Raise attic floor over wires with 2x2s?

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Old 02-02-16, 11:03 PM
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Raise attic floor over wires with 2x2s?

ok so imagine an attic with about 15 wires running perpendicular to the joists. I want to put plywood flooring in. The wires are basically through the center of the attic - if they were on the edge, I would just leave them and not put plywood at the edge. I know most people with wires etc like this will build a 2x6 (and sometimes 2x4) perpendicular frame over the joists and then put the plywood on that. Is there any reason I can't just raise up the joists by screwing 2x2s on top of them along the whole length except where there's wires? (I would bunch the wires up tight together to minimize the spaces with wires and thus without 2x2s).




Whole reason is that this would be much faster than building a perpendicular box (although that's not so hard but it could run into issues with the rim joists meeting obstacles etc. It's less cost and materials to use 2x2s. The head room is a lot more if raised up only 1.5" with a 2x2 vs raised up 5.5" with 2x6s (or 3.5" raised up if using 2x4s but I don't realty trust the strength of a 2x4 joists even though it technically can span such a small space over existing joists 24" OC but I would rather just screw 2x2s over the existing joists and put the plywood over that. The wires might not have a lot of slack. If you build a perpendicular 2x6 frame over the existing joists, you need slack in the wires so they can weave under the new joists.

I mean, I don't really see why not, it's like saying you can't because raking/ sideways movement would actually break the 2x2s off of the joists which is not going to happen. But I'm baffled why no ones else does this instead of a 2x6 perpendicular frame.

I made a picture, it's not the actual attic, there is more than just one wire. but the red lines are how most people build the new frame over the wires, and the blue lines are 2x2s screwed on top of the joists.
The picture of the perpendicular frame without the red and blue lines is what I don't want to do.
 
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Old 02-03-16, 05:13 AM
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You can run your 2x2's on top of the existing framing, skipping the wiring, BUT, you would need to ensure screws or nails aren't subsequently nailed into the wiring, so No Nail plates will be required to jump the gap across your 2x2's. What is the purpose of the flooring? Are you planning a room, or just for storage. Have you determined the ceiling joist system will actually handle the added weight without vertical support?
 
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Old 02-03-16, 10:51 AM
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2x2s will add ZERO structural strength but they, along with whatever you use for flooring, WILL add dead weight to the existing structure. Depending on what size the existing joists are AND their unsupported span, you may be overloading the existing structure. In addition, any live load (people, furniture, storage items, etc.) that you pile on top of the new floor will increase the loading on the existing structure.

If you are planning on this to be an "occupied" space (not just dead storage) then you really need the blessing of a structural engineer or a competent architect BEFORE starting construction. Most areas will also require a building permit and that will most likely require "stamped" drawings from an engineer or architect before the permit is issued.

Or, if it is going to just be a dead storage area you may want to rethink the entire idea. Attics are generally poor places to store just about anything for a number of reasons. The existing construction probably was never intended to support anything more than the ceiling drywall from below and the attic insulation. Some pictures of the actual attic (not a similar picture from the Internet) as well as the dimensions and spans of the joists would help.
 
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Old 02-03-16, 01:05 PM
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someone mentioned to predrill the 2x2s to avoid splitting which I will do.


With fresh wet exterior pressure treated lumber, it probably won't split, but this kiln dried interior wood usually splits, especially with the thinner 2x2s (which are extra dry because they sit in the store unbought for a while, some are so bowed from drying they are like corkscrews.



I wasn't planning to put nail plates in. I have done this a million times in basements drywalling over wires and never hit one. But In case the homeowner needs to add more screws years form now if it's creaking or if they remove a board(s) to run new wires, they might put the screws back and hit a wire. They do have some pretty long nail plates but if I have to custom cut them from flat plate metal I guess I have to.



I could use flat plates or hurricane ties to secure the 2x2s to the joists (sort of like adhesive) but I think that's overkill.



It's just for storage, not a living space. Here are actual photos of it. Solid 2x8s 16 on center so that's all good for support, it's just like a second floor frame for a bedroom, it will hold but I'll let them know not to put thousands of pounds on it.



That 2x4 brace going perpendicular through the center of the attic will stay since it's for bracing (although all the decking will be bracing but I just don't want to remove that long 2x4 and add in flush blocking/bridging. Usually that 2x4 is on the flat and not as much of a nuisance but I don't want to go banging on it with a nail puller to put it on the flat (or use a nail gun for anything) because I don't want to possibly crack the drywall spackle in the ceiling under it.



One photo shows a step down, If those are 2x8s, then I'll raise them up a little more, possibly only building a perpendicular box over that area or seeing if they can live with a step down, but if they are 2x4s, they I won't do that area but this is NJ, not the south, and usually in this area all attics can support stuff. Mine is only 2x6s with like a 15' span 16on center and holds a ton of stuff stored.



There's no insulation as you can see but I don't really want to get into that if they don't mention it but I know rafters are sort of controversial to insulate or not (with rigid foam) but I think maybe I should throw some cheap R12 fiberglass in the joist bays. Faced or unfaced? I have to research that but pretty much every attic is insulated with faced r12 fiberglass in the joist bays, paper side down.
 
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