You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to rainwater guttering systems for roofs of buildings, and is particularly concerned with a method and apparatus for preventing the blockage of internal corner roof gutters located at the bottom of valley gutters.  
           [0002]    A roof valley is the region where two inclined roofs meet. This region has a substantially V-shaped cross-sectional configuration and generally slopes in one direction toward the edge of the building. A metal tray or gutter is located in the roof valley to collect water flowing from the roof cladding and to direct the water to a roof gutter. During downpours, very large volumes of water and debris can be collected from the roof and wash down into the roof gutter. The design of the roof gutter is such that the flow from the valley gutter is split in half, with one portion going with the flow in the roof gutter and the other portion being pushed against the flow. This can create blockage in the roof gutter if debris is present, and cause a back-up of water invariably leading to overflow and, in some instances, internal water damage to the building.  
         OBJECT OF THE INVENTION  
         [0003]    It is therefore an object of this invention to provide a satisfactory solution to the aforementioned problem or to at least provide the public with a useful alternative.  
         SUMMARY OF THE INVENTION  
         [0004]    According to one aspect of the present invention there is provided a method for preventing the blockage of an internal corner roof gutter to be located at the bottom of a valley gutter, which method comprises the steps of:  
           [0005]    (i) Transversely cutting a rear wall and base of a roof gutter, in which an internal corner is to be formed;  
           [0006]    (ii) bending the gutter at right angles at the cut so as to produce an opening in the base and rear wall thereof;  
           [0007]    (iii) fixing the roof gutter to an internal corner of a building fascia or other support means; and  
           [0008]    (iv) fitting a rainwater head with attached downpipe to the internal fascia or other support means, so as to extend at least partly below the roof gutter opening.  
           [0009]    The rainwater head comprises a second aspect of the invention.  
           [0010]    According to this second aspect of the present invention there is provided a rain head for fitting beneath a roof gutter located at an internal corner of a building, said rain head having a substantially quadrangular or triangular cross-sectional configuration to enable it to be snugly located between the relatively perpendicular walls defining the internal fascia or other support means for the roof gutter, the said rainhead including a compartment with an upwardly facing inlet and a downwardly facing outlet, said inlet incorporating a primary screen which is supported in such a manner as, in use, to deflect debris away from the compartment whilst permitting water to flow through it and into the compartment for discharge through the outlet.  
         DESCRIPTION OF THE INVENTION  
         [0011]    The compartment can optionally include a secondary screen located between the primary screen and the outlet, to prevent the ingress of vectors such as mosquitoes to the outlet. Such a secondary screen is mandatory to meet government requirements if used in conjunction with the catchment and storage of rain water.  
           [0012]    Preferably, the internal corner rain head will include flanges projecting upwardly from two adjacent sides to enable connection to the fascia or other support means by screws, nails or like fixing arrangements. Such flanges also act as “a splash back” to prevent the fascia from water damage.  
           [0013]    The primary screen is typically angled so that the majority of rainwater and debris hits the screen as it falls through the gutter at between about 45° and 60°. This angle is skewed towards 45° for light rainfalls and towards 60° for high rainfalls by notching the upper edge of the primary screen upwards or downwards while maintaining the bottom edge of the screen in a fixed location. The screen can be manufactured from a range of non-corrosive materials such as plastics material, metal, composites, or a combination thereof. Powder coated galvanised iron stranded screens are particularly suitable as they enable the maximisation of the open spaces in the screening surface while simultaneously breaking any water capillarity in the openings. Preferred sizes for the openings in the primary screen are between 4×4 mm and 9×9 mm, most preferably about 6×6 mm.  
           [0014]    The secondary screen when present can be manufactured from a similar range of materials to the primary screen. Preferably, however, it is manufactured from welded or wire woven stainless steel, zincalum, galvanised steel, brass, copper or fibreglass. The mesh size can typically be 0.9×0.9 mm and can include an appropriate support framework to enable retention of shape and ease of placement. A particularly preferred framework comprises a rectangle of plastics material in which the screen is embedded during the production thereof. Finger extensions are provided on opposing edges of the framework to enable the secondary screen to be placed in, and removed from, a recess which snugly holds the secondary screen when it is press-fitted therein.  
