Skip to main content Skip to footer

California Cool Roofing Code Requirements

May 15, 2007

In 2000 and 2001, California’s energy
crisis came to a head when the
state suffered from rolling blackouts.
In response, Title 24, Part VI of the
California Code of Regulations
(which provides energy efficiency
standards for buildings) included a cool roof
prescriptive requirement in October 2005.
The purpose of this revision was to reduce
building energy consumption and mitigate
the rolling blackouts. These changes have
minimally affected some roof systems and
resulted in modifications to other systems.
Definitions of Terms
• California Energy Commission
(CEC): Primary state agency responsible
for energy policy and planning.
• Cool Roof: A roof with high reflectivity
and emissivity that improves
the energy efficiency of a building.
Title 24 defines a cool roof as having
a minimum reflectance of 0.70 and a
minimum emittance of 0.75.
• Cool Roof Ratings Council
(CRRC): The only organization recognized
for testing and certification
of roof surfacing products for Title
24 compliance.
• Emissivity (E): A measure of the
amount of heat that a roof material
can emit back into the atmosphere.
It is the ratio of radiant heat flux
emitted by a black body at the same
temperature (expressed in decimal
form with 1.0 being the highest).
• Energy Star: A voluntary labeling
program developed by the U.S. Environmental
Protection Agency that
identifies energy-efficient products.
• Reflectance (R): The amount of
sunlight that is reflected off the roof
surface. It is the ratio
of reflected light to
incident light (expressed
in decimal
form, with 1.0 being
the highest).
• Title 24: Part VI of
the California Code
of Regulations that
sets energy design
and construction
standards for residential
and non-residential
buildings.
This is part of the
state building code.
How a Cool Roof Works
Sunlight striking a roof
is either reflected or absorbed
into the roof membrane.
The absorbed sunlight
will heat the roof
assembly. This heat will
either be transferred back to
the atmosphere by convection
or radiation (i.e., emittance)
or flow downward
through the roof assembly
and into the building interior.
A cool roof reflects more light and emits
more heat back to the atmosphere than a
conventional roof (Figures 1 and 2). This
results in less heat transferred into the
building interior and reduced cooling needs.
Figures 1 and 2 – Conventional and cool roof heat absorption.
F E B R U A RY 2007 I N T E R FA C E • 3 3
Figure 1
Figure 2
Title 24 Cool Roof Provisions
Title 24, which is updated every three
years, now has a prescriptive cool roof
requirement for non-residential roofs with
slopes of 2 inches per foot or less and with
underlying conditioned interior spaces. Title
24 defines a cool roof as having a
reflectance of 0.70 and an emittance of
0.75. Table 1 compares the Title 24 requirements
with other cool roof standards. An
ENERGYSTAR® product may not comply with
Title 24, since it has a lower minimum
reflectance requirement.
Since reflectance deteriorates over time
without maintenance or repair, some standards
have aged (3-year) values. Title 24
does not have requirements for aged
reflectance or maintenance of the roof surface.
Future editions may include an aged
reflectance requirement. The California
Energy Commission (CEC) assumed an
aged reflectance of 0.55 when evaluating
cool roof performance.1
How to Comply with Title 24
The Cool Roof prescriptive requirement
is not mandatory. The three approaches to
comply with the Title 24 Cool Roof requirement
are: (1) Standard Prescriptive Approach,
(2) Building Envelope Trade-off,
and (3) Entire Building Performance. A cool
roof is required if the Standard Prescriptive
Approach is used, whereas a cool roof may
not be required if approaches 2 or 3 are
used. Approaches 2 and 3 allow the designer
to vary the energy features of the building,
provided the code-defined energy budget
is satisfied.
1. Standard Prescriptive Approach:
This is the simplest yet least flexible
approach. Each building component
must satisfy Title 24 requirements.
A cool roof is required using this
approach.
2. Building Envelope Trade-off: This
approach is more flexible. Energy
losses from one building envelope
component may be offset by increased
performance by another envelope
component. If calculations
show that the overall building envelope
energy budget is already in
compliance with Title 24, a cool roof
is not required.
3. Entire Building Performance: This
approach provides the most flexibility
but is the most complex and expensive.
Calculations are performed
using a CEC-approved, proprietary
computer software. Presently, there
are two approved programs: EnergyPro
Versions 4.1 to 4.3 and Perform
2005.2 If the computer simulation
shows the building energy consumption
budget is satisfied, the
building is considered to be in compliance,
and a cool roof is not required.
This approach also allows
for partial credit if the roof does not
fully meet the cool roof requirement.
The CEC calculates the energy budget
used in Approaches 2 and 3 based on a
building energy consumption simulation.
This simulation assumes the standard prescriptive
energy features (e.g., a cool roof)
and calculates the energy consumption of
the building.
All three approaches apply to new construction.
