CA2015212A1 - Underlay for a roof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
An underlay in the form of a rectangular tile for supporting and positioning slates in constructing a roof. One end of the underlay defining an overlap portion for overlying the slates of the roof and directing moisture thereover. The underlay also including a tapered recess formation, which in the preferred embodiment is in the form of a plurality of tapered channels, for supporting the slates and for directing moisture to the overlap portion. The channels including at one end a shoulder formation presenting abutting surfaces which position the underlay and slates on the roof, conserving the number of slates used.

Description

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Field of the Invention This invention relates to improvements in an underlay for a ,, roof, and, more particularly, to an underlay in the form oP a tile for supporting and positioning the roof slates thereabove in a manner to conserve the number of roo~ slate~ used in constructing the roof, yet protect the integrity of the sub-roof structure from moisture penetration.
More particularly, this proposal is directed towards an improved method of laying a roof wherein a plurality of the underlays of this invention are positionPd on the 3ub-roof ~tructure in side-by side relation and a plurality of conventional natural slate~, man-made slate-like products, or any other roof product~ that imitate a slate-like appearance, hereinafter referred to as slates, are laid in side-by-side relation overlying and . ~ :. ~ . . :: ~
supported by the plurality of underlays; the combined arrangement of slates and underlays secured to the sub-roof structure by nails.
: . :, Further, the combined arrangement of slates and underlays form a -cour~e, and the roof is completed by laying subsequent like courses :~
in overlapping arrangement to one another; the position of : .. ..: ;~ .
subsequent courses being determined by the underlay of this ;

invention.
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Moreover such method of laying a roof using the underlay of : ::::
: the invention requireslless slates in the actual construction and laying of the roof than conventional means yet eliminates penetration by moisture of the roof which could damage the integrity of the sub-roof ~tructure.
Ba~ground o~ the In~e ion ,........................................................................... .... ... ... ... .................................... , ., .: .
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2~32~ 2 Roofs cons~ructed with the underlays to which this invention relates typically comprise, in combination with a plurality of tha underlays, a plurality of 61ates which substantially overly and are supported by the plurality of underlays. Such underlays and slates are combined to form courses with adjacent courses arranged in overlapping relati.on to one another to complete the roof.
It is assential that an underlay for a roof provide suficient support for the overlying slates to prevent breaking o the slates when a load is applied thereto, such as, ~or example, a construction worker installing ox repairing the roof, positioning the overlying slates conserving the number of slates used in constructing the roof and acilitating the installation of ~ame, yet also act as a water barrier to prevent moisture penetration of the roof which damages the integrity of the sub-roof structure.
One underlay for a roof is disclosed in U.S.P. 3,232,020 wherein an elongated aluminum tile or pan acts as an underlay or a course or layer of shake shingles which axe secured at one end thereof by nails within an elongated recess formed by a flange along one end of the tile or underlay.
In laying a roo~ as disclosed in U.S.P. 3,232,020 there is provided a three inch overlap between successive courses of the elongated tiles and associated shake shinyles, which results in a twelve inch `exposure of the fiteèn inch wide tiles (more specifically the associated shake shingles supported thereabo~e) which providas the desired reduction o materials used and weight of the roof structure.

Such a tile or underlay as provided for by U.S.P~ 3,232,020, ~ ~
however, cannot provide adequate support for the overlying shake ~ ;
shingles ~nd could bend or break when a load is applied thereto. ~ ~
Another patent of interest is that of U.S.P. 3,415,029. This ~-patent discloses a shingle for a roof structure which is comprised of four slates secured to a backing sheet. The backin~ sheet is composed of asphalt, asbe~tos, and felt without filters.
The slates in ~.S.P. 3,415,029, are positioned side by side and in alignment with one another on the backing sheet. Further, the slates only cover the lower portion of the backing ~heet while ~he upper portion remains uncovered; the slates are po~itioned to overlap the backing sheet on one side and along one edye thereof.
S~/~119 -Such a combination as provided for by U.S.P. 3,415,029, does ~
not effectively reduce the number of slates required nor provide an ` -effectiva ~eal against moisture penetration which could result in damage to the sub-roof structure.
Ob~9cts o~ the Xnvention It i~ therefore a principal object of this invention to provide an improved underlay for a roof lending considerable support to the overlying slates, acts as a barrier for the prevention of moisture penetration to the sub-roof structure, and yet allows for a sig~ifican't reduction in the number of slates used when constructing a roof resulting in substantial cost savings. ;
More particularly, it is an object of this invention to provide an underlay in the form of a tile which is both durable and long-lived such that the life expectancy of the resulting roof, ''" ' ''"', .

