I built an outdoor sandbox for the kids that's about 4' x 5' but haven't had the time to put a real roof on it yet. To keep the rain (and the poo of roaming cats) out, we have thus far been using a piece of plastic sheeting held down with a bunch of bricks on the edges, but we have to go out and empty a giant puddle of water from the middle of it after each rainstorm so obviously that's a temporary solution.

I would like to build an extremely simple and inexpensive lid/roof for the box that will last at least a few years. Shingles seem like overkill, but all of the ideas online that don't use shingles seem like they're going to fail as soon as they get wet (ie this guy who just painted an OSB sheet).

What would be a good material for roofing? Can I just tar some plywood? Would painting OSB actually work long-term?

3 Answers 3


Purchase a 4'x8' sheet of southern yellow pine (SYP) plywood that's been pressure treated for ground contact applications.

Typically that's an ACQ treatment at 0.40 or 0.60 pounds per cubic foot, and SYP because that species of wood accepts and retains treatment extremely well.

"Ground contact" is the highest level of treatment, and I chose it over the lesser "above ground" treatment because it is directly exposed to the elements, and the additional cost should be negligible for just 1 sheet.

You wouldn't even have to paint it, but if you do, use a paint designed/intended for use on treated decks.

The only thing I'd be concerned about is a finding a way to prevent the sheet of plywood from flying away during storms and periods of high wind gusts.

Depending on the thickness you purchase, it will begin to warp as the main failure mode, not decay or rot. To prevent that you may want to build a frame for it by screwing treated SYP 2x4s on the bottom around the perimeter, and maybe one or two running down the middle of it. Make sure the screws are short enough so they don't stick through the other side and poke little fingers when removing the sheet to play.

  • I'm a little suspicious of using treated lumber, assuming that it might leech into the sand. I did a fence with ACQ lumber last summer and had to start using gloves all the time after the skin on my fingers was getting really rough and cracked. Always assumed it was the treatment that did that but I don't know if I'm being too paranoid. If I applied a few coats of stain to untreated plywood, do you think it would hold up for a few years?
    – Egg
    Jun 22, 2019 at 19:47
  • 1
    @Egg CCA is the old way they treated lumber and it's scary stuff. Chromium and Arsenic are bad. The new way is ACQ and while it's harder on metal fasteners and hangers, it's a much less toxic treatment. The ammonia off-gasses quickly after treatment, and leaves behind the copper which is the primary anti-fungal and anti-bacterial. A plumber touches pure copper all day, a little in your wood isn't going to hurt anyone. Just paint the treated plywood and you'll be extra protected. Don't use regular plywood, it'll delaminate, rot, mold, and just fall apart with repeated moisture/water contact.
    – Dotes
    Jun 22, 2019 at 22:57

OSB is not rated for outdoor use, so I wouldn't even use it under proper roofing materials, since you will get condensation underneath.

I like Dotes' Southern Yellow Pine idea and framing it for weight including the center cross brace. But since you'll have a bit of extra plywood, I would propose to make it a slight "peaked roof", maybe 1 in 12, with the center cross brace running under the peak. That will keep water from pooling in the middle of it and making it soak in, weaken the plywood, sag, rinse wash repeat.

If you are hauling the plywood in a small car, that also means you can have it pre-cut to size, giving three <3'x4' sections, so it will fit in your car.

To be sure, let the plywood get plenty good and dried out, and prime it with original Kilz and then topcoat it with any old thing that isn't epoxy. (epoxy dislikes sunlight).

Monitor it, and if topside conditions are still rough on the plywood, get rubber roofing material and glue it in the middle so it doesn't flap. That performs well on near-flat roofs.


At Walmart they sell a sand box cheaper than you can build on. Comes with cover and stays on in wind.Easy to keep clean. Been down this road and kids let there kids play in it now. Sand box turtle . Will even fit into old frame as extra sand catcher. If out of wood and screws to hold down is a pain. My kids could remove and cover box.

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