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FIELD OF THE INVENTION 
     This invention relates to gutter guards used to prevent debris from clogging a rain gutter. 
     BACKGROUND OF THE INVENTION 
     Gutter guards include a perforated planar surface that spans the rain gutter opening to allow water to drain into the gutter while preventing debris from doing so. The front of the guard is usually secured or retained on the front lip of the gutter, for example by means of fasteners, a clip system or by shaping the front edge of the guard such that it is physically engaged on or under the lip. 
     In some cases, such as disclosed in U.S. Pat. No. 7,614,185 to Brochu, the guard is designed to seat in a recessed position in the gutter. Such an arrangement creates a lip or wall at the front of the guard to stop fast moving water from simply flowing across the guard and to the ground, which risks defeating the purpose of the gutter. Despite the front lip or wall formed by a recessed gutter guard, large quantities of fast-flowing water from the roof can overwhelm the apertures in the forward portion of the guard where accumulating water can spill over the front lip of the recessed gutter guard before it can drain through the apertures. 
     Older-style prior art rain gutters are typically secured to the fascia of the building by a spike and ferrule system in which a nail or spike is inserted into a ferrule extending from the front of the gutter and through the rear wall of the gutter, so as to embed in the fascia. Spike and ferrule systems usually involve unthreaded nails or spikes that may not provide a secure fastening to the fascia and are sometimes difficult to install, particularly for do-it-yourselfers. More recently, the use of gutter hangers has become the preferred means of installing gutters. Gutter hangers extend between the front and rear walls of the gutter and a wall screw is inserted through the hanger, through its rear wall and into the fascia. Gutter hangers are provided at spaced locations along the length of the gutter as illustrated in  FIG. 1 . The present applicant supplies gutter hangers with a pre-installed threaded fastener to facilitate installation. 
     However, gutter hangers present a potential obstacle to installation of recessed gutter guards. Guards are typically manufactured in predetermined lengths of roll-formed product having a uniform profile along their lengths. As some gutter hangers have shoulders near the top rear of the gutter, the presence of the shoulders inhibits the ability to install a guard any deeper into the gutter than the height of the gutter hangers. For example, Canadian Patent No. 2,597,976 to Brochu discloses a guard that includes a planar top portion and a rear wall that extends along the rear of the gutter to support the guard on the bottom of the gutter. The presence of the rear wall renders the disclosed system unusable with gutter hangers that have a shoulder as the rear wall of the guard would be impeded by the hangers. 
     The rear of the guard may be secured by fasteners or it may passively abut either the rear of the gutter, the fascia or in some cases be wedged under the shingles of the roof. The use of fasteners at the rear of the guard increases the chance of water seepage into the underlying fascia of the building. US Patent Publication No. US 2009/0031638 to lannelli avoids the use of fasteners at the rear of the guard by wedging the guard between the roof structure and the roof shingles. That approach is obviously labour intensive, requires skill, risks snapping the shingles if they are brittle and may be difficult to achieve after construction of the roof has been completed. It is also limited by the proximity of the roof line to the gutter, which may vary from building to building and allows rainwater to shoot off the front of the gutters. 
     US Patent Publication No. US 2009/0108144 to Brochu discloses a passive abutment of an angled rear portion of the guard against the fascia or a hook that engages the rear wall of the gutter. Such passive support systems have the advantage of being easy to install and of not requiring additional fasteners or specialized tools. However such systems run the risk of improper installation if the rear of the guard is pushed down hard enough to seat the rear of the guard below its most effective height. The same result can follow from the weight of snow or ice. This can result in bending of the guard along its length or if installed too low, obstruction of the flow of water along the gutter. 
     It is an object of the present invention to provide a partially recessed roll-formable gutter guard that is easy to install in conjunction with gutter hangers. Another object of the invention is to avoid the use of fasteners at the rear of the guard. It is a further object of the invention to minimize the accumulation of water at the front of the gutter guard. 
     These and other objects of the invention will be better understood by reference to the detailed description of the preferred embodiment which follows. Note that not all of the objects are necessarily met by all embodiments of the invention described below or by the invention defined by each of the claims. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a gutter guard comprises a downwardly extending support leg that is designed to rest on all styles of gutter hangers and to provide longitudinal rigidity to the guard. In a related aspect, the leg is omitted for a short distance adjacent a side edge of the guard or the side edge is provided with a notch to accommodate the support leg, thereby permitting lengths of gutter guard to be joined in partially overlapping relationship in the gutter. 
     The support leg also serves to provide longitudinal rigidity to the guard which facilitates handling and facilitates the use of a friction fit of the rear of the guard with the fascia. 
