IRC section R602.6.1 has this to say about "Drilling and notching of top plate:"
When piping or ductwork is placed in or partly in an exterior wall or interior load-bearing wall, necessitating cutting, drilling, or notching of the top plate by more than 50 percent of its width, a galvanized metal tie not less than 0.054 inch thick (1.37 mm) (16 ga) and 1 ½ inches (38mm) wide shall be fastened across and to the plate at each side of the opening with not less than eight 10d (0.148 inch diameter) [nails] having a minimum length of 1 ½ niches at each side or equivalent. The metal tie must extend a minimum of 6 inches past the opening. See Figure R602.6.1.
The figure demonstrates only a notched top plate, and shows the metal tie on the side of the top plate that is notched, but not (apparently) the side of the top plate that isn't notched. It also shows only the topmost plate in the double top plate being tied. This left me with several questions that I don't feel were fully answered by this section:
- Nonbearing walls are not mentioned at all. Does this mean that no reinforcement/tying is necessary? Seems like that would weaken the wall. I know it's not bearing weight from above, but people do lean on and occasionally fall against walls, both of which put lateral stress on the top plate. Scratching my head on why there would be no reinforcement, and assuming I'm missing a section somewhere.
- This (especially the figure) seems fully-tailored to notching only, even though it says "drilling or notching." If I drill (instead of notching) a hole greater than 50% of the top plate's width, and that hole is centered on the top plate (assuming no sheathing on either side of the wall), on which side of the wall do I attach the metal tie? Should it be attached to both sides of the wall? Or do I just pick one side to which to attach it?
- The figure only shows the tie on the topmost section of the top plate. So no reinforcement is required on the bottom section of the top plate? The text doesn't say. To add to the confusion, Simpson Strong Tie RPS (specifically listed for R602.6.1), one of the few SST connectors for which I can't an official installation instruction document, has pictures on the website showing the tie being installed on both plates, and says, "Only one strap may be necessary to meet IRC requirements" (emphasis mine). That's more than less than unhelpful.
(Even if the bottom tie strap, or straps on both sides, aren't required for structural purposes, I'm thinking that I'll need something to meet the nail/screw-penetration-prevention code requirements to protect the pipe, so maybe just using a second/third/fourth strap is the best approach.)
Anyone have any suggestions on what the best practices are here, and/or what the intent of the code is?