JP2018184708A - Balcony ventilation structure and installation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a balcony ventilation structure capable of preventing dew condensation in an air layer in an upper part of a rigid floor of the balcony, and an installation method of the balcony ventilation structure exhibiting a ventilation function and allowing easy installation.SOLUTION: A balcony ventilation structure 11 comprises a rigid floor 31a installed on upper faces of beams 21a and 21c set at an upper part of the ceiling 4 of a lower floor and formed with openings 33a and 33b penetrating through the front and rear faces thereof; a handrail 41 installed on an outer periphery of a part 7 extended outward from a building 1; and a plywood 51a installed above the rigid floor 31a via an air layer 50. The openings 33a and 33b of the rigid floor 31a are formed in a non-abutting area 32a excluding an abutting area 39a of the rigid floor 31a abutting on the beam 21a. Thus, the air in the air layer 50 is discharged downward of the rigid floor 31a via the openings 33a and 33b; therefore, the dew condensation in the air layer 50 is prevented.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a balcony ventilation structure and an installation method thereof, and particularly to a balcony ventilation structure installed on a balcony of a building and an installation method thereof.

  FIG. 8 is a diagram for explaining a structural part of a balcony by a construction method for a conventional rooftop facility disclosed in Patent Document 1. As shown in FIG.

  Referring to the figure, a balcony 71 according to a conventional construction method of a rooftop facility is installed above a rigid floor 78 via a rigid floor 78 directly installed on a girder 76 and an air layer 85, and F is used as a finishing material. A waterproof heat insulating material 80 on which a walk (noncombustible finishing material) 81 is constructed, a member (dedicated pipe) 82 for ventilating an underfloor space 89 between the indoor ceiling 87 and the rigid floor 78, and a surrounding girder 76 It is comprised including the wall handrail 79 provided on the top.

  At the time of installation, the girder 76 is attached with the gap 74 opened on the roof beam 73. Then, the rigid floor 78 is directly fixed on the beam 76 and installed.

  Next, the wall handrail 79 is installed above the rigid floor 78 and the girder 76. Thereafter, the waterproof heat insulating material 80 is installed above the rigid floor 78 through the air layer 85. Then, an F walk (noncombustible finishing material) 81 that is a surface finishing material is applied to the surface of the waterproof heat insulating material 80.

  A member (dedicated pipe) 82 is attached to the gap 74. Finally, the installation process of the balcony 71 is completed by attaching the aluminum headboard 83 to the wall railing 79.

  By installing the balcony 71 in this manner, the underfloor space 89 between the indoor ceiling 87 and the rigid floor 78 is ventilated via the member (dedicated pipe) 82.

JP 2006-2477 A

  In the conventional balcony 71 as described above, condensation may occur in the air layer 85 between the rigid floor 78 and the waterproof heat insulating material 80. Further, in order to prevent the occurrence of condensation in the air layer 85, it is necessary to take special measures separately, which is troublesome.

  The present invention has been made in order to solve the above-described problems, and has a balcony ventilation structure that prevents condensation in the air layer above the rigid floor of the balcony, and a ventilation function that is easy and effective. It aims at providing the installation method of the balcony ventilation structure which can be installed in.

  In order to achieve the above-mentioned object, the invention according to claim 1 is a balcony ventilation structure, and is installed on the upper surface of the ceiling of the lower floor, and is installed on the upper surface of the beam and penetrates the front and back surfaces thereof. A rigid floor formed with at least one opening, a handrail installed on the outer periphery of the overhanging portion of the building, and a plywood installed above the rigid floor via an air layer, the opening is The non-contact area is formed except for the contact area of the rigid floor that is in contact with the beam.

  If comprised in this way, the air in an air layer will be discharged | emitted below the rigid floor through opening.

  According to a second aspect of the present invention, in the configuration of the first aspect of the invention, the rigid floor includes at least one vent hole formed so as to communicate with the internal space of the handrail, and the internal space of the handrail is It communicates outward.

  If comprised in this way, the air of the lower part of a rigid floor will enter the interior space of a handrail through a vent hole, and will be discharged | emitted outside.

  According to a third aspect of the present invention, in the configuration of the first or second aspect of the present invention, the rigid floor is formed from a single plate-shaped material having a rectangular shape.

