How Big Is Your Mountain of Manure?

Tired of looking at that Mt. Rainier-sized mountain that is your manure pile? Worried about where all that black leachate coming from the pile of manure is going?

A 1,000-pound animal will generate 50 pounds of manure per day, or as much as 9 tons of manure per year.

Building a manure bin to contain manure can be the first start to improved manure management. It prevents water quality issues and increases chore efficiency. Regular collection of manure from stalls and confinement areas is essential to the health of your animals and your property. Good manure management can

  • Reduce mud

  • Limit parasite re-infestation and fly breeding grounds

  • Prevent nutrients and pathogens from contaminating surface and groundwater

  • Improve aesthetics

Collected manure can be composted and applied to pastures or gardens, providing essential nutrients for grass and beneficial organisms that improve the soil.

Locating a bin starts by asking yourself 6 key questions about the location:

  1. Is it convenient to where I collect the manure?
    My good friend, Alayne Blickle, from Horses for Clean Water says, “If it is too much like work, then it is!” Think about moving manure after work on a rainy and dark winter night and then locate the bin near to where you collect it to save time.

  2. Is it convenient to where I spread the finished compost?
    Can you access the location easily? Can you travel to the location year-round? Can a tractor or a truck access the spot if you need to haul off site? Is the location near existing gravel? Locating the bin in a good location will help reduce the chore of spreading or hauling manure away.

  3. Is it wet in the winter or after heavy rains?
    Not only will this make accessing the bin very difficult, but you’ll have a waterlogged soggy mess. That potentially leads to the leaching of nitrogen into ground and surface water. Make sure nearby buildings have gutters and downspouts and that the water is directed away from the bin. Locate the bin in a high a dry location.

  4. Is it far enough from the property line or well?
    In King County, manure bins are required to be at least 35 feet away from property lines. And Washington State also requires that they be 100 feet from a wellhead.

  5. Is it far enough away from streams or wetlands?
    King County Code states that bins cannot be within 50 feet of surface water. Bins within 50 to 100 feet are required to have a roof and a concrete pad. And bins within 100 and 200 feet must be covered in the winter.

  6. Is it going to obstruct your or your neighbors’ view?
    Do you want the bin next to the back patio or somewhere you’d rather not see? Think about the aesthetics of the location for you and those surrounding you.

Now that you have a location, how big should your bins be? The amount of manure and compost ingredients/feedstock can vary greatly depending on several factors:

  1. Number of animals.

  2. Days on pasture per year.

  3. Type of bedding (if any) is used while the animals are in a stall or shelter.

  4. Amount of “dead” hay being added to pile.

  5. Amount of “active management” you plan to do.

Without going into too much detail regarding all of the potential options for the five factors mentioned, a typical 1000-pound animal that is kept in confinement for the 6-month wet season and bedded with an average amount of bedding will produce about 10 cubic yards of stall and confinement area waste per year. An example of a 1000-pound animal could be one horse, two llamas, or 5 or 6 goats or sheep.

This means that 3 horses will produce about 30 cubic yards of manure per year and 18 goats will produce about the same amount. Here’s how to determine what size manure bin will hold that 30 cubic yards of manure or compost:

  • 30 cubic yards x 27 cubic feet (in a cubic yard) = 810 cubic feet.

  • 810 cubic feet ÷ 4 feet = 202.5 square feet
    (4 feet tall is a typical height for a manure bin wall)

  • 202.5 square feet ÷ 8 feet = 25.3 feet
    (8 feet is a convenient length, as it is a standard lumber length)

  • 25.3 feet is close enough to 24 feet
    You’ll need three 8-foot wide by 8-foot long by 4-foot high bins.

Since manure is generated all year long, a bin this size might work for 4 horses or a similar animal size as well. Just remember to spread composted manure in April and August.

What type of bin to build?

There many types of materials build manure bins with. Wood and concrete are really at the top the list, but there are more. No surprise that deciding a bin design will depend on these factors:

  • What type of animal and type manure? Dairy manure is much different than alpaca manure, so the bin will need to reflect that.

  • Will you collect and turn by material by hand (to aerate) or will you use a tractor once in a while? When there is a tractor involved, the bin needs to be built to withstand more forces than just by hand.


Typically, pressure treated lumber is used. This could be simply made with posts and side walls. They are covered with a tarp or a roof. A concrete pad could also be installed as the base.


Pre-cast ecology-blocks are “Lego”-like stacking blocks with 6-foot by 2-foot by 2-foot dimensions. They make a sturdy “instant” bin, but take up additional space. Poured-concrete makes a narrower and sturdier bin, but takes more time building a footing and setting up concrete form work beforehand.

Building and managing a well-thought out manure composting system will help create a healthy farm for you, your family, your livestock and the environment.

Contact KCD for free assistance with developing a site-specific manure management plan for your needs and property.
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