In this adaptation from Horse Housing: How to Plan, Build and Remodel Barns and Sheds, award-winning authors Richard Klimesh and Cherry Hill explain how a good barn design addresses airflow, temperature regulation and humidity.

Heating
If you live where it gets cold in the winter, you’ll have to decide how much of the barn to heat, if any. Ask yourself: “Is the barn primarily for my comfort or my horse’s health?” Horses are generally more comfortable–and much healthier–living outside or in an unheated barn.

It has been found that horses living in a stable rather than outside have higher antibody titers, meaning they have been fighting infectious agents likely caused by bad air and dirty bedding. If you can, build a variety of paddocks, runs and sheds so horses can live outside most of the time.

All but very young foals and sick horses will do fine in an unheated barn as long as they are protected from drafts. When it gets really cold, below 0°F, it is healthier for a horse to wear a blanket and have plenty of fresh air than to close the barn up tight and blast him with a heater. When a horse does require additional warmth, because of sickness or injury, you can use an infrared (radiant) heater or a well-protected heat lamp.

Most barns only require heating in one or two rooms, commonly the tack room and utility room. A warm tack room will provide a place to prevent freezing of medications and grooming products and give you a place to warm up between chores or horses. A heated utility room will keep your washing machine, pressure tank, water heater or other water appliances from freezing. An exception is a show barn where horses are kept with a short hair coat year round. A temperature of 50°F is comfortable for people to work and is healthy for horses, too.

Any space that is heated, whether one room or the entire barn, needs to be insulated and have a vapor barrier on all sides (as well as the ceiling, walls and floor) to prevent damage from condensation and to make efficient use of energy.

Condensation
Damp air contributes to respiratory ailments, stiffness, and bacterial and fungal growth. It also promotes condensation, which can drip down onto your horses, tack and feed; rot framing; rust metal siding and roofing; ruin insulation; and cause ice to form on ceilings and walls.

Condensation problems occur mostly in climates where temperatures dip below 35°F for an extended period of time. Barns in the desert and uninsulated barns where the inside and outside temperatures are about the same seldom have condensation problems.

You can prevent or minimize condensation by:

• keeping humidity low
• providing plenty of ventilation: in a heated barn this will allow humid air to escape; in an unheated barn, it can keep the inside air temperature close to the outside temperature
• installing insulation: it can keep the inside surfaces of the barn close to the inside air temperature

Humidity
Humidity fuels condensation, and be assured that respiring horses and wet stalls supply plenty of moist air. Respiration from a 1,000-pound horse puts two gallons of moisture into the air each day. Four horses supply eight gallons of humidity per day, and that’s not counting moisture from evaporation of urine and manure. A good humidity level for horses is 50-75%, with 60% being optimum; however, too dry is better than too humid.

A dehumidifier, although suitable for an enclosed room, is impractical for an entire barn. Better to eliminate the primary source of moisture by using stalls only when necessary and by removing wet bedding as often as possible when horses are in stalls.

Ventilation
Good ventilation begins with good design. Ventilation designs (or lack thereof) that work for animals like cows, pigs and chickens are seldom ideal or even adequate for horses. Horses typically spend many more years in a barn than other animals. Plus, they are usually required to perform as athletes and so require a plentiful supply of clean air for optimum health and fitness.

Besides contributing to condensation, poor ventilation prevents stalls from drying out and leads to moldy bedding. And it can make air downright unhealthy.

Contamination by ammonia fumes from decomposing urine and dung, dust from hay and bedding, bacteria, and mold and fungal spores all can contribute to allergy and respiratory problems in horses and humans. Foals are especially vulnerable to high levels of ammonia and are unfortunately subjected to higher concentrations because they live close to the ground where ammonia tends to layer. Respiratory infections often set in once a foal’s developing immune system has been weakened by ammonia fumes. The goal of ventilation is to exchange stale inside air with fresh outdoor air without chilling horses in the process.

Air Movement
Air moves through a barn in three ways. Convection causes a cycle called the “stack effect” where warm air rises and flows out through roof or high wall vents, drawing in cool air through openings lower in the barn. Aspiration is when wind blowing across the roof creates a low-pressure area, a vacuum, which pulls air out of the barn through vents or any other openings. Perflatation is when air moves through a barn by passing through openings (windows, doors and vents) located on opposite walls. Locating a barn to take advantage of breezes can facilitate ventilation by aspiration and perflatation. You can use the smoke from a stick of incense to help you evaluate air changes, how fast the smoke dissipates and airflow–where the smoke goes.

