U.S. patent application number 16/237999 was filed with the patent office on 2019-05-16 for ballast system for roof protection.
This patent application is currently assigned to Watershed Geosynthetic LLC. The applicant listed for this patent is Watershed Geosynthetic LLC. Invention is credited to BRADFORD H. COOLEY.
Application Number | 20190145056 16/237999 |
Document ID | / |
Family ID | 59851262 |
Filed Date | 2019-05-16 |
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United States Patent
Application |
20190145056 |
Kind Code |
A1 |
COOLEY; BRADFORD H. |
May 16, 2019 |
Ballast System For Roof Protection
Abstract
A tufted geosynthetic lightweight ballast system for roof
protection in which the system comprises a composite of one or more
geotextiles tufted with one or more synthetic yarns.
Inventors: |
COOLEY; BRADFORD H.;
(Chattanooga, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Watershed Geosynthetic LLC |
Alpharetta |
GA |
US |
|
|
Assignee: |
Watershed Geosynthetic LLC
Alpharetta
GA
|
Family ID: |
59851262 |
Appl. No.: |
16/237999 |
Filed: |
January 2, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15459638 |
Mar 15, 2017 |
|
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16237999 |
|
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62390053 |
Mar 17, 2016 |
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Current U.S.
Class: |
52/302.1 ;
428/87 |
Current CPC
Class: |
E04D 3/32 20130101; E04D
3/351 20130101; E04D 7/005 20130101; E04D 11/002 20130101; E04D
13/1662 20130101; E01C 13/08 20130101; E04D 3/18 20130101; E04D
5/12 20130101; A01G 9/033 20180201 |
International
Class: |
E01C 13/08 20060101
E01C013/08; E04D 13/16 20060101 E04D013/16; E04D 7/00 20060101
E04D007/00; E04D 11/00 20060101 E04D011/00; E04D 3/32 20060101
E04D003/32; E04D 3/35 20060101 E04D003/35 |
Claims
1. A roof tufted geosynthetic lightweight ballast system for a
roof, comprising: a roof structure for closing a building; a
ballast system overlying an upper surface of the roof structure,
comprising: a composite of one or more geotextiles tufted with one
or more synthetic yarns, wherein the one or more synthetic yarns
are tufted into the one or more geotextiles to produce slender
elongate elements having an appearance of grass, wherein each of
the slender elongate elements has a length of about 0.25 to about 4
inches and wherein the weight of the ballast system without infill
is between about 0.15 to about 2.0 pounds per square foot whereby
the ballast system, overlaid on the roof structure and exposed to
wind loading, breaks up a wind air flow stream proximate a tuft
surface of the composite and forms in situ a boundary layer
proximate thereto having a normal pressure against the ballast
system for resisting wind uplift forces thereon.
2. The roof ballast system as defined in claim 1 wherein each of
the one or more geotextiles comprises a polymeric material.
3. The roof ballast system as defined in claim 2 wherein the
polymeric material is polyethylene, polypropylene, nylon, polyester
or an acrylic polymer.
4. The roof ballast system as defined in claim 1 wherein each of
the one or more synthetic yarns comprises a polymeric material.
5. The roof ballast system as defined in claim 4 wherein the
polymeric material is polyethylene, high density polyethylene,
linear low density polyethylene, a polyester, polyvinyl chloride,
nylon, polypropylene or other UV resistant polymeric material.
6. The roof ballast system as defined in claim 1 wherein the
slender elongate elements are tufted to have a density of between
about 12 and about 100 ounces per square yard.
7. The roof ballast system as defined in claim 1 wherein each of
the slender elongate elements have a thickness of at least about
100 microns.
8. The roof ballast system as defined in claim 1 wherein the one or
more geotextiles comprise a single layer or more than one
layer.
9. The roof ballast system as defined in claim 1 wherein each of
the slender elongate elements comprise slit film, tape, fibrillated
fibers or monofilament fibers.
10. The roof ballast system as defined in claim 1 wherein infill is
used between the slender elongate elements.
11. The roof ballast system as defined in claim 10 wherein the
weight of the ballast system with infill is between about 1.0 and
about 15.0 pounds per square foot.
