CA1290130C - Protected membrane roof system for high traffic roof areas - Google Patents

Abstract

ABSTRACT

An insulated roofing system is provided in which a waterproof membrane is applied to the roof deck. Extruded panels of closed cell polystyrene foam are provided on top of the membrane, thus protecting the membrane from thermal cycling, ultraviolet rays, and physical damage. The foam panels provide excellent insulation and are resistant to water. A waterproof plastic film is bonded to the undersurface of each panel positively to exclude water. The foam panels are cut mechanically or are grooved to provide on the upper surface integral ribs spaced by channels. Concrete panels are said directly on top of the polystyrene foam and rest gravitationally on the ribs. The ribs provide for ventilation and moisture removal on hot, dry days.
Removal of water vapor is enhanced by the increased area exposed to the ambient environment and derived from the cratered surfaces generated by cutting sections out of the foamed plastic panels. The composition, texture, and the physical contour or configuration of the cut surfaces bounding the cut grooves or channels formed in the foam plastic panels enhance the dissipation and dispersion of moisture, as compared with surfaces covered with a dense skin such as is produced upon generating the channels in an extrusion process.

Description

PROTECTED MEMBRANE ROOF SYSI'EM
~OR HIGH TRAFFIC ROOF AREAS

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For mahy years it was the universal practice~to ;~ ~' construc~t roofs with a waterproof layer or membrane on the outer ~ur~ace thereof. Such roofing is still used in many inistallations, but~ha3 numerous diqadvantages.
The waterproof membrane, which may be bituminous built~
up sheet or which~may be~single sheet o~ water;proof material, is;~exposed to~extreme temperature~variatlons,~
as much as 210F9 to ul~traviolet radiation9 and to~
phys~cal~abrasion, all of which have a deleterious~
effect on the life of the roofing.
It is~also an establi~hed common practice to 15' provide insulation~in roof construction. When inouIation i~ located~below the waterproof membrane, in~
; the roofing system outlined above, it is o~ten necessary to provide~a second waterproo~ membrane ~
beneath the lnsulation to prev,ent moisture from within the building from condensing in the insulation and isubstantially vitiati,ng or essentially destro~ing its insulation attribute3. ~
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: ' : ,, :~ . ,: i - ~290~30 An alternative "upside-down" or inverted roofing construction is known in which the insulation is applied over the waterproof membrane, see for example U.S. Patents 3,411,256 and 3,76396140 In this alternative roof construction the waterproo~ membrane (which may be a built-up membrane or a single waterproof layer such as of elastomeric, plastomeric, liquid applied or modified bitumen) is applied directly to the surface of the roof. Blocks of foam plastic insulation are then placed to overlie the waterproof membrane. Polystyrene plastic resin foam is a superior product for such u e, and STYROFOAM~ brand plastic foam made by The Dow Chemical Company is a preferred example. It is a tough, closed cell rigid plastic foam ~; having excellent moisture resistance and high compressive strength.
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The polystyrene foam insulation placed over the~
waterproofing membrane (rather than under the membranè)~
protect the membrane from~the effects of thermal ~; ¢ycling, temperature extremes, and physical abuse, thus reducing maintenance oosts and prolonging the useful ife of the entire roof~ing system. It has been found that the membrane so protected; remains at stable :
temperatures below 100F, even in hot~summer weather.
In Yact, under normal conditions, the temperature of the membrane will remain within a rang~e of 15 to 20F of the building'~ inside temperature.
3o ; ~ Typically, a polymeric fabric is installed over the foam to stabilize the 9yqtem, and cru~hed 9tone or gravel ballast i~ applied to counteract the buoyancy of ~` the insulation boards, to provide flammability resistance to the roof surface, and to shield the foam and fabric foam ultraviolet radiation. As an ~ .: -~ 32,V61A-F ~ 2- ~ ~

