A smelly coop is not only unpleasant to humans, but dangerous to your chickens; harmful bacteria, wet bedding or dust can cause respiratory ailments. One of the most common causes of coop odor is a leak in the building, which allows the bedding to get soaked and then stink. Once you have ruled out this problem, make a change to the coop's cleanliness to hide those unwanted smells.
Keep the coop cleaned out weekly to remove smelly droppings. Scoop out the old bedding to compost; clean out the nesting boxes and sweep out the floor of the coop to remove remaining dust. If the odor is not improved, wash the floor and boxes with a solution of 2 gallons of warm water and mild dish detergent. Add 1/4 cup bleach or vinegar to disinfect the coop if the smell persists. Allow the structure to air dry before laying new bedding.
Spread fresh pine shavings on the floor for bedding, at least 4 to 6 inches deep. Avoid using straw -- it will rot and release ammonia from the droppings into the air. To use a deep litter method simply, add more bedding occasionally and turn the pile weekly. This allows it to compost inside the coop while hiding the smell. Sand may also be used, absorbs well and does not need to be cleaned as often.
Without proper ventilation year-round, toxic fumes can build up inside the chicken coop. However, the vents should not be placed so that cold air can blow into the coop, either. Ceiling vents or small windows on the sides of the coop -- avoiding the north and west sides, if possible -- allows fresh air to pass through the structure, allowing unwelcome odors to blow out and dissipate.
Use a special enzymatic cleaner designed for barns and farm animals; this treatment breaks down the enzymes in urine and feces to neutralize the smell. Follow the manufacturer's directions to add the cleaner to water; then apply it to the floor and nesting boxes of the coop to break down the odors.