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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to the field of sub-floor systems for balcony, patio or terrace of homes and roof. 
       Prior Art  
       [0002]    Our research among patents revealed some systems that caught our attention: 
         [0003]    CA 1,225,252 is a floor with twin cells to protect electric wire. 
         [0004]    CA 2,340,371 is an evacuation drain for plumbing installed within a building. 
         [0005]    U.S. Pat. No. 6,539,681 is a spacing for a hollow floor which supports piping for heating or air-conditioning. 
         [0006]    EPO JP20000320034 is a sheet looking like a net for preventing infestation of termites. 
       OBJECTS AND ADVANTAGES 
       [0007]    The general objective of this invention is to permit building galleries with openwork planks to shy from rain and snow, for storing objects and protecting a structure against water. 
         [0008]    A specific objective is to prevent rainwater from being introduced and remain caught between the boards and the wooden structures which constitute the coating and the braces of a patio or a balcony. This invention allows the draining and the water running off far from the structures composing a patio, a balcony or a terrace. 
         [0009]    Another objective is to allow an arrangement under a patio including humps and valleys positioned such that the rainwater will not run any more between the boards so as to maintain dry the lower part of a patio. 
     
     
       BRIEF DESCRIPTION OF DRAWING FIGURES 
         [0010]      FIG. 1  is a side view of an under-plank 
           [0011]      FIGS. 2A and 2B  are cut views according to line  2 - 2  of  FIG.4   
           [0012]      FIG. 3A  is a perspective view of an under-plank sheet 
           [0013]      FIG. 3B  is a perspective view of a wood board 
           [0014]      FIG. 4  is a side view of a patio juxtaposed with a building support 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]    In the following description and in the accompanying drawings, the numeral numbers refer to identical parts in the various Figures. 
         [0016]      FIG. 1  shows by an arrow a side view of an under-plank  20 , a sloping section  23  surrounded by an accentuated left crest  26 , central crest  27  and widened crest  35 ; on which water slips before arriving in the various zones of drainage of water  22 ,  22 ′. Zones of screwing  24 ,  24 ′ correspond to a zone where the screws of a deck board will be most effective when piercing the under-plank  20 , between boards  30  which constitute a coating of a patio and beams  44 . The zones of screwing  24  are defined in widened zones of screwing  38  and abrupt zones of screwing  42 . An accentuated crest  26  is encased in an accentuated crest  28  which has an edge  48  of a connection zone  41  in order to allow the connection of another under-plank  20  to the following and to maintain the sealing between them. An overlap zone is according to the spacing between boards of the patio. A typical variation is 0 to ½ inch. 
         [0017]      FIG. 2A  Defines water flow direction first vertically along a screw or between two boards then along a slope and finally away from an observer and longitudinally of the board  30 .  FIG. 2  shows a side view of the assembly of a sub floor sheet  20  maintained in place with screws  32  between wood boards  30  of the coating of the patio and beams  44 . Screws  32 ,  32 ′ are placed close to crests  35  and  26 , but preferably in the widened zones of screwing  38 ,  38 ′ because the water infiltrated through the holes made by screws  32  will run out by slipping along the crests  35  and  26  in the zones of evacuation  22 ,  22 ′. There are indeed a broader zone of screwing  25  on the crest  27  which allows screwing and the drainage of water, but it is necessary to take care not to screw too close to the zones of evacuation  22 ,  22 ′ because water would then be retained at the place where the screw would be entering a metal shield. It is better to target the widened zone of screwing  38  which gives more play. Water infiltrating through a hole made in a deck board sub floor sheet  20  runs between the zones of evacuation  22 ,  22 ′ which are in the direction of the relief of these zones. The dotted arrows show the direction water can follow while running out on or between boards  30  of the covering of the patio before being evacuated by the zones of drainage of water  22 ,  22 ′ or by the flat bottom  40  of the zone of connection  41 . 
         [0018]      FIG. 2B  shows a side view of the assembly of an under-plank  20  wherein boards  30  are closer than those of  FIG. 2A  to provide adjustment between similar boards  30  laid out on  FIG. 2A . 
         [0019]      FIG. 3A  shows an under-plank  20  which is corrugated, an under-plank strip appears rolled over itself several times such as for a grass roll. 
         [0020]      FIG. 3B  shows a deck wood board  30 . 
         [0021]      FIG. 4  shows a patio  46  juxtaposed at a building  58  with a slope  50  such as ¼ inch per foot in length in order to allow the drainage of water in the direction opposed to that of the building. 
       Applications  
       [0022]    The applications of this invention relate to the protection of a patio, a balcony or a terrace deck board; a tight sub-floor for patio is a semi-rigid under-plank of corrugated polymeric installed between beams and transverse boards constituting the covering of the patio. The corrugated under-plank has a design of crests and dips, crests widened to make possible to receive of screws and dips where there will be no perforation of screwing, to allow the water run-off in order to protect the wood structures of patios, balconies or terraces against moisture causing their premature rot. 
       SUMMARY OF THE INVENTION 
       [0023]    A corrugated semi-rigid under-plank intended to be used between a board  30  and a structure element  44 , the under-plank having a number of crests  26 ,  27 ,  28 ,  35  among which a group of widened crests  26 ,  35  intended to provide a spacing to receive screws  32 ,  32 ′ in a zone of screwing  24 ,  24 ′, and a flat upper zone  27  of screwing intended to receive a screw  27 ′ fixed upwardly. 
         [0024]    The under-plank has a number of dips  22 ,  22 ′,  40  to provide support over the structure element  44 , and to provide means of drainage of a liquid found on a surface of the board  30 . 
         [0025]    Water infiltrating around screws result in a flow of water along a slope  23 ,  23 ′ towards the dips  22 ,  22 ′ called zones of drainage, 
         [0026]    The under-plank may be placed between two rows of boards, a top row a covering may be a floor, a patio, a balcony, a terrace, or a roof. The under-plank may be placed between two rows of boards, the lower row being beams or foundations of a floor, a patio, a balcony, or a terrace. 
         [0027]    The under-plank may be a roof. 
         [0028]    The under-plank being corrugated according to the higher and lower crests and whose top and base are all at corresponding height, each crest being a point of support. 
         [0029]    The under-plank being sufficiently rigid in order to maintain its form during the screwing and when a significant load will be deposited on it in addition to the people who will circulate and objects which will be deposited on a first rank of boards defined as covering, the form also need to be maintained between the beams in order to preserve the functions of a sub floor. 
         [0030]    The under-plank whose zones of drainage of water  22 ,  22 ′,  40  are intended to provide a means of drainage of rain, water coming from snow melt or water washing accumulating in a natural or artificial way. 
         [0031]    The under-plank consisting of an impermeable material to water, the absence of porosity jams the passage of liquid through the under-plank. 
         [0032]    The under-plank consisting of a material which does not deteriorate upon moisture, solar radiation and freezing and thaw. 
         [0033]    The under-plank is made according to a central axis on in each side of the axis the crests are distributed symmetrically. 
         [0034]    The under-plank is formed of crests laid out symmetrically, which implies the disposition according to a regular spacing of boards  30  which constitutes the covering of a patio, in order to allow a screwing in the zones of screwing  24 ,  24 ′ of the under-plank. 
         [0035]    The under-plank whose crests have a sufficient height to allow the flow of water when it rains abundantly. 
         [0036]    The under-plank whose lower crests correspond to zones of drainage of water  22 ,  22 ′. 
         [0037]    The connection zone  41  having a flat dip  40 , which is also a zone of drainage, terminated on a terminating edge  48  which matches a forward edge  36  of a second under-plank in order to allow the alignment of several under-plank  20  and the sealing of a sub floor. 
         [0038]    The connection zone  41  allowing a variation in the adjustment of the under-planks thereby making possible adjusting boards for the covering of a patio laid out above the flat dip  40  of the connection zone  41 . 
         [0039]    The under-plank whose higher crests are indicated according to the shape of their slope; accentuated left crests  26 , central  27  and the widened crests  35 . 
         [0040]    The under-plank whose zones of screwing  24 ,  24 ′ correspond to spaces on both sides of higher crests. 
         [0041]    The under-plank whose zones of screwing of the widened crests  26 ,  35  are indicated according to the extent of the available zone for screwing; widened zone of screwing  38 ,  38 ′, and the abrupt zone of screwing  42 ,  42 ′ narrower than the wide zone of screwing. 
         [0042]    The under-plank whose widened zones of screwing  38  and the abrupt zones of screwing  42  have a slope of at least 2 degrees which permit water to run out than instead of remain imprisoned between boards  30  of covering and the under-plank  20 . 
         [0043]    The corrugated under-plank is not necessarily rigid in composition so as to permit the wrapping thereof into a four foot diameter bundle for extension to one hundred feet. The board means may be a coating or a paste or fibreglass spread over the top surface of the under-plank for providing a roof surface without any top board element. The sloping sections may be provided with a clip arrangement to be maintained together. The number of crests  26 ,  27 ,  28 ,  35  and dips  22 , 22 ′ providing support over structural elements  44 , a number of sloping sections  23  to provide a spacing to receive screws  32 ,  32 ′ in a so-called zone of screwing  24 ,  24 ′, sloping sections to provide means of drainage of a liquid found on a surface of a board  30  and around the screws, the zone of screwing being limited to the sloping sections, water infiltrating around screws, during screwing and afterwards, resulting in a flow of water towards the dips  22 ,  22 ′ and resulting in a zone of drainage. 
         [0044]    It is to be clearly understood that the instant description with reference to the annexed drawing is made in an indicative manner and that the preferred embodiments described herein are meant in no way to limit further embodiments realizable within the scope of the invention. The matter which is claimed as being inventive and new is limited only by the following claims. 
       PARTS 
       [0000]    
       
