Low-Slope Inspection & Maintenance

By properly maintaining a low-slope asphalt roofing system,
building owners can greatly impact its service life, reliability and
performance. The Asphalt Roofing Manufacturers Association
(ARMA) has identified six steps all owners should follow to properly
care for a roof.

Step 1) Maintain historical records.

A building owner should keep a historical
record of the roof system. This should
include information about the following:
• original installation
• roof plan
• membrane type
• system components
• contractor’s contact details
• membrane manufacturer
• warranty
All roof inspections, maintenance and
repairs should be documented as well.

Step 2) Control roof access.
Building owners should allow roof access only to trained
professionals and only when maintenance is required. Roofs are not
generally designed for extensive foot traffic.

Step 3) Conduct regular inspections.
Each spring and fall, a roof should be inspected by a professional roofing
contractor. The contractor should inspect each visible component of the roof
and identify areas that may require additional attention. Inspections can help
to identify potential roof damage or leaks before they occur.

Step 4) Ensure routine maintenance.
Routine maintenance can be conducted by the building’s trained
maintenance personnel. This includes removing debris, such as
construction waste or tree limbs from a roof. Leaves and dirt
should be removed from drains and gutters to ensure proper
drainage. Tree limbs that overhang a roof should be trimmed.

Step 5) Report leaks or roof damage immediately.
If evidence of roof damage or a leak is found during routine
maintenance or an inspection, building owners should contact a
roofing contractor immediately to address the issue before it
gets worse.

Step 6) Use a professional roofing contractor for major
maintenance and repairs.
All major maintenance procedures and roof repairs should be
handled by a professional roofing contractor after consulting the
membrane manufacturer. Do not attempt these actions yourself.
By following these steps, owners
can maximize the value and service
life of their roofing investments.

The formation of a “tobacco juice” residue, so named for its color, has been widely attributed
to the weathering of asphalt roofing (i.e., roof coatings, base and cap sheets and shingles – to
name a few) or the exudation of asphalt fractions from the roofing material.
In fact, similar brown residues have been found on other, non-asphaltic materials, indicating
that the phenomenon can be environmental in nature and not wholly attributable to asphalt
roofing. An investigation of this phenomenon concluded that environmental contamination or
pollutant deposition was the major contributor to tobacco juicing.
Factors commonly present with “tobacco juicing” are excessive air pollution accompanied by
nighttime dew conditions and prolonged lack of rain. Air pollutants can collect on roof surfaces
with the formation of dew and subsequently run down onto lower roof surfaces, fascia, and
other finish surfaces. For steep slope applications, such as asphalt shingled roofs, tobacco
juicing may drip off the shingles and stain the adjacent components (see photos 1-3 below for
examples). This accumulation of residue can continue until the surfaces are washed or
significant rainfall occurs. The residue typically will not affect the performance of the roof and
should not be considered a performance problem.
For low slope applications, if any accumulation of this liquid residue occurs prior to coating, the
proper bonding of coatings to the roof surface may be adversely affected. Preparation of the
roof for coating should conform to the recommendations of the Roof Coatings Manufacturers
Association (RCMA) and the Asphalt Roofing Manufacturers Association (ARMA) to help ensure
proper adhesion. Coated smooth-surfaced roofing systems which are continuously subjected to
tobacco juicing should be hosed off regularly, as tobacco juicing residue may cause the peeling
of acrylic and aluminum coatings.
Though it may not be possible to control environmental elements that cause the formation of
the residue, the following recommendations can be utilized by the specifier, contractor or
owner to minimize the aesthetic conditions associated with tobacco juicing.
• Require edge metal with a drip lip on parapet walls where the metal slopes outward, is
rounded, and has no existing lip on the outside edge to assure the residue-laden runoff
will fall away from the building.