12. The roof ballast system as defined by claim 10 wherein the
infill is sand, coated sand, soil material, gravel, pea gravel,
stone, organic materials, granular or cork rubber, coated rubber or
ethylene propylene diene terpolymer.
13. The roof ballast system as defined in claim 1 wherein the
system additionally comprises a binding agent.
14. The roof ballast system as defined by claim 13 wherein the
binding agent is lime, an organic emulsion, a polymeric emulsion, a
cementitious-based material or a pozzolanic-based material.
15. The roof ballast system as defined by claim 1 wherein the
slender elongate elements are fire resistant.
16. The roof ballast system as defined by claim 1 wherein the
slender elongate elements are reflective.
17. The roof ballast system as defined by claim 1, wherein the roof
structure comprises a protected membrane roof.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This non-provisional application is based upon, and claims
priority to, U.S. Provisional Patent Application Ser. No.
62/390,053, filed Mar. 17, 2016.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
TECHNICAL FIELD
[0003] This invention relates to a ballast system for a roof. In a
more specific aspect, this invention relates to a tufted
geosynthetic lightweight ballast for a protected membrane roof.
[0004] In this application, the term "protected membrane roof" will
be understood to refer to an inverted roof assembly in which the
insulation and ballast are located on top of the membrane. This
type of roof is also referred to as an "insulated roof membrane
assembly".
[0005] In this application, the term "membrane" will be understood
to refer to an impermeable polymeric material, examples of which
are polyethylene, high density polyethylene, very low density
polyethylene, linear low density polyethylene, polypropylene,
polyvinyl chloride, ethylene propylene diene terpolymer,
polyurethane, asphalt and bitumen.
[0006] In this application, the term "synthetic grass" will be
understood to refer to a composite of one or more geotextiles
(woven or nonwoven) tufted with one or more synthetic yarns that
has the appearance of grass.
[0007] In this application, the term "ballast" will be understood
to refer to a material that is used to improve stability and/or
control, examples of which are stone, gravel, soil, sand and
concrete paving slabs (also referred to as concrete pavers).
BACKGROUND OF THE INVENTION
[0008] As known in the art, a protected membrane roof requires a
weight of typically 10 to 25 pounds per square foot (psf) of stone
ballast in the field interior condition (i.e., the interior area of
the roof), and a ballast of 15 to 25 psf of stone ballast around
the perimeters and penetrations of the roof. Challenges with
conventional stone ballast include wind scour of the stone, heavy
weight to put on a roof, difficult to repair and maintain the
underlying roof components, cannot easily clean dirt and debris
from the roof and unsightly aesthetics. There is the potential for
the stone ballast to blow off the roof. If this happens, there are
significant risks of property damage and/or personal injury and
safety. Building owners and design architects have concern with
this potential liability when using a stone ballast for a protected
membrane roof.
[0009] Concrete pavers are also used as roof ballast, and these
pavers have a typical ballast weight of between 15 to 25 psf.
Concrete pavers are typically strapped together where they are next
to the perimeter of a roof or in areas of potentially high winds.
Concrete pavers are expensive, heavy, prone to crack and have
unsightly aesthetics. There is a potential for concrete pavers to
blow off the roof. If this happens, there are significant risks of
property damage and/or personal injury and safety. Building owners
and design architects have concern with this potential liability
when using concrete pavers for protected membrane roofs.
[0010] The purpose of the ballast layer is to protect the
underlying membrane and insulation layers of a protected membrane
roof from ultraviolet degradation, wind uplift, weather and
physical damage/abuse.
[0011] Due to the challenges with use of a conventional ballast,
there is a need in the industry for a new and improved ballast
system for a protected membrane roof.
SUMMARY OF THE INVENTION
[0012] Briefly described, the present invention provides a new and
improved ballast system for enhanced protection of a protected
membrane roof.
[0013] The ballast system of this invention provides a protected
membrane roof with enhanced protection from degradation by
ultraviolet light, wind uplift, weather and physical damage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic view of a prior art protected membrane
roof having a typical stone ballast.
[0015] FIG. 2 is a schematic view of a prior art protected membrane
roof having a typical concrete paver ballast.
[0016] FIGS. 3 and 4 are views of a ballast system of this
invention showing a tufted geosynthetic lightweight ballast on a
protected membrane roof.
