Walk into your poultry house at ten in the morning and the air seems fine. Curtains up, sun on the roof, birds spread out. Nothing to fix.
Now go back at four in the morning, before anyone has opened anything, and put your head at the height of a bird's head. That is the air your flock has actually breathed for ten hours, and on most Kenyan farms it is nothing like the air you inspected in daylight.
Ventilation costs nothing and is almost never measured, yet it decides how much value you get out of every other input. Bad air rarely gives you a mortality spike to point at. It shaves daily gain, pushes feed conversion the wrong way, and leaves a flock that looks acceptable and performs below what you paid for.
The Air in a Poultry House Is a Chemical Process, Not a Smell
A house full of birds is a slow reactor running day and night, adding heat, carbon dioxide, dust and above all water. Poultry drink roughly twice as much water by weight as they eat feed, and nearly all of it leaves again: some as vapour from the airway, most into the litter.
That moisture is the fuse. Birds excrete nitrogen as uric acid, which on its own is stable and almost odourless. Bacteria in the litter break it down into ammonia gas. The reaction needs warmth, which the birds supply, time, which the crop supplies, and moisture, the only one of the three you control.
Dry, crumbly litter holds the reaction back. Wet litter, especially litter capped into a crust under drinkers and along the walls, runs it hard. Ventilation and litter management are therefore one subject seen from two ends: every litre of water that does not leave as vapour stays in the litter and becomes gas your birds inhale.
Why Bad Air Costs More Than Feed
Ammonia is highly soluble in water, which is exactly why it does damage: it dissolves into the first moist surface it meets, and in a poultry house those are eyes and the lining of the airway.
A healthy airway is swept clean by cilia, microscopic hairs that move a blanket of mucus and trapped dust up and out. Ammonia flattens and paralyses them. Once the sweeping stops, dust and bacteria settle and stay, and every respiratory challenge on the farm gets a better foothold than it deserved. That is the honest reason a flock keeps relapsing despite a vaccination programme correct on paper.
The production cost runs alongside. Birds in irritating air spend less time at the feeder, and damp litter gives coccidial oocysts what they need, softens footpads into lesions that downgrade a carcass, and dirties eggs. None of it arrives as one dramatic loss. It arrives as a margin thinner than your figures promised.
Draught and Airflow Are Not the Same Thing
Airflow is exchange: the volume of air being replaced, carrying out moisture, ammonia, carbon dioxide and surplus heat. A draught is air speed at the birds, fast enough across their bodies to strip heat away.
Adult birds in hot weather want air speed. Chicks on a cold night do not. The trap is that a farmer who feels a chill closes the building, which stops the draught but stops the exchange too, leaving a house that is both cold and foul rather than merely cold.
The way out is geometry, not sealing. Get the air in high, aim it along the underside of the roof, and give it distance to warm and mix before it reaches the birds. Cold air is denser and will fall on its own; your only job is to decide where. In cool weather, lower the curtain from the top and leave the bottom closed, never the reverse.
How a Naturally Ventilated House Actually Moves Air
A house with no fans has two engines and both are free. The first is the stack effect: birds warm the air, warm air is less dense, so it rises and escapes through the highest opening, drawing replacement in low behind it. The stack needs a temperature difference and vertical distance between inlet and outlet. Two metre walls with a sealed ridge give almost no stack at all, which is why so many houses sit in dead air on a calm night.
The second engine is wind, generous but unreliable and usually absent on exactly the still nights when you need exchange most. Design for the stack and treat wind as a bonus.
Siting matters too. Run the long axis roughly east to west so the sun strikes the gable ends rather than the long open sides, and keep the surroundings clear, because a hedge, a wall or another building within a few metres of a long side kills the airflow along it. Natural cross ventilation also runs out of reach as a house widens, and the common guideline for open sided houses is around nine to twelve metres.
Sizing the Openings and the Ridge
On an open sided house the long walls should carry a solid knee wall about thirty to sixty centimetres high, keeping litter in and rain splash out, then open mesh from there to the eaves, closed only by a curtain you can move.
Eave height is where Kenyan houses are usually short changed. Two point four to three metres is a sensible minimum, taller at the coast, because it is what gives the stack its vertical distance. Pair it with a roof overhang approaching a metre so you can leave the sides open in rain.
Then the ridge. Cut a continuous gap along its full length and fit a raised cap wider than the gap, so rain is thrown clear while air passes underneath. Twenty to thirty centimetres on a house eight to ten metres wide is a common starting point. Finally, vent both gables: the triangle above the tie beam is a dead pocket where warm, moist air collects, and a mesh panel there costs almost nothing.
Your Birds and Your Litter Are the Instruments
You do not need a gas meter, only the habit of checking three things before anyone opens up in the morning.
Bird distribution. Stand still in low light for two minutes. Evenly spread birds mean comfort; one central pile means plain cold; birds crowded away from a wall mean a draught from that side; birds pressed to the walls with wings out and beaks open mean heat. Snicking and head shaking mean airway irritation, which shows before anything visible does.