           [0015]    In a further modification, the internal corner rain head can be designed to include a projection formed on its unattached peripheral side which which extends upwardly to the same height as the outer face of the roof gutter, so as to, in effect, extend across the corner of the roof gutter and thereby provide an attractive finish to the product.  
           [0016]    The internal corner rain head permits the unimpeded flow of water and debris from the valley tray directly through the opening in the roof gutter and to the rain head, thereby obviating any blockage in the roof gutter and hence avoiding overflow and potential water damage to the building. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a top perspective view of a roof incorporating a typical valley gutter and internal corner gutter;  
         [0018]    [0018]FIG. 2 is a cut-away perspective view of an internal corner rain head according to one aspect of the present invention, and  
         [0019]    [0019]FIG. 3 is a cut-away perspective view of an internal corner rain head juxtaposed with respect to a roof gutter according to another aspect of the present invention.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENT  
       [0020]    A preferred embodiment of the invention will now be described with reference to the accompanying drawings, in all of which like reference numerals refer to like parts.  
         [0021]    Referring firstly to FIG. 1, a pitched roof is depicted comprising roof sections  10  and  11  which slope towards each other and towards their respective roof gutters  12 ,  13 . The roof sections  10 ,  11  are separated by a valley gutter  14 . In this arrangement, blockage and overflow typically occurs in the circled region  15 .  
         [0022]    [0022]FIG. 2 shows an internal corner rain head  16  which is adapted for fitting beneath the intersections of the two gutters  12 ,  13  depicted in FIG. 1. Firstly, an opening is made in the bottom wall of the intersecting gutters to enable water flowing down the valley gutter  14  to pass straight through the roof gutters. This opening can be reinforced by gussets, brackets or other known means. The internal corner rain head  16  is then fitted to the intersecting fascia plates  17 ,  18  by screws inserted through flanges  19 ,  20 , directly below the opening in the gutters which has been created.  
         [0023]    The internal corner rain head comprises a compartment  21  having an upwardly facing and inclined opening which is covered by a primary screen  22  and an outlet  23  for connecting to a rainwater downpipe of the building. A horizontal secondary screen is located within the compartment between the primary screen  22  and the outlet  23 . The location of the secondary screen is indicated by the dotted line  24 .  
         [0024]    The primary screen has a planar configuration with square apertures measuring 6×6 mm.  
         [0025]    The secondary screen is a planar  955  micro mesh designed to meet statutory requirements for vector exclusion.  
         [0026]    An alternative embodiment of the internal corner rain head is depicted in FIG. 3. This rain head  30  differs from the preceding embodiment in that it is designed to cover over the corner section  31  of the intersecting roof gutters  12 ,  13 . To this end, the rain head includes a projecting, segmental section  32  which extends in an arcuate fashion between the roof gutters  12 ,  13 . An opening  33  in the wall of the rain head permits ejection of debris being washed down from the valley gutter  14  while the water flows on down through an inclined primary screen  34  to an outlet  35 .  
         [0027]    Although the FIG. 3 embodiment shows the screen sloping forward, it is also possible for the screen to slope backward to the wall of the building.  
         [0028]    The invention described above avoids any blockage or overflow in the region  15  of internal intersecting gutters  12 ,  13  at the foot of a valley gutter  14 , and therefore provides a useful, commercial product.  
         [0029]    Whilst the above has been given by way of illustrative example of the invention, many modifications and variation may be made thereto by persons skilled in the art without departing from the broad scope and ambit of the invention as herein set forth.

Summary:
A method and apparatus for preventing the blockage of an internal corner roof gutter ( 31 ). An opening is formed at the intersection of the two gutters ( 12, 13 ) and a rainwater head ( 30 ) with attached downpipe is fitted under the opening. The rainwater head can be designed to include an arcuate section ( 32 ) which extends between the two faces of the gutter.