  If comprised in this way, a rigid floor can be formed easily.

  The invention according to claim 4 is a method for installing a balcony ventilation structure, comprising preparing a beam above the ceiling of the lower floor and a rigid floor in which at least one opening penetrating the front and back surfaces is formed. A step of installing a rigid floor on the upper surface of the beam, a step of installing a handrail on the outer periphery of the overhanging portion of the building, and a step of installing a plywood above the rigid floor via an air layer And the opening is formed in a non-contact area excluding the contact area of the rigid floor contacting the beam.

  If comprised in this way, the air in an air layer will be discharged | emitted below the rigid floor through opening only by installing a rigid floor in a beam.

  According to a fifth aspect of the present invention, in the configuration of the fourth aspect of the present invention, the rigid floor is further provided with at least one vent hole so as to communicate with the internal space of the handrail communicating outward. It is what.

  If comprised in this way, only by installing a rigid floor to a beam, the air under the rigid floor will enter into the interior space of a handrail via a vent hole, and will be discharged | emitted outside.

  As described above, according to the first aspect of the present invention, the air in the air layer is discharged to the lower part of the rigid floor through the opening, so that condensation in the air layer is prevented.

  In addition to the effect of the invention of the first aspect, the invention according to the second aspect allows the air below the rigid floor to enter the internal space of the handrail through the vent hole, and is discharged outward. Condensation below the hard floor is prevented.

  In addition to the effects of the invention described in claim 1 or 2, the invention described in claim 3 can easily form a rigid floor, so that the manufacturing efficiency is improved.

  According to the fourth aspect of the present invention, since the air in the air layer is discharged to the lower part of the rigid floor through the opening only by installing the rigid floor on the beam, the balcony ventilation that exhibits the ventilation function. The structure can be easily installed.

  In addition to the effect of the invention of claim 4, the invention described in claim 5 simply installs the rigid floor on the beam, and the air below the rigid floor enters the interior space of the handrail through the vent hole. Since it is discharged to the outside, it is possible to easily install a balcony ventilation structure that exhibits a more efficient ventilation function.

It is a schematic perspective view which shows the rigid floor of the balcony ventilation structure by 1st Embodiment of this invention. It is the schematic sectional drawing seen from the II-II line shown in FIG. It is a schematic perspective view which shows the other rigid floor of the balcony ventilation structure by 1st Embodiment of this invention, Comprising: It is a figure corresponding to FIG. It is a schematic sectional drawing which shows the balcony ventilation structure using the rigid floor shown in FIG. 1, and the other rigid floor shown in FIG. FIG. 5 is a schematic enlarged cross-sectional view of a portion “X” shown in FIG. 4. It is a part of schematic process drawing which shows the installation method of the balcony ventilation structure shown in FIG. FIG. 7 is another part of the schematic process diagram showing the installation method of the balcony ventilation structure following the schematic process chart shown in FIG. 6. It is a figure for demonstrating the structure part of the balcony by the construction method of the conventional rooftop facility disclosed by patent document 1. FIG.

  FIG. 1 is a schematic perspective view showing a rigid floor of a balcony ventilation structure according to a first embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view taken along line II-II shown in FIG. .

  With reference to these drawings, the rigid floor 31a of the balcony ventilation structure 11 according to the first embodiment is installed on a balcony of a building to be described later, and is formed from a single plate-like material having a rectangular shape in plan view. The four openings 33a to 33d having a circular shape in plan view, which are arranged in the vicinity of the four corners in plan view and formed so as to penetrate the front and back surfaces, and the circular shape in plan view formed in the vicinity of one long side 29a. The twelve vent holes 35a and the like, the six vent holes 35b having a circular shape in plan view formed in the vicinity of one short side 30a, and the circular shape in plan view formed in the vicinity of the other short side 30b. It consists of six vents 35c and the like and notches 37a to 37e formed on one long side 29a. By comprising in this way, since the rigid floor 31a can be formed easily, manufacturing efficiency improves. In the rigid floor 31a installed in the building described later, handrails described later are formed in the vicinity of the long side 29a, the vicinity of the short side 30a, and the vicinity of the short side 30b.

