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scool 11-05-2010 01:40 PM

Laying attic floor: what should I do about exposed wiring?
I want to lay subfloor in my attic and wonder what to do with the exposed wiring that will be in storage areas.

We have an attic that we use for storage. We have a hip roof, and there is an area in the center with good headroom and a floor, surrounded on all sides by low headroom areas with no floor and exposed cellulose insulation. I want to extend the floor into the low headroom areas to increase storage and seal in the cellose (it's causing dust problems downstairs, we access the attic several times a week to retrieve stored items).

Our wiring was run in the low headroom areas, romex and junction boxes run on top of the joists. What should I do about the wiring? Should I pull the wire staples and junction boxes and slide the OSB under the romex and leave it exposed? Should disconnect wires at the junction boxes, drill holes in joists and pull wires back through and reconnect? Should I install firring and put OSB over the wiring, and cut holes for junction boxes?

Note that the ultimate goal is to finish the central area of the attic and the low headroom area will be accessible storage.

jogr 11-06-2010 08:18 PM

I'd be inclined to tack down 1x2 furring strips on top of the joists leaving gaps for the wiring. It's a lots easier than any other alternative.

Thurman 11-07-2010 08:36 AM

Local building codes/NEC will dictate this in your area, but: I bore a hole just below the top of the ceiling joist, then cut out the top area of the hole with a wood chisel. This allows the wiring to be placed into this new U-shaped "groove". Do remember to nail a protective plate over this area after the wire is in place to prevent a nail from entering the wire. David

J. V. 11-07-2010 10:38 AM

I like the idea to raise the sub floor. Its cheap and you do not have to touch the cables. Great suggestion jogr!

scool 11-08-2010 10:39 AM

Thanks for the suggestions! I'm inclined to do the firring. Notching the joists is a great idea, but I've only got 1x6 joists and there is a big span below where most of the wires happen to be so I want to keep all the strength I've got.

I guess I'll cut a hole for each junction box and either add a box extender or just fill gaps with expanding foam. Any tips on how to easily place those holes in right spot on the subfloor panel? Thanks again!

Gary in WA 11-08-2010 02:48 PM

Good call! You cannot notch in the middle 1/3 of the joist anyway.
I would just rip some plywood (not OSB) into 12" pieces to lay for storage. Space them 3/4" apart on the long side to let the rising air/moisture through rather than condensing on the bottom of the material. One on each side of the wiring instead of furring. 5-1/2" of cellulose is minimal, where are you located?


scool 11-11-2010 11:23 AM

I'm in western Washington State. I'm reluctant to not completely encapsulate the cellulose because of the dust issues we are having in the house and because the ultimate plan is to make the attic a finished space. But your concern about moisture troubles me a bit. I'd like to know more about how much of a barrier subfloor material might be. Note that while our area does get a lot of rain, it's mostly in the colder months when the home is heated, so we do not have the humidity issues that much of the US has.

As for R-value, I think I can get by with 6.5 inches of cellulose insulation - that's about what we have now and our gas bills are very reasonable. Eventually the plan is to finish the attic, which will require a new roof, skylights, and insulation in the rafters. I plan to re-roof next summer.

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