Q. While working on a kitchen renovation project for a client, I was asked to take a look at his deck. He had noticed that a few of the galvanized lag screws used to fasten the ledger to the house had developed some rust and wanted me to replace the rusty screws. Is it OK to put the replacement screws in the same holes, or will the potential pre-existing rust and corrosion in the hole promote early rust on the new ones?
A. Bruce Barker, a licensed contractor and certified ICC inspector who owns Dream Home Consultants, in Fernandina Beach, Fla., responds: First, determine if it is necessary to replace the screws. If the surface rust can be easily removed and if the deck ledger and the band board/rim joist inside the structure appear to be in good condition, then it is usually acceptable to leave the lag screws in place. You should advise your client to monitor the screws and the wood for deterioration and to replace them if the deterioration becomes significant.
If the rust is deeper than the surface or if the deck ledger or the band board/rim joist is deteriorated, then replacement is recommended. Installing new fasteners—whether screws or bolts—in existing holes is not recommended, however, especially when screws are involved. If the fastener is rusted where you can see it, the wood around the fastener may be deteriorated where you can’t see it. It doesn’t take much wood deterioration to decrease the load-bearing capacity of the wood and to decrease the withdrawal resistance of the fastener.
Assuming that the wood in both the ledger and the house framing that it is fastened to appears to otherwise be in good condition, the recommended procedure is to fill the existing holes in the ledger so that they are watertight, then install new fasteners in new holes.
If you install new fasteners, be sure to leave enough distance between the old holes and the new ones. Good practice is to locate fasteners at least seven fastener-diameters from other fasteners (3 1/2 inches for a 1/2-inch fastener). You also need to maintain at least 2 inches of clearance between fasteners and the top and sides of the ledger, and a minimum of 1/2 inch between a fastener and the bottom of the ledger.
Fastener holes can be a water infiltration point. Check the ledger flashing to be sure it is properly installed.
Galvanized fasteners, and all galvanized hardware, are subject to rusting. This is especially true when used with lumber with copper-based preservative treatments in wet environments. The steel rusts when it reacts with the copper (galvanic corrosion of dissimilar metals) in the presence of water. In most environments, the corrosion process can take a long time because of the sacrificial zinc layer that protects the steel, but it can happen rapidly near salt water. This is why the 2018 IRC requires stainless steel fasteners and connectors for all decks exposed to salt water or within 300 feet of bodies of salt water.
For more information about fastener and hardware corrosion, see “Red Rust on Coastal Decks Is a Safety Warning,” (a review of “Coastal decks: red rust on decks is a safety warning” by Frank Woeste, Joseph Loferski, and Bruce Barker, ASHI Reporter, January 2019, as reprinted in Building Safety Journal) and “BRANZ Study Focuses on Fastener Corrosion” by Skip Walker.