[0017] FIGS. 5, 6A, 6B and 6C are views of a ballast system of this
invention with different configurations.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The present invention provides a tufted geosynthetic
lightweight ballast for a protected membrane roof, in which the
ballast system comprises a composite of one or more geotextiles
tufted with one or more synthetic yarns.
[0019] The tufted geosynthetic lightweight ballast is a continuous
system that is attached to the edges of the roof. The system can be
delivered to the site of the roof in various forms, such as rolls
or panels which can be seamed together by various methods, such as
sewing, heat welding, adhesive, glue or mechanical means, such as
staples, clips, screws or nails. The seaming creates the continuous
system.
[0020] In the ballast system of this invention, the geotextile
functions as a backing for the synthetic yarn to form the
composite. The synthetic yarn is tufted to appear as slender
elongate elements (also referred to as synthetic vertical
filaments, turf grass or vertical filaments). The tufted synthetic
yarn may have the appearance of blades of grass, filaments, tufts,
follicle-like elements, fibers and narrow cone-sloped elements.
[0021] The ballast system of this invention does not require
infilling between the synthetic vertical filaments, but infill may
be used for additional protection against higher wind velocities
and physical damage. If used, the infill between the synthetic
vertical filaments can be a granular material, examples of which
are sand, coated sand, soil material, pea gravel, gravel, stone,
organic materials (such as natural cork and coconut shell fibers),
granular or crumb rubber, coated rubber and ethylene propylene
diene terpolymer. The synthetic vertical filaments cover and hold
the granular material in place. This granular material may or may
not be bound. If used, a binding agent is applied to the granular
material, and the binding agent may be lime, an organic emulsion, a
polymeric emulsion or a cementitious-based material.
[0022] In a preferred embodiment, the present invention comprises a
tufted geosynthetic lightweight ballast, including synthetic
slender elongate elements secured into a backing material.
Advantageously, the ballast of this invention does not require
piled-on weight to resist wind forces and can be deployed over a
large area with little or no additional weight or anchoring.
[0023] The tufted geosynthetic lightweight ballast includes slender
elongate elements attached to the backing to break the wind
aerodynamics on the exposed roof. The testing of this ballast
system shows the wind velocity on the surface becomes turbulent
near the surface of the roof, thus greatly reducing the actual wind
velocity at the tufted geosynthetic lightweight ballast surface and
decreasing associated uplift.
[0024] The reaction of the slender elongate elements to the wind
forces may also create a downward force on the ballast system. This
reaction may be caused by the slender elongate elements applying an
opposing force against the wind which is transferred as a downward
force on the geosynthetic backing. The use of slender elongate
elements is a departure from typical roof ballast materials.
Examples of slender elongate elements encompassed by the present
invention include structures that resemble blades of grass, rods,
filaments, tufts, follicle-like elements, fibers and narrow
cone-shaped elements.
[0025] Advantageously, the tufted geosynthetic lightweight ballast
system of this invention can create a larger distance from the
material surface to the "free stream" (i.e., when the wind flow is
unaffected by the material). The tufted geosynthetic lightweight
ballast breaks up the flow stream, increasing the boundary layer
(i.e., the distance from surface to the free stream) to the point
where uplift forces are very small. This is in contrast to a prior
art ballast of stone or pavers, where there is a small distance to
the uninterrupted free stream air flow. This small distance in the
prior art ballast means there is a large velocity differential over
a very short distance, which creates much higher uplift and the
need for significant weight or anchoring.
[0026] The positive/downward force is a result of a reaction of the
slender elongate elements of the lightweight ballast of this
invention, with the individual vertical elements acting as springs
pushing against the wind. This reaction and opposing force will
vary based on the type of cover and the length of the slender
elongate elements, which will be shorter or longer depending on the
wind design flow for the disruption provided by the ballast system
of this invention. Typically, the length of the slender elongate
elements will range between about 0.25 and about 4 inches.
[0027] The tufted geosynthetic lightweight ballast system of this
invention also acts as a protective layer to provide protection to
the underlying insulation and membrane layers below from physical
damage and weathering. Infill may be added for additional
protection. Thus, the ballast system of the present invention can
extend the longevity of the roof components over a longer period of
time than prior art roof ballast materials.