Here, the rigid floor 31a is made of, for example, a structural plywood and has a thickness of 28 mm. The length _{L 1} of the long side 29a and long side 29b of Tsuyoshiyuka 31a is set to 1820mm. The length _{W 1} of the short side 30a and the short side 30b of Tsuyoshiyuka 31a is set to 910 mm. Each opening 33a~ opening 33d has a length _{D 1} of the diameter in plan view is set to 100 mm. Each of such vents 35a~ vents 35c has a length _{D 2} of diameter in plan view is set to 16 mm. In addition, these dimensions are examples and are not limited to these. By forming in this way, the necessary structural strength is ensured even when the rigid floor 31a is installed in a building to be described later.

  FIG. 3 is a schematic perspective view showing another rigid floor of the balcony ventilation structure according to the first embodiment of the present invention, and corresponds to FIG.

  The other hard floor 31b has the same basic configuration as the hard floor 31a shown in FIG. Here, the difference will be mainly described.

  Referring to the drawing, the rigid floor 31b has a point where one of the long sides 29c is not formed with a vent hole and a notch, and the other long side 29d is formed with a notch 37f and a notch 37g. Are different from the rigid floor 31a shown in FIG.

  That is, the rigid floor 31b has four openings 33e to 33h that are arranged near the four corners in plan view and penetrate the front and back surfaces, six vent holes 35d that are formed near one short side 30c, and the like. And six vent holes 35e formed in the vicinity of the other short side 30d, and a notch 37f and a notch 37g formed in one long side 29d. By comprising in this way, there exists an effect similar to the rigid floor 31a. In addition, in the rigid floor 31b installed in the building mentioned later, the handrail mentioned later is formed in the short side 30c vicinity and the short side 30d vicinity.

  4 is a schematic cross-sectional view showing a balcony ventilation structure using the rigid floor shown in FIG. 1 and another rigid floor shown in FIG. 3, and FIG. 5 is an “X” portion shown in FIG. FIG.

  With reference to these drawings, the balcony ventilation structure 11 is installed in the beams 21a to 21c installed above the ceiling 4 on the lower floor, the upper surface 22a of the beam 21a, and the upper surface 22c of the beam 21c. 3, the hard floor 31 b shown in FIG. 3 installed on the upper surface 22 b of the beam 21 b and the upper surface 22 c of the beam 21 c, and the outer periphery of the portion 7 projecting outward of the building 1. The plywood 51a installed above the rigid floor 31a and the rigid floor 31b through the air layer 50 formed by the handrail 41 and the transverse floors 54a to 54d installed above the rigid floor 31a and the rigid floor 31b. And the plywood 51b.

  The openings 33a and 33b of the rigid floor 31a are formed in a non-contact area 32a excluding the contact area 39a of the rigid floor 31a that contacts the beams 21a and 21c. Here, the contact area 39a of the rigid floor 31a is an area in contact with the beam 21a.

  Similarly, the openings 33e and 33f of the rigid floor 31b are formed in the non-contact area 32b excluding the contact area 39b of the rigid floor 31b that contacts the beams 21b and 21c. Here, the contact area 39b of the rigid floor 31b is an area in contact with the beam 21b.

  By configuring in this way, the air in the air layer 50 located between the rigid floor 31a and the rigid floor 31b and the plywood 51a through the crosspieces 54a to 54d is indicated by broken-line arrows in FIG. In the direction, the air is discharged to the underfloor space 59 located below the rigid floor 31a and the rigid floor 31b through the opening 33a and the opening 33b and the opening 33e and the opening 33f, so that condensation in the air layer 50 is prevented. Here, the underfloor space 59 is a space located between the rigid floor 31a and the rigid floor 31b and the ceiling 4 on the lower floor via the beams 21a to 21c. Note that the openings 33c and 33d of the rigid floor 31a shown in FIG. 1 have the same effects as the openings 33a and 33b. Further, the openings 33g and 33h of the rigid floor 31b shown in FIG. 3 have the same effects as the openings 33e and 33f.

  The vent hole 35 a of the rigid floor 31 a is formed so as to communicate with the internal space 43 of the handrail 41. Further, the internal space 43 of the handrail 41 passes through an opening 65a and an opening 65b formed in an upper portion of the handrail 41, and via a headboard lower structure 62a and a headboard lower structure 62b installed below the headboard 61. And communicates outward.