           20 —Under-plank 
           22 —Zone of drainage of water 
           23 ,  23 ′—Sloping sections 
           24 —Zone of screwing 
           25 —Boarder of screwing 
           26 —left accentuated Crest 
           27 —Central crest 
           27 ′—Screw fixed upwardly 
           38 —Edge 
           35 —Right accentuated Crest 
           30 —Board 
           32 —Screw 
           35 —Right widened Crest 
           36 —Forward edge 
           38 —Widened Zone of screwing 
           40 —Flat bottom of the connection zone  41   
           41 —Connection zone 
           42 —Abrupt Zone of screwing 
           44 —Structural element 
           46 —Patio 
           48 —Terminating edge 
           50 —Slope 
           52 —Beam 
           54 —Support 
           58 —Support building

Summary:
The present invention relates to a watertight sub-floor system for balcony or roof, in the form of a semi-rigid rollable plank of corrugated polymeric type installed in juxtaposition to form a waterproof flooring between boards and beams. Under-plank are unwrapped and cut at a desired length to avoid transverse junction with respect to water flow. Under-planks overlap parallel to water flow without loss of sealing. The corrugated under-plank has a design of crests and dips, crests widened and sloping to make possible the receiving of screws from deck board, thereby permitting the descent of water trickling from around the damaging screwing of the under-plank, and dips which bear no perforations from screwing and merely allow water to run off to protect wood structures of patios, balconies or terraces against moisture causing premature rot and to protect objects (bike, mowers . . . ) under a deck.