Vents
Windows and doors that open will allow air to move through the barn, especially when they are placed on opposite sides of the barn and there are few solid walls between them. Drafts can have an unhealthy chilling effect, especially if a horse is wet. Stall windows that open inward and slope upward will direct air over a horse, rather than causing drafts to blow on him. Inward opening windows, however, do present installation and safety problems.

A vent on the outer wall of each box stall, just under the roof, will encourage airflow by letting warm air out so fresh air can move upward. High-placed windows serve the same function, with the added advantage of letting in sunlight–but they can be difficult to reach for opening and closing. Vents placed low in walls admit fresh, cool air into the barn. Be careful about placing a low vent in a stall where drafts could blow on a horse or where a horse might be injured on the vent or damage it.

Dutch doors on outer stall walls can allow the top door to be latched open to admit outside air and to let a horse put his head out directly into fresh air. An open top door generally provides adequate ventilation for a stall.

Grillwork on the top portion of stall walls and using walls that stop short of the ceiling will enable air to flow throughout the barn more freely than having solid walls from floor to ceiling. Using stall guards (straps or chains) across open stall doors also encourages airflow, but can lead to safety and behavioral problems and will allow bedding to spill into the aisle.

While large doors at the ends of a barn can provide good ventilation, they will also admit birds, insects and other unwanted animals. A solution is to install giant sliding screens to keep out pests and strong wind while still admitting gentle airflow.

There are many ways to let warm air escape through the roof. A pot vent is a simple metal dome that covers a hole in the roof. A cupola is a short and usually square tower with louvers on all sides built over a hole in the roof ridge. One or more cupolas can serve as large vents and add a bit of character to your barn in the bargain.

Continuous ridge vents are perhaps the easiest and most effective roof vents to install. Some are concealed by shingles, while others serve as a ready-made ridge cap to finish off steel and other types of roofing.

Fans
If your barn is sheltered from natural airflow–for example, by trees or land formations–or if you keep it closed tight, you’ll need to install exhaust fans and intake vents to move air through the barn. Exhaust fans are rated in cubic feet per minute (CFM), or how many cubic feet per minute of air they move.

When researching an exhaust system, figure 1 square foot of vent or inlet space for every 750 CFM fan capacity. More than this will create a draft, and less than this simply will not ventilate the barn adequately.

Ceiling fans that draw air up toward roof vents are one solution. Make sure they are at least 11 feet high to prevent horse contact. Portable fans mounted on stands or fastened to the walls or trusses can also be used to move air through the barn and can be focused on stalls to cool horses and to dry bedding and on grooming areas to keep flies away.

Vents with integral fans placed high on the outside walls in each stall are another option. Use screened vents with louvers or downward pointing hoods on the outside to cut down on drafts and to keep out insects, birds, rain and snow.

How Much Venting
There should be sufficient air intake and exhaust openings, with or without fans, to ensure six to eight air changes per hour (one air change is the time it takes for all of the interior air to be replaced with fresh air). A large air volume and good airflow is important for distributing fresh air throughout the barn without drafts and for minimizing concentration of bad air around the horses. The air volume inside a barn can be increased by having higher walls or a gambrel, monitor or steeper-pitched roof.

Vents are rated by “net free area,” which refers to the size of the opening while taking into account blockage from insect screens or other obstructions that interfere with free airflow.

There are two rules of thumb for calculating vent requirements:

• allow 1 square foot of vent for every 300 square feet of floor space
• 60% of the venting area should be lower intake vents and 40% should be higher exhaust vents

For example, if your barn is 40 feet wide by 60 feet long, you have 2,400 square feet of space. Divide 2,400 by 300 to get 8 square feet, or 1,152 square inches, of vent. Sixty percent of 1,152 equals 691 square inches of lower vent required, leaving 461 square inches of upper vents. A standard ridge vent supplies 18 square inches per lineal foot: 461 ÷ 18 = 25 feet of continuous roof vent, which will fulfill the thumb rule; installing vent the entire 60-foot length will more than double it.