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comprising underlays and, particularly, conventional natural slating, man-made slate-like products, or any other products khat imitate a slate-like appearance, can be of the order of thirty years or greater.
Fe ture~ of the Invention One feature of this invention resides in providing an underlay in the form of a tile comprising a tapered recess formation, which, in the preferred embodiment, comprises a plurality of parallel tapered channel formations providing considerable support to the overlying slates. Such support provided by the underlays to the overlying slates prevents warping or cracking of same upon a given load being applied to the roof by, for example, a worker on the roof installing or repairing same.
It is a further feature of the underlay of this invention to provide a moisture penetration barrier between the slates and the roof ~ase or sub-roof structure. In par~icular, the underlay of this invention comprises, in addition to the recess formation or plurality of channels, an overlap portion for carrying possible moisture over nail holeæ created by the nails which secure the 2~ slates and underlay to the sub-roof structure preventing penetration by moisture to the sub-roof structure and preserving the integrity of same.
~ Furthex, it is a feature of this invention that the!underlay include a shoulder formation presented between the overlay portion and the recess formation, or, more particularly, the plurality of channel formations of the preferred embodiment. The shoulder formation presents a first abutting surface to the respective . ..

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channel formations, and a second abutting surface to the overlap portion of the underlay. Such abutting surfaces act to po~ition an adjacent course of underlays and corresponding overlying slate~
In particular, the first abutting surface engages an underlay of an adjacent course, and the second abu~ting surface engages the corresponding slate of such course.
It is yet a urther feature of this invention that the underlay be made of lightweight high-density polyethylene, having a substantially black appearance in o:rder to maintain high ultra~
violet resistance, aiding in the prevention of breakdown of the underlay through exposure to sunlight and other environmental concerns throughout the lifetime of the roof.
Further, it is a feature of this invention to construct the underlay so that a high resistance to temperature variance is provided so that the underlay can exist in a roof with slates without affecting its performance between temperature ranges of -: 60C to +200C.
It is also a feature of this invention that the underlay bealkali resistant, and substantially indestructible during installation, and life expectancy of the roof.
Finally, it is a feature of this invention to provide a method of installing a roof wherein a plurality of underlays o ~his invention are~first positionéd on the sub-roof structure !in side-by-side relation and a plurality of slates are laid in side-by-side relation overlying and supported by the plurality of underlays and such combination of slates and underlays secured to the sub--roof structure by nails and forming a first course. Subsequent like .. .. . .

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courses are positioned in relation to ~he first or an adjacent course by the abutting surfaces of the shoulder formations of the channel form~tions of the underlays of such subsequent course and the subsequent courses are placed in overlapping relation to the first or an adjacent course therebelow to complete the roof. ~
_~ ription of the Invention ~ .;:
Figure 1 of the drawings illustrates the conventional means of installing a roof utilizing natural slating, man~made slate-like . .~ .;
products, or any other roof products that imitate a slate-like appearance; ; :
Figure 2 illustrates a roof stxucture comprising the slates used in the conventional roof illustrated in Figure l, and the ;~
underlay of the invention;
Figure 3 is a cro~s-sectional view taken along lines 3-3 of Figure 2 illustrating the overlapping relationship between the underlay of the invention and the slates when arranged in courses;
Figure 4 is a perspective view of the underlay taken ~rom a .
point uppermost and to the right thereof; : .
Figure 5 i8 a front elevational view of a section of the underlay as illustrated in Figure 4; and Figure 6 i~ a perspective view of the underlay taken from a point lowermost and to the left thereof.
A con~entional'rdof 10 for a building 12 is illustrated in Figure 1, and comprises a sub-roof structure 14 consisting of ~; ~ .;.
plywood 16 over which is laid an asphalt impregnated roofing felt 18 to which the slates 20 are secured.

