Yours is NOT "so inadequate", the "rabbit hutch" coops are. Look at almost any commercially available coop. They are very cute, built with substandard materials and will claim "houses 6-8 chickens" in about 9 sq ft, 3' high. It is pretty much impossible to have adequate ventilation without drafts on the birds. The roosts might be off the ground, barely, so the birds don't even have 9 sq ft to walk around. Marketing (ie MONEY) is driving that, not ANY experience with raising chickens.
The generally stated minimum floor space (meaning USABLE space not areas where there are waterers, feeders or roosts robbing floor or headroom) is 2 sq ft/chicken. But consider that a large fowl is a foot or more from beak to tail. Envision packing birds in that tight unless they are NEVER confined to the coop except when they are sleeping (on their minimum 1 linear foot per bird roosts). Consider YOU living in a space twice your width. And doing it with others. Tensions mount. A "common accepted minimum" is 4 sq ft/bird. Even then, plot that out on the floor, 2'x2', it still isn't a lot of room when they decide to flap their wings. A "commonly accepted minimum" for run space is 10 sq ft/bird.
Take advice from whomever you like but consider how long they have had chickens and how their climate compares to yours. Do they have personal experience or are they just repeating something they read? And consider that "popular" doesn't mean right. Feeding them cracked corn, whole oats and bread will NOT yield an egg a day from each hen. Nor does poop on an egg mean your hen has worms. You will adjust your operation as you see fit based on how your chickens are doing.
The windows all prop open for warmer months.