  By forming in this way, the air in the underfloor space 59 located below the rigid floor 31a and the rigid floor 31b moves in the direction of the solid line 67 shown in FIG. It enters the internal space 43 of the handrail 41 from the lower gap 58 and the lower gap 57 of the structural face material 66a, passes through the opening 65a and the opening 65b, passes through the underhead structure 62a and the underhead structure 62b, Therefore, condensation is prevented in the underfloor space 59 located below the rigid floor 31a and the rigid floor 31b. Note that the vent hole 35b and the vent hole 35c of the rigid floor 31a shown in FIG. 1 and the vent hole 35d and the vent hole 35e of the rigid floor 31b shown in FIG. 3 have the same effect as the vent hole 35a.

  Therefore, after the air in the air layer 50 located between the rigid floor 31a and the rigid floor 31b and the plywood 51a is discharged to the underfloor space 59 through the opening 33a, the opening 33b, the opening 33e, and the opening 33f. Then, the air enters the inner space 43 of the handrail 41 through the vent hole 35a, passes through the opening 65a and the opening 65b, and is discharged to the outside through the headboard structure 62a and the headboard structure 62b. Thereby, dew condensation in the air layer 50 and the underfloor space 59 is prevented, and the plywood 51a and the plywood 51b can be efficiently dried, so that the durability of the balcony ventilation structure 11 in the building 1 is improved. Note that it is also possible to ventilate the outside air through the reverse path to enter the underfloor space 59 and the air layer 50.

  6 is a part of a schematic process diagram showing a method of installing the balcony ventilation structure shown in FIG. 4, and FIG. 7 shows a method of installing the balcony ventilation structure following the schematic process diagram shown in FIG. It is another part of schematic process drawing.

  With reference to (1) of FIG. 6, in the building 1, the beam 21a-the beam 21c are installed above the ceiling 4 of a lower floor.

  Next, as described above, the rigid floor 31a shown in FIG. 1 and the rigid floor 31b shown in FIG. 3 are prepared. That is, in the rigid floor 31a, four openings 33a to 33d penetrating the front and back surfaces shown in FIG. 1 are formed in the non-contact area 32a excluding the contact area 39a of the rigid floor 31a that contacts the beam 21a. At the same time, as shown in FIG. 4, vent holes 35a to 35c are formed at positions communicating with the internal space 43 of the handrail 41 communicating outward. Further, in the hard floor 31b, four openings 33e to 33h penetrating the front and rear surfaces shown in FIG. 3 are formed in the non-contact area 32b excluding the contact area 39b of the hard floor 31b that contacts the beam 21b. In addition, as shown in FIG. 4, a vent hole 35d and a vent hole 35e are formed at a position communicating with the internal space 43 of the handrail 41 communicating outward.

  Then, the rigid floor 31a prepared in advance as described above is installed on the upper surface 22a of the beam 21a and the upper surface 22c of the beam 21c. The rigid floor 31b prepared in advance as described above is installed on the upper surface 22b of the beam 21b and the upper surface 22c of the beam 21c. At this time, the long side 29b of the rigid floor 31a and the long side 29c of the rigid floor 31b are installed so as to overlap each other. By installing in this way, an underfloor space 59 is formed between the rigid floor 31a and the rigid floor 31b and the ceiling 4 of the lower floor via the beams 21a to 21c. Further, as described above, the opening 33a and the opening 33b of the rigid floor 31a are formed in the non-contact area 32a, and therefore communicate with the underfloor space 59. Since the opening 33e and the opening 33f of the rigid floor 31b are formed in the non-contact area 32b, they communicate with the underfloor space 59.

  With reference to (2) of FIG. 6, the handrail 41 is installed in the outer periphery of the part 7 which the building 1 protruded. That is, in the rigid floor 31a shown in FIG. 1, handrails are installed near the long side 29a, near the short side 30a, and near the short side 30b. In the hard floor 31b shown in FIG. 3, handrails are installed near the short side 30c and near the short side 30d. Here, the handrail 41 installed in the vicinity of the long side 29a of the rigid floor 31a in (2) of FIG. 6 will be described. The other handrails are installed in the same manner as the handrail 41 and have the same effects.

  Above the beam 21a, a structural face material 66a having an opening 65a and a structural face material 66b having an opening 65b are installed. Thereby, the internal space 43 of the handrail 41 is formed between the structural face material 66a and the structural face material 66b. At this time, as shown in FIG. 5, the internal space 43 and the underfloor space 59 communicate with each other by providing a gap 57 below the structural face material 66a.