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, 1~90~3 alternative, paving blocks may be used in place of stone, particularly i~ traffic is to be expected on the rooP.
When traffic is expected (as in the construction of a plaza deck) pedestals or stones are provided to space the paving blocks above the top of the foam insulation to per~it adequate air circulation for drying of the roo~ing system on warm, dry days. It will also be appreciated that a base roof or deck of substantial strength must be provided to support the weight of such a roofing system.
In contrast to the aforementioned prior art, the present invention provides an improved roofing system of the type in which a waterproof membrane is;
applied directly to the surface of a roof. Specific novel panels of rigid foa~ insulation having a plasti~c fi~lm laminated to the lower surface are then applied over the membrane; and paving blocks (generally made oP
concrete) are applied directly to the foam insulation without the necessity of pedestals or stones. More specifically, the novel insulation panels are made of ; 25 o~ closed~Poam plastic and have elongated ribs arrayed on an upper qurface~of the panels, which ribs are coextensive with cu~t-out;channels or valleyB i nterposed between and demarking the ribs.
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Another aspect oP the present invention is that it provides a roofing~ystem in which the upper surPaces of the Poam~plastic in~ulating blocks are ribbed, having alternating rib~ and valleys, with the concrete paving blocks laid directly on the ribbed 35-~surfaces of the foam blocks.
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" ~Z9013 It is also an optional feature o~ the present invention that the roof system includes foam plastic panels which, subsequent to forming, are cut longitudinally to provide grooves or channels having bounding walls in which exposed crater-like recesses resulting from a cutting through o~ pockets in the foam panel are exposed, thus significantly increasing the panel surface area exposed and accelerating evaporation of moisture from the channel-delineating walls.
Foam plastic panels of the type finding utility in the roof system of the present invention may be produced using any preferred technique, including casting or by extrusion. The panels are then physically modified b~ cutting grooves longitudinally across an upper surface zone of the panels to form alternating -;
channels and ribs, the latter defining a discontinuous planar top of the panels.

Extruded panels of polystyrene foam insulation are known which have one surface with integrally~formed, alternating rubs and grooves of equal width. In such extruded panels it was found that the polystyrene foam plastic material in the ribs is stiffer, stronger, and more resistant to deformation than the foam plastic material in the valleys, and throughout the body of the panels. It was believed that this strength increase was due to molecular orlentation of the materlal brought about as it foamed during extrusion.
In ao¢ordance with the present invention it has been found that in panels in which alternate ribs and grooves are produced by excising lineal sections from 32,461A-F -4- ~
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plastic panels, the panels still exhibit enhanced physical strength in the ribs zones.
In a preferred embodiment of the lnvention the rib array configuration in the foam plastic insulation panels is formed by cutting grooves or channels in extruded plastic sheet material, that is, by excising lineal sections from the panels, after extrusion.

An important feature of the insulation panels of the present invention is that in cutting the channeIs in the panels, an outer, essentially smooth, high-density skin is removed to pre~ent a surface which has been found to be much more conducive to releasing and dispersing of moisture accumulating on the outer upper surface of the panel.
~ Yet another feature of the foam plastic ;~ ~ insulation panel components of the roofing system of the present invention is that the undersurfaoe of each panel has an intact high density outer skin produced during extrusion and operative to deter invasive entry of water and moisture vapor into the panels, the lower surface of each panel also being bonded to a co-continuous water-impervlou~ film or sheet further to obviate intrusion oP mol~ture lnto the body of the panel.
A related feature of the invention is that in 3 outting the plastic panels to form the channel and ribs array, hollow cells pre~ent within the body of the foam plastic panel are qliaed through to establish channel-bounding walls having crater-like receqses in the exposed surface thereof, the wall3 presenting outwardly directed faces in which the area of exposed plastic 32,461A~F -5-~:

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material to the ambient environment and embraced in the reoess-marked surface is significantly increased as compared with planar areas delinea~ed by the perimetric borders of the channel-bounding walls.
A practical advantage derived from the increase in exposed surface area of the plastic panels, and realized by excising lineal sections from the panels to form channels therein, is that the resulting increase in surface area exposed to the ambient environment effects a corresponding increase in the effective rate of evaporation of moisture from the panels at the exposed walls of the channels ~ormed in the panels.
Yet another important advantage realized by ; producing the channels by a cutting process rather than by generating the channels during an extrusion process is that the smooth, high-density and essentially impermeable outer film produced during extrusion is removed to expose a cratered surface which is much more effective in the dispersion of water and moisture vapor ~ from the plastic panel to a surrounding ambient system.
;~; In accordance with the present invention the ribbed and grooved foam pla~tic insulation material, havirg a plastic film laminated to the lower surface, , is placed on top of a waterproof membrane, and concrete pavin~ blocks are then laid direetly on the ribs of the pla~tic panels and are then laid directly on the ribs of the plastic panels and are held gravitationally thereon.
~he invention will best be understood ~ro~ the followin~ specification taken in connection with the accompanying drawing~ wherein:
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~Z901 Figure 1 i~ a fragmentary cross~sectional view through a roofing system constructed in accordanoe with the principles of the present invention;
Figure 2 is a top view thereof with a portion broken away; and Figure 3 is a fragmentary exploded perspective view showing the recesses in the sur~aces of the channel-bounding wall~ and the relation of parts of the roofing system to one ar.other.
A based roof or deck 10 is shown in Figure 1 as comprising a concrete slab. This slab would preferably be reinforced. The roof deck could equally well be of~
wood construction, or o~ metal construction, and concrete simply has been chosen by way oP illustration ~; A waterproof membrane 12 overlies the roof deck 10.
The membrane can be~attached to the roof deck, or it can be loose. The membrane can be a single sheet o~
~polymeric material, liquid applied, modified bituminous ~heet, or it can be an asphaltic built-up membrane.
Panels 14, preferably of extruded polystyrene 25~ foam, are laid on top of the membrane 12. The foam panels include, on the top surface onIy, integral ribs 16 interspaced by grooves or valleys 18.~ The ribs and the grooves in the illustrated embodiment are of equal lateral extent, being approximately one inch wide, and about 1/8 to 1/2 inch deep.
In accordance with one aspect of the present ~ invention the upper ~urface zonal configuration of ;~ alternating ribs and groove~ is produced by physically removing elongated sections of plastics material from the preformed, extruded panels. Suitable cutters may :
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129~ 3 be used for this purpose. An important advantage achieved by producing the channels ~and ribs) by cutting the plastic panels 14 rather than by extrusion techniques is that in the cutting method of the present invention the operation has the effect of exposing crater-like recesses 20 as elements of the cut surfaces 22 bounding the grooves or channels 18. The recesses 20 greatly increase the surface area exposed to the ambient environment and thus increase the rate of moisture di~sipation from the panels, by evaporation at the walls 22 bounding the channels 18. Additiona~ly, the cutting removes the smooth, high-density outer film formed upon extrusion and exposes a surface much more favorable to the dissipation of water and moisture.
It has been ~ound that the foam material at the rib sections 16 is stronger, more rigid, and more deformation resistant than is the material 24 beneath the grooveq or valleys 18. The polystyrene foam panels 14 are butted together along the longitudinal side edges 30 thereof. The ends 32 of the panels also are butted together. The thickness dimension selected for the foam panels 14 is governed by the degree of in~ulating quality desired, but typically would be of the order of one to six inches thick. The extruded polystyrene foam is of the enclosed cell variety to prevent moisture penetration. the foam panels 14 by way of illustration are two feet by four feet, but the 3 dlmen~ions are not critical. The lengths could be nine Peet, or a~ much as sixteen feet, while the width could be from as little as sixteen inches, to perhaps a~ much as four feet. Product ~ize i~ not a critical factor, but handleability is. In windy area~ the panels must 32,461A-F -8- ~