[0028] In a preferred embodiment, this invention uses a geotextile
(i.e., as a backing) which is tufted with slender elongate
elements. This backing may have one or more geotextile layers and
may or may not have a polymeric coating. Preferably, the geotextile
is manufactured of polypropylene, but may also be manufactured from
polyethylene, nylon, an acrylic polymer or a polyester. The
construction of the geotextile with the slender elongate elements
may be woven, knitted or non-woven. The polymeric coating provides
binding for the slender elongate elements.
[0029] The polymeric coating, if used, may be impermeable or
perforated. The geotextile backing, with or without the polymeric
coating, may be smooth or may have roughened, textured or
structural components to increase the friction resistance against
the underlying components of the roof system. Preferably, when
roughened, the polymeric coating may have an angle of friction
which can be higher than 15 degrees. The polymeric coating can be
applied by gluing, spraying, coating or extruding a material (such
as polyurethane, ethylene propylene diene terpolymer, polypropylene
or polyethylene) to the back of the tufted geotextile.
[0030] The slender elongate elements also have the added advantage
of being fire resistant. Flammability of the tufted geosynthetic
lightweight ballast of this invention has been tested and passes
the requirements of ASTM D 2859 and meets the standards of the U.S.
Consumer Product Safety Commission Standard for Carpets and
Rugs.
[0031] The slender elongate elements may or may not have infill,
which can be loose or bound.
[0032] Reflectivity is important for roof structures. Reflectivity
lowers the heat in the building as well as reduces the heat island
effect. The slender elongate elements provide reflection of
ultraviolet radiation. The amount of reflection may be altered by
changing the length, shape, size, cross-section and/or color of the
slender elongate elements or by including special additives to the
synthetic makeup of the elements. In areas where more reflection is
needed, the slender elongate elements can be optimized to meet
local codes or EnergyStar guidelines.
[0033] The reflectivity of a surface depends on the surface's
reflectance and emittance, as well as solar radiation. The Solar
Reflectance Index (SRI) is used to estimate how hot a surface will
get when exposed to full sun. The SRI is calculated from the
surface's reflectance and emittance in accordance with ASTM
E1980--"Standard Practice for Calculating Solar Reflectance Index
of Horizontal and Low-Sloped Opaque Surfaces." The roof ballast
system of this invention has a SRI that ranges between 20 and 100.
The SRI depends upon the length, shape, size, cross-section, color
and/or material composition of the slender elongate elements.
[0034] For a typical reflective roof, reflectivity is difficult to
maintain. Dirt, dust and debris cover the reflective surface in a
short period of time. For a reflective roof with the ballast system
of this invention, dirt, dust and debris will fall between the
slender elongate elements and not block their reflective
properties.
[0035] Referring now to the drawings, FIG. 1 shows a prior art
system of a cross section of a protected membrane roof 100 with a
stone ballast 50. The protected membrane roof sits on the roof deck
10 and is overlain by the membrane 20 which is covered by an
insulation layer 30, typically a polystyrene foam insulation. A
filter fabric 40 which acts as a separation layer is placed over
the insulation layer 30. A layer of stone ballast 50 is placed on
top of the entire roof system 100. The weight of this stone ballast
50 is typically 10 to 25 psf in the field interior condition, and
15 to 25 psf around the perimeters and penetrations, depending on
the design wind speeds.
[0036] FIG. 2 shows a prior art system of a cross section for a
protected membrane roof 200 using concrete pavers 60 as roof
ballast. The concrete pavers 60 sit atop the filter fabric 40,
insulation layer 30, membrane 20 and roof deck 10. The concrete
pavers 60 have a typical ballast weight of between 15 and 25 psf,
with the pavers 60 next to the perimeter of the roof being strapped
together.
[0037] FIG. 3 shows a 3-dimensional view of the ballast system of
the present invention, which is a tufted geosynthetic lightweight
ballast 70 for a protected membrane roof 300. Other than the
ballast layer 70, the roof 300 has the components of a prior art
protected membrane roof which include a filter fabric 40,
insulation layer 30, membrane 20 and roof deck 10.
