Abstract:
Apparatus and a method for extending the length of a vent pipe for a predetermined distance above the elevation of a building roof includes an elongated extension pipe connectable with the vent pipe, a flashing attachable to the roof while fitted as a sleeve over the extension pipe, and a vent cap fittable over the flashing and the extension pipe. The vent cap includes an opening for venting to external atmosphere gases received by the extension pipe from the vent pipe. The extension pipe and the vent cap are sized so as to maintain a venting pressure in the extension pipe not greater than the venting pressure in the extension pipe.

Description:
BACKGROUND TO THE INVENTION  
         [0001]    The present invention relates to vent pipes for building roofs and to methods for extending the length of such pipes.  
           [0002]    Many existing flat roof buildings are simply flat and lack a suitably effective roof drainage system. Depending on the size of the roof, hundreds and sometimes thousands of gallons of water can collect, and this may lead to significant structural damage. When it comes time to upgrade or to repair the roof, the water must be removed and this can be a very difficult job. To avoid reoccurrence of the problem, it is not uncommon for the roof to be redesigned with an effective drainage system.  
           [0003]    When an existing roof is redesigned, one technique that has evolved is to build a new roof atop the old roof. The old flat roof is built up higher on its perimeter with a new roof that slopes to a slight but sufficient degree towards one or more appropriate drains. Once installed, water cannot pond on the roof and the risk that water will produce a significant amount of weight on the roof is eliminated.  
           [0004]    However, as representationally illustrated in FIG. 7, the raising of an old roof can lead to other problems. FIG. 7 depicts part of an old building roof  100 , an existing cylindrical vent pipe  150 , a new building roof  200  constructed atop the old roof, and insulation  250  carried between the old roof and the new roof. Although imperceptible in the drawing, care will have been taken to ensure that new roof  200  has sloping characteristics (lacking in old roof  100 ) to ensure adequate drainage.  
           [0005]    With the addition of a new roof  200 , but not in all cases, a decision may also be made to add a layer of insulation such as insulation  250 . Styrofoam insulation, tapered to provide the desired sloping characteristics of the new roof, may be used to provide insular qualities.  
           [0006]    Typically, the purpose of a vent pipe such as vent pipe  150  is to vent gases* from one or more areas of a building (e.g. the building plumbing system, a kitchen, a shower, etc.). Several such vent pipes may be present in any given building. As is plainly evident from FIG. 7, an immediate problem is that vent pipe  150  does not extend above the elevation of new roof  200 . Other vent pipes (not shown) similarly may not extend above the elevation of new roof  200  or, if they do, not by a sufficient amount.  
           [0007]    Parenthetically, it may be noted that existing plumbing vent pipes typically may be extended approximately  11  inches above an existing flat roof deck. Depending on the overall size of the existing roof, a new sloped roof such as roof  200 , including a layer of insulation such as insulation  250  may, in some cases, add more  16  inches to the height of the existing roof.  
           [0008]    Accordingly, pipes such as vent pipe  150  have to be extended. Typically, this has been done by inserting an extension pipe of desired length within the existing vent pipe. A flashing, sleeved over the extension pipe and attached to the new roof, is added in a conventional manner, and a vent cap is placed over the extension pipe and flashing in a conventional manner. However, this convention has been found to lead to further problems. It has been realized that moisture from venting gases may pass between the extension pipe and the flashing with consequent damage to the building structure, and that this problem is not resolved by conventional designs.  
           [0009]    Thus there is a need for improved apparatus and a method to extend the length of existing vent pipes which discourages or at least does not encourage the passage of moisture laden gases between an extension pipe and its flashing.  
           [0010]    It is an object of the present invention to provide new and improved apparatus for extending the length of an existing vent pipe for a predetermined distance above the elevation of a building roof - more specifically, apparatus that serves to obstruct or discourage venting gases from passing between an extension pipe and related flashing.  
           [0011]    Further, it is an object of the present invention to provide a new and improved method of extending the length of an existing vent pipe in an building above the elevation of a new roof added atop the old roof of the building.  
           [0012]    In meeting the foregoing objects, it is also an object of the present invention to provide apparatus for extending the length of a vent pipe which is easy to manufacture, and which is easy to assemble and install on a roof, including a new roof which is constructed atop an existing roof.  
         SUMMARY OF THE INVENTION  
         [0013]    In a broad aspect of the present invention, there is provided apparatus for extending the length of an existing vent pipe for a predetermined distance above the elevation of a building roof, the apparatus comprising  
           [0014]    an elongated extension pipe connectable with the vent pipe to receive gases flowing upwardly from the vent pipe;  
           [0015]    a flashing attachable to the roof while fitted as a sleeve over the extension pipe; and,  
           [0016]    a vent cap fittable over the flashing and the extension pipe to shield the annular region between the flashing and the extension pipe from external precipitation.  