  On the building 1 side of the structural face material 66a, a trunk rim 67 and a trunk rim 63a, and an underarm structure 62a on the upper end of the trunk rim 63a are installed. At this time, as shown in FIG. 5, the internal space 43 and the underfloor space 59 communicate with each other by providing a gap 58 below the trunk edge 67.

  A trunk edge 63b is installed on the outer side of the structural face material 66b, and the underhead structure 62b is installed on the upper end of the trunk edge 63b.

  Note that the notches 37a to 37e of the rigid floor 31a shown in FIG. 1 and the notches 37f and 37g of the rigid floor 31b shown in FIG. The floor 31a and the rigid floor 31b are fixed.

  With reference to (3) of FIG. 6, the plywood 68a and the plywood 68b are installed in the building 1 side of the trunk edge 67. FIG. Moreover, the exterior material 64a is installed on the building 1 side of the trunk edge 63a.

  The exterior material 64b is installed on the outer side of the trunk edge 63b.

  Then, the headboard 61 is installed above the headboard structure 62a and the headboard structure 62b. In this way, the handrail 41 is installed.

  With reference to (1) of FIG. 7, the crosspieces 54a to 54d whose height increases as they are arranged on the building 1 side are installed on the upper surfaces of the rigid floor 31a and the rigid floor 31b.

  With reference to (2) of FIG. 7, the plywood 51a and the plywood 51b are installed in the upper part of the crosspieces 54a-54d. Thereby, the air layer 50 is formed between the rigid floor 31a and the rigid floor 31b, and the plywood 51a via the crosspieces 54a to 54d.

  With reference to (3) of FIG. 7, the FRP waterproof 69 is given to the upper surface of the plywood 51b installed above the rigid floor 31a via the air layer 50. Thereby, as shown in (2) of FIG. 7, since the crosspieces 54a to 54d are arranged so that the height increases as they are arranged on the building 1 side, they fall on the upper surface of the plywood 51b. Rain or the like flows outward and is discharged by a drainage groove (not shown).

  By doing in this way, the installation process of the balcony ventilation structure 11 is completed. According to this installation method, since the rigid floor 31a in which the opening 35a and the opening 35b are formed in advance and the rigid floor 31b in which the opening 35e and the opening 35f are formed are prepared, the rigid floor 31a and the rigid floor 31b are connected to the beams 21a to 21a. As shown in FIG. 4, the air in the air layer 50 is positioned below the rigid floor 31a and the rigid floor 31b through the opening 33a, the opening 33b, the opening 33e, and the opening 33f only by being installed on the beam 21c. Since it will be discharged | emitted to the underfloor space 59, the balcony ventilation structure 11 in which a ventilation function is exhibited can be installed easily.

  Further, since the rigid floor 31a in which the vent holes 35a are formed in advance is prepared, the rigid floor 31a and the rigid floor 31b are positioned below the rigid floor 31a and the rigid floor 31b simply by installing the rigid floor 31a and the rigid floor 31b on the beams 21a to 21c. The air in the underfloor space 59 enters the internal space 43 of the handrail 41 through the vent hole 35a and is discharged to the outside. Therefore, the balcony vent structure 11 that exhibits a more efficient vent function is provided. Can be installed easily. That is, in the installation site of the balcony ventilation structure 11, it is possible to save the trouble of separately providing a process for ventilation, and the installation work becomes more efficient.

  In the above-described embodiment, the rigid floor is formed in a specific shape, but may be formed in other shapes such as a square shape in plan view.

  In the above embodiment, the rigid floor is formed in a specific size, but may be formed in other sizes.

  Furthermore, in the above embodiment, the rigid floor is formed from one plate-shaped material, but may be formed from a plurality of different materials.

  Furthermore, in the above-described embodiment, the balcony ventilation structure is composed of two rigid floors, but may be composed of at least one rigid floor. Alternatively, it may be composed of three or more rigid floors. In this case, the shape and size of each rigid floor may be different.

  Further, in the above-described embodiment, the rigid floor has a specific number of openings formed therein, but it does not contact the surface except for the contact area of the rigid floor that penetrates the front and back surfaces and contacts the beam. As long as it is formed in the region, at least one may be formed.

