Fire and Wind Resistance Standards for Vegetative Roofs

MIKE ENNIS, RRC
Single-Ply Roofing Industry (SPRI)
1100 Rosehill Road, Reynoldsburg, OH 43068
Phone: 614-578-7875 • E-mail: m.ennis@mac.com
Fire And Wind Resistance Standards
For Vegetative Roofs
Proceedings of the RCI 25th International Convention Ennis – 59
ABSTRACT
During the 2006/2007 International Building Code (IBC) code change cycle, a proposal
was presented and adopted to require vegetative roof systems to be evaluated
for their wind and fire resistance. Currently available procedures could not be used
to evaluate these types of systems due to the vast array of variables that could be present,
such as plant material present, water content of the soil, spacing of the plant
material, and many others.
Recognizing this disconnect, SPRI, Inc., the trade association representing the singleply
roofing industry, along with Green Roofs for Healthy Cities and numerous manufacturers
and consultants involved in the vegetative roof industry, undertook a project
to develop standard design guides for vegetative roof systems for wind uplift and
fire-spread resistance. This presentation will summarize the requirements contained
in these standards and the data used to support the development of these standards.
SPEAKER
Mike Ennis has been technical director for SPRI, the association representing the single-ply
roofing manufacturers and component suppliers, for three years. Prior to this, he worked for
the Dow Chemical Company and was the North American application technology leader for
commercial products in Dow’s Building Solutions business, where he led the development of
new products and applications. Mike has 32 years of building and construction experience to
his credit.
Ennis is a Registered Roof Consultant (RRC) and is a member of the board of directors of the
Roofing Industry Committee on Weather Issues (RICOWI) and the Cool Roof Rating Council
(CRRC). He is a member of ASHRAE and ASTM Committees D08, Roofing and Waterproofing;
E5, Fire Standards; and E60, Sustainability.
Ennis – 60 Proceedings of the RCI 25th International Convention
ABSTRACT
Vegetative roof systems have
become a popular alternative to conventional
systems. They have demonstrated
their ability to be sustainable,
providing the following positive benefits,
to name a few:
• Initial retention and slow
release of stormwater
• Reduction of urban heatisland
effects
• Improved energy performance
• Improved aesthetics and
workplace environment
During the 2006/2007 Inter –
national Building Code (IBC) change
cycle, a proposal was presented and
adopted to require vegetative roof systems
to be evaluated for their wind
and fire resistance. Currently available
procedures could not be used to
evaluate these types of systems due to
the vast array of variables that could
be present, including plant material,
water content of the soil, spacing of
the plant material, and many others.
Recognizing this disconnect, SPRI,
Inc. (the trade association representing
the single-ply roofing industry),
along with Green Roofs for Healthy
Cities GRFHC) and numerous manufacturers,
consultants, and contractors
involved in the vegetative roof
industry, undertook a project to
develop standard design guides for
vegetative roof systems for wind uplift
and fire-spread resistance.
The wind uplift design guide uses
data developed in wind tunnel testing,
initially used for ballasted single-ply
roof systems, and historical industry
Proceedings of the RCI 25th International Convention Ennis – 61
Fire And Wind Resistance Standards For
Vegetative Roofs
Figure 1 – Chrysler-Daimler Headquarters, Stuttgart, Germany.
practices that have demonstrated
acceptable levels of wind-load resistance
for over 40 years.
The fire design standard uses the
concept of setbacks, firebreaks, roof
maintenance, and in some instances,
sprinklers to control the fire-spread
potential of vegetative roof systems.
This paper details the requirements
of the IBC, along with these
consensus standard design guides.
INTRODUCTION
Vegetative roofs became popular in
Europe about 50 years ago, and while
they are not new to the United States
(see Figures 1 and 2), they have not
gained the popularity that they
achieved in Europe. This all began to
change about five years ago with the
increased emphasis on utilizing sustainable
building techniques.
The use of vegetative roofs as part
of a sustainable building design is
being driven by local codes, energy
codes, and green building design
guides such as LEED®. Examples
include the following.
LEED®
LEED® is a third-party certification
program developed by the U.S. Green
Building Council (USGBC). This certification
program recognizes performance
in five areas as follows: site
development, water savings, energy
efficiency, materials selection, and
indoor environmental quality. The use
of vegetative roofs can contribute to
points in the following categories:
• Site development—protect or
restore habitat category
• Site development—maximize
open space
• Stormwater design—quantity
control
• Heat island mitigation
Green Globes
The Green Globes system is a
building environmental design and
management tool that provides thirdparty
recognition of buildings’ environmental
attributes. The use of vegetative
roofs can contribute to points
in the following categories:
• Heat island mitigation
• Building energy performance
ASHRAE
The American Society of Heating,
Refrigeration, and Air Conditioning
Engineers (ASHRAE) is working on an
addendum to Standard 90.1, Energy
Standard for Buildings Except Low-
Rise Residential Build ings; and
Standard 189.1, Proposed Standard
for the Design of High-Performance
Ennis – 62 Proceedings of the RCI 25th International Convention
Figure 2 – Rockefeller Center, constructed 1933.
