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how to rewire to add insulation?

rafterman's Avatar
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12-16-04, 01:42 PM   #1  
how to rewire to add insulation?

hi all,

i recently bought a house built in '66 (my first!). i knew beforehand that the insulation was sub-standard, so my first major project is to add insulation. the house has about 2-3 inches of cellulose in the attic and nothing else. i'm using a combination of removing and redistributing the existing cellulose, guided by previous rodent activity. i've purchased r-19 fiberglass with vapor barrier to go in the spaces (2x6 rafters). i'm also going to add partial plywood decking for storage and easier access. here's the kicker: the wiring. there's a lot of 14 ga. romex just laid across the rafters, and all fed by 20 amp breakers. definitely not a pretty scene. i'll have to replace this with 12 ga.- or should i use 10 in the attic? should i bore through the rafters near the bottom edge to pass the cables, and lay the insulation across it? that would slightly compress the insulation at those crossings, and i don't like the idea of pitch and paper vapor barrier laying on wiring. or should i run across the tops of the rafters, properly securing the cables above the insulation? i could then scab up with 2x2's to lay the decking across. i'm comfortable with wiring, but it's always been in commercial work with conduit and raceways that were nowhere near the thermal structure of the building, and i'm not used to this. i feel like i just can't see the forest for the trees. any bright ideas?


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resercon's Avatar

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12-16-04, 04:37 PM   #2  
I would first find out what is on the circuit for the 20 amp breaker. If it is just lighting or bedroom outlets, I would swamp out the breaker to a 15 amp breaker than re-wire.

If you need the 20 amp breaker on that circuit, you have to re-wire. Then drill holes in the middle of the 2x6's and run the wire through. Lay the insulation between the joists and under the wires. Once all the insulation is installed, take a scissor and cut through the top half of the insulation under the wires. Pull both sides around the wires and snug the insulation together. Just make sure you cut deep enough so not to compress the insulation. It doesn't matter if you cut too deep, as long as you do not cut through the entire thickness of the insulation.

homebild's Avatar
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12-16-04, 07:27 PM   #3  
Multiple Problems

You have multiple problems that need to be addressed individually.

First, if you have 14ga wire coupled with 20 amp breakers, it is much more reasonable and cost effective to simply install 15amp breakers instead of re-wiring the entire circuit unless there is some specific reason to have a 20 amp circuit here as resercon stated.

Second, it is a building code violation to drill holes in the middle third of any floor or ceiling joist span....so be careful where you drill....and you shouldn't even be concerned about moving any wiring at all...

And finally, it would serve you much better to simply use unfaced fiberglass insulation in your situation and quite worrying about wires and pitch because
your ceiling paint and drywall in the room below is about as much vapor barrier as you will need.

gsbaker's Avatar
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01-05-05, 12:42 PM   #4  
..it is a building code violation to drill holes in the middle third of any floor or ceiling joist span....so be careful where you drill....

The above statement is not true.

from 2000 IBC
2308.10.4.2 Notches and holes. Notching at the ends
of rafters or ceiling joists shall not exceed one-fourth
the depth. Notches in the top or bottom of the rafter or
ceiling joist shall not exceed one-sixth the depth and
shall not be located in the middle one-third of the span,
except that a notch not exceeding one-third of the depth
is permitted in the top of the rafter or ceiling joist not
further from the face of the support than the depth of
the member.
Holes bored in rafters or ceiling joists shall not be
within 2 inches (51 mm) of the top and bottom and
their diameter shall not exceed one-third the depth of
the member.

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