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Sub~roof structure 14 also includes a cant strip 22 extending along the lowermost edge of plywood 16. Cant strip 22 supports thereover a metal drip edge 24 for directing moisture or run-off water to an eavestrough 26. Eavestrough 26 is, in turn, secured along one side thereof to a fascia board 28 which is secured along its upper edge to plywood 16 and along its opposing edge to building 12 by means of a soffit 30.
Slates 20 used for roof 10, as shown in Figure 1, provi~e for an attracti~e, yet durable roof structure having a long life expectancy -typically 30 years or greater. The weight o~ the slates is considerable, however. In particular, slates 20 have approximate dimensions 24" by 12" and weigh approximately 3.~ lbs.
each. In a conventional roof, as illustrated in Figure 1, approximately 123 slates are required per 100 square feet of roof.
With the overlap of the slates shown in Figure 1, and hereinafter detailed, the weight per installed square foot of roof is approximately 4.~ lbs. Further, a great number of slates are required in in~talling roof 10. Since each slate can be relatively expensive, the cost of installing a roof 10l taking into account labour, can be prohibitive.
In conventional methods of installing roof 10 utilizing slates 20 a plurality of slates are laid hori~ontally in a side-by-side relation on asphal~ impregnated roofing felt;18 forming à ~irst course 32. As ~een in Figure 1, the lowermost edges 36 of slates 20 which form first course 32 are coextensive with the lowermost : :. : :, edge of asphalt impregnated roofing felt 18 and, together with the feltr overlap metal drip edge 24 and corresponding cant strip 22.
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2 ~ 2 The first horizontally disposed course 32 of slates 20 is secured to plywood 16 of sub-roof structure 14 by mean~ o~ nails 38~ In a , ~ ., ...,:~
conventional roof two nails per slate are used.
After the first horizontal course 32 of slates 20 is secured ~ ;
to plywood 16 of sub-roof structure 14 a second course 40 of slates ~ ~;
is laid. In order to position the second course, and all ~ ~
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subsequ~nt courses, horizontal chalk lines 42 are drawn on asphalt impregnated felt 16. In particular, each line is separated from the other by a distance of approximately 9-13/16~ with the first lQ chalk line being set back from the lowermost edge of the asphalt impregnated felt 18 by a distance of 14". The second and all subsequent courses of slates are positioned by aligning the up~ermiost edges 44 of slates 20 with chalk lines 42, as best illustrated in Figure 1 and hereinafter explained.
In particular, second course 40 of slates 20 is positioned in overlapping relation to first course 32. Slates 20 of second course 40 are arranged vertically in side-by-side relation and overlap the slates of first cours~ 32 such that the lowermiost edges 46 thereof are coextensive to the lowermost edges 36 of the slates of ~irst course 32. Further, slates 20 of course 40 are half-, :
bonded to the slates of course 32, that is a given slate of courie ;~
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40 overlaps equally two adjacent slates of course 32. Againl each ; ~ ~
slate 20 df course 40 i's secured to plywood 16 of sub-roof ~ ~ ;
structure 14 by means of nails 38, and particularly, two nails per ~ ~ -~5 slate are used. `~
A third course 48 of slates 20 is laid by placing such slates `~
in vertical side-by-side relation and by aligning the uppermost , ~:
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edges 44 of slate~ 20 of course 48 with the correspondiny chalk line 42 of asphalt impregnated felt 18. By aligning uppermost edges 44 of slates 20 of course 48 with the corresponding chalk line 4~ of fel~ 18, the slates of course 48 overlap the slates of course 40 by a~pproximately 14". Slates 20 of course 48 are half-bonded to the slates of course 40. Again, each slate of course 48 i8 secured to plywood 16 of sub-roof structure 14 by two nails 38.
Subsequent courses of slates are laid half-bonded to the pre~ious course in a similar manner as course 48 is laid in relation to course 40 until the roof is covered.
It can be appreciated from Figure 1 that water impinging on slates 20 of roof 10 runs over the top surface of slates 20 under gravity towards eavestrough 26. Such moisture can penetrate the boundary 50 between two adjacent slates of a given course. Once boundary 50 is penetrated moisture runs between overlapping courses over the top surface of the slates of the ~ourse therebelow under gravity in its decent towards eave~trough 26. Further, once moisture has penetrated boundary 50 and runs between overlapping courses it can encountar in its decent to the eavestrough the nail holes created by nails 38 which secure the slates to plywood 16 of sub-roof structure 14. Moisture encountering the nail holes can penetrate through asphalt impregnated fe`lt 18 to plywiood 16 damag~ng the integrity of the sub-roof structure.
Not only does a con~entLonal roof as illustrated in Figure 1 not prevent moisture penetration to the sub-roof structure, damaging the integrity thereof, but also, because of the : " ~,.` ,, . .',"`',';