           [0017]    The vent cap includes an opening for venting to external atmosphere gases received by the extension pipe from the vent pipe. Further, the extension pipe and the vent cap are sized so as to maintain a venting pressure in the extension pipe not greater than the venting pressure in the extension pipe.  
           [0018]    The present invention recognizes that the problem noted above can be attributed to back pressures caused by the reduction of flow areas. Since the region within the extension pipe will be a region of reduced pressure compared to the pressure within the existing vent pipe, the present invention serves to avoid any undue choking effect at the outlet as provided by the opening in the vent cap. This is advantageous because when gases are choked at the vent cap outlet, the higher choke pressure may force at least some of the gases into the annular space between the extension pipe and the flashing. Since this space is a sleeve space it typically may have a small width. Nevertheless, it exists. In the absence of glues or other sealing mechanisms which are desirable to avoid (and which in any event may deteriorate over time), the space provides a path where some moisture carried by venting gases may find its way with eventual damage to the building structure. This risk can be higher when the venting gases are moisture laden and have a relatively high temperature. At higher temperatures components that are otherwise relatively tight fitting may expand and loosen.  
           [0019]    In a preferred embodiment, the extension pipe is characterized by a lower end having a cylindrical outside diameter sized to fit snugly within an inside diameter of the vent pipe, and an elongated tubular portion extending upwardly from the lower end. The tubular portion has an inside diameter greater than the inside diameter of the vent pipe. The flashing comprises a base attachable to the roof and a centrally positioned tubular portion extending upwardly from the base. The tubular portion of the flashing is characterized by an inside diameter sized to fit as a sleeve over the extension pipe. The base of the flashing includes a centrally aligned opening having a diameter corresponding to the inside diameter of the tubular portion of the flashing. The opening extends through the base for permitting the flashing to be lowered as a sleeve over the extension pipe. The vent cap comprises an inner wall and an outer wall with an annular space defined between the walls, the annular space having a closed top and an open bottom. The inner wall defines a centrally aligned opening extending lengthwise through the cap. Also, the inner wall has an outside diameter sized to slidingly fit within the inside diameter of the extension pipe. The outer wall has an inside diameter sized to slidingly receive the outside diameter of the tubular portion of the flashing.  
           [0020]    In another aspect of the present invention, where a new building roof is constructed atop an old building roof, and where an existing vent pipe extending above the old roof is of insufficient length in relation to the new roof, there is provided a method of extending the length of the existing vent pipe above the elevation of the new roof, the method comprising:  
           [0021]    connecting an upwardly extending, elongated extension pipe with the vent pipe to receive gases flowing upwardly from the vent pipe, the extension pipe having sufficient length to extend from the vent pipe to a desired distance above the new roof;  
           [0022]    fitting a flashing as a sleeve over the extension pipe;  
           [0023]    attaching the flashing to the new roof when so fitted; and,  
           [0024]    fitting a vent cap over the flashing and the extension pipe to shield the annular region between the flashing and the extension from external precipitation, the vent cap including an opening for venting to external atmosphere gases received by the extension pipe from the vent pipe.  
           [0025]    The extension pipe and the vent cap are sized to maintain a venting pressure in the extension pipe not greater than the venting pressure in the extension pipe.  
           [0026]    The foregoing and other features and advantages of the present invention will now be described with reference to the drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]    [0027]FIG. 1 is an exploded view of component parts of vent pipe extension apparatus in accordance with the present invention.  
         [0028]    [0028]FIG. 2 is an enlarged section elevation view of the coupler shown in FIG. 1.  
         [0029]    [0029]FIG. 3 is an enlarged section elevation view of the extension pipe shown in FIG. 1.  
         [0030]    [0030]FIG. 4 is an enlarged section elevation view of the flashing shown in FIG. 1  
         [0031]    [0031]FIG. 5 is an enlarged section elevation view of the vent cap shown in FIG. 1.  
         [0032]    [0032]FIG. 6 is an enlarged section elevation view of the apparatus shown in FIG. 1 when installed on a roof and connected to an existing vent pipe  
         [0033]    [0033]FIG. 7 is a representational view illustrating an old roof, a new roof, insulation therebetween, and an existing roof vent pipe that is too short to extend beyond the elevation of the new roof.  
