Wiring through joists in an insulated floor

[albrechtmyers]

Hello
I'm about to start a complete house refurbishment, including rewiring and insulating between floors.
As I understand it building regs require you to drill holes through the center of joists 0.25-0.4 along the span of the joist - this is going to put my cable run ~75cm away from the wall. Joists are 180mm high - I intend on completely insulating the void between ceiling/floor.
In an ideal world, I'd like to drill my holes right next to the wall so cable passing through joists are adjacent to walls. Cables running in the direction of the joists would be supported by P-clips allowing fast & easy installation. Installing the insulation, the cables would then be touching the joist/wall and could be argued as being installation method 100/102.
With my cables ~75cm into the room, will I either have to leave an insulation gap around the cables, or install a conduit between each joist and call it method A*? Or do I notch the joists (will have to be the bottom of the joist) and can this be classed as installation method 100/102?
Do cables have to be tightly clipped to joists along their run, or is running them in P-clips and pushing them against the joists with the insulation acceptable?

 

[LarryFine]

You could do strapping and run cables like this plumbing. Some debate whether that violates the 1.5" minimum.

Added: Debated here: https://forums.mikeholt.com/threads/wiring-between-strapping.13337/




By " P-clips", do you mean what we call Colorado Jims? (The second pic is one of mine that I found on Google!)

 

[Fred B]

Hello
I'm about to start a complete house refurbishment, including rewiring and insulating between floors.
As I understand it building regs require you to drill holes through the center of joists 0.25-0.4 along the span of the joist - this is going to put my cable run ~75cm away from the wall. Joists are 180mm high - I intend on completely insulating the void between ceiling/floor.
In an ideal world, I'd like to drill my holes right next to the wall so cable passing through joists are adjacent to walls. Cables running ........, will I either have to leave an insulation gap around the cables, or install a conduit between each joist and call it method A*? Or do I notch the joists (will have to be the bottom of the joist) and can this be classed as installation method 100/102?
Do cables have to be tightly clipped to joists along their run, or is running them in P-clips and pushing them against the joists with the insulation acceptable?

1. My understanding is holes need to be a minimum of 1.5 inches from edge of joist or stud (one of my inspectors will insist on measuring from edge of hole, a challenge on 2x4 walls), to keeps sheetrockers screws away from wire. The image of notches as pictured would be a violation perlings will not give the 1.5 inches or cable protection.

One building inspector here would say the notch would compromise the structural integrity of the joist, whereas a hole in center would not. The only way around that was to oversize joist so the notch depth would still leave the engineered structural dimension, and include cable protection.
2 We will simply split the insulation so cable is in center of insulation, no compression of insulation and no attempt to push cable toward wall contact. If you need it completely sealed, consider spray foam.

 

[gadfly56]

1. My understanding is holes need to be a minimum of 1.5 inches from edge of joist or stud (one of my inspectors will insist on measuring from edge of hole, a challenge on 2x4 walls), to keeps sheetrockers screws away from wire. The image of notches as pictured would be a violation perlings will not give the 1.5 inches or cable protection.
View attachment 2553657
One building inspector here would say the notch would compromise the structural integrity of the joist, whereas a hole in center would not. The only way around that was to oversize joist so the notch depth would still leave the engineered structural dimension, and include cable protection.
2 We will simply split the insulation so cable is in center of insulation, no compression of insulation and no attempt to push cable toward wall contact. If you need it completely sealed, consider spray foam.

He wouldn't be wrong. The load carrying capacity of a structural member is proportional to the square of the depth. Notching top or bottom can severely reduce that capacity as that's where the real strength is. Think of an 'I" beam; the strength is in the top and bottom chords. It's the same for a solid piece of lumber. That's why you can bore through the middle without killing the joist, within reason. IIRC, the limit is 1/3 the beam depth.