Green Buildings Except Low-Rise
Residential Buildings. Add en dum F to
Standard 90.1 provides prescriptive
requirements for the use of highly
reflective roofs in Climate Zones 1, 2,
and 3. The use of a vegetative roof is
recognized as an exception to this
requirement.
City of Toronto
In May 2009, the city of Toronto,
Canada, passed a Green Roof Bylaw.
This by-law requires the use of green
roofs for all new development above
2,000m2 (21,528 sq ft) gross floor
area. The requirement became effective
on January 31, 2010. The green
roof coverage requirement is graduated
based on the gross floor area of the
building as shown in Table 1.
Currently, the bylaw does not
cover industrial buildings. Coverage
requirement for industrial buildings,
which starts in 2011, equals 10% of
the available roof space up to a maximum
of 2,000 m2 (21, 528 sq ft).
These are just a few examples of
regulations that are driving the
growth of the vegetative roofing market.
WHAT IS A VEGETATIVE
ROOF?
A vegetative roof typically consists
of the following components from the
top down (see Figure 3):
1. Vegetation
2. Growing medium
3. Filter fabric
4. Optional reservoir layer
Proceedings of the RCI 25th International Convention Ennis – 63
Figure 3 – Typical vegetative roofing system (NRCA, 2008).
Table 1
Gross Floor Area Coverage of Available Roof Space
(Size of Building) (Size of Green Roof)
2,000 – 4,999 m2 20%
(21,528 – 53,809 sq ft)
5,000-9,999 m2 30%
(53,820 – 107,628 sq ft)
10,000-14,999 m2 40%
(107,639 – 161,448 sq ft)
15,000-19,999 m2 50%
(161,459 – 215,267 sq ft)
20,000 m2 or greater 60%
(215,278 sq ft or greater)
5. Moisture-retention layer
6. Aeration layer
7. Thermal insulation
8. Drainage layer
9. Root barrier
10. Protection course
11. Waterproofing membrane
12. Structural deck
In some instances, the insulation
can be installed below the waterproofing
layer. Whichever design is used, it
is most desirable to adhere the waterproofing
layer to a very stable substrate,
as this helps minimize potential
problems with this layer. As one
would expect, damage in the waterproofing
layer can be difficult to find
and repair.
There are many options for the
vegetative covering. The vegetative
covering can be low-lying plants
installed as plugs (see Figure 4), or a
vegetative mat (see Figure 5) to provide
ground cover, all the way to
plants typically used in natural landscapes,
ranging from 1 to 15 ft high.
There are also tray systems that are
typically interlocking to provide the
vegetative covering
(see Figure 6). The
type of vegetative
covering used will
dictate the depth of
growth media
required for the vegetative
roofing system.
While there are
no consensus definitions
for types of
vegetative roofing
systems, there are
generally three types
of vegetative roofing
systems referred to
(NRCA 2008):
• Extensive vegetative
roofs –
These systems
are designed to
be lightweight,
with a growing
medium of 2 to
6 in. These systems
are typically
covered with
sedums or native ground covers.
These types of roofs are
not generally designed to be
walked on;
Ennis – 64 Proceedings of the RCI 25th International Convention
Figure 4 – Vegetation being planted as plugs.
Figure 5 – Example of vegetative mat (Xero Flor, 2007).
• Semi-intensive
vegetative roofs
– These systems
are heavier in
weight, having 6
to 10 in of growing
media. Be –
cause of the
greater depth of
the growing me –
dia, a wider variety
of plants can
be used and the
rooftop can be
designed to provide
walking surfaces;
• Intensive vegetative
roofs –
These systems
have more than
10 in of growing
medium and can
contain the wid –
est variety of vegetation.
This type
of system is used
when the building
owner wishes to have a vegetative
space that can be used
by building occupants or the
general public.
BENEFITS OF A VEGETATIVE
ROOF
There are many benefits associated
with the use of vegetative roofing
systems. According to GRFHC, these
benefits include:
Stormwater retention
Vegetative roofs have demonstrated
the ability to store stormwater in
the substrate and return it to the
atmosphere through transpiration
and evaporation. This reduces the
runoff and delays the time that runoff
occurs, resulting in decreased peak
loads on the sewer systems. The ability
of the vegetative roof system to
reduce stormwater runoff is dependent
upon the depth of growing medium
and type of plants, but in general,
they retain 70% to 90% of the precipitation
that falls on them in the summer
months and 25% to 40% in the
winter months. However, the ability of
the vegetated roof to absorb moisture
and reduce stormwater runoff is
dependent upon the level of saturation
of the growth media prior to rainfall.
