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STORY ABOUT TINGWALL SOLVING
THE MOLD PROBLEM |
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Written
By Raymond Ting
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An
article entitled "Mold Lawsuits Have Industry Feeling
Vulnerable as Larger Projects Are Eyed" by William
Krizan with William Angelo and Janice Tuchman published
in the 3/31/03 issue of Engineering News-Record.
This article highlighted the significant liability
exposure of building contractors and designers.
To complete the exterior building skin, many pieces
of facing panels must be joined together and sealed
against air and water infiltration. The majority
of the curtain wall problems is related to the panel
joint design.
The well-known term of "Sick Air Building" is the
result of toxic molds growing inside the building
and spreading into the interior air through the
air conditioning system.
To prevent the problem, it is essential to understand
the following two conditions necessary to cause
the growing of molds.
1. Wetting of Moisture Absorbing Building Material
or Wetting in an Entrapped Area:
Typical examples of wetting locations are roof
or wall insulating material, inter-floor fire safing
material, floor carpet, and space behind or under
equipment or furniture.
2. Long Term Wetted Condition:
If the wetted material or area can be dried out
quickly, there will be no chance for the molds to
grow.
WATER PROBLEMS
The typical sources of water causing the wetting
problem include the following items.
(1). Interior Water Condensation: Typical examples
are thru-thermal-conductivity of metal components
in the roof or the curtain wall system and poorly
insulated air cooling pipe or duct.
(2). Leaking Pipe in the Interior Water Supply or
Drainage System.
(3). Water Infiltration Through the Roof System.
(4). Water Infiltration Through the Curtain Wall
System.
To evaluate the liability exposure of the potential
"Sick Air Building" problem, the following questions
must be answered.
1. What does it take to prevent the problem ?
2. Is early detection of the problem possible ?
3. What does it take to remedy the problem ?
4. What is the chance of recurrence of the problem
after remedial work ?
It can be readily understood that Problems (1) and
(2) have the least liability exposure. Except the
skylight area and roof penetrations, the roof water
infiltration problem has been largely solved by
using standing seam roof system or membrane roof
system with good erection practice. The leakage
through a skylight area normally results in a well
vented open area allowing quick manual or natural
drying, therefore, there is little potential for
growing molds. Based on the above discussions, Problem
(3) has a higher liability exposure than Problems
(1) and (2). Problem (4) has the highest liability
exposure due to the huge surface area, the aesthetical
requirement, the vision area, the mixture of various
facing material, the infinite variables of architectural
shaping, and the effects of various structural displacements
of the building. This paper is intended to identify
the causes of Problem (4) leading to the establishment
of curtain wall design parameters for minimizing
the liability exposure of "Sick Air Building".
CAUSES OF MOLD PROBLEM DUE TO CURTAIN WALL WATER
LEAKAGE
It is well known in the industry that water infiltration
through a curtain wall will occur when three elements,
namely, water on the wall due to rain, positive
exterior air pressure due to wind, and imperfect
wall joint seal, exist simultaneously at one location.
If any one of the three elements can be eliminated
at the location, water will not infiltrate through
the curtain wall. The conventional method of preventing
water leakage is trying to make perfect seal in
the wall joints. This would require long lasting
sealant material property and perfect workmanship
in installing the sealant lines. Due to the extreme
total length of wall joints in a building and the
impossibility of visual judgment of perfection of
the sealant line, the execution of perfect seals
throughout the building is deemed to be nearly impossible
for a newly erected building. Even if perfect seals
are assumed to be possible, sealant material aging
effect due to sun exposure and sealant stress cycles
due to various forms of structural displacements
will cause the eventual sealant functional failure.
Therefore, the perfect seal concept can not be relied
on for prevention of curtain wall water leakage.
The initial stage of water leakage through a curtain
wall is practically undetectable. The infiltrated
water will normally be trapped within the wall cavities
and in more severe cases will cause the wetting
of the insulating material and/or the fire safing
material behind the curtain wall. This condition
can be unnoticeable for a long time since it is
normally hidden behind the interior wall board and/or
above the ceiling. The space within the wall cavity
and the space for the insulation or the fire safing
are normally largely closed area which does not
allow the trapped water to evaporate easily setting
the environment of mold growing. Due to the difficulty
of preventing curtain wall water leakage and the
nature of undetectable condition for mold growing,
water leakage through a curtain wall poses the greatest
liability exposure for "Sick Air Building".