[0038] FIG. 4 shows a cross section of an embodiment of the present
invention, which is a tufted geosynthetic lightweight ballast 70
for a protected membrane roof 300. The tufted geosynthetic ballast
70 sits upon the roof system 300 of a filter fabric 40, insulation
layer 30, membrane 20 and roof deck 10. The tufted geosynthetic
ballast 70 is comprised of synthetic strands of slender elongate
elements 71 tufted into backing material 72. The tufted
geosynthetic is infilled with granular material 73.
[0039] FIG. 5 shows a cross section of another embodiment of the
present invention, which is a tufted geosynthetic lightweight
ballast 70 for a protected membrane roof 300. The ballast 70 is
comprised of synthetic strands of slender elongate elements 71
which are tufted into backing material 72. The ballast 70 is not
infilled. This view shows a drainage composite 80 (instead of a
filter fabric) under the ballast 70. The function of the drainage
composite is to provide drainage as well as diffusion of moisture
through the system. This embodiment shows the roof deck 10 under
the membrane 20 and insulation layer 30.
[0040] FIG. 6A shows a tufted geosynthetic lightweight ballast 70
of the present invention. The ballast 70 is comprised of synthetic
strands of slender elongate elements 71 which are tufted into
backing material 72. This ballast system 70 is infilled with a
granular material 73.
[0041] FIG. 6B shows a tufted geosynthetic lightweight ballast 70
with an impermeable coating 74 on the geotextile backing 72 which
is tufted with synthetic strands of slender elongate elements 71.
The tufted geosynthetic ballast 70 in this embodiment is not
infilled with granular material.
[0042] FIG. 6C shows a tufted geosynthetic lightweight ballast 70
with synthetic strands of slender elongate elements 71 tufted into
a geotextile backing 72, but without infill.
[0043] The present invention allows the use of a protected membrane
roof over large areas without heavy ballast or anchorage. The
tufted geosynthetic lightweight ballast of this invention can
resist wind uplift to protect the components of a protected
membrane roof. The ballast system of this invention incorporates
slender elongate elements tufted into a geotextile backing, and may
or may not be infilled. Infill can be placed between the slender
elongate elements. Typically, for the field interior condition of
the roof, infill will not be required. For the perimeter areas,
infill may be needed. The need for infill will be determined based
upon the design wind speeds for the specific application and/or the
need for additional protection against physical damage.
[0044] The weight of the tufted geosynthetic lightweight ballast of
this invention without infill is preferably between about 0.15 to
about 2.0 psf, while the weight of the ballast with infill is
preferably between about 1.0 to about 15.0 psf. The infill can be
loose granular or bound material.
[0045] If infill is used as part of the tufted geosynthetic
lightweight ballast, the infill will be placed and fall between the
slender elongate elements. The infill can be a granular material,
examples of which are sand, coated sand, soil material, pea gravel,
gravel, stone, organic materials (such as natural cork and coconut
shell fibers), granular or crumb rubber, coated rubber and ethylene
propylene diene terpolymer. The synthetic slender elongate elements
cover and hold the granular material in place. This granular
material may or may not be bound. If used, a binding agent is
applied to the granular material, and the binding agent may be
lime, an organic emulsion, a polymeric emulsion, a
cementitious-based material or a pozzolanic-based material.
[0046] As used in this application, the term "slender" indicates a
length that is greater than its transverse dimension(s). The
synthetic slender elongate elements extend upwardly from a backing
and form a mat or field to simulate a field of grass, pine straw or
similar material.
[0047] Preferably, the chemical composition of the synthetic
slender elongate elements should be selected to be heat resistant,
reflective, flame retardant, resistant to ultraviolet rays (UV) and
to withstand exposure to sunlight, which generates heat in the
vertical elements and contains ultraviolet rays. Furthermore, the
vertical elements should not become brittle when subjected to low
temperatures. The synthetic vertical elements should have a color
and texture that are aesthetically pleasing and/or reflective.
[0048] While other materials can be used for the slender elongate
elements, polymeric materials are preferred, such as polyethylene.
The vertical elements can be made of high density polyethylene,
linear low density polyethylene, polyethylene, polyester, polyvinyl
chloride, nylon, polypropylene, or other UV resistant material.
While not a requirement of the ballast system of this invention, UV
resistance provides an important long term stability for the
synthetic slender elongate elements, adding to the overall
performance of the ballast system of this invention. For
applications where the tufted geosynthetic ballast has the added
advantage of reflectivity, the vertical elements may be constructed
to be effective by using color, foil or other reflective
materials.
