Rainwater drainage structure
The rainwater drainage structure integrates an upper downpipe and drain with a siphon effect to merge rainwater from different sources efficiently, addressing inefficiencies and improving workability and aesthetics in building drainage systems.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- PANASONIC HOUSING SOLUTIONS CO LTD
- Filing Date
- 2022-02-25
- Publication Date
- 2026-05-26
Smart Images
Figure 0007865748000001 
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Abstract
Description
Technical Field
[0001] The present disclosure relates to a rainwater drainage structure for draining rainwater in a building having a basement.
Background Art
[0002] Conventionally, rainwater flowing down to a eaves gutter attached to the eaves tip of a building roof is collected and sent to a downspout, and is discharged from below through the downspout. At this time, in order to increase the drainage treatment amount in the downspout, it is conceivable to efficiently drain a large amount of rainwater by a siphon phenomenon.
[0003] Patent Document 1 describes a rainwater drainage structure including an eaves gutter having a through hole on the bottom surface and a downspout connected to a cylindrical portion below a drainage member passing through the through hole. The drainage member of this rainwater drainage structure has a plate-shaped lid member disposed at the upper end, a mounting cylinder having a cylindrical portion, and a plurality of vertical ribs connecting the upper surface of the flange of the mounting cylinder and the lower surface of the lid member, and is said to cause a siphon phenomenon.
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] Incidentally, it is conceivable to install a rainwater drainage structure that utilizes the siphon effect to efficiently drain large amounts of rainwater on a building with a lower roof, and to efficiently drain rainwater from the lower roof gutter attached to the eaves of the lower roof. In this case, it is also conceivable to run a drain pipe down from the roof above the lower roof, for example from the main roof side, and drain the rainwater into the lower roof gutter. However, in this configuration, there is a possibility that water will splash as the drainage from the drain pipe hits the bottom surface of the lower roof gutter. For this reason, it is conceivable to run a drain pipe from above through a part of the lower roof gutter, connect a drain at a location in the gutter other than where the drain pipe penetrates, and connect the downstream end of the branch pipe connected to the drain pipe below the gutter. In this way, the rainwater flowing from the upper side of the drain pipe and the rainwater from the lower roof gutter will merge at the lower side of the drain pipe before being discharged.
[0006] However, this method requires passing the drainpipe from above through the gutter, creating a drain connection hole in the gutter at a different location from where the drainpipe penetrates, and connecting branch pipes to the drainpipe to form a rainwater drainage structure so that rainwater from the gutter flows into the drainpipe. Such a rainwater drainage structure is quite labor-intensive to construct, resulting in poor workability. Furthermore, a drainage structure with branch pipes connected to the drainpipe has the problem of poor aesthetics.
[0007] Therefore, the purpose of this disclosure is to provide a rainwater drainage structure that can efficiently drain rainwater from the roof above the lower roof and rainwater from the eaves gutter of the lower roof, and that can improve the workability and aesthetic appeal of the construction. [Means for solving the problem]
[0008] The rainwater drainage structure according to this disclosure is installed on a building with an extension roof and is a rainwater drainage structure that drains rainwater from the roof above the extension roof and rainwater from the extension roof, and comprises a gutter attached to the eaves of the extension roof and having a through hole, an upper downpipe that allows rainwater from the roof above the extension roof to flow down, and a drain attached to the through hole that discharges the rainwater from the gutter downward and induces a siphon effect, the drain having an upper drain member and a lower drain member, the upper drain member having an upper flange attached to the upper surface of the bottom plate of the gutter and the radial direction of the upper flange The lower drain member has an upper cylindrical section that extends downward radially inward from the inner end and passes through a through hole, vane sections erected at multiple circumferential positions on the upper surface of the upper flange, and an upper downpipe connection section supported by the vane sections and connected to the upper downpipe. The lower drain member has a lower flange attached to the lower surface of the bottom plate of the gutter, and a lower cylindrical section provided below the lower flange into which the upper cylindrical section is inserted. The lower cylindrical section is connected to a lower downpipe that discharges rainwater downward, and the lower end of the upper downpipe connection section is located higher than the upper surface of the upper flange, thus forming a rainwater drainage structure. [Effects of the Invention]
