Frequently
Asked Questions: Mold/Mildew as relates to the building envelope and
gypsum building materials
What are molds and why should we be concerned about them?
Molds are classified as microscopic fungi. Microbes need four basic
ingredients to grow: (1) organic nutrients or "food"; (2) moisture
in the form of standing or absorbed water or humid air; (3) a surface on which
to grow; and (4) darkness. It is reported that well over 100,000 molds presently
exist, with more being discovered. The most common species of molds found in
structures include Cladosporium, Penicillium, Aspergillus, Alternaria and
Stachybotrys. Of these, the particular species Stachybotrys chartarum,
Aspergillus versicolor and Aspergillus niger (less commonly found) are of greater
IAQ/SBS health related concern for indoor environment.
What is “black mold”?
The news media often refers to “black mold” or “toxic black
mold.” It is usually associated with Stachybotrys chartarum, a
type of greenish-black mold commonly associated with heavy water damage. Not
all molds that appear to be black are Stachybotrys. The known health
effects from exposure to Stachybotrys are similar to other common molds,
but have been inconclusively associated with more severe health effects in some
people.
What are the primary design considerations for designing a mold/mildew free
building envelope?
Mold and mildew are fungi that grow on surfaces of materials,
within pores and in deteriorated building materials. Mold needs water to grow
and will typically be found where there is moisture migration or high humidity
environments. A properly designed building envelope must include a properly engineered
HVAC system with water-tight assemblies. Most importantly water management includes
drainage systems and materials.
According to MASTERSPEC – EVALUATIONS – GENERAL COMMENTS, For
ideal wall envelopes water tight performance, joint sealants, and flashings for
exterior barriers must be perfect, and is difficult to achieve because of materials,
construction, workmanship, and life-span realities. Currently EIFS and cladding
systems may be designed as surfaced-sealed barriers or as water and weather-resistive
cladding functioning as part of moisture-draining wall assemblies. Part of an
assembly may include a less water absorptive gypsum core with embedded fiberglass
mat exterior as per ASTM C 1177C/1177M (instead of paper). Responsibility for
determining the sheathing’s water-absorption and water-resistance performance,
and exposure classification remains with the specifiers..
What information should I know about various kinds of mold/mildew when designing
assemblies and selecting gypsum board wall substrates?
Controlling building airflow
is essential because air carries water. Water enters buildings both as liquid
and as water vapor. Water vapor moves in and out of buildings as designed with
natural ventilation and engineered HVAC systems. Water vapor diffusion through
building materials is less likely than moisture entry through failed assemblies,
holes in the building envelope or internal moisture release through normal building
uses. However, some building materials are more likely to hold moisture as opposed
to properties that resist moisture such as fully embedded glass mat gypsum sheathing.
Exterior and interior walls should be designed to dry as moisture moves through
or into the system making permeability a desirable building material property.
What are typical areas of moisture migration and absorption in building
envelope materials?
Moisture migration is typically found in improper sealing of doors, window
openings and flashings, exterior surfaces, plumbing leaks, roof leaks, roof penetrations,
natural ventilation, improperly engineered HVAC systems, non-drainage wall systems,
miscalculating dew point, condensation points in assemblies, improper use/placement
of vapor barriers, and placement of thermal barriers.
Why do I smell mold and mildew
but I don’t see it’s
visible presence or signs of water leaks?
In many cases mold/mildew problems are more a result of improper operation
of building systems. Convention centers, hospitality facilities, and churches,
as examples, many times will shut down HVAC systems when spaces are not in use.
In certain climates, especially high humidity areas, moisture infiltrates these
spaces through natural ventilation, normal use and holes in the building envelope
allowing moisture absorption in building materials. This practice may save facilities
managers some energy costs, but the moisture infiltration from the lack of proper
HVAC pressure may result in certain building materials absorbing moisture that
ultimately propagates the growth of mold/mildew. The specification of materials
that resist moisture like a fully embedded glass mat gypsum board substrate are
critical components in proper assembly design.
Doesn’t the building
code have design and performance compliance standards that reduce chances of
mold/mildew?
Building standards were developed over the
years to assist builders and design professionals build structures that meet
the needs of those utilizing the facilities. Building codes are currently undergoing
revision and consolidation of BOCA, SBCCI, ICBO to the International Building
Code (IBC).
