Running cables thru joists: cool or not?

Old 05-29-23, 04:21 PM
Thread Starter
Join Date: Dec 2017
Location: USA
Posts: 8
Upvotes: 0
Received 0 Upvotes on 0 Posts
Running cables thru joists: cool or not?

I'm looking at a home listing and noted some wires in the ceiling area that appear to be routed through wooden beams with no conduit. Wondering if this is a code violation or safety hazard or if there are any other concerns. Thx in advance!

Old 05-30-23, 12:40 AM
Join Date: Mar 2014
Posts: 921
Received 147 Upvotes on 123 Posts
It is not really against code (check with local AHJ but may be grandfathered in anyway).
Fine as long as the holes are not too big where they may compromise the integrity of the floor joist.
Also less chance of damage with the cables going thru the joists than on top of them. I would be more concerned if there were open splices in the floor joists. Those could be put into jboxes though.
I would not turn down a purchase based on the cables going thru the floor joists though only on that fact. I would be more concerned with the quality of the breaker panel and service entrance cable condition.
Old 05-30-23, 07:03 AM
Join Date: May 2015
Location: USA
Posts: 3,087
Received 134 Upvotes on 110 Posts
Drilling holes through joists to run cables is typical and permitted, but there are guidelines for where and how to do it and your photo seems to show several violations of permitted practices, especially the rule against drilling too close to the edge of the joist or notching in the middle third of joist span, although it is hard to tell for sure from your photos.

This rule exists because the strain on the joists is greatest in the middle third of the span so drilling or notching there has the greatest potential to weaken the joist.

Would I decline to buy a house just because of this? In an older house, with no cracking of the joists near the holes, I would not let this prevent me from purchasing the house. As AFJES said, there are other more important things to worry about.

Old 05-30-23, 04:40 PM
Join Date: Oct 2015
Location: Ct.,USA
Posts: 2,909
Received 258 Upvotes on 230 Posts
Personally I would check with the local building authority to see if any wiring permits were ever pulled because the wiring does not look professional. I would also get the inspectors opinion on wiring in the photos because if you buy and someday sell, you don't want to get stuck with repairing old code violations discovered by the potential buyer who used a home inspector.
Old 05-30-23, 07:01 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: United States
Posts: 14,069
Received 778 Upvotes on 658 Posts
Running cables through joists is the proper way to install cables in an unfinished space.
CasualJoe voted this post useful.
Old 05-31-23, 10:26 AM
Join Date: Oct 2015
Location: Ct.,USA
Posts: 2,909
Received 258 Upvotes on 230 Posts
Toyln, a hole or notch in a joist weakens the joist in my opinion whether the space is finished/unfinished. Can you clarify what the difference is? I know of a situation where the ceiling joist part of roof trusses were drilled for cable. The AHJ would not approve wiring (required inspection point by permit) until each truss at each hole was sandwiched by plywood that was specified, shaped and located (including nail type and location) by documents from the truss manufacturer. There was no flooring in the attic so I would classify it as unfinished space.
Old 06-01-23, 03:17 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 13,920
Received 175 Upvotes on 153 Posts
Roof trusses should not be drilled. Drilling dimensional lumber is fine when the holes are drilled properly and do not weaken the structure.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: