Start with the bottom most shelf. The largest and heaviest items should go here. Do you have some large heavy books? Or a collection of large books? Or you could slide some really nice woven baskets onto the bottom shelf and have them hold your paperback stash. The point here is that the bottom shelf should have the weight.. both the visual weight and the actual weight. The items you place on this shelf don't necessarily have to be books. Maybe a large vase or urn... or a large globe.
Storage racks have become a practical alternative to shelves in many storage situations, as they are both practical and functional, and far more affordable than typical shelving units. Selecting the right size and materials is important, however, as both the environment and the storage items can make certain materials and designs more favorable than others.
Yes, you are using the garage for storage already, but the space is not being used efficiently and you can never find what you want. It seems to have become home for all types of sports equipment, tools, machines, and a collection of family stuff. The garage's original purpose for parking the cars and a small workout area seem to have been lost in the mess of it all.
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