Since a roof replacement project
is typically a stand-alone project, the standard
prescriptive approach is most commonly
used. Title 24 requirements are triggered
for roof replacement projects if the
roof area exceeds 2,000 square feet or 50%
of the roof area (whichever is less). An
exception is taken if only the aggregate of an
existing roof is being replaced, provided
special conditions are satisfied.
Table 2 summarizes the building types
that need to comply with Title 243.
Title 24 and Roof Top Features
Some roofs have features such as
pavers, green roofs, and photovoltaics that
do not meet cool roof reflectance, emissivity,
or both reflectance and emissivity
requirements. The performance approach is
used to show that the new building with a
green roof or pavers satisfies the allowed
energy budget. If the installation of a new
green roof or pavers is part of a roof replacement
(i.e., an existing building), heat gain
calculations are needed to show that the
new green roof or pavers will not allow more
heat gain into the building than the prescribed
cool roof. Additional roof insulation
may be required for compliance.
The cool roof regulations apply for photovoltaics
set in frames that are mounted to
CODE/STANDARD SOLAR REFLECTANCE (R) EMITTANCE (E)
INITIAL 3 YEAR AGED
Title 24 0.70 None 0.75
ENERGY STAR(1) 0.65 0.50 None
ASHRAE 90.1 0.70 None 0.75
LEED 0.65 0.50 0.90
(1) For steep slopes, ENERGYSTAR® requires an initial R of 0.25 and 3-year R of 0.15.
Table 1 – Cool Roof Definition Comparison
Table 2
34 • I N T E R FA C E F E B R U A RY 2007
TITLE 24 COMPLIANCE BUILDING TYPE
REQUIRED A (Assembly) H (Hazardous)
B (Business) M (Mercantile)
E (Education) S (Storage)
U (Utility)
OPTIONAL • Roofs with slopes over 2 inches per foot.
• Unconditioned warehouses.
• High-rise residential (four or more stories).
• Hotels and motels.
• Buildings cooled with swamp coolers.
• Process spaces not meant for human occupancy, held
at temperatures less than 55˚F or greater than 90˚F.
NOT REQUIRED I (Institutions – e.g., hospitals, prisons)
the roof, since this
equipment can be removed
in the future,
leaving it exposed to
the sun. Photovoltaics
integrated into the roof
material are typically a
dark color and do not
satisfy the reflectance
requirement. For these
roofs, the same procedures
as for green roofs
are followed.3
Roof Coatings
Some systems (e.g.,
built-up roofs) need
coatings to enhance
the reflectance and/or
emittance to qualify as
a cool roof. Title 24
requires that the coating
have a minimum
dry thickness of 20
mils. In addition to the
reflectance and emittance
testing, coatings
must satisfy ASTM
weathering, elongation,
and flexibility requirements.
Quality Assurance
Title 24 has a quality assurance
requirement that all roof surfacing products
be tested, rated, and certified by the Cool
Roof Rating Council (CRRC). The initial
reflectance and emittance test data must be
printed on the label of the product. If a
product not tested by CRRC is specified, a
default reflectance value of 0.10 must be
used.
Cool Roof Rating Council (CRRC)
The CRRC, a non-profit organization
founded in 1998, develops methods to evaluate
and label solar reflectance and emittance
of roofing materials in an accurate
manner. One of the CRRC’s main functions
is to administer the product-rating program
required by Title 24. This program tests the
reflectance and emissivity of roof surfacing
products such as coatings, mineral-surfaced
cap sheets, single-ply membranes,
metal panels, shingles, and tiles. Each
product tested is given a unique CRRC
Identification Number. The CRRC tests the
initial and 3-year aged reflectance and the
emittance. The aged reflectance testing is
currently in progress and no results are
available. CRRC-certified laboratories perform
the testing.
Test results are listed in the product
rating directory on the CRRC Web page.
This directory, a database presently containing
over 700 products, lists the CRRC
Identification Number, manufacturer information,
product name and type, steep- or
low-slope application, initial reflectance,
and emissivity. Aged reflectance is stated as
pending. The directory can be sorted by one
or more variables, such as roof type, manufacturer,
and steep- or low-slope applications.
This database provides product test
results and does not state if a product complies
with Title 24. It is the designer’s choice
to make that determination. It is similar to
the ENERGYSTAR® product summary and is a
good information source.
[EDITOR’S NOTE: For more information
on the CRRC, see “Cool Roofing and the
Cool Roof Rating Council: The Evolution of
a Rating System,” on page 5 of this issue.] Photo 1 – Typical Title 24-compliant single-ply roof.
www.rci-mercury.com
F E B R U A RY 2007 I N T E R FA C E • 3 5
Title 24 and Roof Systems
The new Title 24 requirement has minimal
impact on some roof systems and
requires modifications for other systems.
Three roof systems most commonly used in
California are discussed below.
Metal Roofs
Metal has been minimally affected by
the change, since most applications are for
steep slopes. If installed on low-slope, the
color pallet is limited. Advances in cool pigment
paint technology have provided a
wider color pallet than single-ply or built-up
systems.