If the growth media is already
highly saturated, little stormwater
retention benefit is observed (K.Y. Liu
et al., 2005).
In addition to retaining stormwater,
a vegetative roof moderates the
temperature of the water and acts as
a filter for any of the water that does
run off.
Moderation of the Urban Heat-
Island Effect
The urban heat-island effect is primarily
due to dark-colored surfaces in
cities absorbing and reradiating solar
energy, resulting in higher temperatures
in the city as compared to the
surrounding countryside. Vegetative
roofs can moderate this effect through
a process known as evapo-transpiration.
In this process, plants are able
to cool cities in hot summer months
by using heat energy from their surroundings
to evaporate water. In
recognition of this benefit, the
USGBC’s LEED® program provides
one credit for the use of vegetative
roofs as a method to mitigate the
urban heat-island effect. In order to
obtain this credit, at least 75% of the
roof surface must be covered by the
vegetative roofing system.
The impact of a vegetated roof on
the roof membrane surface temperature
was documented in research
conducted at the National Research
Council of Canada. In this work, the
surface temperature of a black roof
membrane surface was 158ºF, and
the membrane surface temperature of
the vegetated roof was 77ºF. This
reduced temperature also lowers the
temperature of surfaces and air
around the roof surface (Liu K.Y. et
al., 2005).
Insulating buildings
Vegetative roofs insulate buildings
due to the mass of the growing medium
and the vegetation on top of the
roof system. As noted under the
urban heat-island effect, the vegetation
absorbs heat energy and shades
Proceedings of the RCI 25th International Convention Ennis – 65
Figure 6 – Example of tray system being installed.
the roof surface. To maximize the
shading effect, broadleaf plants are
most beneficial. SPRI initiated a study
in June 2008 to document the potential
energy savings of vegetative roofing
systems. One of the objectives of
this study was to provide data that
can be used to develop a method of
modeling the thermal performance of
vegetative roofing systems, including
the impact of plants and moisture in
the soil.
Other Benefits
In addition, vegetative roofs can
provide the following additional benefits:
• Sound insulation
• Improved aesthetics
• Food production
• Garden spaces
• Local credits for building
owners to help offset the cost
of the vegetative roof
These are just a few of the benefits
associated with vegetative roofing systems.
For more detailed information
on vegetative roofing systems, refer to
the GRFHC Web site, www.greenroofs.org
/index.php/about-green-roofs/greenroof-
benefits.
BUILDING CODE
REQUIREMENTS
Due to these benefits and the
increased emphasis on utilizing sustainable
building practices, vegetative
roofing systems have gained popularity
in the United States. With this
increased popularity, a need was perceived
to establish building code
requirements for these systems.
During the 2006/2007 code change
cycle for the IBC, the following section
was added:
Section 1507.16, Roof gardens
and landscaped roofs.
Roof gardens and landscaped
roofs shall comply
with the requirements of this
Chapter, Section 1607.11.2.2
and Section 1607.11.2.3.
DISCUSSION
Due to the addition of Section
1507.16 to the IBC, vegetative roofing
systems now must be evaluated for
wind and fire resistance, but how?
There is a 50-year history of
proven performance in Europe and a
more limited history in the United
States. This history has demonstrated
an excellent track record of performance
for vegetative roof systems
with respect to fire and wind resistance.
However, more work needs to
be completed to understand the wind
performance of these systems when
exposed to design wind speeds.
In 1988, a series of fire tests were
conducted on vegetative roofing systems
in Stuttgart, Germany. In these
tests, fires were set on vegetative roofs
using dry wood as the fuel source.
The result of all of these
experiments and research
was a short answer: it is
nearly impossible to set an
extensive vegetative roof on
fire which [sic] spreads over
the roof or starts a glowing/
burning of the growing
media. The risk of fueling
fires is 15-20 times higher
on bare roofs with fully
adhered bituminous waterproofing
membranes than
on extensive vegetative roofs
with grasses, perennials,
and sedums. Today in
Germany, there are at least
2 billion square feet of
extensive vegetative roofs
built, and there is no fire
recorded. (Breuning 2007)
There has been a concern ex –
pressed over the years with the potential
fire performance of vegetated roof
systems using tall grasses and trees.
A wide variety of possible scenarios
exists when considering this type of
system. More work is necessary to
quantify their potential hazards.
