Natural ventilation for horse barns

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Recommendations to keep horses and customers happy /

Proper horse barn ventilation can be difficult to wrap your head around. What’s good for you is not necessarily good for horses. Here are some recommendations for natural ventilation in your horse barn projects.  

Permanent openings
• Furnish stalls with some sidewall openings that are permanently open year-round

• The best location for this permanent opening is at the eave, where sidewall meets roof

• A slot opening along the eave, that runs the entire length of the stable, provides every stall with fresh air since air is equally distributed down the length and on both sides of the stable

• Since a slot opening at the eave is 10-12 feet above the floor, incoming cold air is mixed and tempered with stable air before reaching the horse

• During cold weather a long slot opening admits a thin sheet of cold fresh air, rather than the large drafty mass of cold air admitted by an open window or door

• A minimum guideline for cold climates is to provide at least 1 inch of continuous-slot, permanent opening for each 10 feet of building width

• Supply each stabled horse the equivalent of at least 1 square foot of opening into its stall

• For a 12-foot-wide stall, a 1-inch-wide continuous slot will supply 1 square foot (144 square inches) of permanent opening

• Openings which are slightly above the minimum recommendation can help ensure good ventilation during cold and cool conditions when other stable openings are often kept closed

• If ridge venting is insufficient, double the eave vent opening sizes

• Eave openings ideally should be left completely open; covering them with insect screening or metal soffit treatments severely restricts airflow and will soon clog with dust and chaff

• In double-aisle stables where central stalls are not near a fresh-air opening (or when stables share a common sidewall with an indoor riding arena), the stable interior must have an open design with no ceiling and with grillwork on stall walls

Seasonal openings
• In stables with interior central aisles, large endwall doors can be opened to allow cooling breezes during warmer weather

• When horses are kept indoors during warm weather, allow breezes to enter the horse stall with windows or doors that open from the stall to the outside

• Provide openings equivalent to at least 5 to 10 percent of the floor area in each stall

• For a 12×12-foot box stall, a 3×2½ window provides a 5 percent opening and a 4×3½ window (or top of Dutch door) provides a 10 percent opening

Ridge vent
• The ridge opening area should match the eave opening area with a minimum of 1 square foot of opening per horse

• As with eave openings, ridge openings should provide at least 1 inch of continuous slot opening per 10 feet of building width

• If no ridge opening is provided, double the minimum recommended eave opening

• The simplest and most effective ridge vent is an unprotected opening, where trusses or rafters are protected from precipitation and the stable interior can tolerate occasional rain entry

• The ridge vent can be a continuous opening or a series of uniformly spaced vent assemblies

• During winter a portion of the vents can be closed to provide only the recommended permanent opening area, and then opened during hot weather when more air exchange is needed

• Do not cover ridge openings with insect screens, and avoid residential and commercial ridge vent assemblies that are overly restrictive to air movement

• Ridge vent assemblies made for agricultural buildings offer relatively unrestricted airflow with modest protection from precipitation

• Since warm moist air flows up and is not inclined to move down to exit a ridge vent assembly, avoid designs that prevent natural upward flow when no wind is blowing; trapped air blocks ventilation and may condense in cold weather

• The actual ridge opening is measured at the most restrictive part of the ridge vent assembly, so that the key measurement for air movement is where the airflow path is narrowest

• Cupolas can be used as ridge openings but provide no way for stable air to move through them, while louvers commonly block 50 percent of the open area they are protecting

The breathable wall
• Traditional barn board siding provides a “breathable wall” with miles of small cracks between the boards that allow bits of air movement at each juncture

• Air coming in the cracks is nicely uniform throughout the structure, while the tiny air jets are quickly dissipated without becoming drafty

• This effect is reduced when battens added to the wall, and eliminated when tongue-and-groove siding or modern 4×8 (or larger) construction panels are used

• Stables can be built with a breathable wall concept by spacing vertical barn boards 1/4 inch to 1 inch from each other, or using roughcut green lumber siding that leaves gaps once it dries
Three ways to improve
ventilation

• Open grillwork on the top portion of front and side stall partitions is highly recommended versus solid stall partitions

• When the interior has no ceiling and is open to the ridge vent, more air exchange and distribution can occur

• Do not incorporate overhead hay and bedding storage in the stable, or at least construct the storage over the work aisle so that horse stalls have no ceiling

Measuring ventilation rates
• Measure the velocity of air entering or leaving the stable through ventilation openings and multiply this by the opening size

• Air velocity is measured with an anemometer (in feet per minute) and multiplied by the opening area (in square feet) to get the ventilation rate in cubic feet per minute

• To calculate air changes per hour, divide the ventilation rate by the building air volume

• The stable volume is the floor square footage multiplied by the average roof or ceiling height

• Measure the incoming ventilation air speed at several openings and at several locations on large openings, then average the velocities and multiply by the open area of airflow

• The primary difficulty in accurately estimating natural wind-blown ventilation rates is the frequent change of air speed and direction at each ventilation opening as measurements are made.

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