  Further, in the above-described embodiment, the opening is formed in a specific shape, but may be formed in other shapes such as a rectangular shape.

  Further, in the above-described embodiment, the opening is formed in a specific size. However, the opening may be formed in another size so that the diameter is formed smaller, for example.

  Further, in the above embodiment, the rigid floor has a specific number of air holes formed, but at least one of the rigid floors is formed as long as it communicates with the internal space of the handrail communicating outward. It only has to be done. Or the ventilation hole does not need to be formed.

  Further, in the above-described embodiment, the vent hole is formed in a specific shape, but may be formed in other shapes such as a slit-like rectangular shape.

  Furthermore, in the above-described embodiment, the vent hole is formed in a specific size. However, for example, the vent hole may be formed in other sizes so that the diameter is smaller.

  Further, in the above embodiment, the vent hole communicates with the internal space of the handrail through the gap below the trunk edge and the gap below the structural face material. You may make it communicate with the interior space of a handrail by other methods so that a surface material may be installed in a building side rather than a ventilation hole.

  Furthermore, in the above-described embodiment, the air layer is formed through a cross, but may be formed by a spacer other than the cross.

  Furthermore, in the above embodiment, the rigid floor has a notch, but the notch need not be formed. Or you may form in the position different from this application, a different magnitude | size, and a different number.

  Furthermore, in the above embodiment, the handrail is formed from a specific member, but may be formed from other members as long as it is installed on the outer periphery of the overhanging portion of the building. good.

  Furthermore, in the above-described embodiment, two plywoods are installed. However, as long as the plywood is installed above the rigid floor via the air layer, it is sufficient that at least one plywood is installed. .

  Furthermore, in the above-described embodiment, the plywood has been subjected to FRP waterproofing. However, the FRP waterproofing may not be performed. Alternatively, other waterproof treatment may be performed.

  Furthermore, in the above-described embodiment, the handrail communicates with the outside through the opening and the underbody structure. However, the handrail may communicate with the outside by other methods.

  Furthermore, in the above-described embodiment, the opening was formed in the rigid floor in advance before installing the rigid floor on the upper surface of the beam. It may be formed on the floor.

  Furthermore, in the above embodiment, the vent hole was formed in the rigid floor in advance before installing the rigid floor on the upper surface of the beam. It may be formed on a rigid floor.

DESCRIPTION OF SYMBOLS 1 ... Building 4 ... Ceiling 7 ... Overhang part 11 ... Balcony ventilation structure 21 ... Beam 22 ... Upper surface 31 ... Rigid floor 32 ... Non-contact area 33 ... Opening 35 ... Vent hole 39 ... Contact area 41 ... Handrail 43 ... Internal space 50 ... Air layer 51 ... Plywood In addition, the same code | symbol in each figure shows the same or an equivalent part.

Claims (5)

Balcony ventilation structure,
A beam installed above the ceiling of the lower floor;
A rigid floor installed on the upper surface of the beam and having at least one opening penetrating the front and back surfaces thereof;
A handrail installed on the outer periphery of the overhanging part of the building,
A plywood installed above the rigid floor through an air layer;
The balcony ventilation structure according to claim 1, wherein the opening is formed in a non-contact area excluding a contact area of the rigid floor that contacts the beam. The rigid floor includes at least one vent hole formed to communicate with the internal space of the handrail,
The balcony ventilation structure according to claim 1, wherein an internal space of the handrail communicates outward.   The balcony ventilation structure according to claim 1 or 2, wherein the rigid floor is formed from a single plate-like material having a rectangular shape. A method for installing a balcony ventilation structure,
Installing a beam above the ceiling of the lower floor;
Providing a rigid floor in which at least one opening penetrating the front and back surfaces is formed;
Installing the rigid floor on the upper surface of the beam;
Installing a handrail on the outer periphery of the overhanging part of the building;
Providing a plywood above the rigid floor via an air layer,
The opening method of the balcony ventilation structure formed in the non-contact area | region except the contact area | region of the said rigid floor which contact | abuts the said beam. 5. The method for installing a balcony ventilation structure according to claim 4, wherein at least one ventilation hole is formed in the rigid floor so as to communicate with an internal space of the handrail communicating outward.

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