• Hose down the roof at regular intervals during long, dry periods of the first summer
after installation. Note: this is not recommended where proper fall protection is not in
place, or where steps have not been taken to protect exterior surfaces that may come
into contact with the wash-off, e.g., siding on a house without gutters.
• For low slope applications, the use of an aluminum coating or acrylic coating can
minimize the aesthetic conditions. Coat all asphalt emulsions after they are thoroughly
dried. Coat plastic cements and other solvent-based vehicle asphaltic products after
they have cured for at least 30 days.
• Consult the specific material manufacturer for additional recommendations.
The effects associated with tobacco juicing can be minimized if the necessary steps are taken by
the specifier, contractor and owner.

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While volatile organic compound (VOC) regulations have tightened over the years, there
continue to be compliant adhesive, cement, primer, and coating options available for the
installation and maintenance of asphalt roofing systems. Asphalt roofing systems—installed and
maintained with VOC-compliant adhesives, cements, primers, and coatings—continue to
provide long-term performance on the roof while achieving compliance with a wide variety of
VOC regulations that exist throughout North America.
Background on VOC Regulations
When exposed to sunlight, nitrogen oxides (NOx) and VOCs combine to produce ozone. The
U.S. Environmental Protection Agency (EPA) has prescribed National Ambient Air Quality
Standards (NAAQS) for ozone to protect the public health, with an adequate margin of safety,
including the health of at-risk populations, and protect the public welfare from adverse effects.
A region in which ground-level ozone is found to exceed the NAAQS is said to be in
“nonattainment.” Once a state or region is found to be in nonattainment, that area is required
to submit a State Implementation Plan (SIP) setting the regulatory actions that will be taken to
come into attainment.
Those regions and states in nonattainment often employ VOC regulations as part of their air
quality management program to achieve lower ground-level ozone concentrations. In several
areas of the country where there is widespread nonattainment, such as California and the
northeastern United States, regulatory bodies suggest model rules for governing VOCs. These
model rules can be adopted locally by states and regional districts as part of their ozonereduction programs. Additionally, the EPA has the authority to set VOC regulations for certain
product types that become applicable across the country.
Primary Rules Affecting Roofing System Components
The main regulations affecting the installation and maintenance of asphalt roofing system
components are the Architectural and Industrial Maintenance (AIM) Coatings Rules and the
Adhesive & Sealants Rules. Although regulations affecting these products may be introduced
anywhere in the US, there are geographic areas that have historically had high levels of VOC
regulatory activity. Regulatory bodies for these areas include:

• California Air Resources Board (CARB): CARB is the regulatory body that oversees
California’s statewide air quality initiatives and guides the regulatory activities of its 35
local air districts. In the case of AIM Coatings, CARB publishes “suggested control
measures” (SCMs) that the air districts may choose to adopt as part of their air quality
compliance efforts.
• Ozone Transport Commission (OTC): Comprised of the northeast states that are
included in the EPA-designated Ozone Transport Region (OTR), the OTC publishes Model
Rules that participating states typically use as a template for their state or regional air
quality regulations.
• Lake Michigan Air Directors Consortium (LADCO): LADCO encompasses the Great
Lakes-area states. LADCO typically does not draft its own model rules, but recommends
to its participating states that they use the OTC Model Rules.
• South Coast Air Quality Management District (SCAQMD): One of the air districts in
California, the Los Angeles-area SCAQMD is typically at the forefront of creating and
implementing new VOC regulations. The VOC content limits and breadth of VOC
regulations in the SCAQMD far exceed those of anywhere else in the country;
additionally, SCAQMD regulations typically serve as a precursor to future CARB SCMs
and OTC Model Rules.
Complying with VOC Regulations
When a state or air district adopts a VOC rule, they have the choice to adopt a model rule as
written, to make certain modifications to a model rule, or to create an entirely new rule.
Therefore, it is essential that you work with the manufacturer of your asphalt roofing system
components to ensure that the system being specified will comply with all federal, state, and
local VOC regulations.
Adhesive, cement, primer, and coating manufacturers continue to make developments to their
products to ensure the effectiveness and longevity of each roofing system installed using these
components while also minimizing their potential impact on the environment. With everchanging air quality regulations, adhesive, cement, primer, and coating manufacturers have
many years of experience ensuring that products can comply with new regulations without
sacrificing those products’ proven long-term performance in a broad range of climatic regions.
Contact an ARMA Member today to hear more on the latest VOC-compliant adhesive, cement,
primer, and coating innovations available for your location. Refer to local jurisdictional codes,
regulations, and specific project site requirements that may apply to roofing and related
products.