The litter squeeze. Pick up a handful and close your fist. Good litter crumbles when you open your hand. Litter that holds the shape of your fist is too wet. Litter that has formed a crust you can lift like a biscuit has been making ammonia for days.
The dawn checks. Condensation under the roof sheets means the house's moisture is not leaving. A static dust haze in a torch beam means air is not being replaced. And an intact cobweb across a vent proves no air has moved through it in weeks, the cheapest airflow test there is.
Add one instrument if you add any: a thermometer and hygrometer at bird level, read at five in the morning for a week. Humidity above about seventy percent overnight means a moisture problem you can still fix before it becomes an ammonia problem. Log the readings in the Fuga FarmKit app.
Highland Cold Nights and Coastal Humidity Are Different Problems
The highlands
In Limuru, Kinangop, Molo, Eldoret and anywhere the night drops sharply, the enemy is not cold air but the response to it. The house is shut tight at six, the birds carry on making heat and moisture, that moisture condenses on the coldest surface it can find, the iron roof, and drips back into the litter. The ammonia reaction then runs all night at a temperature it enjoys.
Physics is on your side here if you let it. Cold air holds very little water in absolute terms, so as it enters and warms its capacity to carry water rises steeply, and a modest amount removes a surprising quantity of moisture. You do not need much air movement to dry a highland house at night. You need the opening to exist. So treat the ridge as permanently open, manage the side curtains instead, add heat rather than removing air, and insulate the roof rather than sealing walls.
The coast and the hot lowlands
Around Kanamai, Kilifi, Malindi and the hot lowlands the physics inverts. Incoming air is already close to saturation, so exchange removes little moisture and the birds' own cooling fails. Panting is evaporation from the respiratory tract, and it slows badly when the air already carries nearly all the water it can hold.
The priority shifts from exchange to air speed and heat load. Air moving over a grown bird removes heat by convection even when evaporation has stalled, so what would be a harmful draught in Limuru is a lifeline in Kilifi. Build taller and more open, keep the long sides clear, and use circulation fans at flock sizes well below where a highland farmer would. Attack the heat itself with a reflective or insulated roof, a generous overhang, shade set well back, and lower stocking density in the hottest months.
The Cheap Fixes, in Order
Open the ridge permanently and cap it. Vent both gables. Bring curtains down from the top, never the bottom. Fix every water leak the day you find it, because a dripping line is a wet litter machine. Stir the litter and lift out caked patches. Cut back the hedge along the long walls. Only then spend money on fans.
Most of that is a morning with a tape measure and tin snips. If you want help sizing the ridge and openings for your own house, or you are pricing curtains, mesh, brooders, thermometers or circulation fans, our poultry equipment range is stocked across all six branches with prices on the price list.
Key Takeaways
- Ammonia starts as moisture in the litter, so ventilation and litter management are one subject, not two.
- Airflow is exchange; a draught is air speed on the birds. Sealing a house to stop a draught stops the exchange too.
- Let air in high and slow so it mixes along the roof. In cool weather, lower curtains from the top, never from the bottom.
- Keep the ridge permanently open with a rain cap, vent both gables, and size side inlets at roughly twice the ridge outlet.
- Read the house at five in the morning: bird spread, the litter squeeze, roof condensation and cobwebs across the vents.
Frequently Asked Questions
How do I know if my poultry house has an ammonia problem?
Kneel at litter level early in the morning, before anyone opens the curtains, and breathe. If your eyes sting or you can clearly smell ammonia, the level is already past what damages a bird's airway. Your own nose height understates it badly, because the gas is made at the litter surface where the birds live. Confirm with the litter squeeze: a handful should crumble, not hold its shape.
Should I close my poultry house at night in cold highland areas?
Never fully. Sealing the house stops the exchange that removes moisture, ammonia and carbon dioxide, and the birds keep producing all three until dawn. Keep the ridge permanently open and manage warmth with a brooder or heater rather than by closing the building. Lower the side curtains from the top, in stages, so air enters above the birds.
What size should the ridge vent be on a poultry house?
The ratio matters more than the absolute figure. Side inlet area should be about twice the ridge outlet area, so the ridge is the restriction and air enters slowly instead of as a jet. A continuous gap of about 20 to 30 centimetres along the ridge of a house eight to ten metres wide is a common starting point, with a raised cap wider than the gap to shed rain.
Is a draught the same thing as good ventilation?
No, and confusing them is the most expensive mistake in poultry housing. Airflow is the volume of air exchanged, which removes moisture, ammonia and heat. A draught is fast air moving across the birds, which strips body heat and chills chicks. You want high exchange with calm air at bird level, achieved by letting air in high so it mixes and loses speed before it descends.
How do I ventilate a poultry house at the coast where it is humid?
At the coast the air is already close to saturation, so exchange removes little moisture and the birds cannot cool themselves by panting. The priority shifts to air speed over the birds and to cutting heat gain: taller and more open walls, a wide overhang, a reflective or insulated roof, circulation fans, and lower stocking density in the hottest months.