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Mold Information

The diagram demonstrates the role of fungi in relation to other living organisms.  Fungi are not plants or animals.  Fungi belong to a taxonomic classification, or kingdom, of their own.  Plants convert carbon dioxide directly into carbohydrates for food.  Animals and fungi must find complex carbon in the environment for food.  While animals ingest the food and degrade it internally, fungi excrete chemicals (enzymes) into the environment that degrade the complex carbon into soluble form.

Fungi do not make their own food the way that green plants do.  Fungi get nourishment from other living organisms.  The main role of fungi in the ecosystem is to break down dead materials, such as fallen leaves, trees, insects and animals carcasses.  The same enzymes that assist fungi in breaking down dead materials are what help fungi to damage wooden components in a building.  Molds can damage food, stored goods, and building materials of houses.  

Yeast, mold, mildew and mushrooms are common forms of fungi.  Mold is essentially a description of fungi that grows on surfaces, such as the black substance on a moldy shower wall.  Mold and mildew often refer to the same type of fungi.  All mold is fungi, but not all fungi is mold.
   
Molds grow in many colors, including white. "Black mold" is not a species or specific kind of mold, and neither is "toxic mold."  Sometimes, the news media use the terms "toxic mold" and "black mold" to refer to molds that may produce mycotoxins, or for a specific mold known as Stachybotrys chartarum.  Molds that produce mycotoxins are often referred to as toxigenic fungi.

Molds can multiply by producing microscopic spores (2 to 100 microns [μm] in diameter) similar to the seeds produced by plants.  Many spores are so small, they easily float through the air and can be carried for great distances by even the gentlest breeze.  The number of mold spores suspended in indoor and outdoor air fluctuates from season to season, day to day, and even hour to hour.

No one knows how many species of fungi exist, but estimates range from the tens of thousands to perhaps 300,000 or more.   Some of the more common indoor molds are Penicillium, Aspergillus, Cladosporium and Alternaria.

        a) Penicillium                b) Stachybotrys                     c) Alternaria              d) Cladosporium

Mold is Everywhere

Mold spores are ubiquitous; they are found both indoors and outdoors. Mold spores cannot be eliminated from indoor environments. Some mold spores will be found floating through the air and on settled dust; however, they will not grow if moisture is not present.

Why Be Concerned?

Mold is not usually a problem indoors—unless mold spores land on a wet or damp spot and begin growing.  As molds grow, they digest whatever they are growing on. Unchecked mold growth can damage buildings and furnishings; molds can rot wood, damage drywall, and eventually cause structural damage to buildings.  Mold can cause cosmetic damage, such as stains, to furnishings. The potential human health effects of mold are also a concern. It is important, therefore, to prevent mold from growing indoors.

Discovering fungi in the indoor environment raises three major concerns:

1)    the potential health effects of exposure to fungi and their byproducts;

2)    the effects of fungal contamination on the structural integrity of a building; and

3)    the negative aesthetic effects fungi can produce both visually and on the human olfactory
       system.


Although the issue of whether exposure to indoor fungi causes adverse health effects is controversial, there is no doubt that a seriously mold-contaminated building can suffer structural damage, and that a foul-smelling, fungus-filled building is aesthetically unpleasing.  Controversies about health effects aside, the latter two reasons are sufficient to merit a Complete Mold Inspection and remediation when an environment is found to have fungal contamination. 

People who have concerns about structural damage or the aesthetic effects of indoor fungi should seek the services of a certified mold inspector.  People who have concerns about health effects of mold exposure should seek the advice of a healthcare professional.

             

A mold has long, thread-like strings of cells called hyphae.  Hyphae form into a tangled mass called mycelium.  The mycelium growth is the fuzzy stuff on bread.  The strings that grow down into the bread are the mycelium, which is not seen.  The whole fungus body is called a thallus.  Spores are produced in large numbers.  They are located on the hyphae. 

Some hyphae grow down into the food material.  Cells of the hyphae produce chemicals.  Those chemicals break down the material (fruit, paper, wood) into nutrients that the fungus can absorb.

Fungi grow well in moist, dark areas, but can be found wherever organic material is available.  Molds can grow on a variety of surfaces, including paint, jet fuel, wallpaper, glass and stainless steel.  Moisture is necessary for mold growth.  Moisture may come from the air and from the material upon which mold grows.  If the environment becomes very dry, fungi can survive by going dormant or by producing spores that resist drying out. 