With respect to wind performance,
we can also learn from experience
how vegetative systems perform
under wind loads.
Through 15 years of experience
and 300 million sq ft of vegetative roof
installations, the following has been
learned:
1. Wind erosion can happen on
a building, regardless of the
height of the roof or the
height of the parapet.
2. Most erosion on roofs below
60 ft is hardly recognized
since it typically starts during
the establishment phase of
the plants, and the plants
usually cover these areas
soon.
3. Large organic particles (wood
chips, etc.) and very lightweight
aggregates are blown
away fairly easily and are
often found everywhere on
the roof where they shouldn’t
be.
4. Most of the (hard-to-see) wind
damage on buildings below
60 ft is also caused by unique
aerodynamics of the buildings
themselves.
5. All installers agreed that even
the smallest wind damage
has to be fixed immediately
with appropriate solutions to
prevent further damage
(Breun ing 2007).
In 1997, a 560,000-sq-ft extensive
vegetative roof was installed on a
building over 60-ft tall. It was located
in an open field on top of a hill. The
roof was exposed to a storm with wind
speeds up to 90 mph and wind gusts
up to 115 mph. During this storm,
some large areas of the famous Black
Forest were gone, along with 0.8% of
the vegetative roof on this big box
(4,000 sq ft). This vegetative roof survived
and performed well because it
was designed according the existing
standard and the FLL Guideline for
the Planning, Execution, and Upkeep
of Vegetative-Roof Sites to withstand
very high wind loads (Breuning 2007).
As mentioned, more information is
needed on the performance of vegetated
roof systems at design wind
speeds. Of particular concern are veg-
Ennis – 66 Proceedings of the RCI 25th International Convention
etated roof systems
that in clude
large plants and
trees. An example
of this type of system
is shown in
Figure 7. This roof
was exposed to
Hurricane Ike.
Few, if any, tree
limbs were blown
away during this
wind event. Shel –
tering from nearby
buildings may
have prevented
limb damage. Al –
so, the low-level
wind speeds in the
downtown area
were not sufficiently
high to
cause substantial
loss of limbs. The
concern with
limbs is their po –
tential to damage
glazing, particularly
when trees
are placed many
floors above grade
(FEMA MAT P-757
2009).
While there have been no significant
issues with fire and wind resistance
of vegetative roofing systems,
there are also no consensus standards
to test their fire and wind resistance.
The standards currently referenced
in the code are not appropriate
for evaluating vegetative roofing systems.
For example, the code currently
references the use of FM4450,
FM4470, UL580, or UL1897 for evaluating
the wind uplift resistance of
roofing assemblies. All of these procedures
use pressure either above or
below the roof deck, or a combination
of both, to determine the load at
which the roofing assembly will fail.
This approach is not appropriate for
vegetative roofing assemblies, since
the top covering is loose-laid. These
systems perform like ballasted roofing
assemblies and require techniques
such as wind-tunnel testing to understand
the performance of these systems.
For evaluating the fire resistance
of the top surface of roofing assemblies,
the code states, “Roof assemblies
shall be divided into the classes
defined below. Class A, B and C roof
assemblies and roof coverings
required to be listed by this section
shall be tested in accordance with
ASTM E108 or UL790.”
While these test procedures could
be used to test a vegetative roof system,
the question is what system to
test. As noted earlier, there are many
variables in a vegetative roofing system:
plant types, plant spacing, trays
or landscape plantings, and growing
media conditions (wet or dry), to
name a few. Both UL and FM are evaluating
methods to fire-classify vegetative
roofing systems. One option being
considered is to classify only very specific
systems, such as sedum-based
or lawn-grass-based vegetative roof
systems.
TEST METHOD DEVELOPMENT
Due to a lack of consensus standards
and the need for these standards
to meet the requirements of the
International Building Code, SPRI,
and GRFHC teamed up to develop the
required standards. For the reasons
noted above, it was decided to take a
design approach vs. a test approach
in their development.
After completion of these consensus
standards, the intention is to propose
that they be included in the IBC
to address the requirements of
Section 1507.16.
The wind and fire performance of
vegetative roof systems is influenced
by the maintenance of these systems.
For example, the excellent wind performance
of these systems is due to
the tenacity of the root system holding
everything together. The moisture
content of the plants can influence
the fire performance of the system.
Since maintenance is an important
Proceedings of the RCI 25th International Convention Ennis – 67
Figure 7 – Example of vegetative roof with trees.
factor, it will also be necessary to submit
code change proposals to the
International Property Maintenance
Code to describe maintenance
requirements for vegetative roof systems.
