Excerpt from page 4 - Space Requirements

The more room your chickens have, the healthier and more content they'll be. Except in extremely cold climates, home flocks are rarely housed entirely indoors but have room to roam outside whenever they please. Yet even in the best of climates, chickens may sometimes prefer to remain indoors due to rain, extreme cold, or extreme heat.
Minimum space requirements, including those shown in the chart below, indicate the least amount of indoor space birds need when they can't or won't go outside for an extended period of time. Birds that never have access to an outside run will do better if you give them more space than the absolute minimum. On the other hand, birds that spend most of their time outdoors, coming in only at night to roost, will do nicely with less space.
To encourage chickens to spend most of their daytime hours outdoors, even in poor weather, give them a covered area adjoining the coop where they can loll out of rain, wind, and sun. Encouraging your chickens to stay out in the fresh air has two advantages: They will be healthier, and their coop will stay cleaner.

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