How does moisture move through building materials/assemblies?
Water vapor moves
from warm areas to cool areas. Various building materials have greater resistance
to water vapor movement (water diffusion) while other materials are more supportive
for water vapor diffusion. Materials, like gypsum board, allow for easy water
vapor diffusion because it is considered permeable. A fully embedded glass mat
gypsum board substrate is the best of both worlds as the glass mat is water resistant
while being permeable so the wall-assembly that will breath.
In most cases, moisture problems are directly related to poor construction
or building components, or to the failure of a building system, such as plumbing
or a roof in humid areas of the United States, outdoor air is a major contributor
to moisture in buildings
Assemblies including components with drywall materials, vapor barriers, Glass
matted wallboard, EIFS systems need to be scientifically engineered to assure
proper functioning of intended design.
Why is a wall drainage system important in reducing the growth of mold/mildew?
In many cases water drainage comes in the undesirable form of detectable leaks
such as condensation, plumbing or HVAC systems. It is the undetectable water
leaks that create greater damage and likelihood of the growth of mold/mildew.
These types of construction defects may exist for years before seeing the effects.
Wall system design should include either an air space, material to channel the
water out of the assembly to reduce or prevent moisture absorption of substrate
materials along with a breathable system. Products like fully embedded glass
mat water resistant gypsum board assists in directing water to these drainage
areas.
What ASTM and other standards should be referenced in specifying fully embedded
glass mat gypsum products and assemblies that are moisture and mold/mildew resistant?
Current
liability and litigation has risen around the problem of mold growing on building
materials. Recommended specifications for testing products
for mold/mildew include: MIL-STD-202, 810; ASTM D 120, D 470, D 518, D 1049,
G21, 22, 29; Fed. Test Method Standard No. 191; RTCA/DO-160
Are there any other reference standards addressing mold/mildew that should
be included in Part 2 specification language?
PART 1 GENERAL
1.2 SUMMARY
A. This
Section includes the following:
1. Embedded glass-mat gypsum sheathing board.
2. Sheathing joint-and-penetration treatment.
1.3 DEFINITIONS
A. Gypsum
Board Construction Terminology Standard: Refer to ASTM
C 11 for definitions of terms for gypsum sheathing board construction not defined
in this Section or in other referenced standards.
1.4 REFERENCES
A. ASTM C 514:
Specification for Nails for the Application of Gypsum Board
B. ASTM
C 954: Specification for Steel Drill Screws for the Application of Gypsum Panel
Products or Metal Plaster Bases to Steel Studs from 0.33 in. (0.84 mm) to
0.112 in. (2.84 mm) in Thickness
C. ASTM
C 1002: Standard Specification for Steel Drill Screws for the Application of
Gypsum Panel Products or Metal Plaster Bases
D. ASTM
C 1280: Standard Specification for Application of Gypsum Sheathing
E. ASTM
C 1397: Practice for Application of Class PB Exterior Insulation
and Finish Systems
F. ASTM
E 84: Test Method for Surface Burning Characteristics of Building Materials
G. ASTM
E 96: Test Methods for Water Vapor Transmission of Materials UL Design U425 (Load-Bearing)
1-Hour Fire Resistance Rating
H. ASTM E 119: Test Method for Fire Tests of Building
Construction and Materials
I. UL Design U425 (GLASROC sheathing type X -Load-Bearing) 1-Hour
Fire Resistance Rating
J. UL Design U425 (GLASROC sheathing type X - Steel Stud
- Load-Bearing 80%) 2-Hour Fire Resistance Rating
K. UL Design U301 (GLASROC sheathing type X - Wood Stud Load-Bearing)
2-Hour Fire Resistance Rating
L. UL Design U305 (GLASROC sheathing type X- Wood Stud Load-Bearing)
1-Hour Fire Resistance Rating
M. UL Design U501 (GLASROC sheathing type X- Floor/Ceiling
)
1-Hour Fire Resistance Rating
N. UL Design U502 (GLASROC sheathing type X- Steel beam and Column )
2-Hour Fire Resistance Rating
What
ASHRAE standards and tools should I be referencing for proper HVAC and building
envelope performance?
