Adding plywood flooring in attic

I see no reason why 2 x 8 joists spaced at 16 inches apart would not be MORE than sufficient to support a plywood deck.

Besides, those joists going over the tops of walls that divide your living area offer a lot of structural support.

You could chisel down a bit into the joists to get the electrical wire off the top of the joists, but that surely won't be up to code as the joists should have bored through holes to run the wire well below the top surface of the joists.

But if you go the chisel route, put those small metal plates over the area of the wire so you won't accidentally run a screw or nail through the wire.


ETA: If you chose to set the wires below the surface of the joists, I'd suggest not using a chisel to do most of the work. Use a saw to cut the depth, then the chisel to remove the small piece of wood. Too much pounding on the joists could result in cosmetic ceiling damage with nail or screw heads being exposed.

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Most sources are saying you shouldn’t do this without talking to a structural engineer

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maybe if you plan to store engine blocks up there and thousands of pounds of car parts

use 3/4" plywood if you expect to put a lot of heavy stuff in there, otherwise 1/2" is fine for normal storage, and be sure not to cover over any junction boxes so it meets code

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Also, I'd recommend 5/8 deck. 1/2 just doesn't feel right especially if you are carrying something heavy.

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Especially if the previous owner just missed a joist and you walk on it while carrying something large. You won’t go through, but it’ll flex enough to scare the shot out of you making you think you’re going through

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Also, if I have an electrical wire running over a joist can I chisel out a shallow channel to run the wire in so I don’t pinch the wire between the joist and plywood?

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Instead of chiseling a channel add shims on top of the joist to raise the plywood over the wires.

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Instead of chiseling a channel add shims on top of the joist to raise the plywood over the wires.

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This is exactly what I did. I used 1/2 plywood strips for shims and raised everything up over the wires.

Is that up to code?

Someone mentioned not covering junction boxes. Is there anything else I can’t cover? What about can lights?

Use screws instead of nails. Banging nails can crack the Sheetrock on your ceiling.

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Be careful about the weight.

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And don't listen to people that say 2x8 @ 16 are fine. If your span is 25' they won't handle any additional load.

My offer still stands to run a check and get the actual allowable load but at least look into the tables or use one of the suppliers calculators. Weyerhauser's Forte is easier to use but Boise's BCCalc seems more accurate and both are free to use.

Use the span tables. 2x8x16 is dramatically different than 2x8x8.

I ran 2x12 anywhere I wanted to put decking in the attic of my shop. 2x8’s will work but the span makes a difference.

AKA 2" X 12" and 16" on center.