WIND STANDARD
Since the top covering on the vegetative
roof assembly is loose-laid, it
behaves like a ballasted roofing
assembly. Extensive wind-tunnel
testing has been conducted over the
years to understand the performance
of ballasted roofing assemblies. These
test programs lead to understanding
the impact of such variables as wind
speed, ballast particle size, ballast
weight, building height, parapet
height, and the location at which the
wind impacts the building.
These data were used in the development
of ANSI/SPRI RP-4. This
standard provides ballast system recommendations
for various design
wind speeds, building heights, and
parapet heights. Since these data and
approach already existed, it was
viewed as an excellent starting point
for the development of a wind standard
for vegetative roof assemblies.
One of the differences between an
aggregate ballasted roof and a vegetative
roof is that the growth media
used in vegetative roofs contains
small particles. If left exposed, these
small particles can be displaced at
relatively low wind speeds. For this
reason, the NRCA sponsored windtunnel
testing. One of the objectives
of this testing was to determine the
maximum area that could be left
exposed without resulting in significant
amounts of growth media blowing
off and providing wind-borne
debris. This work determined that
additional measures must be taken to
prevent wind blow-off of growth media
in any exposed areas in excess of 5 sq
in.
BSR/SPRI RP-14 Wind Design
Standard for Vegetative Roof Systems,
is the designation for the wind design
standard. Fundamentally, this standard
takes the same approach as
ANSI/SPRI RP-4, providing design
recommendations based on the
design windspeed, exposure category,
building height, and parapet height.
This standard provides a method
of designing wind-uplift resistance of
vegetative roofing systems. It is
intended as a design and installation
reference and should be used in conjunction
with the installation specifications
and requirements of the manufacturer
of the specific products
used in the vegetative roofing system.
SYSTEM OPTIONS FOR
VEGETATIVE ROOFING
SYSTEMS
There are three basic design
options for vegetative roofing systems
in the RP-14 standard: Systems 1
through 3. As the number of the system
increases, its ability to resist
wind loads also increases. There are
two ballast options provided in the
standard.
Ballast Option #4
Growth media installed at a rate of
1,000 pounds per 100 sq ft plus or –
ganic material and protected by vegetation,
with maximum bare spots of 5
sq in, or provisions have been made to
prevent wind scour. In the NRCAsponsored
wind-tunnel tests, liquid
tackifiers were found to be particularly
successful in preventing blow-off of
growth media. Other allowable forms
of ballast:
• Nominal 1.5-in, smooth,
river-bottom stone ballast,
gradation size #4, (or alternatively,
#3, #24, #2, or #1) as
specified in ASTM D448,
Standard Sizes of Coarse
Aggregate, spread at a minimum
rate of 1,000 pounds
per 100 sq ft.
• Standard concrete pavers
(minimum 18 psf).
• Interlocking, beveled, doweled,
or contour-fit lightweight
concrete pavers (minimum
10 psf dry weight plus
organic material).
• Modular preplanted or pregrown
vegetative roof trays
that are independently set
(minimum size of 2.25 sq ft),
interlocking, contoured-fit, or
strapped together (minimum
10 psf dry weight plus organic
material).
Ballast Option #2
Growth media installed at a rate of
1,300 pounds per 100 sq ft plus
organic material and protected by
vegetation, with maximum bare spots
of 5 sq in, or provisions have been
made to prevent wind scour. Other
allowable forms of ballast:
• Nominal 2.5-in, smooth,
river-bottom stone of ballast
gradation size #2 (or alternatively,
#1), as specified in
ASTM D448, Standard Sizes
of Coarse Aggregate, spread
at a minimum rate of 1,300
pounds per 100 sq ft.
• Concrete pavers (minimum
22 psf) or approved interlocking,
beveled, doweled, or contoured-
fit, lightweight concrete
pavers (minimum 10
psf) when documented or
demonstrated as equivalent.
• Modular preplanted or pregrown
individually set vegetative
roof, minimum 22 psf dry
weight, plus organic material.
• Modular preplanted or pregrown
trays that are interlocking,
contoured-fit, or
strapped together, minimum
13 psf inorganic material dry
weight, plus organic material.
DESIGN OPTIONS
The design options are:
System #1
Install ballast #4 over the entire
membrane.
System #2
In the field of the roof, the
installed membrane shall be ballasted
with ballast #4. Number 2 ballast
Ennis – 68 Proceedings of the RCI 25th International Convention
shall be the minimum ballast used in
wind-borne debris areas. Corner and
perimeter areas shall be ballasted
with #2 ballast.
System #3
In the field of the roof, the
installed membrane shall be ballasted
with #2 ballast. In corner and perimeter
areas, install an adhered or
mechanically attached roof system
designed to withstand the uplift loads
in accordance with ANSI/ASCE 7 or
the local building code. No loose
stone, growth media, or modular vegetative
roof trays can be placed on the
membrane. When a protective covering
is required over the membrane, a
fully adhered system shall be used.
