The proposed Denver ordinance is suggesting 1 square foot per bird for the nighttime, predator-proof structure. Since chickens don't move around at night (as everyone here knows) 1 s.f. per bird is adequate to contain them when they're sleeping. During the day, chicken owners would be required to provide at least 10 square feet of permeable space per bird. Chicken owners with a particularly small nighttime enclosure may choose to provide something addition for their chickens to have shade/shelter during the day, but it is not mandated that the daytime shelter be predator-proof.
In Denver we have very low precipitation rates, and my chickens hardly ever use their daytime shelter. In my experience, chickens' use of a daytime shelter is not related to cold weather (at least not Denver-type cold weather) -- it's related to precipitation. When it's cold during the day they're outside, when there's snow on the ground they're usually outside, but if there's snow or rain falling from the sky they stay under their daytime shelter. I have a fairly small nighttime coop (just 1 s.f. per bird), but lots of daytime roaming space, plus an addition shed for daytime shelter whenever it's needed. This is a perfectly acceptable situation for raising healthy chickens in Denver, and under the proposed ordinance a setup like mine would be allowed.
Of course, if people *choose* to build bigger nighttime structures, they're certainly able to do so.
It's worth noting that Seattle, Portland, Chicago, Los Angeles, and New York do not have any shelter space requirements in their laws that I'm aware of. We need to be careful do draw a line between what we legislate and what falls under the realm of "best practices." Over-legislating one person's idea of how a chicken setup should look takes away the ability of others to be creative and come up with lower cost solutions (for example, my small nighttime coop and larger daytime shelter).
Have you ever raised a flock of urban backyard chickens, Eileen? Did you go on the Denver coop tour last year and see all the wonderful varieties of successful setups that are possible?