Single-ply Roofs
There has been minimal impact on
design and installation of single-ply systems,
except for
the color limitation.
Presently,
white-colored
membranes satisfy
cool roof
r equirements
(Photo 1).
Built-up Roofs
B u i l t – u p
roofing has been most affected by the Title
24 change. The commonly-used, conventional,
gray-colored, mineral-surfaced cap
sheet or aggregate does not satisfy the Title
24 reflectance requirement of 0.70. Noncompliance
results in changing to a coated
cap sheet or changing the type of aggregate
(Photos 2 and 3).
A white-colored surface is required to
obtain a 0.70 reflectance. This is achieved
by applying a white, elastomeric, acrylic
coating on the top of the cap sheet. This
coating can be either factory-applied or
applied in the field by the roofing contractor
and must satisfy the Title 24 20-mil thickness
requirement. Both options result in
increased installation
costs and additional
maintenance.
A factory-applied,
coated cap sheet typically
requires less
installation time since
the coating is preapplied.
Touch-ups
are needed at asphalt
bleed-out on cap
sheet laps and on
damaged or marked
areas of the coating.
The amount of touchup
is dependent upon
the quality of the roof
installation crew and
the amount of roofrelated
construction
activity on the completed
roof.
Careless installation
can result in
Photo 2 – Title 24-compliant coated (left) and conventional,
mineral-surfaced cap sheet (right).
Photo 3 – Conventional (left) and
Title 24-compliant aggregate (right).
Photo 4 – Factory-coated cap sheet with field-applied touch-ups in progress. Note asphalt bleed-out at laps in left
side of photo.
36 • I N T E R FA C E F E B R U A RY 2007
extensive asphalt
marking. Damaged
coating results in
reduced reflectance.
Touch-up
repairs will be visible
(Photo 4) and
can affect aesthetics.
Factory-coated
cap sheets are approximately
$0.50
per square foot
more expensive
than conventional
cap sheets. The
cost of touch-ups is
dependent upon labor
and materials
to repair the damaged
area. Designers
should include
an allowance for
touch-ups in the
bid documents to
mitigate change orders,
particularly if other trades damage the
coating after the roofing contractor has
completed its work.
Field-applied coatings are applied after
all roof-related construction (e.g., HVAC) is
completed and are less susceptible to damage
by other trades. The conventional mineral-
surfaced cap sheet is cleaned and
primed, and two coats of the coating are
applied (Photo 5). This option is more costly
than factory-applied ($1.00 to $1.50 per
square foot), but provides a more uniform
appearance.
Both cap sheet options will result in
additional maintenance to ensure long-term
reflectance. The roof will typically need to be
recoated every five to seven years, resulting
in two coatings over a 20-year lifespan.
Currently, a crushed white marble
aggregate set in white adhesive is the only
product that has been tested to comply with
the Title 24 reflectance requirement. The
white adhesive will not darken the aggregate
with a coating of asphalt from the flood
coat and will provide a uniform white color
(i.e., no reduced reflectance). It is more
costly than the conventional aggregate.
Title 24 and the Owner
Owners should be informed of the following
items during the design phase:
• The Title 24 Cool Roof requirements
and compliance options should be
explained.
• The new roof will need maintenance
to maintain its reflectance.
• A coated or built-up roof will cost
more to install and maintain.
• The new roof will be noticeably
brighter than the previous one,
resulting in potential aesthetic complaints
if the roof is visible from
ground level or from above.
Summary
• Title 24, part of the California State
Building Code, now has a cool roof
prescription requirement for nonresidential,
low-slope roofs. The intent
is to reduce building energy
consumption.
• A cool roof is required unless the
designer performs calculations
showing that the building envelope
or building satisfies the building
energy budget.
• The new requirement has resulted
in increased installation and maintenance
costs for built-up and coated
roof systems.
FOOTNOTES
1 Blueprint No. 83, California Energy
Commission, December 2005.
2 www.energy.ca.gov/title24/
2005standards/2005_computer_
prog_list.html.
3 Blueprint No. 83, California Energy
Commission, page 6, December
2005.
INFORMATION SOURCES
• 2005 Building Energy Efficiency
Standards.
• 2005 Non-residential Compliance
Manual.
• California Energy Commission,
www.energy.ca.gov/title24/index.
html.
• Cool Roof Rating Council,
www.coolroofs.org.
Photo 5 – Field-applied coating on a mineral-surfaced cap sheet.
Alan Burnett, PE, is West Coast regional manager for Gale
Associates, Inc. Gale is a 110-person consulting engineering
firm specializing in building envelope technology (investigation,
evaluation, and design of repairs to all building envelope
components, including roofs, walls, windows, waterproofing,
and the structure). Mr. Burnett my be reached at
aeb@gainc.com or 800-704-0325.
Alan Burnett, PE
F E B R U A RY 2007 I N T E R FA C E • 3 7