Ventilation is:
Attic ventilation is the flow of outside air through the space at the underside of the deck of an asphalt shingle roof system.
The benefits of ventilation are:
Ventilation moves heat and moisture out of an attic space. Ventilation helps to prevent premature shingle deterioration and
roofing system failure by keeping the attic temperature closer to the outside temperature. Ventilation may also help reduce the
risk of moisture-related problems by removing moisture-laden air that may collect in the attic space caused by day-to-day
activities in the living space. Ventilation also helps to reduce the risk of ice damming.
Ventilation is achieved by:
Natural attic ventilation is effective because hot air rises. Outside air flows through an attic space when vent openings allow this
hot air to rise out of the attic space at the top (exhaust) while cooler air is drawn in at the bottom (intake). To achieve the
benefits noted above, there must be sufficient air flow. Ventilation systems that provide exhaust but no or inadequate intake
(or intake but no or inadequate exhaust) severely limit air flow and are unlikely to be effective. Wind can increase air flow but
an effective ventilation system assures air flow whether the wind is blowing or not.
The following practices are components of an effective attic ventilation system:
 Install intake vents at the eaves or in the lower portion of the roof or attic space.
 Install exhaust vents at the ridge or in the upper portion of the roof or attic space.
 Locate the intake and exhaust vents to assure air flow in all areas of the attic space. When using eave and ridge vents,
they should be continuous and run the entire length of the eave and ridge. Do not allow blockages or restrictions to
the air flow, such as by sky lights or incorrectly installed insulation. Maintain open air flow from eave to ridge between
each rafter space. When using static vents, they should be equally spaced and close enough to each other to ventilate
the entire attic. A combination of different types of intake vents and different types of exhaust vents may be necessary
to properly ventilate each attic space. However, combining different types of exhaust vents on the same roof above a
common attic space could cause short-circuiting of the attic ventilation system and does not follow vent
manufacturers’ installation instructions.
 Install a balanced system of intake and exhaust. Balance is achieved when intake vents provide 50 to 60% of the open
venting area and exhaust vents provide 40 to 50% of the open venting area. The intake amount should always exceed
the exhaust amount. This ventilation system balance is compatible with the requirements in the International Building
Code (IBC) and the International Residential Code (IRC).
 Install sufficient ventilation. For many years, the standard recommendation has been to provide 1 sq. ft. of net free
venting area for every 150 sq. ft. of attic floor area. The codes generally allow this to be reduced to 1 sq. ft. of net free
venting area for every 300 sq. ft. of attic floor area when certain building features, such as balanced ventilation in
combination with vapor barriers are incorporated into the attic space.
 When reroofing, replace ventilation devices within the field of the roof (e.g., static vents, ridge vents). It is possible to
retain intake and exhaust vents not in the field of the roof (e.g., soffit vents, gable vents), provided they remain
functional when reroofing is complete.
Attic Ventilation Best
Practices for Steep
Slope Asphalt Shingle
Roof Systems
2 of 2 A member service provided by the Asphalt Roofing Manufacturers Association Revised May 2017
 Follow vent product manufacturers’ installation instructions. Model building codes require that the product
manufacturers’ installation instructions be followed.
Please note that some building codes require ventilation to be updated to code required levels when reroofing.

