If your chicken coop smells like ammonia, the cause is almost always too much moisture in the bedding combined with not enough airflow. Chicken droppings are rich in uric acid, which rapidly breaks down into ammonia gas. That sharp, eye-stinging smell means ammonia levels have climbed high enough to harm both your flock and you. The good news: this is a fixable problem, and usually a fast one.
Why Chicken Manure Produces Ammonia
Unlike most animals, chickens excrete nitrogen primarily as uric acid rather than urea. Uric acid is the white, pasty part of their droppings. Once it hits the bedding, bacteria begin converting it into ammonia gas almost immediately. Warm, wet conditions accelerate this process dramatically. A dry, well-ventilated coop slows the conversion enough that ammonia dissipates before it accumulates. A damp, still coop traps the gas and concentrates it.
This is why you can have the same number of chickens in two identical coops and only one smells terrible. The difference is moisture and airflow, not flock size.
How Ammonia Affects Your Chickens
Poultry health guidelines set 25 ppm as the maximum acceptable ammonia level in a coop. That’s a concentration you may not even smell yet, since the human nose picks up ammonia starting around 5 ppm but doesn’t register it as alarming until higher levels. Your chickens, however, live with their heads much closer to the litter.
Research from Avian Diseases found that broilers exposed to just 25 ppm of ammonia for 28 days developed eye abnormalities. Birds exposed to 50 and 75 ppm developed the same problems faster and more severely. Broilers raised in 25 to 50 ppm ammonia environments weighed about half a pound less at seven weeks than birds kept below 25 ppm, according to Penn State Extension research. For laying hens, chronic ammonia exposure can reduce egg production and make birds more susceptible to respiratory infections.
If you can smell ammonia when you open the coop door, levels are above 5 ppm. If your eyes sting or you cough, you’re likely above 20 to 25 ppm and your birds are already being harmed.
How Ammonia Affects You
Ammonia isn’t just a nuisance smell. The OSHA permissible exposure limit for workers is 50 ppm over an eight-hour period, and even at that level, people experience rapid irritation of the eyes, nose, and throat along with coughing and airway narrowing. At 300 ppm, ammonia becomes immediately dangerous to life. You’re unlikely to reach that level in a backyard coop, but repeated exposure to lower concentrations (the kind you get from daily cleaning and egg collection in a poorly ventilated coop) can cause chronic respiratory irritation, persistent cough, and eye membrane inflammation over time.
Fix Ventilation First
Ventilation is the single most important factor in controlling coop ammonia. A common guideline is 1 square foot of ventilation opening per 10 square feet of floor space, though your specific climate and flock density may require more. In hot or humid climates, err on the side of too much ventilation rather than too little.
Effective coop ventilation means openings near the roofline where warm, ammonia-laden air naturally rises and escapes. Ideally, you want airflow that moves through the coop without creating a direct draft on roosting birds. Vents on opposite walls allow cross-ventilation. Hardware cloth over the openings keeps predators out while allowing air to move freely.
A common mistake is sealing the coop too tightly in winter to keep chickens warm. Chickens tolerate cold far better than they tolerate ammonia. If you can smell it when you enter the coop on a winter morning, your birds have been breathing it all night. Open more vents, even in freezing weather.
Choose the Right Bedding
Bedding controls ammonia by absorbing moisture from droppings before bacteria can convert uric acid into gas. Not all bedding performs equally.
- Hemp hurd is the top performer for ammonia control. Made from the absorbent inner stalk of the hemp plant, it pulls moisture into its porous structure so droppings dry quickly. Drier manure produces less ammonia. It stays loose as chickens scratch through it, which prevents the dense, wet mats that generate the worst smells. It costs more than other options but lasts longer between changes.
- Pine shavings are the most popular budget option. Kiln-dried shavings offer good absorbency and are available at any farm store. Medium or large flakes work best because they produce less airborne dust and resist compaction. Fine shavings pack down and hold moisture against the floor.
- Straw is the least absorbent common option. It works in dry climates and in nest boxes, but in a humid coop or with a larger flock, straw mats quickly, traps moisture underneath, and becomes an ammonia factory. Chopped straw performs somewhat better than long-stem straw because it allows more airflow.
Whatever bedding you use, depth matters. A thin layer saturates quickly. Start with 3 to 4 inches of fresh bedding and spot-clean wet areas every few days.
Use the Deep Litter Method Correctly
The deep litter method lets bedding and manure compost slowly inside the coop, with beneficial microbes breaking down waste and generating gentle heat in winter. When it works, it controls odor beautifully. When it fails, it’s usually the source of the worst ammonia problems.
The key is the carbon-to-nitrogen ratio. Chicken manure is extremely high in nitrogen. Carbon-rich bedding absorbs and balances that nitrogen before it converts to ammonia gas. Kiln-dried wood shavings have a carbon-to-nitrogen ratio of roughly 500:1, making them an excellent deep litter base because they can absorb a large volume of manure before the balance tips. The higher the carbon content of your litter, the more droppings it can handle before ammonia production spikes.
Moisture is the other critical variable. Deep litter should feel like a wrung-out sponge: damp enough to support microbial activity, dry enough that you can’t squeeze water out of a handful. Soaked litter goes anaerobic (oxygen-deprived), which kills the beneficial composting microbes and instead supports pathogens while generating ammonia much more rapidly. If you provide water inside the coop, place waterers on a raised platform or drip tray to keep spills out of the litter. Powder-dry litter isn’t ideal either, as it won’t support the composting process, but it’s far less dangerous than wet litter.
When you notice ammonia building in a deep litter coop, add a thick layer of fresh, dry carbon material on top and turn the litter to introduce oxygen. If the smell persists after a day, the litter has likely gone too far and needs to be stripped out and restarted.
Other Factors That Make Ammonia Worse
Overcrowding concentrates droppings in a smaller area, overwhelming bedding faster than it can absorb moisture. The standard recommendation of 4 square feet of coop space per bird exists partly for this reason. More birds in less space means more nitrogen per square foot and faster ammonia buildup.
Dirt floors without a moisture barrier allow ground moisture to wick up into the bedding from below, especially in rainy seasons. A layer of sand, gravel, or a vapor barrier under the bedding can make a significant difference.
Droppings boards under the roost collect the overnight manure (chickens produce most of their droppings while sleeping) and let you scrape them clean each morning. This removes the single biggest source of uric acid before it ever reaches the bedding, and it’s one of the most effective ammonia-reduction strategies for small coops.
Quick Steps When the Smell Is Bad Right Now
If you’re dealing with an ammonia problem today, work through this sequence. First, open every vent and door to flush the coop with fresh air. Second, remove any visibly wet or caked bedding and replace it with dry material. Third, check for water leaks from waterers, the roof, or rain blowing in through openings. Fourth, add more ventilation openings if the existing ones aren’t adequate. Finally, evaluate whether your bedding type and flock density are a sustainable match for your coop size.
Ammonia problems rarely fix themselves. Warm weather makes them worse, not better, because heat accelerates the uric acid breakdown. Addressing moisture and airflow together is what eliminates the smell for good.