I would think you should be okay with just Silkies in there. I was told by our city that they needed 4 square feet per chicken to have a legal chicken coop. I've read on here that 4 square feet is ideal, but nothing under 3 square feet. So really 4 x 4 would only be 4 chickens. But if you just have Silkies, you should be fine since they are so little, but if you had larger chickens, not really sure. I guess I'm just used to my huge 12 foot by 9 foot coop. So not sure what 4 by 4 would look like. I can't even imagine it.