Is my coop large enough (AKA: Chicken Math)

[ShockValue]

I have a 4x8x4+ coop as shown here:




We started with 8 chicks which would satisfy the 4sq feet per bird, but 1 rooster and a dog "incident" later we now have just 5 healthy girls. I love seeing them wandering my yard, and am now totally spoiled on fresh eggs. Unsurprisingly chicken math has now set in and I'm anxious to get more, but I don't want to add more at the expense of health or stress levels.

Our typical day:

Wife gets up early and lets chickens out slightly after dawn.
I get home from work and close the pop door shortly after sunset.
Occasionally this "morning release" might be delayed if we are out of town and have "chicken sitters" letting them out.

The girls free range for all daylight hours on about 1+ acres.
Terrain is mixed from "mowed back yard" to natural WA growth.
I have 2 feeders and a water source in the coop.
2 more water sources at different points in the yard where the chickens seem to hang out most.
7.5 feet of roost space, but I could probably add more without much trouble.
At latitude 48° our days range from 16 hours of daylight at it's longest to 8 hours at the shortest.

I know this is all probably bird/breed/size dependent, but any recommendations and or experiences similar to this would be much appreciated

Edit: P.S. Bird Size: Currently 4 Faverolles and 1 Sussex. Looking to add from the following breeds: Marans, EE/Olive, Leghorn, Welsummer, Rock, Australorp

 

[Ozarkhomesteader]

I would not add more that 5 more. 10 would most likely we your max. Because they are free range you could get away with that many, but not if they were cooped all the time.

 

[donrae]

Have you overwintered your birds yet? I think that's going to be your biggest challenge. In the good weather, they only need that coop for laying and sleeping. Rainy, wet weather is going to challenge that, they'll need more time under a roof. My advice would be to get through the winter and see how you feel in the spring. All that wet can add a new dimension to chicken keeping, trust me. Then, if you want to add birds, they'll be readily available and you can add a group. Your new pullets will start laying when your current ladies taper off in the fall of '15.

 

[ShockValue]

Sounds like sound advice. So far the girls don't seem bothered by the cold and wet, but it's been a dry year so far (at least by W.WA standards.)

Patience is a virtue for a reason, I guess