Fungi can spread via tiny spores through the air.  When a spore lands upon a surface that is moist and has material that can be used for food, it germinates and begins to grow.  Hyphae grow out of the spores.  Some grow up to the air.  Spores are produced on the hyphae that grow upward, above the food material.  Spores can then be blown by the wind and spread to new areas. 

A change in the humidity level can increase spores in the air.  A high relative humidity (RH) can burst the moist, swollen cells of the mold body that form spores.  This is true for Penicillium and Aspergillus, two common indoor molds.  Foot traffic, vacuum cleaners and increased ventilation can boost the number of airborne mold spores.   

Most of the mold body is the hyphae that is buried in the food material and is out of sight.  What is visible is the part of the mold body that produces spores.

Negative Health Effects and Mold

Topics Covered in this Section:

•    Symptoms
•    Infections
•    Mycotoxins
•    ODTS and HP
•    PPE
•    Contaminants

                         

Inhalation exposure to mold indoors can cause negative health effects in some people. Molds produce allergens (substances that can cause allergic reactions), irritants and, in some cases, potentially toxic substances (mycotoxins). Inhaling or touching mold or mold spores may cause allergic reactions in sensitive individuals. Mold does not have to be alive to cause an allergic reaction in some people.

There are some specific groups of people who are potentially more easily or severely affected by mold than the average individual with no sensitivities to mold.  They include infants, children, elderly people, individuals with respiratory conditions (such as allergies and asthma), and people with weakened immune systems (people with HIV/AIDS, chemotherapy patients, and organ transplant recipients).

Sensitive people should avoid areas that are likely to have mold, such as compost piles, cut grass and wooded areas. 

Allergic reactions to mold in buildings do occur for many sensitive people.  However, there is no conclusive evidence that proves that mold in a building directly causes human illnesses.  More research is needed, and mold research has been continuous.  Mold-related exposure and its effects on human health is a complex and emerging science.

Symptoms of Mold Exposure

There are many symptoms of mold exposure.  Current evidence indicates that allergies are the type of diseases most often associated with molds.   An allergic reaction is the most common symptom that could include wheezing and difficulty breathing.

Inhalation of fungal spores, fragments (parts), or metabolites (mycotoxins and volatile organic compounds) from a wide variety of fungi may lead to or exacerbate immunologic (allergic) reactions, cause toxic effects, or cause infections. 

A single or repeated exposure to mold, mold spores, or mold fragments may cause non-sensitive individuals to become sensitive to mold, and repeated exposure has the potential to increase sensitivity. Allergic responses include “hay fever”-like symptoms, such as headache, sneezing, runny nose, irritated eyes, and skin rash (dermatitis). Molds can cause asthma attacks in people with asthma who are allergic to mold.  Fungi in buildings may cause or exacerbate symptoms of allergies, especially in persons who have a history of allergic diseases (such as asthma and rhinitis).  In addition, molds can irritate the eyes, skin, nose, throat, and lungs of individuals, whether or not they are allergic to mold. Other symptoms include nasal and sinus congestion, burning, watery and red eyes, a sore throat, a dry cough, and skin irritation.

These and other symptoms may be associated with exposure to mold. But all of these symptoms may be caused by other exposures or conditions unrelated to mold growth. Therefore, it is important not to assume that mold is the cause of such symptoms.

The effects of mold exposure can be acute or chronic.  An acute effect is an immediate, severe reaction to a large exposure.  A chronic effect may take days, months or years to manifest, and usually comes from small, repeated exposures.

If a person experiences these symptoms only when occupying a particular building, then that person may possibly be experiencing symptoms of mold exposure.

There are four important indoor allergenic molds.  They are Penicillium, Aspergillus, Cladosporium and Alternaria.  Alternaria and Cladosporium are outdoor molds that can be found indoors if the doors or windows of a building are left open and the spores are carried by air currents.

For more detailed information on mold and its health effects, consult a healthcare professional or the state or local health department.

Certified mold inspectors should not offer medical advice to clients.  People with health problems that may be related to mold should seek a physician trained in occupational, environmental or allergy medicine.  Recommend that clients may wish to consult with a healthcare provider regarding any health problems they might be experiencing.

