D ISCUSSION
5.4 Seasonality and extent of human occupation
Mold growth is controlled by a few variables; mold spores, temperature, moisture and nutrients.
Mold spores must be present for the fungi to reproduce and spread. The spores range in size from 3-40 microns (human hairs are 100 microns) so unless they are growing in a colony they are
impossible to see with the human eye (without magnification) and controlling them is extremely difficult in both naturally ventilated and mechanically ventilated buildings. This is because mold spores are constantly around us, there is no way to completely rid the environment of them and frankly we wouldn’t want to. Even if a home is sanitized and cleaned frequently mold spores may travel back inside from clothes, pets and outside air. Further, when mold spores multiply they do so by the millions; uncontrolled mold growth may lead to a costly remediation issue due to countless spores constantly floating around the home It is of the utmost importance to control mold growth by controlling the other variables which allow them to reproduce since controlling the spores themselves is nearly impossible.
Temperature between 70 and 90 °F is optimal for mold growth but some genera may live in temperatures as low as 32 °F and up to 120 °F.107 This does not come as a surprise as we can see some species of mold growing in our refrigerators and even in the hot and dry desert. Unfortunately, the range of human comfort falls well within the range of optimal mold growth too. This means controlling temperature as a means of controlling mold growth is impossible. In fact, sources of cooling and indoor climate control can often exacerbate a mold issue; this will be discussed further, later in this project.
Nutrients are required for all living things, mold included. Anything with carbon can be used as food for mold, which is a vast majority of materials in the world. Building materials, especially those derived from wood, paper and fabric are particularly vulnerable to mold growth. Even dust has enough nutrients for mold sustenance which means that if other materials like concrete, plastic or
107 Centers for Disease Control and Prevention, “Mold Prevention Strategies and Possible Health Effects in the Aftermath of Hurricanes and Major Floods,” Morbidity and Mortality Weekly Report, 55 (2006). accessed November 5, 2016. https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5508a1.htm
glass become saturated with dust they can become hosts for mold as well. Mold spores can also bind to other specs of dust and travel throughout the home this way. Controlling the source of food for mold would also be an extremely difficult to impossible way of controlling its growth.
Moisture is the only reliable and effective way to prevent mold from growing. According to the Center for Disease Control, the primary method of limiting mold growth indoors is by reducing moisture.108 Large colonies of mold growth is almost always an indicator of water or moisture infiltration of the building envelope.109 This may come from a leaky roof, windows, water pipes, water intrusion due to flooding, condensation due to improper insulation and / or heating, ventilation and air conditioning system (HVAC) or often the case in Hawaii, elevated humidity and lack of proper ventilation.110
The specific level of moisture needed for growth varies by genera of mold. Although there is evidence that demonstrates mold growth on some building materials can occur as quickly as 24 to 48 hours of consistent wetness111 and will almost always occur after flooding.112 Researchers into indoor mold growth use a variable called water activity (aw) (aw x 100 = % relative humidity) of building materials to determine the specific moisture content required for mold to grow.113 Generally the longer aw is over .75 for a specific building material, the greater chance mold grows on that material.114 Determining the aw for a building material in residential houses in Hawaii could only be done on a case by case basis due to the numerous variables which may occur. As we know, flooding or direct wetting of a material from leaking or flooding causes an increased aw which usually leads to mold growth. However, increased aw may also occur from condensation and humidity and can be more difficult to control. In any type of building, reducing overall aw would prove to create a healthier indoor environment. The easiest way to do this is to ensure proper and sufficient ventilation to dry the air and reduce surface aw.
108 Ibid.
109 Ibid.
110 Ibid.
111S.C. Doll., Determination of limiting factors for fungal growth in the built environment Cambridge, MA: Harvard University School of Public Health. (2002).
112 Centers for Disease Control and Prevention, “Mold Prevention Strategies and Possible Health Effects in the Aftermath of Hurricanes and Major Floods,” Morbidity and Mortality Weekly Report, 55 (2006). accessed November 5, 2016. https://www.cdc.gov/mmwr/preview/mmwrhtml/rr5508a1.htm
113 K. F. Nielsen, G. Holm, L.P. Uttrup and P.A. Nielsen, “Mould growth on building materials under low water activities. Influence of humidity and temperature on fungal growth and secondary metabolism,” International Biodeterioration & Biodegradation, vol. 54, (2004): 325–336.
114 H. Viitanen, et al. “Moisture and bio-deterioration risk of building materials and structures,” Journal of Building Physics, vol. 33, (2010):201–224.
SOLUTIONS
In the case of both dust and mold there are a few things that can be done to improve indoor air quality and reduce illness. First, is to ensure that there is proper ventilation diluting the inside air with fresh outside air. Even though dust and mold exists outside as well, air flow helps to reduce the levels of particulates and spores in the air. Reducing the amount of building materials and furnishings which unnecessarily contain paper, fabric and other materials which mold and dust can easily collect on is another important way of reducing the odds of toxic exposure. One of the most important things architects and builders can do to prevent exposure to mold, dust and other particulates is to avoid the use of double wall (cavity wall) construction. Often, in cases of water intrusion through the building envelope or roof, parts of the home can become saturated and mold growth may occur. This is a major issue as unknown mold growth can spread and create a significant health issue without the knowledge of the homeowner. Cavities in the wall and roof also become breeding grounds for insects and other living critters like mice or rats, places where dust from construction or insulation can gather and eventually be dispersed throughout the living area. Whenever possible, solid wall construction could reduce some of these negative effects.