The proper ventilation of attic areas is a critical design and performance consideration. If implemented correctly, proper
ventilation methods can help ensure the maximum service life of roof assembly materials, and can improve energy efficiency of
the building. The minimum amount of ventilation required is defined by the building codes for residential construction. In
addition, ventilation is recommended by shingle manufacturers to help ensure the performance of the roof materials.
Overlooking this consideration may result in the following problems:
 Premature failure of the roofing system
 Buckling of the roofing shingles due to deck movement
 Rotting of wood members
 Moisture accumulation in the deck and/or building insulation
 Ice dam formation in cold weather
In cold climates, internal building moisture is often a cause of roofing system problems. Occupancy generated water vapor may
reach an unconditioned space and condense on cold surfaces. This may cause wood to rot in the roof framing, roof decking,
walls and ceilings. Proper ventilation helps to reduce the occurrence of many problems such as expansion/contraction of
decking and ice damming in cold, snowy climates. Ice dams are formed by the cyclical thawing of snow over the warmer
portions of the roof and re-freezing at the cold eave. Refer to ARMA’s Technical Bulletin “Protecting Against Damage from Ice
Dams.”
During the summer months, roof deck temperatures can significantly increase due to the sun’s energy. The heat from the deck
radiates into the attic space, and could reach the living space if the attic floor/ceiling is not well insulated. This will increase the
demand on the home’s cooling system and energy use. Additionally, it will accelerate the aging of asphalt roofing products. By
properly ventilating the underside of the roof deck, heat buildup and its related problems will be reduced.
Refer to ARMA’s Technical Bulletin “Attic Ventilation Best Practices for Steep Slope Asphalt Shingle Roof Systems.” For any given
home, the minimum amount of ventilation required by code is dependent on three primary factors: the size of the attic, the
placement of the vents and the airflow rating of the vents. When considering air movement, there are two categories of vents –
intake vents and exhaust vents. The optimal attic ventilation installation is a balanced combination of properly located, properly
sized intake and exhaust vents (and there are many types within each category).In some cases, a minimum net free ventilation
area equal to one square foot per 150 square feet of attic floor area must be designed and properly installed to provide proper
ventilation.
In other cases, ventilation can be at a ratio of 1 square foot ventilation per 300 square feet of attic floor area. Ventilation
manufacturers recommend that the free-flow ventilation be equally balanced between intake and exhaust vents regardless of
which ratio is used. Because eave and ridge venting provides continuous airflow along the entire roof peak and eave, instead of
localized as is the case with individual vents, it is generally viewed as the superior venting technique (see Figure A).
The manufacturers of ventilation systems and vapor retarders should be consulted for proper use of their products. It should be
noted that the trends continue toward higher energy conservation, air barriers, and generally tighter housing construction
methods. The code requirements are minimums, and as such, make proper ventilation an important consideration for
minimizing energy usage and optimizing roofing system performance. Standard ‘one size fits all’ solutions are not sufficient.

Homeowners may look at their newly installed roof and think that the shingle color does not look like
the picture in the brochure. In fact, variations in the appearance of asphalt shingle roofs are not
uncommon, and generally occur for five reasons: color shading, back surfacing transfer, staining,
excessive surface asphalt, and deviation from installation instructions.
Color Shading
Color shading is usually the result of variations in surface reflectance in different areas of the roof. Even
slight differences in shingle texture can make color shading perceptible. This may occur more frequently
with black and other dark-colored shingles since only a very small amount of light will reflect from a dark
surface.
The variations that cause shading of black or other dark-colored shingles are so slight that they are
difficult to detect during the manufacturing process. With white and other light-colored shingles, the
total amount of light reflected is considerably greater, resulting in reduced potential for color shading.
Shingle manufacturers will often use surface granule blends to reduce the potential for color shading by
incorporating a variety of different colors, which help reduce shading by making observable differences
less noticeable. Color shading typically varies with the time of day, light intensity, and viewing angle.
Back Surfacing Transfer
Fine particles placed on the backside of shingles so they do not stick together in the bundle can rub off
onto the colored granules on the exposed shingle surface. This may cause temporary appearance
variation immediately after the shingles are installed. However, natural wash from rainfall will
eventually remove this loose backing material from the shingle surface.
Staining
Staining may occur when shingles are stacked or stored for extended periods. Lighter oils in the asphalt
coating may seep between and migrate onto neighboring surface granules. This is generally eliminated
by natural weathering over time.
Excessive Surface Asphalt
One step in the shingle manufacturing process is pressing the surface granules into a hot asphalt
coating. This can occasionally result in small amounts of asphalt rising between the surface granules and
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affecting the appearance in a manner similar to color shading. Natural weathering may reduce the
variability depending on the amount of over-pressed asphalt.
Deviation from Installation Instructions
Deviations from the manufacturer’s printed application instructions by the roofing contractor may also
result in an unanticipated visual patterning. ARMA recommends that installers follow manufacturer
application instructions to avoid patterning.