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~ , . , ,.;' ' ' , ~290~30 not be so large as to be blown from a roof before the paving blocks are applied to hold them down.
A plastic film lamination 34 is seoured to the lower surface o~ each foam insulation panel 14. The film 34 may be adhesively secured to the foam, or may be heat bonded thereto. In one preferred example of ' the invention the film 34 comprises LLDPE (linear low density polyethylene) (1.7 mils) plus EVA (ethylene-vinyl acetate) (0.3 mil). Upon heating, the film is'readily softened to fuse tenaciously to the foam.
There may also be a certain degree of softening of the foam which enhances the adherence~
15Paving blocks 36 (typically made of concrete) are laid directly on top of the foam panels 14. The paving block~ 36 conveniently are two feet square and -, two inches thick, and are not necessarily reinforced. '~
Other dimensions can be used, such as eight inches by sixteen inches; and reinforcement of the concrete can be used if desired. The concrete blocks 36 are simply butted against one another, and preferably are laid so that the butted junctions do not coincide or register with the butted junctions of the underlying foam panels 14.
The exploded, fragmentary perspective view of Figure 3 i~ similar to Figure 1 and emphasizes the adherence of the film 24 to the underside of the panel 14, and the non-securement of other parts to one another, and shows the crater-like ~urface at walls bounding the cut-out channels 18.
The poly~tyrene ~oam panel~,14 are,o,,f,,,,the", closed cell variety and are reasonably waterproof.
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~L29013~) However, constant presence o~ water will cause some water penetration and associated loss of insulating qualities. The film adhered or sealed to the bottom surface o~ the foam panels 14 inhibits water penetration o~ the foam. The alternating ribs 16 and recesses or valleys 18 in the upper sur~ace of the foam permit air circulation so that any rainwater or other mpisture on top of the panels is dissipated on hot, dry days. The increased surface provided by the crater-0 like formations 20 in the out channel surfaces 22enhances the rate oP water evaporation, as does the physical form of the exposed surface~ 22. As will be appreciated, sun shining on the pal;ing blocks will heat the air in the recesses and between the ribbed surfaces and the concrete paving blocks, thereby materially increasing the pressure of such air, thus augmenting the convection forces causing air to exit through the butted joints of the concrete paving blocks.
Moisture penetration of the foam panel, and resulting loss of insulating qualities, therefore, is substantially reduced by the present invention. The accumulation of water over time is alqo minimized. A
~ilm of water such as might lie between a flat topped foam insulation panel and a paver laid directly thereon would act as a vapor barrier to prevent drying out of the foam. With the present construction any film that ~ight lie between the tops of the ribs and the concrete 3 paving blocks is o~ minimal importance, since the sides 22 o~ the ribs 16 and the floors of the grooves or valleys 18 provide a large area ~ree of such film for drying o~ the foam. The exposed craters 20 further increase the area exposed, and otherwise augment the rate of moisture di~persion as compared with a skinned-.
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over surface. Furthermore, some heating of the paving blockq dissipates the water film as water vapor into the grooves or valleys between the ribs, from whence it circulates out though the butt joints between the paving blocks. The ribbed construction alqo facilitates drying of the undersurfaces of the paving blocks. This is important for reasons including the further constant wetness of the undersurfaces of the paving blocks causes the bottom surfaces thereof to spall off in a few years.
In conventional plaza construction using upside-down roof construction, pedestals are used for `
supporting the weight of the concrete paving blocks. ;~
Pedestals occupy space that could otherwise be used fur insulation, and hence do not add to the overall ~- ~ insulating qualities. In addition, the pede~tals are expen~ive, both in ~aterial cost and in labor of ; 20~ installation. In accordance with the present invention the costs of pedestals and the non-insulating area thereof are elîminated. The present construction is ~; not intended as a full substitute for plaza constructîon, but it can support rather considerable 25 ~weight, and iq fully suitable for foot traffic or for small vehicleq for maintenance. STYROFOAM~ insulation, for example, has a design compressive ~tre~ngth of about 25 pounds per square inch. If a safety factor of 5:1 i9 provided, then this reduces to 5 pounds per square 3 inch. A 24 by 24 inoh paving block has approximately 600 square in¢hes, which oover~ a like area of the pre~ent pla~tic foam insulation, but dlvided by two due ~ to the equal widths of the ribs and valleys. Thi~
_ _ 3~_ provide~ 300 square incheq of supporting area for a two ;~ ~oot by two foot paving block, which multiplied by the ~ 32,461A-F
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five pounds per square inch previously noted results in a total o~ 1500 pounds that can be applied to each paving block with a 5:1 safety factor against permanent deformation of the supporting STYROFOAM~ insulation due to creep and compressive fatigue. Probably an even greater total weight can be supported since, as previously noted, the foam plastic material in the ribs is stiffer, stronger, and more resistant to deformation than the foam plastic material in the valleys. Other foam plastic insulating materials have a compressive ~trength as low as 10 pounds per square inch, but with the 5:1 safety factor heretofore used as exemplary, ~;
each paving block can support 600 pounds with such foam plastic material Exemplary dimensions have heretofore been given for the rib width and spacing. However, these dimensions can vary widely. The ribs might be as 20~ little as 1/16th inch high, and the supporting area could be less than 50, percent i.e. the~ ribs could be~
~ ~ narrower than the intervening valléys.
;~ The present roofing system i9 highly des1rable 25~ ~for con~truction o~ insulated roofs in which a certain amount o~ traYfic or maintenance is anticipated.~ The present roof con9truction also is beneficial for use in~
roof oonstruotion below radio and TV antenna towers in cold climates. Icicles dropped from such towers readily penetrate gravel-topped roof constructions, initially damaging the membrane and/or underlying insulation and leaving them vulnerable to posqible further deterioration ~rom water and ice. The paving blocks sued in the present construction are not :