Infections

Only a small group of fungi have been associated with infectious disease.  Aspergillosis is an infectious disease that can occur in immune-suppressed persons.   Health effects in this population can be severe.  Several species of Aspergillus are known to cause aspergillosis.  The most common is Aspergillus fumigatus.  But exposure to this common mold, even in high concentrations, is unlikely to cause infection in a healthy person.

Breathing in mold may also cause hypersensitivity pneumonitis, an uncommon disease that resembles bacterial pneumonia. In addition, mold exposure may result in opportunistic infections in persons whose immune systems are weakened or suppressed. 

There are fungal infections that can affect healthy people.  They are pathogenic fungi sometimes found inside a building:  Blastomyces (which inhabit decaying wood); Coccidioides (found in the southwestern United States); Cryptococcus (in bird droppings); and Histoplasma (in bat guano or droppings).  People without adequate personal protection equipment (PPE) who come in contact with bird or bat droppings, such as may be found in attics, could be at very high risk.  People with compromised immune systems can be seriously affected by fungal infections.

Exposure to fungi associated with bird and bat droppings (Histoplasma capsulatum and Cryptococcus neoformans) can lead to negative health effects in healthy individuals, usually in the form of transient flu-like illnesses.  Severe health effects are primarily encountered in immune-compromised persons.  People with chronic lung illnesses, such as obstructive lung disease, may develop mold infections in their lungs.

Mycotoxins

As molds grow under some conditions, some (but not all) of them may produce potentially toxic byproducts called mycotoxins.   Mycotoxins are fungal metabolites that have been identified as toxic agents.   Some of these mycotoxin-producing molds are commonly found in moisture-damaged buildings.  Exposure to mycotoxins can occur from inhalation, ingestion and/or skin contact.  More than 200 mycotoxins from common molds have been identified, and many more remain to be identified. The amount and types of mycotoxins produced by a particular mold depends on many environmental and genetic factors. 

No one can tell whether a mold is producing mycotoxins just by looking at it.

Many fungi, including species of Aspergillus, Penicillium, Fusarium, Trichoderma, Memnoniella and Stachybotrys chartarum, can produce potent mycotoxins, some of which are identical to the compounds produced by Stachybotrys chartarum.  

There are studies that suggest there is an association between Stachybotrys chartarum and pulmonary hemorrhage/hemosiderosis in infants, generally those under 6 months old.

Toxic substances (mycotoxins) can enter a human body through inhalation, ingestion or skin absorption.  The effects of the toxic substance depend on the chemical or the material, the concentration, the route of entry, and the duration of exposure.

Smoking, alcohol, medication, gender, and existing health problems are all potential factors that can influence the effects of a toxic substance entering a body.

Some mycotoxins are known to affect people, but, for many mycotoxins, little health information is available. Research on mycotoxins is ongoing.

ODTS and HP

Mold inspectors and mold remediators can be at risk of developing Organic Dust Toxic Syndrome (ODTS) or Hypersensitivity Pneumonitis (HP).  ODTS may manifest itself with flu-like symptoms after a single, heavy exposure to dust contaminated with fungi.  It differs from HP in that it is not an immune-mediated disease and does not require repeated exposures to the same causative agent.  A variety of biological agents may cause ODTS, including common species of fungi.  HP may occur after repeated exposures to an allergen and can result in permanent lung damage.

                 

PPE

There have been reports linking negative health effects in office workers to offices contaminated with moldy surfaces, as well as symptoms in residents of homes contaminated with fungal growth.  Fatigue, respiratory ailments and eye irritation were typically observed in these cases.
 
Occupants and workers inside buildings can reduce their exposure by proper use of personal protective equipment (PPE), including respirators (minimum N-95), gloves, protective clothing, and goggles.  Personal hygiene and habits are important to reducing exposure for remediation workers.

What Mold Needs to Grow

                               

In previous sections, we learned what mold is.  Now let’s understand what mold needs to grow.  That knowledge will help guide inspectors to the most likely locations in a building to find growth.

Most of the mold found indoors comes from the outdoors because mold spores can easily float on gentle air currents.  If the spores land on suitable organic material inside a building, mold can begin to grow.  But mold needs two things in order to grow and survive:  moisture and food.



Moisture

Mold does not need a lot of moisture to grow. A little condensation in a bathroom or around a window sill, for example, can be enough. Common sites for indoor mold growth include bathroom tile and grout, basement walls, and areas around windows and sinks.  Common sources of water or moisture include roof leaks, condensation due to high humidity or cold spots in a building, slow leaks at plumbing fixtures, humidification systems, sprinkler systems, and floods.