[0009] According to one embodiment of the rainwater drainage structure of this disclosure, rainwater from the eaves gutter at the eaves of the lower roof can be discharged to the lower downpipe through the drain, and rainwater from the roof above the lower roof can be discharged from the upper downpipe to the lower downpipe through the drain. At this time, the inner side of the lower end of the upper downpipe faces the inner side of the upper cylindrical part, so splashing of rainwater discharged from the upper downpipe in the eaves gutter can be suppressed. In addition, the drain induces a siphon effect. As a result, the rainwater from the upper downpipe and the rainwater from the eaves gutter merge at the drain, and combined with the fact that the upstream side of the lower downpipe tends to become full of rainwater, a large amount of rainwater can be efficiently drained into the lower downpipe by utilizing the siphon effect. Furthermore, in order to drain rainwater from the roof above the lower roof, it is not necessary to form another through-hole in the eaves gutter at a different location from the through-hole for the drain. This improves the workability of the construction work. Furthermore, since it is not necessary to connect the branch pipes connected to the eaves gutter to the drainpipe below the eaves gutter, the aesthetic appearance can be improved. [Brief explanation of the drawing]
[0010] [Figure 1] This is a schematic perspective view showing a portion of a building in which the rainwater drainage structure of the embodiment is installed. [Figure 2] This is an enlarged cross-sectional view of section A in Figure 1. [Figure 3] Figure 2 is a front view of the drain provided. [Figure 4] Figure 3 is a top view of the drain. [Figure 5] Figure 4 is a cross-sectional view of BB. [Figure 6] This figure corresponds to Figure 5 in another example of a rainwater drainage structure of the embodiment. [Figure 7] This figure corresponds to Figure 2 in another example of a rainwater drainage structure of the embodiment. [Figure 8] Figure 7 is a top view. [Modes for carrying out the invention]
[0011] Hereinafter, embodiments of the rainwater drainage structure according to this disclosure will be described with reference to the drawings. Note that if multiple embodiments or modifications are included below, it is intended from the outset that new embodiments may be constructed by appropriately combining their characteristic features. The shapes, arrangements, numbers, materials, etc., described below are illustrative examples for explanatory purposes and can be appropriately changed according to the specifications of the rainwater drainage structure. In the following drawings, equivalent elements will be denoted by the same reference numerals.
[0012] The embodiment will be described using Figures 1 to 5. Figure 1 is a schematic perspective view showing a part of a building 100 in which the rainwater drainage structure 1 of the embodiment is installed. The building 100 in which the rainwater drainage structure 1 is provided includes an entrance door (not shown) and a lean-to roof 102 that protrudes from the wall surface 101 above the windows on the first floor. The upper surface of the lean-to roof 102 is inclined in the vertical direction so as to become lower toward the eaves, which is the front end.
[0013] The rainwater drainage structure 1 consists of a lower roof gutter 10 installed at the eaves of the lower roof 102, an upper downpipe 18 and a lower downpipe 20 arranged vertically along the wall surface 101 near the wall surface 101, and a drain 40 (Figure 2) attached to a through-hole in the lower roof gutter 10 between the upper downpipe 18 and the lower downpipe 20. The upper downpipe 18 receives rainwater 106 from the upper gutter 104 installed at the eaves of the main roof 103, which is a roof above the lower roof 102, via a connecting downpipe 105, and drains the rainwater downwards. In Figure 1, the diagonal grid section shows the rainwater 106. Note that the roof above the lower roof 102 is not limited to the main roof 103, but may also be a lower roof on an upper floor or a roof with a balcony function, etc. In this example, the upper eaves gutter 104 extends along the left-right direction of the building 100, while the lower eaves gutter 10 extends along the front-back direction, which is perpendicular to the left-right direction.
[0014] The lower roof gutter 10 is made of, for example, resin, and has a grooved cross-section that extends in the front-to-back direction, with the lower ends of the first wall 11 and the second wall 12 (Figure 2) connected by a bottom plate 13. The lower roof gutter 10 is suspended and supported by, for example, a hanger (not shown) attached to the building 100, and is attached to the eaves of the lower roof 102, positioned to receive rainwater 106 flowing down from the lower roof 102. The upper surface of the lower roof gutter 10 is open, and both ends in the left-right direction are closed. The lower roof gutter 10 may be fixed to the tip of the lower roof 102 with a bracket that extends to the right. A through hole 14 (Figure 2) is formed at the rear end of the bottom plate 13 of the lower roof gutter 10 for connection to the lower downpipe 20 via a drain 40 (Figure 2), which will be described later.
[0015] The upper downpipe 18 and the lower downpipe 20 are each fixed to multiple positions in the vertical direction of the wall surface 101 and are fixed near the wall surface 101 by multiple fixing members that fit and fix the upper downpipe 18 or the lower downpipe 20 at multiple positions in the vertical direction. The upper downpipe 18 and the lower downpipe 20 discharge rainwater downward.
