Composting Barn Design Manual for New Zealand Dairy Farmers

A composting barn is a covered, open-sided shelter where dairy cows lie on a deep bed of sawdust, woodchip or similar. Dung and urine are ripped into the bedding daily, and the pack composts in place. The heat from composting dries the bed, so cows have a soft, dry surface to lie on.

A standoff pad is mainly a place to hold cows off paddocks for a short time. A composting barn is designed for cows to lie down, rest and often feed for longer periods. The bedding is actively managed as compost, so it stays drier and more comfortable, and the effluent is captured in the pack.

A working compost pack typically runs at around 40 to 60°C below the surface. That heat comes from microbes breaking down the bedding, dung and urine with oxygen. The surface cows lie on is cooler. If the pack goes cold, it usually means it is too wet, short of carbon or not being ripped enough. 

Most composting barns are ripped every day they are being used. Ripping mixes fresh dung and urine into the bedding and lets air in, which keeps the composting going and helps moisture evaporate. The manual covers ripping depth, the equipment to use, and how to tell when the pack needs extra attention. It is possible to stop using the composting barn and let it go dormant for a period of time. If a pack is dormant, it will need a run-in period of daily ripping before putting cows in the barn to restart the aerobic composting.

Wood-based, lignin-rich materials work best, such as sawdust, woodchip or suitable forestry by-product. Particle size matters: you want material that holds air but still breaks down.

Squeeze a handful from below the surface. The ideal moisture range is about 40 to 60%. If water drips out, it is too wet; if it falls apart like dry sawdust, it is too dry. A wet, cold or smelly pack needs more carbon, more ripping or better airflow. Our composting barn design manual explains how to restart it.

Yes, this is one of the biggest advantages for farmers with a SmartShelters Composting Barn. Cows can start to feel heat stress above 20°C, and heat-stressed cows eat less and produce less. A well-ventilated shelter gives cows shade and a place to lie down during the hottest part of the day.

Yes - SmartShelters composting barns are the gold standard when it comes to wintering barns. Many farmers, especially in the South Island, use composting barns to winter cows off paddocks. It keeps cows dry, helps protect soils from pugging and gives you more control over feeding. It also reduces the need for winter crop grazing.

Cost depends on your site, herd, groundwork, shelter design and bedding supply, so there is no single answer, however we often see costs range from $1,500 to $2,000 pew cow for the shelter. For a site-specific quote, talk to our team and we can advise about additional costs your setup will incur such as groundworks and bedding. The SmartShelters Composting Design Manual lists the ten main ways a barn can pay its way and a worksheet to work out your own number.

When the bedding is replaced, the finished compost can be spread on paddocks or cropping land as fertiliser and soil conditioner. One SmartShelters farmer saw a 400% increase in the growth of his crop after using the spent bedding from his SmartShelters Composting Barn as fertiliser!

Usually, yes. A composting barn is a building and typically needs building consent, with engineering to the current NZ wind and snow load standards. Your regional council may also have rules on effluent and the barn base. We provides PS1 engineering certification for its designs and can help you through the process.

It depends on your herd, how long cows will be in the barn each day and season, your bedding and your site. The general rule of thumb is 8-10sqm per cow, however getting the space right is critical to the pack composting properly, so we don't publish a one-size rule. Talk to the SmartShelters team and we'll work it through for your farm.

The shelter provides airflow and light while keeping rain out, and those drive how well the pack composts and how comfortable cows are. Good ventilation removes the moisture cows generate, helps prevent condensation and lets the pack dry. Height, open sides, and a clear span without internal posts all make a difference.