Putting in screws near edge of joist
Hello all!
First time post… Heads up, I’m not a professional builder. I know the rule regarding not drilling a hole within 2 inches of the top and bottom of a floor joist, but what about putting in screws or lag screws within the top or bottom 2 inches? I get that on some level this creates a hole in the wood, but unlike a hole drilled to run wiring, this “hole” would have a piece of metal in it under tension (and thus would aide in transferring a load?). Given that I’m allowed to notch the top or bottom of a joist, I’m not super clear why I can’t drill in the top or bottom 2 inches to begin with.
Anyways, I’m working on a 1920s house that has boards for a subfloor, and I need to support them in the couple of areas with some blocking. I’ve been using GRK lag screws to secure the blocking between 2 joists, but I realized half way through the project that the top screws were about 1.25 – 1.5 inches away from the top of the joist, and that that may not be allowed as it could be considered a hole.
Thank you in advance for any help!
Replies
Screws and other fasteners are not treated the same as notches or holes.
Fasteners are fine - they are not holes.
I'm not an engineer, so take what I have to say below with a grain of salt.
I looked into this issue though myself while figuring out what fasteners to use for my deck. It seems to depend quite a bit on the type of fastener.
Many structural screw manufacturers (e.g., Simpson, SPAX, Fastenmaster, etc.) provide minimum edge and end clearances that are designed to prevent splitting, reduced load capacity of the fastener, etc. These clearances depend on the direction that load is being applied to the fastener relative to the framing member.
For example, Simpson SDWS framing screws require a 1" clearance from the edge of the framing member:
https://p.widencdn.net/a51vnh/C-F-2019TECHSUP-p26-29and119-122.pdf
If you're not using a fastener that has published clearance requirements, the American Wood Council's National Design Specification provides some general guidance (see section 12), but it seems mostly to apply to fasteners with at least 1/4" diameter:
http://www.plib.org/staging/wp-content/uploads/2020/09/AWC-NDS2018.pdf