         [0034]    [0034]FIGS. 8 a  to  8   g  illustrate a progression of steps using the apparatus shown in FIG. 1 to extend the roof vent pipe shown in FIG. 7. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0035]    As best seen in FIGS.  1  to  5 , the vent pipe extension apparatus shown in the drawings comprises an extension pipe coupling generally designated  10 , a tubular, generally cylindrical extension pipe generally designated  20 , a flashing generally designated  30  and a vent cap generally designated  40 . Such apparatus can be used to resolve the problem as described above in relation to FIG. 7 by following the steps indicated in FIGS. 8 a  to  8   g.    
         [0036]    It should be noted that the combination of coupling  10  and extension pipe  20  itself may be regarded as an extension pipe. This combination is sometimes referred to herein as composite extension pipe  60  or composite pipe  60 .  
         [0037]    Also, with reference to FIG. 6 which shows the apparatus of FIG. 1 when installed on roof  200  and connected to vent pipe  150 , it should be noted that for clarity of illustration section lines are not shown in the case of coupling  10 , flashing  30  and cap  40 . Appropriate section lines for these components are shown in FIGS. 2, 4 and  5 .  
         [0038]    Referring now to FIGS.  1  to  6 , coupling  10  includes cylindrical lower and upper ends  11 ,  12 . Extension pipe  20  includes a lower reduced diameter portion  21  and an elongated tubular portion  22 . As best seen in FIG. 6, the inside diameter d 3  of extension pipe  20  is greater than the inside diameter d 1  of vent pipe  150 .  
         [0039]    Lower end  11  of coupling  10  has an outside diameter sized to fit snugly within the inside diameter of vent pipe  150 . The fit should be sufficiently tight to preclude the escape of any gases except into extension pipe  20  under worst case pressure conditions that are apt to develop in vent pipe  150 . To avoid or minimize the choking of gases exhausting through pipe  150 , coupling  10  preferably has a thin wall construction (e.g. 0.050″) such that its inside diameter d 2  is only very slightly less than inside diameter d 1  of pipe  150 . Further, to minimize the likelihood that gases will escape, and although a strong press fit may avoid the necessity, it generally is considered preferable to use a caulking or plumbing sealant (e.g. silicone) between coupling  10  and pipe  150  as indicated by  16  in FIG. 6. As well, to avoid vertical separation between coupling  10  and pipe  150 , it generally is considered preferable to secure these component together by suitable fasteners such as fasteners  15  indicated in FIG. 6.  
         [0040]    Upper end  12  of coupling  10  has an inside diameter sized to snugly receive lower end  21  of extension pipe  20 . Once again, the fit should be sufficiently tight to preclude the escape of gases except into extension pipe  20 . A suitable coupling may be fabricated from various metals (e.g. aluminum, copper).  
         [0041]    Extension pipe  20  may be readily fabricated from off-the-shelf standard size pipe. For example, ABS plastic pipes having standard outside diameters sizes ranging from about 1¼″ to about 12″ and wall thicknesses ranging from about {fraction (1/16)}″ to about ½″ are commonly used for vent pipes for buildings. Reduced diameter portion  21  can be quickly and easily formed using a lathe.  
         [0042]    It will be understood by those skilled in the art that coupling  10  and extension pipe  20  could be fabricated as one integral piece. However, at the present time, it is considered more cost effective to custom fabricate coupling  10  and then to join it with an off-the-shelf pipe in the manner described above.  
         [0043]    Flashing  30  comprises a thin sheet circular base  31  and a centrally positioned cylindrical or tubular portion  32  extending upwardly from the base to a top rim  35 . The inside diameter d 5  (see FIG. 4) of tubular portion  32  is sized such that the flashing fits as a sleeve over the outside diameter of extension pipe  20 . A centrally aligned cylindrical opening  33  having a diameter corresponding to the inside diameter of tubular portion  32  extends lengthwise through base  31  thus permitting flashing  30  to be lowered down over extension pipe  20 .  
         [0044]    Flashing  30  may be readily fabricated from thin sheet metal and thin walled metal tubing (e.g. aluminum, copper); tubular portion  32  being welded around its lower perimeter to base  31 . As indicated in FIGS. 6, 8 e  and  8   f,  flashing  30  is adapted to be attached to roof  200  by means of conventional fasteners  37 .  
         [0045]    As best seen in FIG. 5, vent cap  40  includes a cylindrical inner wall  41  and a cylindrical outer wall  43  with an annular region  45  defined therebetween. Annular region  45  is closed around its top by top  46  and open at its bottom  47 . A centrally aligned opening  48  defined by inner wall  41  extends lengthwise through cap  40  to allow the venting gases to external atmosphere. Lower end  42  of inner wall  41  has a slight inward flair. Likewise, lower end  44  of outer wall  43  has a slight outward flair.  