Over the fully adhered membrane,
install minimum 22 psf pavers.
Mechanically fastened membrane
systems shall not be used when a
protective covering is required.
DESIGN CONSIDERATIONS
1. Definition of Roof Corners
and Perimeter
Corner. The corner is defined as
the space between intersecting walls
forming an angle greater than 45º but
less than 135º, and the corner area is
defined as the roof section with sides
equal to 40% of the building height.
The minimum length of a side is 8.5 ft
(see Figure 8).
Perimeter. The perimeter area is
defined as the rectangular roof section
parallel to the roof edge and connecting
the corner areas with a width
measurement equal to 40% of the
building height, but not less than 8.5
ft (see Figure 8).
Note that 40% of the building
height is used to determine the corner
and perimeter areas, subject to a minimum
of 8.5 feet. As a result, the corners
and perimeter areas are subject
to more restrictive ballast requirements
and are greater in size than the
corner and perimeter areas in
mechanically attached or adhered
roof assemblies. This recognizes the
potential for displacement and possible
blow-off of vegetative roof materials
and requires special detailing of
these areas.
2. Parapet Height
The parapet height for vegetative
roof systems is the distance from the
top of the soil media to the top of the
parapet.
Limitation: If the gravel stop or
parapet is less than 2 in above the soil
media, the vegetative roof shall only
be installed in the field of the roof.
The exposed edge of the vegetative
roof shall be protected with stone,
pavers, or special design-edge treatment
to protect the components of the
vegetative roof and soil media from
the wind.
3. Large Openings in a Wall
If a fully adhered membrane roof
system is not used and the total area
of all openings in a single exterior wall
is between 10% and 50% of that wall
area in the story located immediately
below the roof, a rectangular area
that has a width that is 1.5 times the
width of the opening and a depth that
is 2.0 times the width of the opening
shall be designed as a corner area of
the respective System 2 or System 3
designs. For System 1 designs, they
shall use the corner area specifications
of a System 2 design for the rectangular
area (see Figure 9).
When a fully adhered membrane
roof system is not used and the total
area of all openings in a single exteri-
Proceedings of the RCI 25th International Convention Ennis – 69
Figure 8 – Corner and perimeter layout (BSR/SPRI RP-14 2008).
or wall exceeds 50% of that wall area
in the story located immediately
below the roof, the system design
must be upgraded to the next design
level. That is, a System 1 design must
be upgraded to a System 2 design, a
System 2 design must be upgraded to
a System 3 design, and a System 3
design must be upgraded to a roof
system that is designed to resist the
uplift loads in accordance with ASCE
7 or the local building code. The rectangular
roof area over the opening
must be designed as a corner section.
4. Positive Pressure in Building
Interior.
When a fully adhered membrane
roof system is not used and positive
pressure conditions between 0.5 and
1.0 inch of water are present in a
building, the design roof top wind
speed must be increased by 20 mph
from the basic wind speed from the
wind map. The roof must be designed
to meet this higher design wind
speed. When positive pressures are
greater than 1.0 inch of water, the
design of the roof must be based on a
licensed design professional method
and approved by the authority having
jurisdiction.
5. Rooftop Projections
When rooftop projections rise 2 ft
or more above the parapet height and
have at least one side greater than 4
ft in length, the roof area that extends
4 ft out from the base of such projections
and that does not have a minimum
80% vegetative coverage must
be covered with a wind erosion mat.
6. Overhangs, Eaves and
Canopies
Impervious Decks. Eaves and
overhangs must be designed as
perimeter areas of the applicable
design. Canopies must be designed as
corner sections of the applicable
design.
7. Pervious Decks
When the deck is pervious and a
fully adhered membrane roof system
is not used, overhang, eave and/or
canopy areas must be upgraded to
the corner design of the next-level
system for wind resistance over the
applicable design. For this situation,
the entire overhang, eave, or canopy
of a System 1 design shall be upgraded
to a System 2 corner design; the
entire overhang, eave, or canopy of a
System 2 design shall be upgraded to
a System 3 corner design; the entire
overhang, eave, or canopy of a System
3 design shall be designed to the
System 3 corner design.
When a fully adhered membrane
roof system is used, follow the design
recommendations for an impervious
deck design.
8. Exposure D
For buildings located in Exposure
D, the design wind speed is to be
increased by 20 mph from the basic
wind speed from the wind map.
Under these conditions, a building
roof located in a 90-mph wind zone
would be upgraded to 110 mph.
Installation would then follow all of
the requirements for the higher
design wind speed.
