Sussex chickens are a large, heavy breed that needs more room than bantams or smaller laying breeds. Inside the coop, each Sussex hen should have a minimum of four square feet of floor space, though five or more square feet per bird is preferable for reducing stress and preventing the behavioral problems that arise from overcrowding. In the attached run or outdoor enclosure, plan for at least ten square feet per bird — more is always better, and Sussex chickens that are given generous space tend to forage more actively and maintain better body condition.
Roost space is another dimension of housing that is often underestimated. Sussex hens are heavy birds, typically weighing seven to eight pounds, and they need sturdy roost bars set at a moderate height. Roosts positioned 18 to 24 inches off the ground with a ramp or step-up are ideal — setting them too high increases the risk of leg and foot injuries when the birds jump down in the morning. Allow at least 10 to 12 inches of roost bar per bird, and use bars that are two to four inches wide with rounded edges to support their larger feet comfortably.
Nest boxes should be sized to accommodate the Sussex's larger frame. Standard 12-by-12-inch nest boxes may feel cramped for these hens, and a slightly larger 14-by-14-inch box is a better fit. Plan one nest box for every three to four hens, and position them lower than the roosts to discourage sleeping in the boxes, which leads to soiled bedding and dirty eggs.
Ventilation is a non-negotiable aspect of coop design regardless of flock size. Sussex chickens produce a considerable amount of moisture and ammonia through respiration and droppings, and inadequate airflow leads to respiratory problems, frostbitten combs in winter, and heat stress in summer. A well-ventilated coop has openings near the roofline that allow warm, moist air to escape without creating drafts at roost level.