Mold has been found to germinate, grow and produce spores in as little as 24 hours after water damage occurs. 

Indoor relative humidity (RH) should be between 20% and 40% in the winter, and less than 60% the rest of the year.  Some experts recommended that indoor humidity levels in general should be between 40% and 60%.

Moisture is the most important factor influencing mold growth indoors. Controlling indoor moisture helps limit mold growth.  Moisture control is the key to mold control.


Food

Besides moisture, mold needs nutrients, or food, to grow.  Mold can grow on virtually any organic substance.  Buildings are full of organic materials that mold can use as food, including paper, cloth, wood, plant material, and even soil.  Molds secrete digestive enzymes that decompose the substrate, making nutrients available.  Some molds can even digest synthetic materials such as adhesives, pastes and paints.

Molds can also grow on inorganic material, such as concrete, glass and metal, because it can grow on the dirt or dust that is present on the surface of those materials. 

In most cases, temperature is not an issue; some molds grow in warm areas, while others prefer cool locations, such as bread stored in a refrigerator. 

Mold grows well in environments between 40º to 100º F.  (And the pH is usually between 3 and 8.)  But some mold species have been found in hot springs with water temperatures above 120º F. 

Often, more than one type of mold can be found growing in the same area, although conditions such as moisture, substrate and temperature may favor one species of mold over another.

Building Science in Relation to Moisture and Microbial Growth


Micro-organisms can be found in the air inside a building, on a surface inside a building (on the floor, ceiling, walls and furniture), and inside the HVAC system of a building.  Many of these micro-organisms come indoors from outside.  They come from decaying organic matter or moist earth.

Micro-organisms can enter the a building by floating with outdoor air that enters the building, or  they can travel on people and animals who bring them inside. 

Micro-organisms might be present on the building materials as the structure is being constructed.  Oftentimes, inspectors will find building materials lying on the ground at a new-construction site.  These materials absorb moisture and dirt and may support mold growth inside the building, after construction has completed. 

Mold growth is not desirable in a building and must be prevented.  There are three reasons to prevent fungal growth inside a building:  the potential negative health effects of exposure to fungi and their byproducts; the effects of mold contamination on the structural integrity of the building; and the negative aesthetic effects fungi can produce both visually and on the human olfactory system.

Moisture, Temperature, Food and Time

There are four factors involved in mold growth.  The following conditions are necessary for mold growth to thrive on surfaces:

•    a temperature range between 40° F and 100° F;
•    the presence of mold spores;
•    a nutrient base (most surfaces contain nutrients); and 
•    moisture.

Human comfort constraints limit the practical ability to control temperature in the growth of mold.  Air temperature inside a building that is suitable for occupants is also beneficial for mold growth.  Most buildings are kept between 65° and 75° F, and this temperature range is also suitable for mold to grow, although some fungi can thrive in temperatures as cold as 15° F and as hot as 122° F.

Spores are almost always present in outdoor and indoor air.  Almost all construction materials and furnishings can provide nutrients to support mold growth, and dirt on surfaces provides additional nutrients.  It is virtually impossible to eliminate all nutrients.   A building is filled with an abundant supply of food for mold growth.  Fungi have been shown to colonize on drywall, wood paneling, wallpaper, ceiling tiles, carpeting and pads, furniture, insulated ductwork, and other building components.  The fungi break down the materials for food or use the dust that has collected upon a surface as a nutrient source. 

Temperature, food and time cannot be adequately manipulated to control microbial growth, but moisture can.  Moisture is the controlling factor.  Therefore, moisture control is the primary strategy to focus on in order to limit and prevent mold growth. Once moisture intrusion into a building takes place, mold can start growing in very little time.  Fungi have been shown to be capable of germination, growth and sporulation in as little as 24 hours after water intrusion or damage occurs.

Building Science

To understand how to find mold and prevent its growth in a building, inspectors must study and understand building science.  Building science, in relation to mold, is the study of the building's dynamics as affected by moisture intrusion.  Buildings are dynamic environments influenced by geographic location, season, weather conditions, HVAC system design and operation, moisture intrusion, pest colonization, and human activities.   Building dynamics continually change and affect the conditions for mold growth. 