     According to an aspect of the invention, the friction fit is facilitated by an upwardly angled rear end of the guard, the upward angle also contributing to directing water away from the fascia. 
     In another aspect of the invention, the guard includes a rear shoulder portion to accommodate the shoulder of the gutter hangers in the event that the gutter hangers have a rear shoulder, while still allowing the principal planar surface of the guard to be recessed or partially recessed within the gutter. In a more particular aspect, the invention comprises the arrangement of the walls forming the shoulder. 
     In another aspect, a flat attachment face is provided at the front of the guard for overlying and securing it to the front lip of the gutter. 
     In a further aspect, the central planar portion of the guard has a slight rearward sloping angle to flow water away from the front lip of the guard to avoid the accumulation of water near the front lip and an upstanding wall is provided between the central portion and the attachment flap to discourage water from flushing over the front lip of the gutter. 
     The attachment flap is angled slightly downward from back to front to direct water off the attachment face and to maintain a more closely flush line when viewed from the front of the building. A forward downward angle to the top wall of the rear shoulder assists in isolating the connection between the fascia and the hanger wall screw from water. 
     In yet another aspect, the invention comprises a rain gutter guard adapted for use in a recessed position within a gutter that is mounted to a building wall by a series of spaced gutter hangers. The gutter guard comprises a porous surface for substantially spanning the width of the gutter and includes a leg extending downward from the surface and is adapted to rest on the gutter hangers when the gutter guard is urged downward within the gutter. 
     In another aspect, the invention is an assembly of a rain gutter and a gutter guard comprising a series of spaced gutter hangers for mounting a gutter to a vertical building surface. The gutter guard has a porous surface that substantially spans the width of the gutter and a leg extending downward from the surface and adapted to rest on the gutter hangers when the gutter guard is urged downward within the gutter. The support leg extends downward a distance substantially less than the depth of said gutter. 
     In a method aspect, the invention comprises a method of installing a gutter guard on a rain gutter that is secured to a vertical building surface by a series of spaced gutter hangers. A gutter guard as described above is installed such that the leg rests on the gutter hangers and a rear edge of the gutter guard is substantially proximal to a rear edge of said gutter. 
     Other aspects of the invention relate to the presence of an upwardly angled segment at the rearmost end of the guard for resilient abutment against the building wall, the particular inclination of the central portion, an angle provided to the attachment flap, an angle provided to a second wall forming a part of the shoulder, and an angle provided for a rearmost segment of the guard. 
     The foregoing was intended as a broad summary only and of only some of the aspects of the invention. It was not intended to define the limits or requirements of the invention. Other aspects of the invention will be appreciated by reference to the detailed description of the exemplary preferred embodiment and to the claims by which the invention is defined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described by reference to the detailed description of the preferred embodiment and to the drawings thereof in which: 
         FIG. 1  is a perspective front view of a typical gutter showing a plurality of gutter hangers according to the prior art; 
         FIG. 2  is a perspective view of a gutter, a gutter hanger and a gutter guard according to the preferred embodiment, installed in the gutter; 
         FIG. 3  is a side elevation of the gutter guard of the preferred embodiment; 
         FIG. 4  is a cross-sectional view of a gutter, gutter hanger and a gutter guard according to the preferred embodiment installed in the gutter. For clarity, the apertures in the guard are not shown in this view; and, 
         FIG. 5  is a plan view of the guard. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following describes a preferred implementation of the inventive concepts of the invention. There may of course be various other manners of embodying the same inventive concepts and this section of the specification therefore does not purport to describe the full extent or scope of the invention but merely to illustrate the preferred embodiment thereof. 
       FIG. 1  is a perspective view of a prior art gutter  10  with gutter hangers  12 ,  14 ,  16  being provided at spaced locations to secure the gutter to the fascia of a building. The preferred embodiment of gutter hangers are available with pre-installed wall screws  18 ,  20 ,  22  that are screwed through the rear wall  24  of the gutter and into the fascia of the building (the fascia is not shown in the drawings). A fastening shoulder  36  is provided in the gutter hanger to retain and align the wall screws to the rear of the gutter  10 . While not all gutter hangers have such a shoulder, one feature of the preferred embodiment of the invention is best appreciated by reference to gutter hangers having shoulders as shown. 
       FIGS. 2 and 4  are views of a gutter  10  with gutter hangers  12 ,  14 ,  16 , and a gutter guard  26  according to the preferred embodiment while  FIG. 3  is a side elevation of the gutter guard  26  according to the preferred embodiment. 