[0016] The drain 40 is attached to a through hole 14 (Fig. 4) provided in the bottom plate 13 of the lower eaves gutter 10, and the upper end of the lower vertical gutter 20 is connected to a portion protruding downward from the through hole 14. Thereby, the drain 40 discharges the rainwater in the lower eaves gutter 10 to the lower vertical gutter 20.
[0017] Fig. 2 is an enlarged cross-sectional view of part A in Fig. 1. Fig. 3 is a front view of the drain 40 provided in Fig. 2. Fig. 4 is a view of the drain 40 seen from above. Fig. 5 is a cross-sectional view taken along line B-B in Fig. 4. The drain 40 is formed of, for example, resin and has an upper drain member 41 and a lower drain member 61.
[0018] The upper drain member 41 is installed on the upper surface of the bottom plate 13 of the lower eaves gutter 10 and has an upper flange 42 and an upper cylindrical portion 50. The upper flange 42 is attached to the upper surface of the bottom plate 13 by sandwiching the bottom plate 13 with the lower flange 62 of the lower drain member 61 as will be described later. The upper cylindrical portion 50 extends downward from the radially inner end of the upper flange 42 toward the radially inner side, that is, it has a curved surface portion 51 with an upper cross-sectional circular arc shape and smoothly slopes downward, and the lower side is substantially cylindrical. The upper cylindrical portion 50 penetrates the through hole 14. In addition, a tapered surface with a straight cross-section may be provided on the upper inner peripheral surface of the upper cylindrical portion, and the upper cylindrical portion may be configured to extend downward from the radially inner end of the upper flange 42 toward the radially inner side. A curved surface portion 52 with a cross-sectional circular arc shape or a tapered surface with a straight cross-section can be provided on the upper outer peripheral surface of the upper cylindrical portion 50 according to the shape of the upper inner peripheral surface.
[0019] External threads 53 for screw connection with the lower drain member 61 are formed on the outer peripheral surface below the curved surface portions 51 and 52 of the upper cylindrical portion 50. The upper drain member 41 is formed by injection molding of a resin such as rigid vinyl chloride resin, polycarbonate, or ABS. The upper drain member 41 may be made of metal such as cast iron.
[0020] Furthermore, the upper drain member 41 has a high-efficiency rainwater drainage function that induces a siphon effect when a large amount of rainwater flows into the lower roof gutter 10, such as during heavy rain. For this purpose, the upper drain member 41 is composed of multiple vane portions 54 erected at approximately equal intervals in the circumferential direction on the upper surface of the upper flange 42 and the inner surface of the curved portion 51, specifically at five positions, and a cylindrical upper downpipe connection portion 58 supported coaxially with the upper cylindrical portion 50 by being connected to the radially inner ends of the multiple vane portions 54.
[0021] The lower end 59 of the upper downpipe connection part 58 is positioned higher than the upper surface of the upper flange 42. As a result, when the upper drain member 41 is viewed from one side in the lateral direction as shown in Figure 2, a space S is formed that penetrates horizontally between the lower end 59 of the upper downpipe connection part 58 and the upper surface of the upper flange 42. The upper downpipe 18 is connected to the upper downpipe connection part 58 by fitting and fixing the lower end of the upper downpipe 18 to the inside of the upper downpipe connection part 58. At this time, the lower end 19 of the upper downpipe 18 is positioned higher than the upper surface of the upper flange 42, and is at the same position as or higher than the lower end 59 of the upper downpipe connection part 58. As a result, in this example, when rainwater in the lower roof gutter 10 is drained by the drain 40, it is easier for it to merge with the rainwater flowing down from the upper downpipe 18.
[0022] The multiple blade sections 54 are plate-shaped and extend radially, connected at multiple circumferential positions on the upper end of the upper cylindrical section 50, extending from the upper end of the outer circumference of the upper flange 42 to the inner circumference of the lower end of the curved section 51. The radially outer end of each blade section 54 is a plane approximately parallel to the central axis of the upper cylindrical section 50, or a tapered surface slightly inclined radially outward toward the lower end. Both circumferential sides of each blade section 54 are flat. The number of multiple blade sections 54 is five, but it may be an odd number other than five.