A normal unheated barn could leak enough air around doors and through siding to satisfy the 691 square inch requirement for lower venting without adding vents. The open top of a Dutch door would provide 1,728 square inches, almost three times the required area, but all of the air would enter at one place and wouldn’t serve to mix with stale air as well as more numerous openings throughout the barn would.

Bathroom Vent
For bathrooms up to 100 square feet in area, the Home Ventilating Institute recommends an exhaust fan that provides 1 CFM per square foot of ventilation. For example, an 8 foot by 5 foot bathroom has 40 square feet of area, so would require a fan rated at 40 CFM. A timer switch set to turn off after 20 minutes will make sure the room is vented after use and that the fan is not left running.

Generally, bathroom doors are undercut to allow air to enter the room and replace air exhausted by the vent. But in a barn, it might be a good idea to have doors fit snug to a door sill to keep out rodents. Use a screened vent near the bottom of the door or low in a wall to let in air.

Floor Vents
For a wood floor, such as in a tack room, that has space between the floor and the ground, foundation vents will remove humidity that migrates up from the earth and prolong the life of the floor.

The total vent area should equal 2 square feet for each 100 lineal feet of foundation perimeter, plus one half percent of the crawl space area. A vent fan controlled by a humidistat will turn on and off according to a preset humidity level. It can be mounted in the foundation or connected to the crawl space by ducting.

Ice Dams
Ice dams are often the result of poor ventilation and insulation. They occur when snow melts on a warm part of a roof, then runs down the roof and refreezes along the eaves. Ice dams can build up many inches thick and water backed up behind them can run under shingles, ruining the roof and even leaking into the building. Ice dams are exacerbated by poor insulation in heated barns and by poor ventilation between roofing and insulation. Good airflow under a roof ensures that the roofing stays cool from the peak to the eaves. Building codes of many northern states require an extra waterproofing membrane at the eaves to prevent damage from ice dams.

Gutters can also cause increased ice buildup. Make sure gutters slope correctly and are cleaned out each fall so they can drain properly.

Vapor Barrier
A vapor barrier keeps moist air from migrating through walls and ceilings and into the insulation. If moisture should collect within the insulation, the insulating value is greatly reduced. If moisture moves through the insulation, it will condense on the back of the siding or the underside of the roof and lead to rot and rust. A vapor barrier is always installed on the warm side of insulation. Putting a vapor barrier on the cold side will trap moisture within the insulation. Only one vapor barrier is needed or recommended. A vapor barrier on both sides of the insulation is asking for trouble because if any moisture should get between them, it would be trapped and could lead to rot, mold and mildew.

A vapor barrier can consist of almost any waterproof membrane, including special paints, plastic sheeting, laminated paper, Kraft-backed aluminum foil, foil-backed gypsum board and spray foam.

Insulation
Insulation keeps heat in your barn during the winter and out during the summer, while also absorbing sound. If you are planning a steel roof, think seriously about insulating under the roofing to make the barn quieter during rain and hail. Insulating a barn but not heating it will still result in a slightly higher inside temperature.

The three types of insulation most commonly used for barns are flexible, rigid and reflective. Loose fill cellulose insulation is made primarily of ground-up or shredded newspaper, which is flammable even when treated with fire retardant chemicals; it is not recommended for a horse barn.

Heat Movement
Heat always moves to cooler areas and is transferred in three ways. Conduction is direct heat exchange through an object like paneling or studs. Convection is the transfer of heat through air. Radiation is the movement of heat across open spaces (examples of this include the sun warming the earth and a wood stove heating a house).

Conductive heat loss through walls and ceilings is slowed down by mass fiber insulation (batts, rigid board). Convection heat loss through walls and the roof caused by air infiltration can be prevented by sealing all holes through which air can move. Radiant heat loss can be reduced by using a reflective barrier.

R-Value
The “R-value” of insulation refers to its resistance to heat transfer. A higher R-value means higher insulating capability. R-values can be found printed on the insulation itself, on the packaging, or attached on labels.

The amount of insulation a barn requires depends on where it is located and how it is built. For information on insulation recommendations for your area, contact the local building department or gas or electric utility. A chart by the U.S. Department of Energy that shows recommended insulation levels based on geographic zones can be seen on the website of the North American Insulation Manufacturers Association at www.naima.org.