[0049] Preferably, the synthetic slender elongate elements are
tufted to have a density of between about 12 ounces/square yard and
about 100 ounces/square yard and, more preferably, a density of
between about 20 and about 40 ounces/square yard. The tufting is
fairly homogeneous. In general, a "loop" is inserted at a gauge
spacing to achieve the desired density. Each loop shows as two
vertical elements at each tufted location. Preferably, the
synthetic vertical elements have a thickness of at least about 100
microns.
[0050] The synthetic slender elongate elements are tufted into the
geotextile backing, and preferably compromise one or more
polypropylene or polyethylene filaments with UV stabilizers. The
vertical filaments can comprise slit film, tape, fibrillated or
monofilament fibers. Generally speaking, the lower the surface area
of the fiber per unit weight of raw material, the better the UV
performance. Monofilament fibers typically have a small cross
section relative to their length, which inherently provides for a
smaller surface exposed to UV rays per unit weight. A fiber with a
round cross-section typically will exhibit better UV resistance
than a flat geometric shape.
[0051] The geotextile backing can be a single layer, a double layer
or can be more than two layers. But preferably, either a single
layer or double layer backing is used. The geotextile backing can
be made of polypropylene or polyethylene. Also, a separate
impermeable coating can be added, such as by applying a
membrane-like layer to the back side of the geotextile backing. For
example, a urethane coating can be sprayed onto the back of the
synthetic geotextile and allowed to cure.
[0052] The wind resistant tufted geosynthetic lightweight ballast
of this invention was laboratory tested at the Georgia Tech
Research Institute (GTRI) Wind Tunnel Lab (Atlanta, Ga.) using wind
tunnels to determine the uplift vertical pressures and shear
pressures on the system. The wind tunnel trials indicate that the
lightweight ballast system of this invention resists the uplift
forces of the wind up to at least about 116 miles per hour. The
minimal ballast weight of about 0.28 psf for the tufted
geosynthetic ballast of this invention is typically all that is
required to counteract the shear forces from the wind. For higher
winds and at perimeter roof locations, a ballast weight of
approximately 4.0 psf may be needed.
[0053] The wind-resistant tufted geosynthetic ballast of this
invention creates a larger distance from the roof surface to the
free stream. The tufted geosynthetic ballast radically breaks up
the flow stream, increasing the boundary layer to the point where
uplift forces are very small. This is in contrast to prior art
exposed ballast systems, in which there is a small distance from
the surface (where velocity is 0 feet per second, which is the case
for all materials and wind conditions) to the free stream.
[0054] The boundary layer conditions are created by longer flow
paths over a given surface, and all boundaries grow in thickness
and increase in turbulence with increasing distance. In this
invention, the interaction of the flow with the flexible slender
elongate elements causes the boundary layer growth to occur quite
rapidly. As observed in our testing, little to no deflection
occurred in the tufted geosynthetic at a distance just over 6
inches from the perimeter edge. The measured uplift results show
values requiring minimal uplift resistance that can simply be
achieved by the weight of the tufted geosynthetic ballast.
[0055] The advantages of the ballast system of this invention
include: [0056] Lightweight ballast having significantly less
weight than a traditional system to provide equal performance at
about 1/30 to about 1/4 the weight. [0057] With infill, the system
provides additional insulation and protection to the roof. [0058]
The slender elongate elements provide solar reflectivity. This
reflectivity is maintained because the vertical filaments stand up.
Dust and dirt that may accumulate on a roof falls between the
filaments, and the filaments maintain their reflectivity. Typical
reflective roofs start out performing, but once dust, grime and
dirt build up, these roofs are not useful for reflectivity. [0059]
Since the ballast system of this invention is lightweight, the roof
structure does not have to be built as strong as would be needed to
support the traditional ballast materials. [0060] Extremely durable
system which adds life to the roof, and protects the underlying
membrane from UV, temperatures (thermal shock), weather, the
elements and physical damage/abuse. [0061] Being lightweight and
durable, the ballast system of this invention offers the ability to
have modular garden areas on top of the roof.
[0062] This invention has been described with particular reference
to certain embodiments, but variations and modifications can be
made without departing from the spirit and scope of the
invention.
* * * * *