Single-story, clear span barns are safer, brighter, and more open than two-story barns, in which extra posts and girders support overhead hay mows and the risk of falls or fire increases. Ground-level storage for hay and bedding can be more convenient and safer than overhead hay storage; and the increasing use of high-quality silage decreases the need for hay storage space.
Barns with more than one story may be desirable on a small or steep site. In two-story barns, posts should not interfere with daily chores or traffic patterns, and girders and floor joists should be sized to support any stored feed, hay, or equipment. Equipment, wagons, and small tractors can be moved via access ramps or barn bridges to supported floors. Livestock and manure are more easily moved and cared for on grade or ground floors.
To reduce fire spread in two-story barns, consider constructing tight floors and hay doors of gypsum board between sheets of exterior plywood. Precast, prestressed concrete panels and masonry block walls are also fireproof. Exterior ventilation inlets may delay smoke from reaching animals in basement housing. Many dairy barns with hay mows are destroyed by fire each year, but seldom is a single-story barn completely burned.

Stalls Facing Out or In
Two-row dairy barns are constructed so that the cow stalls will face out or in. “Face out” means that cows face toward a wall, and there is a central litter alley between rows of stalls. “Face in” means that cows in opposite rows face each other, and there is a central feeding alley between rows of stalls. Barns with two rows of stalls facing out allow workers to concentrate traffic and centralize cleaning and milking. Since the time and effort required for milking and cleaning behind stalls exceeds that required for feeding in front of stalls, a central litter alley with stalls facing out is an efficient layout. Allowing a minimum of 12' of open space in front of the cows facing out can make it possible to feed large, round bales or maneuver a mechanical feed cart. Face-in barns with a center alley 15' wide lend themselves to efficient feed handling.
Plan ahead for clearance space around the expected operations, equipment, and animals in the barn. Allow extra ceiling clearance if feed carts will operate beneath a central forage conveyor, and add extra alley width if a tractor and self-unloading wagon will deliver rations into feed mangers. Watch out for interference between feed conveyors or high wagon boxes and milk or vacuum lines.
The floor of a dairy barn is divided into several functional strips, each with different elevations, slopes, and surface finishes. Functional floor areas include the litter alley, gutter or manure channel, stall platform or bed, curb, manger, and feed alley. Cross alleys link the litter and feed alleys at each end of the barn and divide rows of stalls into convenient blocks. The barn length is determined by the number and size of the stalls, cross alleys, and pens, but averages about 2½' per total number of stalls in a two-row dairy barn. Two-row stall barns are usually 40'–56' wide;
four-row barns may be 70'–82' wide.
This is an excerpt from the Dairy Practices Council’s Guideline #37, Planning Dairy Stall Barns. More information can be found at the Dairy Practices Council’s website: http://www.dairypc.org.

John Tyson is a Regional Extension Agricultural Engineer with Penn State Extension, where he conducts educational programming in dairy housing, cow comfort, farmstead layout, feed storage design, manure handling, and agricultural ventilation. John is also involved in the production of various extension publications involving dairy housing facilities. John has been a Licensed Professional Engineer in Pennsylvania since January of 2003. He can be reached at jtyson@psu.edu.