               

Moisture Content

Moisture content ("MC") is often expressed as a percentage (100 x (wet mass – dry mass)) ÷ (dry mass), or in terms of the amount of water in a certain volume (lbs./ft. cubed).

Mold requires moisture to survive, so protecting lumber and wood structures from moisture will help prevent mold growth.  Mold growth can be limited if the MC of wood can be kept below 20%.  An MC below 17% means that virtually no microbial growth will occur on even the most susceptible materials. Southern pine dimensional lumber is typically kiln-dried to a maximum 19% MC or less.  The moisture content is indicated on the grade stamp.  Moisture content is related directly to particular substrates or materials.  Microbial growth is limited when the MC of gypsum board is below 0.6%, when brick is below 0.8%, when wallpaper is below 10.5%, and when concrete is below 5%.   One study showed that a moisture content greater than 5% permitted the growth of Penicillium glabrum and Aspergillus versicolor on ceiling tiles in a laboratory. 

Mold growth does not require the presence of standing water; it can occur when high relative humidity or the hygroscopic properties (the tendency to absorb and retain moisture) of building surfaces allow sufficient moisture to accumulate.  Relative humidity and the factors that govern it are often misunderstood.  This section is intended to give building inspectors an understanding of the factors that govern relative humidity, and to describe common moisture problems and their solutions.

Relative Humidity

Understanding relative humidity in a building is essential to controlling mold growth.  Relative humidity (RH) is a ratio (expressed as a percentage) of the amount of moisture in the air to the maximum amount of moisture the air can hold.  Warm air can hold more moisture than cool air.  RH is a factor in determining how much moisture is present in a room, but it is the available moisture in a substrate (not the RH of the room’s air) that determines if mold can grow or not. 

Many sources recommend maintaining RH in living spaces below 60% to limit microbial growth.  By keeping RH below 60%, one may assume that the moisture content in building materials would be low.  However, this assumption may be false because mold grows on surfaces and in building materials, not in the air.  Therefore, it is the RH in the air adjacent to the surface, not the ambient RH, that must be lowered in order to control mold growth.  Measuring a room with a RH at or below 60% may mean that the building materials are fairly dry, but it does not eliminate the possibility of mold growth because local cold spots and water intrusion may allow the RH of the air adjacent to the surface to exceed 70%. 

Moisture meters are essential for inspectors; they enable inspectors to identify damp areas that would otherwise not be evident.  Infrared thermography cameras are praised for their ability to detect moisture that is not readily visible. 

Water enters buildings both as a liquid and as a gas (water vapor). Water, in its liquid form, is introduced intentionally in bathrooms, kitchens and laundries, but accidentally by way of leaks and spills. Some of that water evaporates and joins the water vapor that is exhaled by building occupants as they breathe, or that which is introduced by humidifiers. Water vapor also moves in and out of the building as part of the air that is mechanically introduced or that infiltrates and exfiltrates through openings in the building's shell.

A lesser amount of water vapor diffuses into and out of the building through the building materials themselves.

The sketch above illustrates the usual locations of moisture entry, and how all those entry paths can add to the moisture gain of the building.

The ability of air to hold water vapor decreases as the air temperature is lowered. If a unit of air contains half of the water vapor it can hold, it is said to be at 50% relative humidity (RH). As the air cools, the relative humidity increases.  RH rises as the air cools, because cooler air has a lower moisture-holding capacity, increasing the risk of condensation in walls. 

If the air contains all of the water vapor it can hold, it is at 100% RH, and the water vapor condenses, changing from a gas to a liquid. It is possible to reach 100% RH without changing the amount of water vapor in the air (its “vapor pressure” or “absolute humidity”), all that is required is for the air temperature to drop to the “dew point.”

Relative humidity and temperature often vary within a room, while the absolute humidity in the room's air can usually be assumed to be uniform. Therefore, if one side of the room is warm and the other side is cool, the cool side of the room has a higher RH than the warm side.

The highest RH in a room is always next to the coldest surface. This is referred as the “first condensing surface,” as it will be the location where condensation first occurs, if the relative humidity at the surface reaches 100%.  It is important to understand this when trying to understand why mold is growing on one patch of wall or only along the wall-ceiling joint.  It is likely that the surface of the wall is cooler than the room's ambient air because there is a void in the insulation, or because wind is blowing through cracks in the exterior of the building.

