Healthier Air Quality in Equine Hospitals
Strive to improve air quality in your equine veterinary hospital by starting with moisture mitigation. Here are some tips on how to do so.
Vet hospital next to a lake
A healthy building protects its occupants from harm via air quality, among other strategies. Courtesy Animal Arts

The COVID-19 pandemic brought useful change to the building and construction industry. One of the most important was the advancement of the science of healthy buildings.

A healthy building protects its occupants from harm via air quality, among other strategies. This topic has always been relevant to both human and animal health, but until recently it has been difficult to discern evidence-based information from pseudoscience. Air-cleaning technologies are a great example: Most of the products sold do nothing at all, and only a few do what they promise.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) releases research and evidence-based guidelines, and building codes are based on these standards. In January 2022, ASHRAE released an Indoor Air Quality Guide that outlines best practices for healthy buildings. Inspired by this guide and other healthy building concepts, we have concluded that moisture mitigation is the single most critical issue for healthy buildings, including equine veterinary hospitals.

Building Moisture Problems

ASHRAE states that moisture is the most significant problem for building air quality because it leads to the growth of microorganisms. Moisture is an enormous problem in modern buildings because today’s buildings are designed to be tight (i.e., trapped moisture cannot escape) and because the construction materials we use grow mold readily. Equine hospitals are naturally prone to moisture problems from low-cost, quasi-agricultural construction techniques, poor ventilation and the use of copious amounts of water for cleaning.

Beginning with moisture issues in slabs and foundations, soil should always be graded to prevent water from collecting near or under buildings. If it’s not, take the problem seriously. Water vapor will migrate across building envelopes and up through the soil toward the drier environment inside. Consequently, a damp foundation can lead to a damp indoor environment. Below are the two most typical soil-related moisture problems and their mitigation requirements:

  • Water or water vapor enters through the concrete slab. In new slab construction, this problem can be mitigated by installing a polyolefin “Class A” vapor barrier under the concrete. In lay terms, this is a thick sheet of plastic. Polyolefin is used in lieu of polyethylene because polyethylene decomposes over time, eventually resulting in loss of the barrier. For existing buildings, slab moisture issues are more difficult to resolve. If you have experienced flooring failures, moisture is often the problem. You can place a moisture-mitigating liquid membrane on top of the slab, and the right time to do this is when replacing flooring materials.
  • Water flows toward the building when it rains. This problem results from soil sloping toward the building instead of away from it. This problem must be fixed. Ways to fix it include regrading and creating a “swale” away from the building by some distance so that the water flows toward and then through the swale to an acceptable low spot elsewhere. If it is not possible to regrade, install a foundation drain to direct water away from the building.

The building envelope itself can be the source of significant moisture concerns. Let’s review the most typical problems for equine building wall and roof assemblies, as well as strategies for repair:

  • Water penetrates through the roof. You must address roofing problems. In historic buildings such as old barns, the loss of a watertight roof heralds the building’s rapid destruction. Do not put new roofs over old roofs. Remove old or leaking roofing materials and their substrates prior to reroofing. For modern structures, leaky roofs are just as insidious, as the water can penetrate into wall systems, insulation and other building materials, creating deterioration and mold growth.
  • Water or water vapor moves through a wall or roof assembly. This might seem like a minor inconvenience, but moisture issues in walls and roofs pose health hazards and create fodder for the multimillion-dollar-per-year lawsuit industry. Moisture can develop due to wrongly installed insulation, air, and vapor barriers. In all climate zones in North America, except for South Florida and some of the Gulf Coast, vapor barriers are installed on the inside (warm side) of the insulation. This is to prevent warm air with higher relative humidity inside the building from reaching its dew point as it moves through the insulation. South Florida experiences the opposite: The air outside is hotter and damper than the inside of the building, so the barrier is placed outside the insulation. In all climates, building scientists recommend adding an air barrier to prevent infiltration into the wall system. If you are building or remodeling, get advice from an architect who can help design a proper vapor and air barrier system.
Tryon Equine Hospital
Soil should always be graded to prevent water from collecting near or under veterinary clinic barns or buildings. A damp foundation can lead to a damp indoor environment. Courtesy Animal Arts

Humidity levels over 60% relative humidity at typical room temperatures will guarantee mold growth. Those with existing buildings can control this risk more easily than they can building envelope problems.

