Compost barns – some points to consider
As interest in compost barns continues to grow it may be helpful to go over some of the design basics to ensure a successful compost is built and managed. Here are 9 points to consider when building a compost barn.
1. A minimum of 9 square metres per cow should be provided within the resting area. When compost barns are overstocked, the amount of moisture added to the pack (through manure and urine) and the amount of cow traffic compaction impedes proper composting.
2. Compost barns should be oriented to take into account the predominant wind patterns and also to minimise the amount of time in which the sun blares down on the cows, which encourages even distribution of cows throughout the barn. Areas in the barn that are either too hot or too cold will have a detrimental effect on the overall composting ability of the barn due to the cows overcrowding some areas and avoiding others.
3. An open ridge vent is critical for maximizing natural ventilation. Our preference is to provide an open ridge with a cap on a roof with an 18o pitch. A continuous ridge vent opening of at least 75 millimetres for each 3 metres of building roof width is recommended with a minimum opening of 300 millimeters for barn widths of less than 12 metres. An overshot roof can provide reasonable air removal when the opening is high enough. However, good air removal only occurs when wind moves across the higher side. When wind moves toward the opening, the wind forces air back into the barn.
4. If sidewalls are part of the barn design they should be constructed to allow for at least 3 metres of open space for airflow above the retaining wall or outside curb for barns that are less than 12 metres wide while a 4.25-metre height is recommended for barns wider than 12 metres.
5. Feed and water space is often overlooked in constructing a compost bedded pack barn. Provide a minimum of 60 to 90 centimetres of feed bunk space per cow, depending on cow stature, 90 centimetres of water tank perimeter per 15 to 20 cows, and at least 2 separate water locations per pen. Do not reduce feed and water access in an effort to build a low-cost facility.
6. Cows will generally use the resting space provided more efficiently when they have multiple entry access points along the long side of the rectangular resting area. Concrete feed alleys should be 4.8 metres wide with access to the bedded pack located every 15 metres and at each end.
7. Because cows defecate and urinate more around feed and water, they should have access to waterers only on the alley side. Alley-only access minimizes excess moisture in the pack and keeps water cleaner. It also eliminates the need to alter waterer height as the pack depth changes.
8. Eave overhangs should be equal to 1/3 the height of the sidewall to minimise rain from reaching the pack and install roof gutters to reduce roof runoff from blowing into the pack.
9. The bedded pack is often surrounded on all sides by 600 millimetres to 1.2 metre walls, including a wall to separate the bedded pack from the feed alley. A concrete retaining wall provides separation between the feed alley and the pack area, which is helpful in managing pack moisture. Additionally, on the outside of the barn the retaining wall keeps bedding material within the barn. These walls may be cast-in-place concrete or moveable concrete panels.