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, ~9013~1 --l3--penetrated by such icicles; no damage is caused by falling icicles.
A figure of 25 pounds per square foot compressive strength for polystyrene insulation has been given heretofore. This is a minimum figure, and the compressive strength typically will run on the order of 40 pounds per square inch. Such forces result in approximately 1/lOth inch deformation, and dimen~ions return to normal upon removal of the compressive ~orce if yield has not been reached.
The present roof system possesses all the advantages of prior "upside-down" insulated roof construction. However, in addition thereto water absorption by the insulation is markedly redu^ed by the ~`
water-impervious ~ilm bonded to the lower surface of the insulation, and by the ribbed upper sur~ace which allows drying of the insulation and the underside of ~20 the paving blocks on warm, dry days. The rate at which water vaporizes from the channelq is enhanced by the added surface provided by the cutting out of sections from the plastic panels, and by the physical form presented by the mechanioally cut sur~aces defining the channels. When the waterproofing membrane applied to the top of the roof deck is a bituminous built-up laminated ~tructure, the membrane is necessarily ~eoured to the deck. However, in instances where a polymeri¢ qheet iq used, it can be applied loo~e over the surface of the deck, and the entire structure is held down by the weight o~ the paving block~.
The specific example of the invention as herein ~35 shown~and described iq for illustrative purposes only.

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~' ' ~, ''` ' ',, ' . , ~;~90~L30 Various changes in structure will no doubt occur to those skilled in the art, and will be understood as forming a part of the present invention insofar as such modifications fall within the spirit and scope of the appended claimsO

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Claims (9)

1. A roofing system of the type including a roof deck, a waterproof membrane above said roof deck, and a plurality of panels of foam plastic insulation overlying said waterproof membrane, characterized by the combination of:
(a) each of said foam plastic insulation panels having bounding perimetric edges and edge surfaces and having a planar lower surface and a plurality of flat-topped, parallel, raised, elongated ribs on an upper face thereof, and spaced part by grooves, (b) said ribs being integral with said panels and defining zonal sectors which are stiffer, stronger, and more resistant to deformation than a remainder of each panel, (c) said grooves in said panels comprising channels including bounding sidewalls and base walls, and said grooves sidewalls being common to said ribs' sidewalls, (d) side bounding sidewalls and said base walls being formed with crater-like recesses in exposed surfaces thereof and opening outwardly of said walls, (e) said ribs having tops forming a discontinuous planar surface substantially parallel to 32,461A-F -15-said lower surface, (f) a waterproof plastic film having peripheral edges coincident with said bounding perimetric edges of a respective panel and being coextensive with and bonded to only the lower surface thereof, and resting on said waterproof membrane in an unsecured, face-to-face contacting relation, (g) each of said panels being otherwise free of plastic film and exposed to ambient air for evaporation of moisture, (h) said plurality of panels being in substantially abutting relation at edges thereof, and (i) a plurality of paving panels carried on said foam plastic insulation panels and resting on said rib top discontinuous planar surface.

2. The roofing system of Claim 1 wherein the foam insulation panels have grooves and ribs formed by extrusion.

3. The roofing system of Claim 1 wherein the foam insulation panels have grooves and ribs formed by excision of laterally-spaced elongated, lineal sections from said panels transversely thereof.

4. The roofing system of Claim 1 wherein the foam insulation panels have grooves and ribs partly formed by extrusion and partly formed by excision.

5. The roofing system of Claim 1 wherein the paving panels are concrete paving panels.

6. A roofing system as set forth in Claim 1 wherein said recesses constitute cell portions of said foam plastic panel and originate interior zones thereof 32,461A-F -16-and are exposed upon excised removal of sections from said panels, said bounding sidewalls and said base walls with said recesses formed therein defining faces presented outwardly, each said face having a total surface area, including surface area embraced by said crater-like recesses, which is greater than an area delineated by perimetric borders of said walls bounding said channels, thereby to increase an effective rate of evaporation of moisture from said panel at said walls bounding said channels.

7. A roofing system as set forth in Claim 1 wherein said plastic film is heat bonded to said lower surface of each said panels.

8. A roofing system as set forth in Claim 7 wherein said film is a composite film having a portion heat softened to fuse said film to said foam panels.

9. A roofing system as set forth in Claim 8 wherein said film comprises low density polyethylene and ethylene-vinyl acetate.

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