Wiring & insulation - where?

[Apropos]

OK. Here's a pretty basic question but I'm not sure which is best.

When you're putting in wiring into an exterior wall framed with 2x4s, is it best to put the wires on the INSIDE or OUTSIDE of the insulation? If on the inside, the insulation would have to be fed in behind the wires.

Just wondering. It would work either way but I wonder which is best

[louie]

wiring should be run through the CENTER of the studs to avoid the possibility of a nail or screw being driven into it. What I've always done when putting in fiberglass is to cut a slit across the width of the batt about 2/3 of the way through the fiberglass side (don't cut into the paper). If done even reasonably close to the wire run, the wire will nest right inside the slit that was made and the fiberglass fits nicely around it. No worries about stuffing insulation behind or in front of the wire.

[Chris Lewis]

According to louie :

Holes should be drilled thru the centre of the studs. Where the wire is "loose" between studs, codewise, it doesn't matter because (a) an errant nail or screw will push the wire aside, and (b), you do try to avoid nails/screws between studs anyway ;-) Codewise, it only matters where nails/screws are likely to be driven - thru the studs.

That said, slitting the batts helps avoid bunching up the insulation and prevents voids. Better insulation value.

[Martik]

What if it's a retrofit and one needs to snake a wire between joists in a finished ceiling?

[Chris Lewis]

According to Martik :

Code is considerably more forgiving with renovations - code is intended to protect the wire primarily before and during the covering of bare studs/joists with drywall or whatever you're using. Once the wall covering is up, the risk factors greatly reduce - the wire is in the wall and can't be snagged any more, and you're not going to be driving very many more wall board fasteners (absent another renovation ;-)

That means, for example, that fished wire doesn't need code-compliant support/strapping every 5'.

[This obviously does NOT apply to exposed wiring in attics and basements.]

Assuming your question is about a non-attic ceiling (floor above). You can fish it any old way. If you have to cross the joists, you drill through.

Yes, you do need to drill your holes _away_ from the joist top and bottom. Not so much from the electrical code perspective (tho "fastening" the wire in harms way is a bad idea regardless), but to avoid weakening the joists.

[Martik]

Thanks for the clarification. Yes, it is a non-attic ceiling and those attic wires hidden under the loose fireglass in the attic are a real PITA when one is walking about up there.