9. Wind-borne Debris Regions
For vegetative roofs used in windborne
debris regions, consideration
shall be taken to minimize woody vegetation
that could become wind-borne
debris. Trees, palms, and woody
bushes could have limbs break off in
the wind, leading to building damage.
10. Wind Erosion Protection
If bare spots exceed a maximum of
5 sq in, provisions must be made to
prevent wind scour. Wind-tunnel
tests have demonstrated that tackifiers
are particularly successful in
preventing blow-off of growth media.
11. Importance Factor
For buildings fitting category III or
IV the design wind speed is to be
increased by 20 mph from the basic
wind speed from the wind map. Under
these conditions a building roof located
in a 90 mph wind zone would be
upgraded to 110 mph etc. Installation
would then follow all of the requirements
for the higher design wind.
Ennis – 70 Proceedings of the RCI 25th International Convention
Figure 9
Determining System Design
To determine the system design (1,
2, or 3) to use for the vegetative roofing
system, use the appropriate
design table and find the design that
matches the wind speed, building
height, parapet height, and exposure
condition after making adjustments
(i.e., importance factor, openings, etc.)
for the building under design.
For example, for a 75-ft building
with a 10-in parapet height in an
Exposure C area and a design wind
speed of 90 mph, a System 2 would be
required (see outlined number in
Table 2).
FIRE STANDARD
The designation for the fire standard
is BSR/SPRI VF-1, Fire Design
Standard for Vegetative Roofs. The
design options provided in this standard
were developed to provide a barrier
to prevent the spread of fire from
the vegetative section of the roof to
other parts of the building. These
design options were developed from
European experience, forest fire prevention,
and roofing experience. The
use of the IBC-prescribed standard
procedures to test vegetative roof
designs using ASTM E108 and UL
790 were considered to be practical
only on a very limited basis. With all
the plant types that could be used in
a roof design, the varying weather
conditions that occur throughout the
year, and the effects of seasons, too
many variables exist to classify most
roof constructions. For this reason,
the barrier design method is used.
This standard provides a method
for designing fire resistance for the
most common and recognized of the
vegetative roof systems. It is intended
as a design and installation reference
for those individuals who design,
specify, and install vegetative roofing
systems. The standard should be
used in conjunction with the installation
specifications and requirements
of the manufacturer of the specific
products used in the system.
Vegetative Roof Design Options
and Generic Fire-Resistive
Vegetative Systems
The standard lists two systems
that have demonstrated excellent fireresistive
characteristics and requires
the use of either of these systems,
systems that have documented an
equivalent performance, or systems
that are approved by the jurisdiction
having authority. The generic fireresistive
systems listed are:
1. Succulent-based systems:
Systems in which the vegetative
portion of the roof is
planted in growth medium
that is greater than 80% inorganic
material, and the vegetation
consists of plants that
are classified as succulents.
Nonvegetative portions of the
rooftop shall be systems that
are classified ASTM E108,
Class A.
2. Lawn grass-based systems:
Systems in which the vegetative
portion of the roof is
planted in growth medium
that is greater than 80% inorganic
material, and the vegetation
consists of plants that
are classified as lawn grass.
Nonvegetative portions of the
rooftop shall be systems that
are classified ASTM E108,
Class A.
Vegetative Roof System
Requirements
Fire protection for rooftop
struc tures and penetrations. For
the purpose of this standard, a penetration
is an object that passes
through the roof structure and rises
above the roof deck/surface. These
may consist of but are not limited to
HVAC units, penthouses, ducts,
pipes, expansion joints, and skylights.
For all vegetative roofing systems
abutting combustible vertical
surfaces, a Class A-rated (per ASTM
E108 or UL790) roof system shall be
achieved for a minimum 6-ft (1.8-m)
wide continuous border placed
around rooftop structures and all
rooftop equipment.
Spread of fire protection for
large roof areas. A firestop as de –
scribed below shall be used to partition
the roof area into sections not
exceeding 15,625 ft2 (1,450 m2), with
each section having no dimension
greater than 125 ft (39 m). One or
more standpipes from the building
sprinkler system shall be provided on
large-area roofs.
Fire-stop Options
1. Walls. Fire-stop walls shall
be of noncombustible construction
complying with the
applicable building code and
extending above the roof surface
a minimum of 36 in.
2. Firebreak roof areas shall
consist of a Class A- (per
ASTM E108 or UL790) rated
roof system for a minimum 6-
ft (1.8-m) wide continuous
border.
MAINTENANCE
REQUIREMENTS
The standard requires that maintenance
be provided as needed to sustain
the system, keeping vegetative
roof plants healthy and dry foliage to
a minimum. Maintenance includes
but is not limited to irrigation, fertilization,
and weeding. Excess biomass
such as overgrown vegetation, leaves,
and other dead and decaying material
shall be removed at regular intervals
not less than two times per year.