2 ~ ~ 5 ~ ~ 2 . ~ . ,, considerable overlap of adjacent courses, requires a great number , ~ :
of slates to be used to complete the roof. Approximately 65% of the ~op surface of slates 20 of a conventional roof i~ hidden or covered by an overlying course. Only 35% of the top surface of slates 20 is exposed to the environment. Consequently, in a conventional roof, approximately 123 slates are used per 100 square feet with a weight per square foot of installed roof approximately 4.4 lbs. Such a roof takes considerable time to construct and is costly due to the high cost of individual slates 20 and labour involved.
A roof 52, illustrated in Figure 2, utilizing an underlay 54 of this invention effectively prevents moist~lre from penetrating to the sub-roof structure, and greatly increa~es the amount of exposure of the top surface of slates 20 to the environment. In particular 85% o~ the top surface of slate~ 20 is exposed.
,: , Consequently, the number of slates required per 100 square feet is only 66 with ~he weight per square foot being approximately 2.5 lbs. The cost savings in material can be appreciated.
Underlay 54 of this invention used in cons~ructing roof 52 is best illu~trated in Figures 4, 5, and 6. In the preferred embodiment the underl~y is in the form of a rectangular tile 56 having dimensions approximately 23~" by 13", a size appropriate for use with slatesl20 ha~ingi!dimènsions of approximately 2~" x 12".
The underlay dimensions can be altered for a given roof, however, ; 25 dependent upon the slate ~i~e used for the roof construction.
Underlay 54 is preferably manufactured by, but not limited to, thermal forming or in~ection moulding. A light weight, high ~..:
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:, density polyethelene is preferably u6ed in the manuacture of underlay 54. Such material provides the necessary resistance ko ultra-violet radiation, is alkali resis~ant~ and has a great tolerance to témperature variance, between -60C to ~200C, allowing for the life expectancy of the underlay to be greater than 30 years and of the order of the life expectancy of slates 20.
Underlay 54, as best illustrated in Figures 4, 5, and 6, comprises a tapered recess formation or, more particularly, in the preferred embodiment, a plurality of parallel tapered channels 58 depending from the lower surface thereof. As best îllustrated in Figure 6 .'.. ~
each channel is tapered to form a substantially wedge-shaped ~:
configuration with the heel of the wedge in the form of a shoulder formation 60. ,' ., :..
Shoulder formation 60 of each channel 58 of underlay 54 . ;,: :.
presents a first abutting surface 62 to the lower surface of tile ',.';: `

5~ of underlay 54 and a second abutting surface 64 to lower surface :-`''.
66 of channel 58, as best illustrated in Figures 5 and 6. First abutting surface 62 and second abutting surface 64 of shoulder formation 60 present therebetween a substantially flat surface 6~. : -:.;
The abutting surfaces, 62 and 64, provide means, to position ,';`'~
underlays 54 and slates 20 of adjacent courses as will hereinafter .::~
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be explained. "'~
As best illust~ated in Figure 6 ùnderlay~54 in the form of a tile 56 presents a portion 70 of such tile extending beyond shoulder formations 60 of channels 58. Portion 70 of tile 56 extends over or overlaps an adjacent course of underlays 54 and .

