Tapered roofing membrane

Novel roof membranes for providing improved lap joints with adjacent roof membranes, wherein opposed edges of the adjacent membranes for the lap joint are tapered.

BACKGROUND OF THE INVENTION 
Various roof membranes are well-known in the art, the most commonly used 
being so-called single ply materials. In general, these single ply 
materials may be separated into four classes: modified bitumens; 
thermoplastics; elastomerics; and uncured elastomers. The modified bitumen 
group includes various membranes having an asphalt or coal tar content in 
them. They may also contain polymer additives or modifiers as well as 
various types of reinforcement (either within the membrane or its 
surface). The thermoplastic-type membranes are primarily polyvinyl 
chloride (PVC) or any sheet which has PVC as a principal polymer. They 
also include other thermoplastic polymers alloyed with PVC. The elastomers 
are predominantly ethylene propylene diene monomer (EPDM) with neoprene 
following in the order of usage. The materials are essentially thermosets 
or cured (or vulcanized) membranes which cannot be welded together. They 
can only be spliced with contact or tape adhesives. The uncured elastomers 
are materials which come to the roof in a thermoplastic state and can be 
solvent or heat welded for lap joint construction. They slowly cure or 
cross-link due to the sun's radiation and become elastomers in place, on 
the roof. 
Since these general classes of roofing membranes are well-known and per se 
comprise no part of this invention, they need not be described in greater 
detail. 
Generally, roof membranes can be used in four different types of roof 
system assemblies: loose laid/ballasted; partially adhered (or 
mechanically attached); fully adhered; and the protected roof membrane 
assembly. 
Irrespective of the means of installation, where the membrane is of 
insufficient size to cover the roof, it will be appreciated that two or 
more membranes must be employed. For optimum protection against moisture 
and/or other environmental conditions, these multiple membranes should be 
seamed together. While the membranes could be butted together along 
adjacent edges and then sealed, the most efficacious way is to provide a 
lap joint wherein one edge of a membrane covers or overlaps the adjacent 
edge of another membrane. 
the present invention relates to improved construction of a roof membrane, 
e.g. a previously known membrane, to provide a superior lap joint between 
two adjacent membranes. Since, as mentioned earlier, EPDM and other 
elastomers can only be seamed or spliced with contact or tape adhesives, 
the invention is particularly directed to roofing membranes of this 
description and will accordingly be discussed hereinafter for purposes of 
illustration by reference thereto. In recent years, EPDM has become very 
popular as a roof membrane. According to the "1984 Handbook of Single-Ply 
Roofing Systems", published by Harcourt Brace Jovanovich Publications, 
there were nineteen (19) different manufacturers offering fifty-one (51) 
different EPDM membranes. 
by way of illustration, mention may be made of the "POLYKEN" (trademark of 
The Kendall Company) Roofing Systems utilizing a black EPDM 45 mils thick, 
having a weight/sq. ft. of 0.28 lb, and commercially available in 7, 10, 
20, 30, 40 and 100 foot widths. Irrespective of the system of installation 
and the insulation or other substrate on which it is laid, adjacent sheets 
should be lap joined, e.g. with a tape which of course should be 
two-faced. 
Pressure-sensitive adhesives of known formulation are particularly suitable 
for this purpose, an especially useful one being a butyl rubber-based 
adhesive. The tape may comprise a suitable support sheet having an 
adhesive layer on each surface or it may comprise a single adhesive layer 
of of appropriate thickness, e.g. on the order of 40 mils. Preferably, a 
release sheet is provided on at least one surface so that the tape may be 
provided in roll form. 
If found desirable to do so, the periphery of the membrane may be provided 
with a primer coat to increase cohesion with the particular tape employed. 
However, when employing rubber-rubber bonds, that is, when a butyl rubber 
or other rubber-based tape is employed with an EPDM membrane, such primer 
coatings have not been found to be necessary. 