Provision shall be made to provide
access to water for permanent or temporary
irrigation. The requirement for
maintenance shall be conveyed by the
designer to the building owner, and it
shall be the building owner’s responsibility
to maintain the vegetative roof
system.
CONCLUSIONS
Fire- and wind-resistance standards
have been developed for vegetative
roofing assemblies. These standards
were developed to help address
requirements of the International
Building Code (IBC). Code-change
proposals have been submitted to
include these standards in the IBC.
Proceedings of the RCI 25th International Convention Ennis – 71
Ennis – 72 Proceedings of the RCI 25th International Convention
A. FOR PARAPET HEIGHTS FROM 2 IN TO LESS THAN 6
MAXIMUM ALLOWABLE WIND SPEED (MPH)
BLDG. SYSTEM 1 SYSTEM 2 SYSTEM 3
HEIGHT (ft) EXPOSURE C EXPOSURE B EXPOSURE C EXPOSURE B EXPOSURE C EXPOSURE B
0-15 100 105 115 115 130 140
> 15-30 100 105 110 115 130 140
> 30-45 90 100 100 115 130 140
> 45-60 NO NO 95 115 120 140
> 60-75 NO NO 90 110 120 120
> 75-90 NO NO NO NO NO NO
> 90-105 NO NO NO NO NO NO
> 105-120 NO NO NO NO NO NO
> 120-135 NO NO NO NO NO NO
> 135-150 NO NO NO NO NO NO
B. FOR PARAPET HEIGHTS FROM 6 IN TO LESS THAN 12 IN
MAXIMUM WIND SPEED (MPH)
BLDG. SYSTEM 1 SYSTEM 2 SYSTEM 3
HEIGHT (ft) EXPOSURE C EXPOSURE B EXPOSURE C EXPOSURE B EXPOSURE C EXPOSURE B
0-15 100 105 115 115 130 140
> 15-30 100 105 110 115 130 140
30-45 90 100 100 115 130 140
> 45-60 NO NO 95 115 120 140
> 60-75 NO NO 90 110 120 130
> 75-90 NO NO NO NO NO NO
> 90-105 NO NO NO NO NO NO
> 105-120 NO NO NO NO NO NO
> 120-135 NO NO NO NO NO NO
> 135-150 NO NO NO NO NO NO
C. FOR PARAPET HEIGHTS FROM 12 IN TO LESS THAN 18 IN
MAXIMUM WIND SPEED (MPH)
BLDG. SYSTEM 1 SYSTEM 2 SYSTEM 3
HEIGHT (ft) EXPOSURE C EXPOSURE B EXPOSURE C EXPOSURE B EXPOSURE C EXPOSURE B
0-15 100 105 115 115 140 140
> 15-30 100 105 110 115 140 140
> 30-45 90 105 105 115 140 140
> 45-60 NO 90 95 115 130 140
> 60-75 NO 90 90 110 120 130
> 75-90 NO NO 90 110 110 120
> 90-105 NO NO 90 100 110 110
> 105-120 NO NO 85 100 100 110
> 120-135 NO NO NO 100 100 110
> 135-150 NO NO NO 95 100 110
Table 2
Code-change proposals have also
been submitted to the International
Property Maintenance Code to require
maintenance of these systems.
In both cases, the standards are
design standards versus test standards.
This approach was taken due
to the extensive number of variables
that are present in vegetative roof system
design, including the thickness of
growth media, plant types, and moisture
content of the assembly at any
point in time.
REFERENCES
J. Breuning, “Do We Need a Belt,
Suspenders, and a Nail in
Our Belly Button to Hold Our
Pants?” The Vegetative Roof
Infrastructure Monitor, Spring
2007, pp. 12-13.
National Roofing Contractors
Asso ciation, The NRCA Vege –
tative Roof Systems Manual,
Second Edition, 2008, pp. 30-
32.
Single Ply Roofing Industry,
BSR/SPRI Standard RP-14,
Wind Design Standard for
Vegetative Roof Systems,
2008.
Single-Ply Roofing Industry,
BSR/SPRI Standard VF-1,
Fire Design Standard for
Vegetative Roof Systems,
2008.
K.Y. Liu and A. Baskaran, “Using
Garden Roof Systems to
Achieve Sustainable Building
Envelopes,” National Re –
search Council of Canada,
Technology Update No. 65,
September 2005.
FEMA Mitigation Assessment
Team Report, Hurricane Ike
in Texas and Louisiana,
FEMA P-757, April 2009).
Proceedings of the RCI 25th International Convention Ennis – 73