Shade. Your kids will want to spend hours in the sandbox, so make sure it’s someplace that is protected from the sun’s harmful UV rays. This can be near the house or a shade tree (be careful you don’t damage the roots when digging). It can also be a portable patio umbrella, which has the advantage of being able to be placed where needed for maximum shade. Sight. Make sure your sandbox is easily within the line of sight so that the adults watching the children can keep an eye on them. Drainage. After a summer shower, you’ll want to make sure your sandbox can drain naturally, so build it at a higher elevation if possible, and definitely not in a low spot in your yard. Try to build it so that there will be a slight slope. This will help with drainage.
For this example, we’ll assume a 6’ square sandbox, so cut each board to 5'8-1/2" in length. If you have a circular saw, you can do this yourself. If not, your lumberyard will be able to do this step for you. 4x4 lumber is actually only 3-1/2 x 3-1/2 square. To make this sandbox you will be joining the boards together, and this is why the individual boards need to be shorter by this amount.
In the example used above where the box is 6’x6’, the short-end joining board would need to be ~38 3/4". The formula for figuring out the length of the short end joining boards is 1/2 the length of your box + ~2. 75".
In the example used above where the box is 6’x6’, the long boards would need to be ~6'9". The formula for figuring out the length of the long side joining boards is your total sandbox side length + ~9".
Make sure the brackets are small enough to fit underneath the support beam without going below the bottom edge of the long side boards. Make your job easier later by marking the center line of the support beam on the front of the long side board. This will later be used to figure out where to nail the seat of the bench.
If you’re following the example, you’ll want 10 boards for each bench, plus an extra which will need to be split lengthwise down the middle with each bench taking a half. In other words, 21 boards total. Use a table saw or jigsaw to cut the board down the center. The spacers between the boards allow air to circulate, helping to prevent mold, but do not allow naughty cats in! If you’re having trouble finding the center to nail down the boards, either measure for the center or use the guideline you put in when you made the brace beam.