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slates 20 position by abutting surfaces 62 and 64, as will hereinafter be explained.
Further, as best illustrated in Figures 4 and 6, at leas~ two channels 58 are interrupted by ~ubstantially flat portions 67 of tile 56 of underlay 54 in a region near the end of the tapering.
Flat portions 67 of tile 56 receive nails 38 when the underlays are secured to plywoad 16 of roof 52, as will hereinafter be explained.
The method of installing a roof 52 utilizing an underlay 54 is best illustrated in Figures 2 and 3. Basically, in constructing roof 52 a plurality of underlays are positioned horizontally in side-by-side relation with channels 58 disposed downwardly with lower surface 66 thereof resting on plywood 16 of sub-roof structure 14 and with overlap portion 70 pre~ented lowermost and ..:
overlying metal drip edge 24 and corresponding cant strip 22.
A plurality of slates 20 are then positioned horizon~ally in side-by-side relation and overlying the plurality of underlays 54 with lowermost edge 36 of such slateci in alignment with and ~; ;
coextensive with lowermost edge 72 presented by overlap portion 70 of underlays 54. In particular, plurality of slates 20 are horizontally positioned to overlie the plurality of underlays 54 in a half-bonded relation to form a first course 74.
Each slate 20 of first course 74 is secured to plywood 16 of ~ub-roof stxucture !!141 bylmëans of nails 38 whose position is determined by the location of portions 67 of underlay 54 therebelow; nails 38 pass through portions 67 and secure the undexlay between the slates and the plywood of the sub-roof ~ ~`
structure.

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2~5~2 As in the method of installing the conventional roof 10, illustrated in Figure 1, only two nails 38 are required per slate.
In the preferred embodiment of the invention 1~ galvanised roofers nails are used, depending on climatic conditions where the roof is constructed.
A second course 76 i8 then laid. Particularly, at least two :: :
underlays 54 are positioned in side-by-side relation with their ' ' overlap portions 70 overlying slates 20 of cour~e 74 therebelow and ~"~.,, with their channels 58 depending therebelow so that surfaces 66 of ~ ' ,:', channels 58 rest on plywood 16 of sub-roof structure 14, and, as ' '. ;:
best illustrated in Figure 3, surface3 68 of shoulder formations 60 ','',,';', rest on the upper surface of the underlays of cour3e 74. , " ', Placement of underlays 54 of second course 76 in relation to ~`",',',' the slates and underlays of course 74 is greatly facilitated by '~
first abutting surfaces 62 and second abutting surfaces 64 of :',''"~'', shoulder formations 60 of underlays 54. ',': '.,-,`,"
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Particularly, the underlays 54 of course 76 are positioned so , '~
that the respecti~e overlap portions 70 of underlays 54 extend over ',,~
slates 20 of course 74 as far~a~ permitted by abutting surfaces 62, ~:' , 64 of shoulder formations 60, and as best illustrated in Figure 3. ` ~:~
Basic,ally the first abutting surfaces 62 of shoulder formations 60 : :.
of underlays 54 of course 76 abut against uppermost edge~ 78 of ,~
sIates 20 ih course' 7~l and the second abutting surfaces 64 of ..
shoulder formations 60 of underlays 54 of course 76 abut against : ..::
~5 uppermost edges 80 of underlays 54 in course 74.
With the underlays 54 of course 76 of roof 52 positioned in :~ .
abutting relation with the slate~ and underlays of couxse 74, a ,.-:: ~ ...
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13 ''~-';','' 2~2~ 2 slate 20 is then positioned in a horizontal relation overlying underlays 54 of course 76 and with it~ lowermost edge 82 thereof extending slightly beyond the lowermost edges 84 of overlap portions 70 of underlays 54 of course 76.
5Further, slate 20 of course 76 is positioned so as to cover the boundary between adjacent underlays 54 of such course, and, more particularly, overlap in half-bonded relation to adjacent slates of course 74 therebelow. ;
Again, ~late 20 of cour~e 76 is secured to plywood 16 of ~ub-lGroof structure 14 by using nails 38 securing the underlays therebetween; the positioning of nails 38 being determined by portions 67 of the underlying underlays 54 of course 76. -Additional underlays required to complete course 76 are positioned as detailed above in side-by-side relation to those . ~, 15underlays of course 76 already laid, with additional slates, as required to complete course 76, positioned overlying the boundaries between adjacent underlays of course 76 and overlapping in half-bonded relation adjacent slates of course 74 th~rebelow.
Further courses of slates and underlays are laid in an 20identical manner to course 76 until roof 52 is completed.
In certain northern States, and Canada, governmental ~ ;~
regulations require that a roof be provided with an eaves protector 88, as illu~trated in Figure 2, to prevent the build-up of ice in ~
~ the~region of the bottom of the roof. Eaves protector 88, iE ;~-; 25required, i8 laid on plywood 16 of sub-roof structure 14 before the .
underlays of first course 74 are laid, and with one end thereof -~
overlying metal drip edge 24 and cant strip 22 of sub-roof .' ' ~

