The following FAQs represent the
primary questions that are had regarding roof coatings.
If these do not provide the answers that you are
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Us form.
| Q. |
Is there a standard for calculating Life Cycle Costs? |
| A. |
The standard is ASTM E-917, “Standard
Practice for Measuring Life-Cycle Costs of
Buildings and Building Systems.” |
| |
| Q. |
What coatings should
be used over different roof substrates? |
| A. |
Asphaltic coatings can be used over asphaltic
and coal tar substrates.
Non-asphaltic coatings
can be used over asphaltic as well as non-asphaltic
substrates. Non-asphaltic coatings include:
acrylic, urethane, silicone, Hypalon®,
butyl and polyurea. Care must be exercised
in using solvent-borne coatings over non-asphaltic
substrates, as the solvent may adversely affect
the integrity of the roofing material. Ultimately,
it is important to follow the manufacturer’s
directions and cautions when applying any roof
coatings. |
| |
| Q. |
What is a “Green
Roof”? |
| A. |
A “green roof” can be defined
in one of two ways. First, the term is sometimes
used to describe an “environmentally
friendly” roof where the roof surface
color is white and the roof assembly is well
insulated. A second definition implies the
use of organic vegetation such as gardens,
planters and trees installed on the roof. |
| |
| Q. |
Which is better:
a white roof coating or a white membrane
roof? |
| A. |
Neither is better, but they are different
with advantages and disadvantages for each.
Either will reduce the cooling load on the
building by reflecting the IR portion of the
solar spectrum. The white coating is a maintenance
practice. This is an important distinction,
as the coating does not add additional “dead
load” or weight to the roof. Thus, if
the roof includes two roofs; the original and
a recover, then the coating can be applied
while still complying with the appropriate
building code. There are also tax advantages
and financial implications that may favor a
roof coating over a new white roof. The white
roof membrane is a true “roof” acting
as the primary waterproofing. The roof coating
is usually not the primary waterproofing, but
rather acts as the first echelon of protection,
keeping water out and shielding the membrane.
Remember that with any type or color roof,
a roof coating can be applied to prolong the
roof life |
| |
| Q. |
If a roof starts
out white, doesn’t it get dirty, thus
reducing the solar reflectance? How much
loss in reflectance can be expected? |
| A. |
The roof will collect dirt during its life
and will have lower albedo, where albedo is
defined as the fraction of incoming solar energy
that is reflected back from a surface. A material
with a high albedo will stay cooler than a
material with a low albedo due to the difference
in solar energy that is absorbed. Studies conducted
by Lawrence Berkeley Laboratory have shown
that the solar reflectance of a white coating
drops to about 80% of its original value due
to weathering and dirt pickup. Of course, this
is critically dependant on the “micro
climate” i.e., how dirty the locale is. |
| |
| Q. |
Is there a proper
thickness for roof coatings? |
| A. |
No. The correct thickness should be driven
by the manufacturer’s recommendation.
Experience suggests a minimum of 18 dry mils
for a white elastomeric coating. |
| |
| Q. |
What is the difference
between Factory Mutual and Underwriters Laboratory? |
| A. |
FM is a group of three property insurance
companies who insure the majority of the Fortune
500 buildings in the U.S. FM also includes
Factory Mutual Research Corporation (FMRC)
which conducts research and develops testing
protocol for evaluation building components.
FM 4470 is the standard protocol for evaluating
roofing systems. It includes pass/fail tests
for fire resistance, wind uplift, hail resistance
and water resistance. Underwriters Laboratory
evaluates a myriad of building and construction
components in the interest
of public safety. UL evaluates
low slope roofing systems for fire under the
UL-790 protocol. |
| |
| Q. |
Can a roof coating
be UL approved? |
| A. |
No. Only the entire roofing system can be “listed” by
UL. This includes all components from the roof
surfacing (coating) down to the roof deck.
Components are not tested individually, but
rather as the complete system. |
| |
| Q. |
What is included
in the UL fire test? |
| A. |
The test has three parts. The first is “Spread
of Flame.” A roof mockup measuring 4’ x
10’ is constructed and allowed to condition
for 30 days. Then the assembly is placed at
an incline in a chamber that simulates a 26
MPH wind. A flame is created using a gas burner
across the bottom of the assembly and allowed
to propagate up the incline for 10 minutes.
The flame spread is measured and rated according
to Class A, B, C with A being the least flame
spread (best rating). The second part is “Intermittent
Spread of Flame.” Here the same process
is recreated, but the flame is turned off and
on during the test. Again the flame propagation
is rated as A, B, C. The third test is the “Burning
Brand Test” where a pine lattice (called
a Crib) is set afire and placed on the roof
assembly. If it burns through to the deck,
it fails that rating. “A” rating
would resist a 12” x 12” lattice, “B” rating
would resist a 6” x 6” lattice
and “C” rating would resist a 2” x
2” lattice. |
| |
| Q. |
What is the brown
stain that sometimes appears on roofs freshly
coated with waterborne acrylic roof coatings
immediately after heavy dew? |
| A. |
This is an exudate that contains water-soluble
components from the roof coating. These materials
easily wash off and should be removed if additional
coating is to be applied. Failing to remove
these will interfere with intercoat adhesion. |
| |
| Q. |
Is there a perfomance
specification for white acrylic roof coatings? |
| A. |
ASTM D-6083, Standard Specification for Liquid
Applied Acrylic Coating Used In Roofing, was
developed in 1995 under the Roofing and Waterproofing
Committee, D-08. The purpose of the development
of this specification was
to establish a minimum
level of quality for acrylic roof coatings.ASTM
D-6083 comprises a group of ASTM test methods
that are used in the roofing and coatings industries,
and the balance of properties necessary to
pass ASTM
D-6083 insures that the acrylic roof
coating will perform well in the field. |
| |
| Q. |
What is California
Title 24?
|
| A. |
Title 24 of the California Code of Regulations
is entitled “California ’s Energy
Efficiency Standards for Residential and Non-Residential
Buildings”.The purpose of these standards
is to make buildings in more energy efficient.
Section 118 and Table 118C of Title 24 Part
6 set the requirements for coatings applied
over low-slope roofs which will take effect
on October 1st, 2005. |
| |
| Q. |
What is “sustainable
development?” |
| A. |
Sustainable development is an economic strategy
that also takes into account the effects of
development on the environment and on the quality
of life of those affected by the development.
White acrylic roof coatings have great benefits
when looked at from the perspective of sustainable
development.
A white acrylic roof coating can significantly lower the air conditioning
costs of a building due to the reflection of the majority of the solar
energy that hits the roof. The roof coating will also extend the service
life of the roof, which in the long run, saves money for the building owner.
Building codes allow for two roofs to be placed on a building, but they
must be torn off before another roof structure can be put on the building.
These torn-off roofing materials are often land filled because they cannot
be recycled. By extending the life of a roof system, a smaller fraction
of land fill space is taken up by roofing materials. |
