 inches on center. In the basement, a plumber drilled a 3-inch-diameter hole through a 2x10 floor joist; the hole edge is 1-1/2 inches from the bottom edge and 4 feet from the support. Upstairs, a roofing crew cut the top chord of a prefabricated roof truss to fit a 2-foot by 4-foot skylight. The framing inspector is asked to approve the deck, the joist hole, and the truss modification.
1. Is the 3-inch hole through the 2x10 floor joist allowed?
Read the worked answer
No as located. R502.8.1 permits holes not larger than one-third the joist depth, but not within 2 inches of the top or bottom edge and not within 2 inches of another hole; holes are also prohibited in cantilevers. A nominal 2x10 is 9.25 inches deep, so one-third is about 3.08 inches; a 3-inch hole is just within the size limit. However, the hole edge is 1.5 inches from the bottom edge, less than the required 2-inch clearance. The hole must be relocated or the joist repaired or reinforced per an engineered design. The inspector should not accept it simply because the diameter is under one-third.
2. Does the deck ledger attachment comply?
Read the worked answer
No. The IRC deck provisions require the ledger to be attached to the house framing with approved fasteners, typically 1/2-inch lag screws or through-bolts with washers, spaced per Table R507.9.1.3(1) or an engineered design. 16d common nails at 12 inches on center do not meet that attachment. The ledger is also installed over 1/2-inch foam sheathing and siding, which is compressible and prevents direct bearing on the rim joist; the siding and foam must be removed at the ledger or an approved standoff detail used, and the ledger must be flashed to shed water. The inspector should require correction and possibly an engineered connection.
3. Can the top chord of the prefabricated roof truss be cut for the skylight?
Read the worked answer
No. Prefabricated trusses are engineered components; R802.10.4 prohibits field modification without the approval of a registered design professional. Cutting the top chord removes a compression member and can cause roof collapse. A skylight also needs a properly framed curb, flashing, and structural support designed for the roof loads. The contractor must either obtain a truss repair design from the truss manufacturer or engineer, or reframe the opening with an engineered header and curb. The inspector should stop the modification and require sealed details before covering.