The advent of national building ventilation standards has brought IAQ to the forefront of building development practice. As a result, moisture control, humidity, and mold have become major concerns for all developers, particularly those in the restaurant and hospitality industries.

It is essential to recognize that moisture is desperately trying to get into your building. Factors that contribute to moisture-related problems include driven rain, floor mopping, cooking steam, dishwashing, changes in vapor pressure and temperature, and even people.

The following water sources demonstrate the many avenues through which moisture can gain access and impact a restaurant environment.

  • Water: rainwater and groundwater sources;
  • Internally generated: kitchens, pipe leaks, people, or combustion;
  • Diffusion: moisture moving through building assemblies;
  • Infiltration: air through cracks in building assemblies;
  • Ventilation air: ASHRAE Standard 62 outside air and makeup air for exhaust systems; and
  • Capillary flows: water wicking in porous materials.

Some obvious signs of moisture-related problems include water leaks, rust, staining, warping of building materials (e.g., baseboards), buckling, decay, corrosion, and degradation of building materials. Mold-related problems can be detected through a specific and lingering musty smell. Odor is a no-cost, yet effective, indicator of mold conditions even when you cannot see the problem.

Another mold barometer that assists in identifying problems is visual. This is evident in colorations that occur when the various strains of mold grow - from yellow to pinkish to the rather ominous black mold. Trust your visual and olfactory senses to help you assess a mold-related moisture problem. Mold growth is very likely when humidity exceeds about 70%, so it is imperative to be aware of the many sources contributing to a potential moisture-related problem.

The Basics of IAQ

IAQ is a serious issue when it begins to negatively affect the customer or the ambiance of the facility. In the worst-case scenario, IAQ can become a liability issue arising from mold or mold-related problems. IAQ concerns are on the rise, and some suggest that mold contamination could become the next major liability concern for building owners. Mold is a significant contributor to various lawsuits directed at sick building syndrome (SBS).

Controlling moisture and resultant mold problems should be a major concern for any restaurant or hospitality company, since the very nature of food preparation plays a major role in the development of moisture-related problems.

Top Ten Moisture-Related Kitchen Issues

The typical casual dining restaurant or hospitality kitchen experiences high moisture loads from several sources making them exceptionally vulnerable to moisture problems.

  • Food preparation: washing fruits/vegetables;
  • Cooking: steam/moisture from cooking/blanching;
  • Serving: hot/moist food releases moisture into the air;
  • Dishwashing: 140 degrees F water typically used in rinse/wash cycles;
  • Floor cleaning: high-volume, frequently mopped kitchens;
  • Infiltration: moisture entering through building cracks;
  • Doorways: many people passing through doors can add large latent loads especially when humid;
  • People: customers/staff create moisture (evaporation);
  • Kitchen exhaust: high-volume cooking hoods demand large amounts of often moist outside air; and
  • Wash, mop/floor sinks: add moisture to the air/remain damp.

There are three identifiable areas that enable moisture to gain access to the restaurant kitchen. Based on this top ten list, the first consideration is moisture generated internally. Secondly, moisture diffusion occurs through the building wall and ceiling assemblies due to the difference in the vapor pressure between the inside conditioned space and the outside atmospheric conditions. And lastly, moisture is brought into the space due to controlled or uncontrolled air movements.

Restaurant kitchens are definitely moisture factories that can contribute to a mold-conducive environment. However, research has shown that the transport of moisture by air movement is significantly worse by a factor of about 100 when compared to simple vapor diffusion.

For comparison, a 2-by 2-cm hole in the wall assembly can transport 30 liters of water into the building, compared to only 1.3 liters of water transported over one square meter by diffusion through the permeable members of the wall assembly.

In Orlando, a hot and humid climate zone, 1 cfm of air will transport 150 pints of water into the building over the cooling season. Therefore, it is important that buildings incorporate adequate design features to control the transport of moisture-laden air into the space.

Designing with IAQ In Mind

Restaurants are a breeding ground for the development of moisture problems. Because of the obvious high moisture loading, the building must be designed and operated to consistently handle these issues on several fronts. The architect must ensure the building is designed to prevent water penetration through proper roof penetrations, correct roof slopes to prevent ponding, and weathertight fenestration at windowsills and doorframes. The building shell must be designed to handle the moisture loads from driving rain and rh.