An EPDM membrane of the foregoing description may be installed by any of 
the aforementioned systems, namely, loose-laid/ballast, partial 
attachment, fully adhered, or by protective membrane roofing assembly, as 
desired. It may be employed for re-roofing or as a new roofing over 
various insulation materials including perlite, urethane, wood fiber, 
fiberglass, expanded polystyrene, composite boards, cellular glass, 
extruded polystyrene, and the like. 
Regardless of the method of installation, if a single sheet is not 
sufficient to cover the roof, a lap joint will be made with one or more 
adjacent sheets. If two or more sheets of sufficient length are to be laid 
side by side, one lateral edge of one sheet will overlap the adjacent 
lateral edge of the next adjacent sheet. In like manner, if two (or more) 
sheets are to be laid end to end, the end portions of adjacent sheets will 
provide a lap joint, e.g. laying the trailing end portion of one sheet 
over the leading end portion of the next adjacent sheet. In any event, the 
lap joint will typically be on the order of at least three inches. 
Following the laying of the membranes in the foregoing manner, the 
overlapping portion is then peeled back, a roll of the two-sided 
pressure-sensitive tape (typically with a release sheet on one side) is 
then adhered to the exposed surface of the underlying sheet edge, after 
which the release sheet is removed from the free surface of the tape and 
the top sheet is then repositioned so that the top (free) surface of the 
tape is adhered to the underside of the overlapping sheet, thereby 
completing the lap joint. 
While in theory, the lap joint seal should be entirely satisfactory over a 
prescribed time period and under the expected or usual environmental 
conditions, it has been found that this is not always the case. 
Specifically, it has been found that, following installation of the roofing 
system, environmental forces such as temperature changes and wind drag 
cause certain degradative changes in the lap joint. 
These degradative changes are manifested as random separations or puckering 
along the lap joint which may be termed "fish-mouth" resulting from 
Poisson's effect. These fish-mouth separations permit moisture to enter, 
which in turn will cause rotting and/or other adverse effects on the 
underlying roof material. 
The present invention is directed to the task of materially reducing if not 
obviating the fish-mouth problem so as to increase substantially the 
longevity of the lap joint seal and thus materially increase the time 
period between installation and repair of the lap joint. 
BRIEF DESCRIPTION OF THE INVENTION 
In accordance with the present invention, the aforementioned task is solved 
if opposed edges of the lap joint membranes are tapered.

DETAILED DESCRIPTION OF THE INVENTION 
As mentioned, the present invention is directed to improving the seaming 
together of adjacent roof membranes against degradative environmental 
forces, particularly improving lap joint seals when the adjacent membranes 
are installed in overlapping relationship, the essence of the invention 
being providing adjacent membranes for the lap joint where opposed edges 
are tapered rather than being the conventional perpendicular cut of the 
roofing tapes heretofore employed. 
When two or more membranes are laid down to cover the roof area, it is 
customary to seal adjacent membranes together in overlapping relationship 
(called a "lap joint") in order to get a good protective seal which 
moisture cannot penetrate. A particularly efficacious way of perfecting 
this seal, particularly with EPDM or similar elastomer membranes is by 
"sandwiching" a two-faced adhesive tape between the superposed 
(overlapping) edges of adjacent membranes. 
The conventional roof membranes heretofore employed for this purpose have 
straight or perpendicular edges which it has been found provide a void in 
the lamination extending along the length (long dimension) of the lap 
joint. The imperfect lamination in time permits the random occurrence of 
fish-mouth (resulting from Poisson's effect), which is seen visually as a 
"puckered" separation or delamination which can be likened to a fish 
mouth. 
When employing tapered membranes in the lap joint in accordance with the 
present invention, the occurrence of this phenomenon is materially 
inhibited if not totally obviated during the projected life of the roofing 
system. 
The present invention will be best understood by reference to the 
accompanying drawings. 
FIG. 1 illustrates a lap joint of the prior art between two membranes 10a 
and 10b. As shown, membrane 10a has lateral edges 16a and an end 18a; 
while membrane 10b has corresponding edges 16b and an end 18b. The 
respective ends are shown to be secured in overlapping relationship by 
adhesive layer 12 to provide a lap joint in the end-to-end positioning 
whose dimensions are defined by the width of the respective membranes and 
the distance between the overlapping ends, 18a and 18b. 