     In this description, the portion of the guard and gutter that are adjacent the fascia of the building will be referred to as the “back” or “rear” and the portions distal from the fascia will be referred to as the “front” or “forward” portions. 
     Guard  26 , which is formed as a single piece of extruded or roll-formed material, includes a downwardly extending leg  28  adapted to either rest directly on the gutter hangers  12 ,  14 ,  16  or to abut them when the guard is urged down into the gutter (for example by the installer, during cleaning or under the weight of snow or ice). Leg  28  also serves to provide longitudinal rigidity to the guard that facilitates handling of long segments of guard and facilitates a friction fit installation of the guard by pressing its rearmost end against the fascia of the building. The support leg  28  extends downward a distance substantially less than the depth of the gutter  10 . 
     The rear of the guard  26  forms a shoulder  34  to provide clearance for the fastening shoulders  36  of the gutter hangers and their associated wall screws. Shoulder  34  is formed by a first upwardly inclined wall  30  and a second upwardly inclined top wall  32  extending rearward from the first inclined wall  30 . 
     According to the preferred embodiment, leg  28  is formed at the juncture between the central planar surface  42  and the upwardly inclined wall  30 . 
     The guard  26  is therefore adapted to be easily positioned in the gutter by resting leg  28  on the gutter hangers  12 ,  14 ,  16  so as to recess the guard within the gutter without interference from the hanger shoulders  36  while also avoiding the risk of inserting it too deep into the gutter  10  during installation. During installation, the rearmost end of the guard is disposed such that it is substantially proximal to a rear edge of the gutter  10 . 
     The front end of the guard  26  is formed to provide a flat attachment flap  34  that provides a surface for securement to the underlying gutter lip  37 , for example by means of a screw  38 . At the rear of the guard, top wall  32  terminates in a segment  40  that is angled upward at about 45° to allow bending and resilient abutment for a friction fit to the fascia boards. 
     In the preferred embodiment, central planar portion  42  extends forwardly from leg  28 . Central portion  42 , diagonal wall  30  and top wall  32  are each provided with a regular pattern of apertures  46  to create a porous surface. Central portion  42  acts as the principal drainage surface of the guard  26 . Preferably an upstanding wall  44  is provided between planar portion  42  and attachment flap  34  to contain water flowing from the roof and to prevent it from spilling over the forward lip  37  of the gutter. 
     Planar portion  42  has a slight (between 1° and 3°, preferably 1.5°) rearward incline to promote the rearward flow of water. Top wall  32  is inclined upward at an angle of between 1.5° and 4°, preferably 3°, from front to back. The slight incline of the top wall  32  is designed to keep water from migrating toward the fascia of the building. 
     The attachment flap  34  extends downwardly from back to front at an angle of between 3° and 7°, preferably about 5°, in order to direct water to the front of the gutter and to provide an approximately flush line when viewed from in front of the building. 
     In order to avoid the risk posed by sharp edges during handling, the attachment flap  34  is folded over at its end to provide a smooth forward edge. Similarly the tip  48  of rear edge  40  is preferably rounded for the same reason and to avoid scoring of the fascia. 
     In installing gutter guards end to end along a gutter, gaps between the guards should be avoided. In the case of gutter guards that are flush stackable, this is achieved by simply overlapping the guards. However, the presence of leg  28  prevents the guards from overlapping in a flush relationship. In order to accommodate partial overlapping of the ends of the guards, the leg  28  is omitted from a short segment of at least one end of the guard and is replaced by a slot  50  of sufficient width to accommodate the leg of an adjacent guard, as illustrated in  FIG. 5 . This allows partial flush overlapping of the guards during installation in a gutter. Alternatively, the leg  28  can simply be omitted from a short segment and the gutter guard from which the leg  28  is omitted can be simply overlaid on the side adjacent guard. 
     Similarly, a portion of the upstanding wall  44  and the attachment flap  34  is omitted along a short segment  52  to allow overlapping of end to end adjacent guards. 
     It will be appreciated by those skilled in the art that the preferred and alternative embodiments have been described in some detail but that certain modifications may be practiced without departing from the principles of the invention, the scope of which is defined principally by the claims.

Summary:
A rain gutter guard comprises a downward leg for abutting gutter hangers when the guard is urged down into the gutter. A shoulder of the guard accommodates the shoulder of the gutter hangers. A front attachment flap secures the front of the guard to the gutter while the rear is retained by friction fit of an angled segment against the building fascia. An upstanding wall separates the central portion from the attachment flap. The central portion is inclined rearward and the attachment flap inclines to the front.