Self-adhering bituminous membranes have been used as underlayments in steep slope (greater than
2:12) roofing for many years. When applied as an underlayment, they are primarily used to help
prevent water entry from ice dams at the eave areas of shingled roofs in cold climates. When used as
ice dam protection, the underlayment is typically installed directly to the deck surface from the eave’s
edge to a point at least 24 inches (measured horizontally) inside the exterior wall line of the building
prior to application of the shingles. If the membrane is not wide enough to reach that point, install
additional course(s) of membrane as needed, overlapping the previous course by 2 inches or as
specified by the manufacturer. Self-adhering bituminous membranes are required by building codes
to meet the requirements of ASTM D1970, and newer codes require these products to have a label
indicating compliance with ASTM D1970. Always check local building codes to confirm eaves
protection requirements. The adhesive asphalt component effectively seals the membrane to itself
and seals around the shanks of nails used in the overlying shingles so that any water forced
underneath the shingle layers by wind or ice dams does not reach the deck or attic space below.
These self-adhering underlayment membranes have also been used successfully in other “critical”
roof situations, such as part of a flashing system in valleys or around roof penetrations (skylights, vent
stacks, etc.), and are commonly applied to the entire deck beneath roofing materials on lower-sloped
(2:12 to 4:12) roofs.
Where the roof area of one slope transitions to a roof area of a differing slope, the underlayment
application should extend at least 24 inches up on the steeper slope roof. The transition area between
the steeper slope and lower slope needs special attention due to potential water buildup.
In certain applications, such as lower-sloped (2:12 to 4:12) roofs or in areas where high winds or
hurricanes are prevalent, homeowners and roofing contractors may apply the underlayment
membrane over the entire roof area, not just the first few feet at the eaves. This application improves
roof protection in the event that water gets under the shingles. Check local codes to confirm that a
self-adhering bituminous membrane is acceptable for full-roof application.
When installed, self-adhering membranes restrict the flow of vapor and air through the roof
assembly, and moist air entering the attic from the conditioned space inside the home may condense
on the underside of the self-adhering membrane at the roof deck joints. Condensation may lead to
problems in roofing systems or attics, including but not limited to wood deck swelling, deterioration,
mold growth, and staining on the interior ceilings below the attic. Potential condensation problems
may be reduced by:
1. Confirming attic ventilation is adequate, balanced, and evenly distributed to assure proper
airflow.
2. Installing a proper vapor retarder on the warm side of the attic floor, which can reduce
intrusion of warm, moist air into the attic space.

3. Installing sufficient insulation that covers the entire attic floor.
4. Checking local energy codes for appropriate ceiling insulation R-values and air barrier
requirements.
For more details on ventilation, see ARMA’s Technical Bulletin “Ventilation and Moisture Control for
Residential Roofing.” Check with a building design professional for advice if the home is in a warm,
humid climate, as a different approach may be necessary. Following the four recommendations
described above is sound practice for all steep-slope roofing systems. If your roofing application calls
for applying a self-adhering underlayment or membrane over the entire roof deck, these good
practices will help reduce condensation and the subsequent problems that can occur.

