There’s no two ways around it. If you have bales delivered to your site, it will rain. Okay, that’s a bit pessimistic; however, it almost always seems to turn out that way. I have baled homes in the middle of the dry summer here is Southern Oregon, where summer rains are very unusual, and had rain clouds show up the day my bales are delivered. The point is you can never be too careful about protecting your bales from rain.
When bales are delivered to the site they will either be in the form of a large block, called a squeeze block, or stacked by hand. either way, the shape of the stack needs to be taken into consideration. Leaving a block flat or stacking your bales flat on top will create areas of depression that can and will collect water. It is best to stack the bales like a pyramid so that the tarp will shed water to the sides. If possible, stretch the tarp to cover the tops of the stacks without covering the sides. In other words, make a trap roof. This allows the wind and air to dry the bales from any condensation that may find its way in from under the tarps.
It can be hard to achieve this if the winds are strong in your area. If that is the case and the bales will only be stored a short time, then you can leave the sides some what unprotected, assuming the weather is not bad. The sides of the bales can handle some moisture. The tops are what you want to keep totally dry. Consider that water on the side of a bale can only get so deep into the bale and can be pushed out with a dry day.
If the top of a bale gets wet, gravity pulls the moisture down into the bale where it is hard to drive out. This can cause rot and long term damage. If the weather will be bad when you are baling, make covered walk ways from the bales to the house with tarps that keep the bales under cover all the way.
Oh yeah. I probably should have said this earlier, but you should always stack the bales on pallets to get them off of the ground. If you don’t, your bottom layer of bales will be brown with mold and, over time, will turn to compost. If the bales are to be stacked over grass or other plant life, put a layer of 6 mil plastic or weed cloth down first, then the pallets, then the bales. The plastic or cloth will kill the grass, but it will also stop it from growing up into your bales. If you plan to move the bales quickly into the structure, then don’t bother with the cloth or plastic.
A final cool tip: When unloading a stack of bales that is tall, like a squeeze block, it is best to make a slide. Take a couple 2×12’s that are long enough to reach the top of the stack while still providing a relatively gentle slope. Once at the top of the stack, climb up and use the ramp to slide the bales to another person on the ground. This keeps the bales from getting knocked out of shape and speeds the delivery to your stacking crew. Just be careful not to stand at the bottom of the ramp! Happy baling.