[0023] A rectangular plate-shaped projection 55 is formed on the radially outer side of the upper end of each blade portion 54, projecting upward. In the upper drain member 41, the portion above the upper surface of the upper flange 42 that is partitioned by the multiple blade portions 54 becomes an inlet 44 for introducing rainwater that has flowed into the lower roof gutter 10 into the upper drain member 41. The multiple blade portions 54 have the function of straightening the flow of rainwater that flows in from the inlet 44. As a result, the rainwater is straightened and flows by the multiple blade portions 54, which induces a siphon effect.
[0024] On the other hand, the lower drain member 61 has a lower flange 62 that contacts the lower surface of the bottom plate 13 of the lower roof gutter 10 and is attached to the lower surface of the bottom plate 13 by sandwiching the upper flange 42 and the bottom plate 13 as described later, and a lower cylindrical portion 70 provided below the lower flange. The upper cylindrical portion 50 is inserted inside the lower cylindrical portion 70 and the lower side is substantially cylindrical. In this example, an inclined cylindrical portion 71 is formed at the upper end of the lower cylindrical portion 70, with the diameter decreasing as it goes downwards. The inner circumferential surface of the inclined cylindrical portion 71 is a tapered surface with a straight cross-section, and the outer circumferential surface of the inclined cylindrical portion 71 is a curved surface with a circular arc cross-section.
[0025] Female threads 72 are formed on the inner circumferential surface of the lower cylindrical portion 70 for screwing into the male threads 53 of the upper drain member 41. The female threads 72 are formed intermittently in the circumferential direction of the lower cylindrical portion 70, but they may also be in a continuous shape overall.
[0026] The lower drain member 61 is connected to the upper end of the lower downpipe 20 by fitting the lower cylindrical portion 70 inside the large-diameter cylindrical portion 21 formed at the upper end of the lower downpipe 20. Like the upper drain member 41, the lower drain member 61 is formed by injection molding of a resin such as rigid polyvinyl chloride resin. The lower drain member 61 may also be made of metal such as cast iron. Alternatively, the lower end of the lower downpipe 20 may be connected to a drain pipe buried underground, and rainwater flowing down the lower downpipe 20 may be drained into the drain pipe.
[0027] Furthermore, the inner diameter d1 of the upper downpipe connection part 58 (Figure 5) is equal to the inner diameter d2 of the lower cylindrical part 70 (Figure 5). It is smaller. This makes it easier for the inside of the lower end of the upper downpipe 18 connected to the upper downpipe connection part 58 to face the inside of the upper cylindrical part 50.
[0028] The method for assembling the rainwater drainage structure 1 including the drain 40 described above will now be explained. First, a through hole 14 is formed in the bottom plate 13 of the lower roof gutter 10 at the position where the upper drain member 41 will be attached. Next, the upper cylindrical portion 50 of the upper drain member 41 is inserted into the through hole 14 from above and made to protrude downwards, and the upper flange 42 is locked to the periphery of the through hole 14 on the upper surface of the bottom plate 13. At this time, adhesive is applied between the lower surface of the upper flange 42 and the upper surface of the bottom plate 13 to create a water seal. For example, with adhesive already applied to the lower surface of the upper flange 42, the upper flange 42 is placed on the upper surface of the bottom plate 13.
[0029] Then, the lower drain member 61 is fixed to the outer circumference of the upper cylindrical portion 50 that protrudes downward from the through hole 14 of the lower roof gutter 10 by screw connection, and the bottom plate 13 of the lower roof gutter 10 is sandwiched and fixed from both the upper and lower sides by the upper flange 42 of the upper drain member 41 and the lower flange 62 of the lower drain member 61. After that, the upper end of the lower downpipe 20 is connected to the lower cylindrical portion 70 of the lower drain member 61, and the lower end of the upper downpipe 18 is connected to the upper downpipe connection portion 58 of the upper drain member 41.
[0030] With this rainwater drainage structure 1, rainwater 106 that falls on the lower roof 102 flows into the lower roof gutter 10, and as shown in Figures 2, 4, and 5, flows in from the inlet 44 of the upper drain member 41, passes inside the upper cylindrical section 50, and is introduced into the lower downpipe 20. Also, rainwater 106 that falls on the main roof 103 is introduced from the upper gutter 104 into the upper downpipe 18, passes through the upper downpipe 18, and then from its lower end passes inside the upper cylindrical section 50 and is introduced into the lower downpipe 20. As a result, rainwater from the main roof 103 and rainwater from the lower roof 102 merge inside the upper cylindrical section 50. When the amount of rainwater flowing through the lower downpipe 20 exceeds a predetermined flow rate, the rainwater that has flowed down the lower downpipe 20 is forcefully drained downwards from the lower downpipe 20 by the siphon effect.