The lower adherend 10b will deform laterally in time under the influence of 
Poisson's effect, whereas the upper adherend is not under this effect. 
Consequently, since they are bonded together, the end portion of the upper 
adherend wants to move with the lower adherend. However, the only way the 
upper adherend can move is to fold, resulting in a plurality of random 
"puckered" separations along the lap joint seam which are defined, because 
of their appearance (and the relationship to Poisson) as "fish-mouth". One 
such separation 14 is shown in the drawing. 
In accordance with the present invention, the fish-mouth problem is greatly 
inhibited if not precluded entirely by the tapered membrane structure as 
shown in FIG. 2. As shown therein, membrane 10 has tapered lateral edges 
16 and ends 18, only one of which ends is shown in the fragmented view. It 
will of course be understood theroetically only the edge or end portion 
forming the lap joint need by tapered. However, for versatility in use, 
all peripheral portions are preferably tapered, as shown in the drawing. 
FIGS. 3 and 4 are top and bottom plan views, showing two similar membranes 
of this invention, i.e. membranes as illustrated in FIG. 2, designated as 
10 and 10.sup.1 with their ends 18 and 18.sup.1, overlapping to form the 
lap joint. With reference to FIGS. 5-6, the lap joint is provided by two 
faced-adhesive 12 consisting of sheet material 20 coated on either side 
with suitable adhesive layer 22, e.g. a rubber-based pressure sensitive 
adhesive. 
The adhesive which may be employed in the lap joints may be of per se known 
composition and dimensions. As examples of adhesives which are typically 
employed, mention may be made of rubber-based adhesives, acrylic 
adhesives, mastic compounds and the like. Of particular interest in the 
practice of this invention are the rubber-based adhesives which, are 
previoulsy mentioned, are most useful in providing lap joints with EPDM 
membranes. 
Preferably, use is made of two-faced pressure sensitive adhesive tape which 
may vary in thickness and will typically be on the order of at least 
twenty mils thick. The width of the tape may also vary, and will generally 
be at least two inches. 
Although the two-faced tape may be provided by coating an adhesive layer of 
desired thickness on both sides of a polyolefin or other suitable backing 
sheet, if the adhesive possesses the requisite dimensional stability, the 
backing sheet can be eliminated so that the tape is in the form of a 
monolayer of adhesive. It will of course be appreciated that in packaging, 
means should be provided to prevent sticking of the adhesive to itself or 
to any other adherend prior to use. The most efficacious way to do this is 
to package the tape in roll form with a release sheet engaging one surface 
thereof so that on unwinding, both adhesive surfaces can be protected by 
the release sheet. 
The degree of taper which may be employed may vary. At least some 
beneficial results may be obtained with an angle of the taper as great as 
40.degree. to the horizontal. However, for optimum results, the degree of 
taper should be no greater than 30.degree.. As will be appreciated, the 
minimum angle of taper is in part dependent upon the thickness of the 
tape. That is to say, the smallest degree of taper reasonably obtainable 
is directly proportional to the thickness of the tape. While this 
thickness, may for example vary from on the order of 5 mils to on the 
order of 120 mils, it would be extremely difficult if not impossible to 
provide a relatively small angle of taper on say, a 5 mil tape. 
Conversely, this would be quite easy on, say, a 120 mil thick tape. 
Consequently, it is not possible to state quantitatively the smallest 
degree of taper without stating the thickness of the tape. It can be 
however, be stated as a general proposition that for optimum results, the 
degree of taper to be employed would generally be in excess of about 10 to 
the horizontal. To achieve this taper, at least with conventional 
production equipment, tape 10 should preferably have a thickness of at 
least 25 mils. 
the method of providing the taper is not critical. It may, for example, be 
provided by conventional slitting devices having a pair of knives with 
adjustable angle positioned on a rotatable shaft at the desired angle, as 
described in detail in the aforementioned parent application, Ser. No. 