CURTAIN WALL DESIGN PARAMETERS FOR MINIMIZING
MOLD PROBLEM
Based on the above discussions, the following three
curtain wall design objectives must be considered
in order to minimize the liability exposure due
to the mold problem.
1. To Minimize the Possibility of Water Leakage
: The water leakage problem must be solved by
design rather than by material (i.e. perfect seal).
Since there are only three elements in the water
leakage theory, to accept the existence of imperfect
seal, the design should try to maximize the separation
of the water seal function and the air seal function.
The water seal is located along the exterior water
path and is air pressure equalized to the exterior
behind the seal. The air seal is located at a location
beyond the exterior water path. Ideally, if the
water seals can be completely separated from the
air seals anywhere in the system, then, the system
would be free from the perfect seal requirement
for water-tightness performance. This ideal condition
is accomplished by using TingWall.
2. To Minimize the Sealant Stress due to Structural
Movements : This is to ensure the long term
performance of the sealant lines. The conventional
design concept is to use stronger sealant material
to resist the sealant stress. However, repeated
stress cycles even with adequate safety factor often
lead to sealant failure due to stress fatigue. The
best way is to free up the degree of fixity within
the curtain components to allow low stress or stress
free relative movements of the curtain wall components
as explained below.
(1). Thermal Movements: It is desirable to use open
joint design throughout the curtain wall system.
The ideal condition is to have each facing panel
individually framed with free space between the
adjacent panel frames. In this ideal condition,
thermal movements will not produce any significant
sealant stress. This ideal condition is accomplished
by using TingWall.
(2). Wind Load Effect: In a conventional curtain
wall system, the sealant lines around a facing panel
are fixed to the panel supporting mullions and girts.
The wind load deflection of the facing panel will
create a force to pull the sealant lines away from
the supports. Repeated load cycles often cause sealant
line failure. The idea condition is to separate
the facing panel frame from the supporting frame
such that the panel frame can partially flexes with
the facing panel deflection to significantly reduce
the sealant line stress. This ideal condition is
accomplished by using TingWall.
(3). Story Drift due to Wind or Earthquake : The
curtain wall supports must undergo the relative
side sway displacement caused by the story drift
of the building frame. The modern building frame
design requires a rather large story drift. This
often causes a big problem for the curtain wall
design. The ideal condition is to design the curtain
wall system to allow the story drift to be absorbed
by relative individual facing panel drifts to render
the sealant line stress to become insignificant.
This ideal condition is accomplished by using TingWall.
(4). Effect of Inter-Floor Deflection : In the conventional
curtain wall system, the curtain wall joint must
be designed to absorb the total amount of the design
inter-floor deflection which is commonly about 3/4".
When the curtain wall joint is designed to absorb
this amount of large stationary deflection, it is
very difficult to maintain the sealing function.
The ideal condition is to design the mullion anchoring
system to limit the curtain wall joint movement
to a much lesser amount (e.g. 1/4") while the inter-floor
deflection reaches the higher amount (e.g. 3/4").
This ideal condition is accomplished by using TingWall.
3. To Minimize the Retention of Water in the
Curtain Wall Cavities: The ideal condition is
to design the system with instantaneous drainage
mechanism and fully vented wall cavities. This ideal
condition is accomplished by using TingWall.
ACTUAL BUILDING EXAMPLE
The IBM manufacturing plant in Rochester, Minnesota
became a Sick Air Building since around 1995. The
problem persisted despite many remedial attempts
with reported annual maintenance cost of about $300,000.
Upon successful laboratory test performance, IBM
awarded the renovation project in 2000 exclusively
using TingWall. The total curtain wall area is estimated
to be around 880,000 square feet. The project has
been proceeded in phases. Up to date, three phases
have been completed with complete satisfaction of
the owner and the total elimination of the mold
problem in the renovated area. The design for the
fourth phase has been completed as of 4/25/03.
*A discussion of the problem was
published in the October, 2003 issue of Glass Magazine. |
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