[0031] Specifically, when the flow rate of rainwater in the lower downpipe 20 exceeds a predetermined level, it becomes easier for a plug to form in a part of the lower downpipe 20 due to the blockage of rainwater. Then, a negative pressure is generated at this plug due to the difference in height, increasing the force pulling the rainwater downwards and causing a siphon effect that causes the rainwater to flow down forcefully. With the drain 40 described above, the effect of straightening the flow of rainwater is greatly enhanced by the multiple vane sections 54, so the generation of vortices can be suppressed when rainwater flows into the inlet 44. This prevents air from being drawn into the lower downpipe 20 by vortices, resulting in better siphon performance and improved drainage. In addition, since the rainwater from the upper downpipe 18 and the rainwater from the lower roof gutter 10 merge inside the upper cylindrical section 50, it becomes easier to achieve a full state of water inside the upper cylindrical section 50. Furthermore, at the inlet 44, the vane sections 54 adjacent to each other in the circumferential direction limit foreign matter from entering the inside of the through hole 14. This prevents the through-hole 14 from becoming clogged with foreign matter.
[0032] According to the rainwater drainage structure 1 described above, rainwater from the eaves gutter 10 at the eaves of the lower roof 102 can be discharged to the lower downpipe 20 through the drain 40, and rainwater from the roof above the lower roof 102 can be discharged to the lower downpipe 20 from the upper downpipe 18 through the drain 40. At this time, the inside of the lower end of the upper downpipe 18 faces the inside of the upper cylindrical part 50, so splashing of rainwater discharged from the upper downpipe 18 on the eaves gutter 10 can be suppressed. In addition, the drain 40 induces a siphon effect. As a result, the rainwater from the upper downpipe 18 and the rainwater from the eaves gutter 10 merge at the drain 40, which, combined with the fact that the downstream side of the lower downpipe 20 tends to become full of rainwater, allows for efficient drainage of a large amount of rainwater into the lower downpipe 20 by utilizing the siphon effect. Furthermore, to allow rainwater to drain from the roof above the lower roof 102, it is not necessary to form another through-hole in the lower roof gutter 10 at a different location from the through-hole 14 through which the drain 40 passes. This improves the workability of the construction work. In addition, since it is not necessary to connect the branch pipes connected to the lower roof gutter to the drain pipe below the lower roof gutter, the aesthetic appearance is improved.
[0033] Furthermore, since the upper cylindrical portion 50 has a curved portion 51 on its upper side that extends downward from the radially inner end of the upper flange 42 toward the radially inner side, it becomes easier to introduce rainwater flowing over the upper flange 42 more smoothly into the lower side of the upper cylindrical portion 50.
[0034] Figure 6 is a diagram corresponding to Figure 5, showing a different example of a rainwater drainage structure in the embodiment. In this example, the lower end of the upper downpipe 18 is fixed inside the upper downpipe connection part 58, and the lower end 19 of the upper downpipe 18 is located lower than the upper surface of the upper flange 42 and inside the cylindrical part of the upper pipe section 50. As a result, in this example, the rainwater from the lower roof gutter 10 and the rainwater from the upper downpipe 18 merge further downstream compared to the configurations in Figures 1 to 5, but when the flow rate of rainwater from the upper downpipe 18 is high, it becomes easier to more effectively introduce the rainwater from the upper downpipe 18 into the upper pipe section 50. Therefore, the configuration in Figure 6 may be selected when the planned drainage amount of rainwater flowing through the upper downpipe 18 is equal to or greater than a predetermined flow rate, and the configuration in Figure 5 may be selected when the planned drainage amount of rainwater flowing through the upper downpipe 18 is less than a predetermined flow rate. In this example, the other configurations and functions are the same as those in Figures 1 to 5.
[0035] Figure 7 is a diagram corresponding to Figure 2 in another embodiment of the rainwater drainage structure. Figure 8 is a top view of Figure 7. In Figures 7 and 8, the upper drain member 80 constituting the drain 40a is shown as a diagonal grid, the lower drain member 90 is shown as a coarse sandy area, and the upper downpipe 18 is shown as a fine sandy area. In the configuration of this example, the number of vanes 54 of the upper drain member 80 in the drain 40a is set to 4, with four vanes 54 provided at approximately equal intervals in the circumferential direction.