For new buildings, you can eliminate this risk through design and HVAC maintenance.

Proper air flow and ventilation help reduce the risk of spreading airborne and surface-borne pathogens.

Below are the most common problems relating to humid indoor environments and their mitigation strategies:

  • The building is improperly pressurized. A commercial building should maintain positive pressure, meaning the inside air pressure gently pushes against the building envelope. If the pressure of a building becomes negative, moisture can be pulled across the building envelope (which is why we discussed the building envelope first as a primary problem). You would be surprised at how common and destructive this issue can be.
  • Veterinary buildings are particularly prone to pressure issues because, for animal health reasons, they exhaust more air than typical buildings. Unless this air is properly replaced with makeup air from the outside, the building can become negatively pressurized. This can happen over time if the building HVAC system gets out of balance. To resolve the issue:
    • Service the HVAC system to ensure filters are cleaned and everything is working.
    • Rebalance the system based on original design intent.
    • If the system cannot be rebalanced, consider adding a makeup air unit to resolve building pressure issues.
  • Short-term humidity mitigation. If your building develops a humidity problem, it might not be possible to mitigate it without a lot of cost. A powerful dehumidifier is currently the easiest way to create a healthier indoor environment. Various plug-in commercial dehumidifiers are readily available for purchase from retailers such as Global Industrial.
  • The building does not have enough air flow. Buildings can have humidity issues due to lack of air flow. This is common in equine hospitals because water is used for cleaning. We have visited many hospitals that feel dampest in the areas that should be dry, such as the surgery zone. Indoor humidity works directly against the design of an aseptic environment. Here are factors to consider:
    • Equine surgery areas should have at least 10-12 air changes per hour and 60% outside air, with MERV 13 filtration, which filters upward of 90% of particles.
    • HEPA filters can hurt rather than help if the building was not designed for HEPA. More fan pressure is needed to push air across a HEPA filter, which is why we only use them if the hospital has a heavy orthopedic caseload, and we design specifically for HEPA filtration.
  • Mitigation for buildings without enough air flow. If you cannot modify the HVAC system to mitigate a damp indoor environment, below are some tips for a healthier building:
    • Use a better disinfectant and less water. For example, if you are currently using bleach, switch to a hydrogen peroxide disinfectant. This disinfectant has a foaming action that helps with cleaning as well as disinfection, thus reducing labor and water.
    • Install an exhaust fan to be used only after cleaning. As discussed, you don’t want to pull in humid outdoor air unless the air outside is less humid than the air inside, which can happen if there is not enough air flow in the building. In the latter case, switching on an exhaust fan to temporarily evacuate humidity, just as you would do in your home bathroom, is an acceptable option.
    • Ensure your finishes are fully sealed. Sanitary wall and floor conditions are more important in overly humid spaces, as biofilms flourish in the presence of moisture. Invest in a fresh coat of paint and some caulking so the space is more cleanable.
HVAC system
Your facility’s HVAC system is critically important to health. Courtesy Animal Arts

Air Cleaning Technology for Healthier Indoor Environments

As we have described, mitigating moisture via envelope and HVAC system design is the priority for a healthy equine hospital. Air-cleaning technology is a good supplement to a system you already have or an enhancement to a new system, but it should never replace basic design principles.

Many air-cleaning systems are ineffective. Purchase one tested for use in health care and/or pet care environments. The easiest and most effective technology for use in equine hospitals is an upper air treatment system with ultraviolet light disinfection. This system is low-tech and, therefore, easy to install in existing buildings. It simply mounts to the ceiling in a room. Upper air treatment can improve indoor air quality significantly by destroying airborne pathogenic particles.

For further information about the design of healthy indoor environments, download ASHRAE’s free Indoor Air Quality Guide at

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