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2~ 2~2 structure 14. The other end of eaves protector 88 extends upwardly over the top surface of plywood 16 a distance as required by governmental relations, and typically of the order of 3 ~eet~ Once eaves protector 88 is in place roof 52 illustrated in Figure 2 is constructed as hereinbefore described.

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It can be appreciated from Figure 3, that the depth of channels 58 of underlays 54 is such that surfaces 66 of channels 58 rest on plywood 16. Further, overlap portion 70 rests on the upper surface of slates 20 of an adjacent course presented therebelow, and surfaces 68, pre~ented between abutting surfaces 62, and 64 of shoulder formations 60 of channels 58 of underlays 54, rest on the upper surface of the underlays of such course. The relationship of these surfaces to one another, together with the tapering of the channels provide~ support for the slate~ overlying the underlay~ of a given course. This ~upport can be appreciated during construction or repair of a roof where a load is applied to the slates of the roof by the weight of workers on the roof which, without such support, would normally resul~ in breakage or cracking of the ov rlying slates.
Roof 52, comprised of slates 20 and underlays 54 arranged in , overlapping courses, effectively prevents moisture from penetrating the roof to plywood 16 of sub-roof structure 14. In particular, any water impinging dn slates 20 and penetrating boundary 86 . ;.
between adjacent slates is collected in channels 58 of underlays S~. The moisture, or run-off water, under gravity collects in the ;; ~-~
heel of the wedge shaped channel formations, and, once full, spills ;~
out over the overlap portions 70 of the underlays to the upper 2 ~ ~
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surface of slates 20 presented by the adjacent course therebelow where it continues its decent to eavestrough 26. The overlap portions 70 of underlays 54, as best illustrated in Figure 2, effectively carry moisture over holes created by nails 38 preven~ing moisture from penetra~ing same to pl~wood 16 of sub-roof structure 14, preserving the integrity of the sub-roof structure. ~ ;
Finally, it can be appreciated that by using underlays 54 and ~ ~ `
the method of installing roof 52 in accordance with thi~ invention, and described above, that considexable savings in materials results.
In particular a roof lO constructed in the conventional manner, as illu~trated in Figure 1, using 24" x 12" slates, typically uses 123 slates per 100 square feet. The weight per square foot of roof is approximately 4.4 lbs, and upwards to approximately 12 lbs, dependent upon the material used.
In using the m~thod of installing a roof 52 described above for Figure 2 and utilizing the underlays of this invention the number of slates required per 100 square feet of roof is only 66, using 24" x 12" slates. The number of underlays used in constructing the roof structure illustrated in Figure 2 is 66 per 100 square feet. The weight per s~uare foot of roof is approximately 2.6 lbs., and upwards depending upon the material uæed. Basically, th'e ~eight per square foot is nearly halved.
Since the cost of manufacturing the underlays is ~ignificantly less than the cost of manufacturing a typical slate the overall savings in cost and materials can be appreciated.

