How can I mitigate water contact with a 2x4 screwed into concrete floor?

Question

In my unfinished basement I am going to be installing some cantilever shelving along the walls. Basically using 2x4's attached to the joists, with a carriage bolt, and to the floor... likely using a 2x4 as a base plate. The plans are based on the 2x4's being secured to the wall. I am trying to avoid that.

The floor part is what I am trying to figure out. The basement floor grades to a drain at the corner of the house so the edge might not be perfectly flat to lay 2x4 for a base plate. I figure I can fix that with some plastic or composite shims.

My basement leaks, like most, and usually only after heavy rains. We keep nothing on the floor that we don't want damaged. However if I screw basic 2x4's into the floor, with tapcon or equivalent, they are going to rot/mold/mildew. I could use PT but I am curious if there is something else I can use. (Wife doesn't like the idea and I understand that modern PT uses CA... the brown stuff as supposed to arsenic which was the green stuff. Very much a case of happy wife happy life).

Is there something I can put under not-PT 2x4's that will have water contact or some alternative that I can use as a base plate for simple shelving? I have not intention of attaching anything to the basement walls.

^{Image from woodgears.ca}

Answer 1

Looking at Mattias' article on woodgears.ca, I think you can hang the uprights from the overhead floor joists and cut them off above the floor.

The 2x4s coming down the wall provide a method to affix the shelving unit to the wall, not provide support from the floor. Some of the other contributors have "half-height" shelves pictured that only come down the wall so far.

You could probably still do it by "hanging" the uprights from the ceiling, but I don't know that it can support as much weight as installing it as designed.

Answer 2

Screw into the floor with galvanized brackets. Attach the 2x4 to the brackets with a gap. Prefably install a rubber flashing product to the bottom of the 2x4 and then use like a polyrurathane adhesive to further prevent wicking

Answer 3

Most lumber outlets should carry a plastic foam barrier (around the Seattle/Everett area I usually see it as a blue, closed-cell foam roll). It may be referred to as 'sill foam' or 'sill barrier'. This is usually used on a foundation wall before laying 2x4's or 2x6's down to build a wall. Or it's used under a 2x wall that's already built and is then rolled up to stand on the foundation, or stand in the middle of the floor area on the concrete slab.

Sill barrier will not protect your lumber if the basement is flooded (it's only 3/16" thick) but it will prevent moisture from wicking up through the slab floor day-to-day.

As for the slope I would correct for it like this:

• Lay the board on the concrete floor, place a level on top and shim the board until the bubble shows level;
• Assess how high the air gap (under the board) is at the biggest, get a block of wood or a shim (or something) slightly taller than the gap;
• Set your pencil on that block and slide the block-with-pencil across the floor to scribe a pencil line (on the side of your base board) that shows how much to remove to make the top level;
• Then I'd flip the board over and use either a powered hand-plane or a belt sander to carve the bottom to that line to allow the board to lay flat (instead of shimming, which only supports the wood at the shim). You then have an even surface to rest the shelving risers upon.

And for earthquakes I would attach the shelving to the wall at the top of each riser. (You mentioned unfinished walls, I'm picturing no drywall covering, just studs. If you tack a 2x4 horizontally across from each stud to each shelf riser you'll have a good quake-resistant unit.)

Answer 4

Your design makes no sense. You are going to nail/screw in the 2x4s how? They would have to be installed directly on the interior framing. So if you are doing that why aren't you allowed to screw or nail on a horizontal plane?

Then the fact that cantilevered shelving is terrible. It moves, it doesn't hold as much load and based on your plans if you have anything at all of weight the shelves would sag.

I love building monster shelves in garages - easiest way is to rip a 4x8 sheet and make you shelves 2'x8' and frame everything with 2x4s. These can be free standing or some people throw in a couple nails on wall side so they don't tip.

If you don't make a free standing shelf then just buy a metal shelving unit - I just saw an 8' tall one at big box for 225. If your basement leaks it is on legs and you can move it around.

I don't attach shelves to garage or basement walls unless they are cabinetry style shelving or if the shelves are very high. The issues with weight and access to the wall make this an easy debate.