Attics, basements, garages, garden sheds: Though they have different uses and dispositions, these non-lived-in spaces all share a functional, substance-over-style quality. But even though they don’t need to be show-off-worthy, they do need to be kept under control—a particular challenge given all the stuff they hold, from cars and lawn equipment to delicate stored valuables. Here are ways to keep these utilitarian spaces serviceable.