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. , , Further, since the underlays provide abutting surfaces for positioning ~ame in relation to the next adjacent course of slates and underla~s, the time in which it takes to install the roof is considerably reduced. This again results in C08t savings a~ the ;~
number of workers required is less and the time ~pent installing a roof is greatly reduced.
While the preferred embodiment of this invention has been described and illustrated, modifications, variations or alternatives may be introduced or undertaken in the structure disclosed without departing from the spirit or ~cope of the ;~
invention as defined by the appended claims.
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Claims (26)

1. An underlay for a roof structure in the form of a tile with one end thereof defining an overlap portion and the opposite end thereof including therein a recess formation which is tapered in thickness in a direction extending away from said overlap portion, and said overlap portion and said recess formation presenting therebetween a shoulder formation.

2. An underlay according to claim 1 wherein said shoulder formation presents a first abutting surface to said overlap portion and presents a second abutting surface to said recess formation.

3. An underlay according to claim 1 wherein said shoulder formation presents a first abutting surface to said overlap portion, presents a second abutting surface to said recess formation, and presents a substantially flat surface therebetween.

4. An underlay according to claims 1, 2, or 3 wherein said recess formation is interrupted in its extent in a region near the end of said tapering by a substantially flat portion of said underlay.

5. An underlay according to claim 1 wherein said recess formation comprises a plurality of parallel spaced-apart channel formations tapered in thickness in a direction extending away from said overlap portion, and said overlap portion and each of said channel formations presenting therebetween a respective shoulder formation.

6. An underlay according to claim 5 wherein each of said respective shoulder formations presents a first abutting surface to said overlap portion and presents a second abutting surface to said respective channel formations.

7. An underlay according to claim 5 wherein each of said respective shoulder formations presents a first abutting surface to said overlap portion, presents a second abutting surface to said respective channel formations, and present a substantially flat surface therebetween.

8. An underlay according to claims 5, 6, or 7 wherein at least two of said channel formations are interrupted in their extent in a region near the end of said tapering by a substantially flat portion of said underlay.

9. An underlay according to claims 5, 6, or 7 wherein each of said channel formations is substantially wedge-shaped in configuration.

10. An underlay according to claims 5, 6, or 7 wherein each of said channel formations is substantially wedge-shaped in configuration, and wherein at least two of said channel formations are interrupted in their extent in a region near the end of said tapering by a substantially flat portion of said underlay.

11. A roof comprising a plurality of overlapping courses wherein each of said courses comprise a plurality of slates arranged in side-by-side relation overlying a plurality of underlays arranged in side-by-side relation; each of said underlays in the form of a tile having one end thereof defining an overlap portion for extending over a plurality of slates in an underlying course and directing run-off water over the top surface of said slates of said course, and the opposite end thereof including therein a recess formation tapered in thickness in a direction extending away from said overlap portion for supporting said overlying slates and distributing said water to said overlap portion, and said overlap portion and said recess formation presenting therebetween a shoulder formation for positioning the underlays in overlying relation to said underlying course.

12. A roof according to claim 11 wherein said shoulder formation of said underlay presents a first abutting surface to said overlap portion and presents a second abutting surface to said recess formation.

13. A roof according to claim 11 wherein said shoulder formation of said underlay presents a first abutting surface to said overlap portion and presents a second abutting surface to said recess formation, and presents a substantially flat surface therebetween.

14. A roof according to claims 12 or 13 wherein said first abutting surface of said shoulder formation of said underlay abuts against one edge of said plurality of slates of said underlying course and said second abutting surface of said shoulder formation of said underlay abuts against one edge of the plurality of underlays of said underlying course.

15. A roof according to claims 11, 12, or 13 wherein said recess formation of said underlay is interrupted in its extent in a region near the end of said tapering by a substantially flat portion of said underlay.

16. A roof according to claim 11 wherein said recess formation of said underlay comprises a plurality of parallel spaced-apart channel formations tapering in thickness in a direction extending away from said overlap portion, and each of said channel formations and said overlap portion presenting therebetween a respective shoulder formation.

17. A roof according to claim 16 wherein each of said respective shoulder formations of said underlay present a first abutting surface to said overlap portion and present a second abutting surface to said respective channel formations.