         [0046]    Annular region  45  is sized to telescopically receive the combined wall thickness of tubular portion  22  of extension pipe  20  and tubular portion  32  of flashing  30 . A corollary is that inner wall  41  of cap  40  has an outside diameter sized to slidingly fit within the inside diameter of extension pipe  20 , and that outer wall  42  has an inside diameter sized to sliding receive the outside diameter of tubular portion  32  of flashing  30 . The inward and outward flairs of lower ends  42 ,  44  of walls  41 ,  43  provide some initial play that assists to guide cap  40  when being installed to the position shown in FIG. 6 (see also FIGS. 8 f ,  8   g ).  
         [0047]    When installed, vent cap  40  will allow rain or other external precipitation to enter a building&#39;s vent pipe system through opening  48 . However, such precipitation is anticipated and a building&#39;s roof vent pipe system typically will interconnect with a suitable building pipe drainage system. Concurrently, top  46  of vent cap  40  shields the preferably tight annular space between extension pipe  20  and flashing  30  from the rain.  
         [0048]    Vent cap  40  is adapted not only to shield rain from entering the annular space between extension pipe  20  and flashing  30  but, in combination with the radial sizing of extension pipe  20 , to discourage or obstruct the movement of venting gases upwardly in the preferably tight annular space between inner wall  41  and extension pipe  20  then downwardly in the annular space between extension pipe  20  and flashing  30 . The obstruction of venting gases from moving in this undesirable path is enhanced because the inside diameters d 3 , d 4  (see FIG. 6 of extension pipe  20  and wall  41  are greater than the inside diameter d 1  of vent pipe  150 . When gases are venting, the region within extension pipe  20  consequently will be a region of reduced pressure compared to the pressure within vent pipe  150 , and there will be no undue choking effect at the outlet provided by opening  48  of cap  40 .  
         [0049]    It may be observed that if diameter d 4  is less than diameter d 1  then a tangible threat of choking may arise. Accordingly, diameter d 4  should not be less than diameter d 1  or, if it is, not by a material amount. Preferably, as is characteristic of the embodiment shown in the drawings, diameter d 4  is greater than diameter d 1 . When extending an existing vent pipe such as vent pipe  150 , this avoids the need for any complex engineering analysis of gas flows, temperatures and pressures under anticipated (but perhaps unknown or uncertain) conditions of operation to determine how much if any constriction can be tolerated, and where the choking threshold might lie.  
         [0050]    The use of the apparatus shown in FIG. 1 will now be described with reference to FIGS. 8 a  to  8   g.    
         [0051]    The first step is to join coupling  10  with extension pipe  20  as indicated in FIG. 8 a  to form composite extension pipe  60  as shown in FIG. 8 b.  Composite pipe  60  is then coupled with vent pipe  150  as shown in FIG. 8 c.  Although not shown in FIGS. 8 a  to  8   g,  this may (and preferably does) include the use of fasteners  15  and caulking  16  as described above in relation to FIG. 6. At this point, no new roof has been installed over existing roof  100 .  
         [0052]    Next, insulation  250  and new roof  200  is added. Then, flashing  30  is lowered down over composite pipe  60  as indicated in FIG. 8 d  until its rests on upper surface  201  of roof  200  as shown in FIG. 8 e.  In this position, it will be noted that a top part  25  of composite pipe  60  extends above rim  35  of flashing  30 . Also, the flashing is ready to be attached to roof  200  by means of fasteners  37 .  
         [0053]    Next, as shown in FIG. 8 f,  the flashing is fully attached to roof  200  by fasteners  37 . Further top part  25  is cut from composite pipe  60  (and discarded) leaving an upper rim  27  flush with rim  35  of flashing  30 . Normally (for example when the pipe to be cut is fabricated from ABS plastic) the cut can be made easily and quickly with a suitable saw. Preferably, the flashing is attached to roof  200  beforehand.  
         [0054]    Finally, the extension is capped and sealed with cap  40  in the manner indicated in FIGS. 8 f  and  8   g  (see also FIG. 2). Optionally, when cap  40  is in position as shown in FIGS. 2 and 8 g , it may be more firmly secured by fasteners (not shown) extending through its outer wall and flashing  30 . However, this merely serves to discourage vandalism. It does not alter or improve the functioning of the cap.  
         [0055]    It will be appreciated by those skilled in the art that many of the details provided above are by way of example only and are not intended to limit the scope of the invention which is to be interpreted with reference to the following claims.