Sampling is the process of selecting material to be tested. The process used for collecting test
samples directly affects the conclusions that can be supported by the test results. Statisticians
use the term “inference” to describe the extension of test results from a sample to a broader
group, or population, of product. An appropriate sampling process allows the ensuing test
results to be inferred to the desired group. Conversely, inference of the results beyond the
group that can be justified by the sampling process will lead to inappropriate conclusions.
From time to time, roofing industry members collect shingle, roll goods, or other product
samples to have their properties tested and publish the results. This may be for a magazine
article, a product rating on a website, or a blog post, among other uses. The conclusions that
may be reached from those results are dependent upon the process used to collect the product
samples.
Before starting a product test program, consider the intended use of the results. This first step
is essential to creating an appropriate sampling program. If the desire is to make broad
statements about a product, the number of samples to be collected will be much larger than if
a specific statement is to be made about a defined collection of product. Figuring out the
question to be answered is critically important.
A key aspect of any sampling program is the statistical concept of a “lot.” One definition of a lot
is found in ASTM E456 – Standard Terminology Relating to Quality and Statistics which states,
“a definite quantity of a product or material accumulated under conditions that are considered
uniform for sampling purposes.” Examples of a lot might include:
• All the shingles of the same brand and style in a distributor’s warehouse
• All the modified bitumen cap sheet rolls delivered to a job site for application on a roof
• All the packages of a specific ventilation product on a single truckload shipping from a
roofing manufacturer
“Random” is another key concept in sampling. Grabbing the first five bundles or rolls available
is not random sampling. Random selection requires that each unit (e.g., bundle, roll, package) in
the lot has the same chance (i.e., statistical probability) of being selected. This includes the
bundle on the bottom row of the least accessible pallet and the roll in the middle of the pallet.
Proper sampling is essential. If a carefully designed sampling plan is followed, the tester can have reasonable confidence that similar results would be obtained if different bundles or rolls
were selected and tested from the same “lot” of material. Results from testing properly
selected samples can be inferred over the entire lot of material.
Suppose five asphalt ply sheet rolls are purchased at a retail outlet, without being randomly
selected, and are subjected to testing. Results from testing the rolls are applicable only to those
five rolls. The tester cannot properly infer those results to the pallet or pallets from which the
rolls were taken, to the stock of those rolls in the retail outlet’s warehouse, or to the specific
brand and style of roll good, because the randomness requirement of the sampling
methodology was not satisfied. All that can be concluded is that the five-roll sample met or
failed to meet the criteria being evaluated.
As another example, consider a situation in which 10 bundles of shingles are purchased from a
roofing distribution outlet and evaluated for one or more properties. What can be concluded
from the results? As in the previous example, the sampling process determines the limitations.
In this case, the sampling process permits the distributor to select the shingle bundles. If the
distributor selects and ships the most easily accessible 10 bundles, the conclusions of the
testing are constrained to the 10 bundles and should not be inferred to apply to any larger
group or population of shingles. If the distributor selects the shingle bundles randomly from
stock of that product in its warehouse, the associated test results may be inferred to apply to
the stock in the warehouse, but not to a larger group.
Conclusion
When considering test results for shingles, roll goods, or any roofing product, remember to
consider the sampling process. Use of proper sampling techniques ensures confidence in
conclusions drawn from testing of product samples.

Self-adhering underlayment is generally applied to the roof deck on the eaves, rakes, and valley
areas of steep slope roofs and as flashing around roof penetrations. Self-adhering
underlayments are installed on critical areas of the roof to minimize the likelihood of water
penetrating the roofing system. In order for self-adhering underlayment to perform well, it
must adhere firmly to the roof deck. As a result, it can be difficult to remove without damaging
the deck material.
Removing self-adhering underlayments is always recommended in situations where it can be
removed without damaging the deck. Removal will facilitate examination of the deck for
deterioration and damage, reduce buildup of material that could interfere with proper
drainage, and eliminate unevenness that may create an aesthetic issue with the newly installed
roof covering. Removal of self-adhering underlayment becomes more important when more
than one layer of self-adhering underlayment is present.
If only one layer of self-adhering underlayment is in place, and it is not possible to remove it
without damaging the deck, check with the underlayment manufacturer’s installation
instructions and local building codes to determine if installation of a second layer of
underlayment is permissible. If a second layer is permitted, offset end and side laps in the new
and existing underlayment to minimize thickness buildup and “feather in” the new
underlayment by extending the new material a minimum of 8” up the slope onto the bare deck.
This will reduce the likelihood of problems with drainage and aesthetics.
If two or more layers of self-adhering underlayment are in place, all layers should be removed.
If removal of the existing material cannot be accomplished without damaging the deck, then
the roofing contractor may have to remove and replace the decking in the areas covered with
self-adhering underlayment.