Building and HVAC design must take IAQ issues into account that are unique to restaurants from the conceptual phase of the development of a restaurant or hospitality kitchen. Properly sized cooking, dishwasher, and exhaust hoods, as well as toilet exhausts, must be properly balanced with conditioned makeup air to maintain building pressure and air balance.

An HVAC engineer must accurately calculate the various zone air volumes, exhaust flows, transfer air, combustion air, and makeup air supply to properly achieve the building air balance. Incorrect air balance can lead to excessive infiltration of unfiltered air and adds additional moisture loads on the building air handling equipment. Additionally, it can cause uncontrolled airflow between various zones in the building.*

When building pressures are not balanced, air can move from an unconditioned attic or soffit area to the occupied space. Unbalanced air pressures can cause air movement from the toilets to the dining space or pull sewer gas into the building. Unbalanced airflows can cause life-threatening combustion problems, like flame rollout or incomplete combustion of gases. These airflows can be passive due to wind effects, temperature differences, or a leaky building envelope. Active uncontrolled airflow is caused by unbalanced airflows from exhaust systems, duct leakage, or unbalanced return airstreams.


It is critical that the experienced restaurant operations professional ensure that adequate IAQ standards are maintained in an effort to eliminate or reduce the risk of toxic mold conditions.

Operations personnel must maintain the equipment to operate at the correct design setpoints. Many operators can easily overlook how seemingly insignificant changes can impact the building IAQ. Dirty filters, whether a grease filter in the hood, or a return air grille with a disposable filter, can dramatically alter airstreams, change static pressures, and affect the cooling ability of the A/C coils.

Air filters have a design pressure loss designed into the HVAC system. The disposable filters should be regularly changed to ensure that they are operating within the design specifications. How often do you see return grilles or exhaust grilles caked with dust and grease? Owners frequently complain about lack of cooling in the summer only to find dirty grilles and filters blocked with weeks and sometimes months of buildup. Something as mundane as a filter change can avoid a costly service call by the A/C technician. Remember the old automobile oil filter commercial, when the mechanic holds up the inexpensive oil filter and says, "You can pay me now, or pay me later."

Once the air filter buildup occurs, it precipitates other operational problems. Clogged filters will slow down airflow, giving you less cfm of airflow. Your energy costs go up since you are using the same fan hp but getting less volume of air. The reduced airflow can contribute to moisture problems in the ducts. The only positive result from clogged filters is that the cooling coil can actually handle the latent moisture load better since the air is moving across the coil somewhat slower.

Moisture is Serious Business

In summary, there are quite a number of design and construction considerations that should be addressed as it relates to moisture-related issues that affect restaurant and hospitality owners, designers, and building operators. You can begin to appreciate the difficulty in simultaneously providing effective solutions for all of the potential moisture entry points - rain drenching the building, water from floor sinks and floor mopping, steam from cooking and dishwashing, moisture from people or humid air, and changes in vapor pressure and humidity.

It is prudent for owners and facility managers to get advice from experienced professionals who can provide effective answers to IAQ issues concerning the restaurant/hospitality industry. This guidance should ensure that adequate IAQ standards are implemented and maintained, and that toxic mold conditions are eliminated or reduced. According to the American Hotel and Motel Association, the cost of industry-wide moisture-related damage is estimated to be tens of millions of dollars per year, not to mention the potential for lawsuits.

* The importance of properly sizing the air-handling equipment, exhaust hoods, and fans is covered in the recent article "Air Balance Fundamentals for the Modern Restaurant," January 2003, Engineered Systems. ES

Water, Water Everywhere...You Can't See It, But It's There.

Moisture will always move from an area of high vapor pressure (outdoors), to an area of lower vapor pressure (inside your building). Your building has a lower rh than the outside since it is air conditioned, so the vapor "pressure" acts from the outside. Moisture then diffuses through the building assembly toward the inside.

Secondly, moisture will move from an area of high temperature (outside summer conditions), to the inside of your building at a lower air conditioned temperature. In fact, this moisture migration makes the placement of vapor barriers, vapor retarders, and air barriers very crucial in the design of buildings in different regions of the country. This moisture that is diffusing through the building assemblies and the occupancy space will condense on objects at the dewpoint temperature wherever they are - in the kitchen, on a ceiling diffuser, inside the building walls, or on the window glass.