18. A roof according to claim 16 wherein each of said respective shoulder formations of said underlay present a first abutting surface to said overlap portion, present a second abutting surface to said respective channel formations, and present a substantially flat surface therebetween.

19. A roof according to claims 16, 17, or 18 wherein at least two of said channel formations of said underlay are interrupted in their extent in a region near the end of said tapering by a substantially flat portion of said underlay.

20. A roof according to claims 16, 17, or 18 wherein each of said channel formations of said underlay is substantially wedge-shaped in configuration.

21. A roof according to claims 16, 17, or 18 wherein each of said channel formations of said underlay is substantially wedge-shaped in configuration, and wherein at least two of said channel formations are interrupted in their extent in a region near the end of said tapering by a substantially flat portion of said underlay.

22 22. A roof according to claims 17 or 18 wherein said first abutting surfaces of said shoulder formations of said underlay abut against one edge of said plurality of slates of said underlying course and said second abutting surfaces of said shoulder formations of said underlay abut against one edge of the plurality of underlays of said underlying course.

23. A roof according to claims 17 or 18 wherein said first abutting surfaces of said shoulder formations of said underlay abut against one edge of said plurality of slates of said underlying course and said second abutting surfaces of said shoulder formations of said underlay abut against one edge of the plurality of underlays of said underlying course, and wherein at least two of said channel formations of said underlay are interrupted in their extent in a region near the end of said tapering by a substantially flat portion of said underlay.

24. A roof according to claims 17 or 18 wherein said first abutting surfaces of said shoulder formations of said underlay abut against one edge of said plurality of slates of said underlying course and said second abutting surfaces of said shoulder formations of said underlay abut against one edge of the plurality of underlays of said underlying course, and wherein each of said channel formations of said underlay is substantially wedge-shaped in configuration.

25. A roof according to claims 17 or 18 wherein said first abutting surfaces of said shoulder formations of said underlay abut against one edge of said plurality of slates of said underlying course and said second abutting surfaces of said shoulder formations of said underlay abut against one edge of the plurality of underlays of said underlying course, and wherein each of said channel formations of said underlay is substantially wedge-shaped in configuration, and wherein at least two of said channel formations are interrupted in their extent in a region near the end of said tapering by a substantially flat portion of said underlay.

26. A method of installing a roof comprising a plurality of overlapping courses secured to the surface of the sub-roof structure wherein each of said courses comprise a plurality of slates arranged in side-by-side relation overlying a plurality of underlays arranged in side-by-side relation; each of said underlays in the form of a tile having one end thereof defining an overlap portion for extending over a plurality of slates in an underlying course and directing run-off water over the top surface of said slates of said course, and the opposite end thereof including therein a recess formation tapered in thickness in a direction extending away from said overlap portion for supporting said overlying slates and distributing water to said overlap portion, and said overlap portion and said recess formation presenting therebetween a shoulder formation for positioning the underlays in overlying relation to said underlying course; the method comprising the steps of:
a. arranging in side-by-side relation a plurality of said underlays on said surface of said sub-roof structure with said recess formations of said underlays depending therebelow and in contact with said surface of said sub-roof structure, and with said overlap portions of said underlays extending downwardly to the lower edge of said sub-roof structure;
b. arranging in side-by-side relation a plurality of said slates in overlying relation to said underlays with the lowermost edges thereof extending slightly beyond said lowermost edges of said underlays;
c. securing said plurality of slates and underlays to said surface of the sub-roof structure by means of nails to form a first course of said roof; and d. laying all subsequent courses required to complete said roof by:
i. arranging in side-by-side relation a plurality of said underlays on said surface of said sub-roof structure with said recess formations of said underlays depending therebelow and in contact with said surface of said sub-roof structure, and with their overlap portions extending over the slates of the underlying course;
ii. arranging said slates in overlying relation to said underlays with their lowermost edges thereof extending slightly beyond the lowermost edges of said underlays; and iii. securing said slates and said underlays to said surface of said sub-roof structure by means of nails and in overlapping relation to said underlying course.