LEED® recommends utilizing VisualDOE 3.1 whichis
a state of the art program for performing whole-building energy analysis using
DOE-2 on PCs running MS Windows 95/98/NT/Me/2000/XP.
Released December 2002, VisualDOE 3.1 is a new green building design tool
that allows users to evaluate energy and demand impacts of design alternatives.
The program covers all major building systems, including building envelope, lighting,
daylighting, water heating, HVAC and central plant. This will help proper design
of the building envelope to minimize mold/mildew issues. http://www.eley.com/gdt/index.htm
How can I tell if mold has developed in my facility?
It is important to understand mold is a natural occurrence and becomes a concern
only when found in excess. Mold is typically visible as a greenish-black stain
and normally has a musty odor. There are many types of mold, some more concern
than others. Most consultants will tell you it is essential to find the source
for the growth of the mold and fix the problem and immediately clean the affected
area.
When is sampling for mold/mildew necessary in building evaluation?
AIHA
(American Industrial Hygiene Association – www.aiha.org)
recommends that if visible mold is present, to immediately clean the area, regardless
of what species are present and whether samples are taken. In specific instances,
such as cases where health concerns are an issue, litigation is involved, or
the source(s) of contamination is unclear, sampling may be considered as part
of a building evaluation. Sampling is needed in situations where visible mold
is present and there is a need to have the mold identified.
If mold is suspected, but not visibly detectable after an inspection, then
sampling may reveal evidence of mold amplification or reservoirs indoors. If
mold is being removed and there is a question about how far the colonization
extends, then surface or bulk sampling in combination with moisture readings
may be useful. Sampling for airborne mold spores can indicate whether the mix
of indoor molds is “typical” of the outdoor mix or, conversely, “atypical” or
unusual at that time.
Professionals experienced with mold issues and familiar with current guidelines
must conduct any sampling. If samples are taken, regardless of the purpose, the
results should help answer a clear question. Sampling without a specific purpose
greatly increases the chances of generating useless data. Note that laboratories
vary in experience and proficiency; using an AIHA EMLAP-accredited lab is recommended.
A listing of accredited labs can be found at www.aiha.org/Content/LQAP/accred/EMLAP.htm.
Why are there no standards for mold/mildew exposure?
Different mold species may be more or less hazardous with respect to any or
all of these categories. However, risks from exposure to a particular mold species
may vary depending on a number of factors. Uncertainty is complicated further
by a lack of information on specific human responses to well-defined mold contaminant
exposures. In combination, these knowledge gaps make it impossible to set simple
exposure standards for molds and related contaminants.
What information resources are there about mold/mildew?
What products does CertainTeed have that specifically are recommended for
moisture resistant wall assemblies?
CertainTeed, the global leader of gypsum
products, manufactures GlasRoc® Sheathing, with its Enhanced Glass Reinforced
Gypsum (EGRG) Technology. It is a
unique, patented technology that combines reinforcing glass mats, fully-embedded
into water-resistant gypsum core positioned beneath a paperless polymer-modified
gypsum surface, and a protective acrylic coating on the exterior face. It is
an enhanced version of the proven GRG Technology* developed by CertainTeed almost twenty
years ago
GlasRoc® Sheathing offers:
• Long term protection to weather exposure.
• Superior liquid resistant
surface that is permeable.
• Excellent fire protection.
• Strong — yet flexible enough to
bend to curved surfaces.
• Mold and mildew resistance.
• Conformity to design and code requirements.
GlasRoc® Sheathing is easy to handle and install. It cuts like regular
gypsum board and minimizes skin irritations due to a fully embedded glass mat.
GlasRoc® Sheathing is the next generation of the industry standard for high-performance,
weather-resistive, gypsum based sheathing. And to back it up, CertainTeed provides a
6 month limited warranty against exposure and a 5 year limited warranty assuring
product performance.
*Covered by U. S. Patent No. 6,524,679 and other patents and patents pending.
Does CertainTeed have a technical hotline to call for assistance on mold/mildew
issues related to fully embedded glass gypsum products?
One of our Customer Service Representatives can assist you with any
mold/mildew & fully embedded glass gypsum product related questions: Visit
our contact page
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