I hate the sheds in my backyard, but I could probably dig the Plant Room. This strap-on shed/porch is perfect for city slickers who wish they were able to grow a little somethin' somethin'.
The Plant Room is "a prefabricated room that bolts-on to a variety of existing apartment types, improving the quality of living, reducing energy and water use, and generally making the building more sustainable." Hopefully the Plant Room becomes a reality soon. I'd move to the city if I could still keep my spice garden.
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Detached Accessory Structures
Victorian Play House
Shell-Like Home Expansions