The chart above showing the relative humidity reading taken in a room will only give an accurate indication of the actual amount of moisture present if a temperature reading is taken at the same time. The chart shows that air at 70° F and 40% RH contains approximately 0.006 pounds of moisture per pound of dry air (as indicated by the bold line), while air that is at 50° F and 40% RH contains approximately 0.003 pounds of moisture per pound of dry air (as indicated by the dashed line). Although both are at 40% RH, the 70° F air contains roughly twice as much moisture as the 50° F air.

Condensation in Cold Climates

The basic idea in controlling condensation due to vapor migration is to prevent warm, moisture-laden air from contacting cool surfaces.  In cold climates, condensation can occur within an exterior wall of a building when warm, moist indoor air flows outward.  This warm, moist air cools as it nears the outer boundary of the exterior wall.  RH rises as the air cools because cooler air has a lower moisture-holding capacity, which increases the potential for condensation forming in the walls.

To control condensation in a building exterior wall in cold climates:

•    Install insulation to prevent large temperature differences between air and surfaces.
•    Install air or vapor barriers on the warm side of the building envelope. 
•    Use ventilation to reduce indoor moisture levels below levels that allow condensation to occur.

Condensation in Hot and Humid Climates

To control condensation in a building's exterior wall in hot, humid climates:

•    Install insulation to prevent large temperature differences between air and surfaces.
•    Install air or vapor barriers on the exterior-side of the building envelope. 
•    Avoid impermeable vinyl or other wall coverings, and use permeable paints and wall
      coverings on the interior surfaces of the exterior walls.
•    HVAC systems should be producing net-positive pressures on the inside of the building, with
      respect to the outdoors, to avoid entry of outdoor air inward.
•    Try to avoid cooling interior spaces below the average, monthly, outdoor dew-point
      temperature for the climate in which the building is located.  In some areas, this may not be
      possible.


Many buildings incorporate vapor barriers in the design of their walls and floors. Vapor barriers must be located and installed properly or the building may develop moisture problems. A vapor barrier is a layer of material that slows or prevents the absorption or release of moisture from or into a wall or floor. Vapor barriers can prevent damp or wet building materials from drying quickly enough to prevent mold growth.

                     

Humidifiers

Moisture from humidifiers may support microbial growth on wet surfaces where moisture can condense during cold weather.  Humidifiers that discharge small droplets of water from a reservoir of water are prone to supporting mold growth.  Moisture accumulation inside dirty ductwork creates a suitable environment for mold growth.  The reservoir of the humidifier is usually contaminated, to some degree.  Humidifiers should be considered potential sources for mold growth.

Windows

In winter, windows are typically the coldest surfaces in a room.  The interior surface of a window is often the first condensing surface in a room.  Condensation on window surfaces has historically been controlled by using storm windows or insulated glass to raise interior surface temperatures.  The advent of higher-performance glazing systems has led to a greater incidence of moisture problems in heating climate-controlled building enclosures because the buildings can now be operated at higher interior vapor pressures (or moisture levels) without visible surface condensation on windows.  In older building enclosures with less advanced glazing systems, visible condensation on the windows can alert the occupants to the need for ventilation to flush out interior moisture (such as opening the windows).

RH and Temperature

Mold is often found on the exterior wall surfaces of corner rooms in cold climates.  An exposed corner room is likely to be significantly colder than adjoining rooms, so it has a higher relative humidity (RH) than other rooms at the same water-vapor pressure.  If mold growth is found in a corner room, then relative humidity levels next to the room's surfaces are above 70%.  However, is the RH above 70% at the surfaces because the room is too cold, or because there is too much moisture present (or high water-vapor pressure)?

The amount of moisture in the room can be estimated by measuring both temperature and RH at the same location at the same time.  Suppose there are two cases:  In the first case, assume that the RH is 30% and the temperature is 70° F in the middle of the room.  The low RH at that temperature indicates that the water-vapor pressure (or absolute humidity) is low.  The high surface-RH is probably due to room surfaces that are “too cold.”  Temperature is the dominating factor, and control strategies should involve increasing the temperature at cold room surfaces.

In the second case, assume that the RH is 50% and the temperature is 70° F in the middle of the room.  The higher RH at that temperature indicates that the water-vapor pressure is high, and there is a relatively large amount of moisture in the air.  The high surface-RH is probably due to air that is “too moist.”  Humidity is the dominating factor, and control strategies should involve decreasing the moisture content of the indoor air.
 
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