[0036] Furthermore, no curved surface is formed at the portion of the lower drain member 90 where the upper end of the lower cylindrical portion 91 connects to the lower flange 92, and the lower cylindrical portion 91 is simply cylindrical. The lower downpipe 20 is fitted and fixed to the lower cylindrical portion 91 while abutting against the lower surface of the lower flange 92. With this configuration, as with the configurations in Figures 1 to 5, it is possible to efficiently drain rainwater from the roof above the lower roof and rainwater from the lower roof gutter 10, and the effects of improving workability and aesthetics during construction can be obtained.
[0037] In the above examples, rainwater from the main roof 103 is introduced into the upper downpipe 18 via the upper eaves gutter 104 and the connecting gutter 105. However, the upper eaves gutter may be positioned along the same wall surface as the lower roof eaves gutter 10, so that rainwater is introduced into the upper downpipe 18 without going through the connecting gutter. [Explanation of Symbols]
[0038] 1 Rainwater drainage structure, 10 Lower roof gutter, 11 First wall, 12 Second wall, 13 Bottom plate, 14 Through hole, 18 Upper downpipe, 19 Lower end, 20 Lower downpipe, 21 Large diameter cylindrical section, 40, 40a Drain, 41 Upper drain member, 42 Upper flange, 44 Inlet, 50 Upper cylindrical section, 51, 52 Curved section, 53 Male screw, 54 Wing section, 55 Protruding section, 58 Upper downpipe connection section, 59 Lower end, 61 Lower drain member, 62 Lower flange, 70 Lower cylindrical section, 71 Inclined cylindrical section, 72 Female screw, 80 Upper drain member, 90 Lower drain member, 100 Building, 101 Wall surface, 102 Lower roof, 103 Main roof, 104 Upper eaves gutter, 105 lower gutter, 106 rainwater.
Claims
1. A rainwater drainage structure installed on a building with an extension roof, which drains rainwater from the roof above the extension roof and rainwater from the extension roof, The aforementioned gutter is attached to the eaves of the lower roof and has through holes, An upper downpipe that allows rainwater to flow down from the roof above the aforementioned lower roof, The system includes a drain attached to the through-hole, which discharges rainwater from the gutter downwards and induces a siphon effect, The drain has an upper drain member and a lower drain member. The upper drain member comprises an upper flange attached to the upper surface of the bottom plate of the gutter, an upper cylindrical portion extending downward from the radially inner end of the upper flange toward the radially inner side and passing through the through hole, wing portions erected at multiple circumferential positions on the upper surface of the upper flange, and an upper downpipe connecting portion connected to the multiple wing portions so as to be positioned radially inward of the multiple wing portions, and connected to the upper downpipe by fitting the upper downpipe to the inside, The lower drain member has a lower flange attached to the lower surface of the bottom plate of the gutter, and a lower cylindrical portion provided below the lower flange, into which the upper cylindrical portion is inserted. The lower cylindrical section is connected to a lower downpipe that discharges rainwater downwards. The lower end of the upper downpipe connection is located higher than the upper surface of the upper flange. Rainwater drainage structure.
2. In the rainwater drainage structure described in claim 1, A rainwater drainage structure in which the inner diameter of the upper downpipe connection portion is smaller than the inner diameter of the lower cylindrical portion.
3. In the rainwater drainage structure according to claim 1 or claim 2, The lower end of the upper downpipe is located higher than the upper surface of the upper flange, forming a rainwater drainage structure.
4. A rainwater drainage structure installed in a building having an extension, which drains rainwater from a roof above the extension and rainwater from the extension, The aforementioned gutter is attached to the eaves of the lower roof and has through holes, An upper downpipe that allows rainwater to flow down from the roof above the aforementioned lower roof, The system includes a drain attached to the through-hole, which discharges rainwater from the gutter downwards and induces a siphon effect, The drain has an upper drain member and a lower drain member. The upper drain member comprises an upper flange attached to the upper surface of the bottom plate of the gutter, an upper cylindrical portion extending downward from the radially inner end of the upper flange toward the radially inner side and passing through the through hole, vane portions erected at multiple circumferential positions on the upper surface of the upper flange, and an upper downpipe connection portion supported by the vane portions and connecting to the upper downpipe. The lower drain member has a lower flange attached to the lower surface of the bottom plate of the gutter, and a lower cylindrical portion provided below the lower flange, into which the upper cylindrical portion is inserted. The lower cylindrical section is connected to a lower downpipe that discharges rainwater downwards. The lower end of the upper downpipe connection is located higher than the upper surface of the upper flange. A rainwater drainage structure in which the lower end of the upper downpipe is located lower than the upper surface of the upper flange.