867,110, filed May 23, 1986, relating to tapered tapes for wrapping metal 
objects, particularly those intended for inground implantation. As 
described therein and shown in the accompanying illustrative drawings, a 
web of tape may be advanced beneath the knives onto a rotating roller 
provided with a series of spaced grooves. Each knife is positioned over 
one of these grooves preselected according to the desired width for the 
tape. Following the cutting or slitting operation, the cut portions of the 
web are advanced to a roll-up operation. 
In the following illustrative examples demonstrating the improvements 
obtainable in accordance with the present invention pieces of membranes 
("coupons") were used for purposes of ease of handling and testing and 
analysis in the laboratory. 
EXAMPLE 1 
Samples of a 45 mil EPDM roofing membrane coupons about 3 inches in width 
and about 5 inches in length were bonded with a conventional 40 mil 
two-faced rubber-based lap seam adhesive tape to provide a lap joint 
(overlap) of about 2.57 inches. In one set of samples (test), the opposed 
leading and trailing edges, respectively, of the two membrane coupons for 
the lap seam were tapered at an angle of 30 degrees (as previously 
described and shown in the drawing.) A similar set of samples was prepared 
(control), except that the edges of the coupon membranes were conventional 
perpendicular cut. One set of the samples was aged at room temperature for 
one week; and a second set was subjected to accelerated aging at 
160.degree. F. for one week. The results for the room temperature 
experiments revealed improvements as high as 41% in ultimate load time and 
44% in "fish mouth" for the tapered (test) lap joint; and 13% in ultimate 
load time and 28% in "fish mouth" for the accelerated aging experiment. 
EXAMPLE 2 
In order to assess the effect of taper on overlap displacements, samples 
similar to the ones described in the preceding example were used, except 
the overlap length was reduced to 3/8 inch. This was done in order to 
increase the magnitude of cleavage stresses and to obtain more noticeable 
results. Four samples prepared in this fashion were tested. The test 
results indicated that the extent of adherend separation in the 
longitudinal direction was reduced with the tapered lap joint tape by 
about 45% and the out-of-plane adherend separation (in the direction 
normal to the overlap) was reduced 47%. 
From the foregoing test results it will thus be observed that with a given 
load-bearing, "fish-mouth" or separation in the lap joint which will 
inherently result with perpendicular cut membranes can be elimianted by 
use of the tapered membranes of this invention. Alternatively or stated 
another way, with the tapered tape, the load-bearing capacity of the lap 
joint can be materially increased before meaningful separation can occur. 
By way of recapitulation, from the foregoing description and illustrative 
examples, it will be seen that the present invention employing tapered 
roof membranes in lieu of the conventional perpendicular cut ones will 
provide very significant improvements in load-bearing capacity and/or 
resistance to separation of the lap joint seam. While, for purposes of 
illustration reference has been made to EPDM roof membranes and to the 
two-faced pressure sensitive adhesive tapes for seaming the lap joint, it 
is to be expressly understood that the invention is not restricted 
thereto. Since the present invention may be regarded as a modification or 
improvement in the physical structure of the membranes, it will be 
appreciated that the chemistry, i.e. the chemical composition of the 
membrane and/or seaming adhesive is not material. Irrespective of the 
chemical nature of the membranes, the material employed to seam them 
together and the manner of installation, the tapered membranes will 
provide significant stability of the lap joint against the degradative 
environmental forces. 
In order to define unequivocally the relationship of the adjacent membranes 
in the lap joint in accordance with this invention, i.e. which sides of 
the tapered membranes are in opposed (superposed) relationship, it is 
appropriate to define the taper as used herein and in the appended claims. 
If one visualizes a sheet material having two opposed sides or major 
surfaces, the taper may be defined as cutting the peripheral edge(s) at an 
angle from the first major surface to the opposite surface so that the 
first major surface has smaller surface area provided by the angle of the 
taper. 
In preparing the lap joint, the first major surfaces having the smaller 
surface area will provide the outer surfaces of the lap joint with the 
respective major surfaces of greater surface area being superposition. 
Since certain changes may be made without departing from the scope of the 
invention herein described, it is intended that all matter contained in 
the foregoing description, including the examples, shall be taken as 
illustrative and not in a limiting sense.