Introduction
Moisture content within a roofing assembly may fluctuate significantly over the life of the roof
depending on a variety of factors including, but not limited to moisture in the existing roof
assembly at time of installation; interior and exterior temperatures; interior and exterior
humidity conditions; deck type; under-deck ventilation; amount and location of insulation; and
presence of vapor retarders/air barriers in the roof assembly.
The potential for condensation and moisture buildup in a membrane roof system from interior
moisture sources has always been and should continue to be an issue that must be accounted
for in the roof system design. Furthermore, the color, solar reflectance, and thermal emittance
of the roof surface can affect a roof system’s drying potential and, therefore, the buildup of
moisture in a roof system.
Moisture buildup in the roof assembly can result in deck deterioration, including rotting wood
decks and corrosion of metal decks, growth of mold and other organisms, deterioration and
reduction of the effectiveness of thermal insulation, premature failure and deterioration of the
roof system, and re-emulsification of certain water-based adhesives.
Effects of Roof Color and Reflectance
The use of light color/reflective roofing is increasing, driven in part by requirements such as the
California Building Standards Commission’s Title 24, LEED, and local code requirements across
the U.S.
Changing the color of a roof membrane from a dark or non-reflective surface to a light color or
highly reflective surface both reduces the amount of time the roof spends in a “drying” mode
and the roof temperature when the roof is in a “drying” mode. When there is a source of
interior humidity, a light colored or highly reflective roof surface can allow moisture and liquid
water to build up in the roof assembly with less opportunity to evaporate or dry. Accumulation
of moisture within roof systems can be exacerbated in buildings with elevated humidity or
periods of excessive moisture generation and if often not addressed in the design of the
building envelope. Some examples of moisture generators include:
• Apartment/condo buildings (showers, cooking, air humidifiers, etc., produce high levels
of interior moisture)
• Swimming pools, food processing, paper mills, and foundries • New construction with high interior construction moisture (i.e., from freshly poured
concrete, space heaters, wet insulation installation, drywall installation, etc.)
• A compact ceiling assembly where there is typically drywall, batt insulation, roof deck
and membrane with little or no insulation above the deck, no vapor retarder or air
barrier in the system, and little or no ventilation below the deck
• Reroof conditions where moisture may be present in the existing system
Things to Consider
In new construction projects, the design professional must evaluate the anticipated interior and
exterior conditions and design the proper water vapor control (including considerations for
transfer of water vapor via diffusion and air flow). This evaluation should include the necessary
calculations to ensure there will not be a condensation problem and a determination regarding
whether a vapor retarder, air barrier, or underside roof deck ventilation is necessary. If
adequate water vapor control measures cannot be integrated in the design, use of light colored
or highly reflective roofing may create condensation issues.
Regarding tear-off, recover, and coating applications, a roofing professional should evaluate the
existing roof assembly for signs of water infiltration and/or condensation issues (water stains,
wet or deteriorated insulation, deck deterioration, organic growth). The professional should
also determine whether there are interior vents (such as bathroom exhaust fans) and, if
present, confirm that they are all properly ducted to the outside and in good condition so they
do not allow moisture to enter the roof system. A roof design professional or climate control
specialist should be consulted to evaluate the existing conditions and to develop a plan to
address moisture issues within the existing roof assembly.
Some things that can be done to help control moisture accumulation in the roofing assembly
include:
• Remove wet areas within the existing roof system prior to recovering the system with a
new assembly
• Provide insulation above the deck to shift the location of the dew point
• Use at least two layers of insulation with staggered joints to prevent moisture migration
through the joints between the insulation boards
• Use an adhered membrane system to minimize moisture migration within the roofing
system
• Provide a vapor retarder and/or air barrier to the system at the proper location within
the roof assembly and seal roof deck penetrations, terminations, and transitions
• Provide adequate ventilation below the deck to remove moisture before it enters the
roofing system (always check with local codes to confirm below-deck venting
requirements are met)

Always refer to roofing manufacturer published requirements and consider local building and
energy code requirements. Consult a roofing professional when questions and decisions are to
be made on condensation and refer to ASHRAE for design guides and standards.