Roof substrate material and roof structure

Abstract

To easily construct a high-quality roof structure even by non-experts.SOLUTION: A roof substrate 20 is configured to include a sheathing roof board 21 and a waterproof sheet 22 provided on the sheathing roof board 21. The sheathing roof board 21 is formed from a rectangular medium density fiberboard containing a water-repellent agent. The waterproof sheet 22 is configured to have a sheet body 22a equal to or larger than an upper surface of the sheathing roof board 21, and an adhesive layer 22b provided between a lower surface of the opposing sheet body 22a and the upper surface of the sheathing roof board 21. The sheet body 22a is adhered to the upper surface of the sheathing roof board 21 by the adhesive layer 22b.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a roof underlayment and a roof structure. [Background technology]

[0002] BACKGROUND ART Conventionally, in order to improve the waterproofing of a roof structure, a roof underlayment material in which a waterproof sheet is laid on the upper surface of a sheathing board has been used (for example, see Patent Document 1 below).

[0003] Patent Document 1 discloses a roof structure that includes a roof underlayment consisting of a waterproof sheet laid on top of a sheathing board made of structural plywood. In conventional roof structures, covering the top of the sheathing board with a waterproof sheet like this prevents rainwater from seeping into the sheathing board. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-293834 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional roof structures, waterproof sheets are formed larger than the sheathing boards, and are laid out at the construction site so as to cover the top surfaces of multiple sheathing boards together, and are fixed to the sheathing boards with staples or the like. Waterproof sheets are thin, soft, and light, so they are easily rolled up by the wind and there is a risk of them wrinkling or tearing during construction. Therefore, in conventional roof structures where waterproof sheets must be laid at the construction site, construction (especially the installation of waterproof sheets) is difficult, and the quality of the finished product may vary greatly depending on the skill of the installer.

[0006] The present invention has been made in view of the above points, and its object is to enable even an unskilled person to construct a roof structure easily and with a good finish. [Means for solving the problem]

[0007] In order to achieve the above-mentioned objectives, the present invention uses a roof underlayment material in which a waterproof sheet has been pre-attached to the top surface of the sheathing board in a factory or the like, and also uses a medium-density fiberboard containing a water-repellent agent for the sheathing board.

[0008] Specifically, the first invention is a roof underlayment material comprising a sheathing board and a waterproof sheet placed on the sheathing board, wherein the sheathing board is made of a rectangular medium-density fiberboard containing a water-repellent agent, the waterproof sheet has a sheet body that is larger than the upper surface of the sheathing board, and an adhesive layer placed between the opposing underside of the sheet body and the upper surface of the sheathing board, and the sheet body is adhered to the upper surface of the sheathing board by the adhesive layer.

[0009] In the first invention, a waterproof sheet larger than or equal to the top surface of a rectangular sheathing board is glued to the top surface of the board before construction and used as a roof underlayment. Therefore, the waterproof sheet can be installed along with the sheathing board simply by laying multiple roof underlayments on the rafters supporting the roof. Therefore, using this roof underlayment eliminates the need to lay a waterproof sheet at the construction site, which is prone to being torn by wind and may wrinkle or tear during construction. Furthermore, by pre-attaching the waterproof sheet to the top surface of the sheathing board at a factory, the waterproof sheet is prevented from wrinkling or tearing, and an adhesive layer is interposed between the waterproof sheet and the sheathing board, preventing gaps from forming. Therefore, rainwater does not penetrate the gap between the waterproof sheet and the sheathing board. Therefore, using this roof underlayment allows even non-experts to easily and satisfactorily construct a roof structure.

[0010] However, when using roof underlayment materials in which a waterproof sheet is pre-attached to the sheathing boards in a factory or the like, the nails used to install the roof underlayment are driven from above the waterproof sheet, so the nail heads are positioned above the waterproof sheet, and nail holes are made in the waterproof sheet. Therefore, when using such roof underlayment materials, there is a concern that rainwater will seep into the sheathing boards through the nail holes and cause the sheathing boards to rot.

[0011] Therefore, in the first invention, the sheathing boards are made of medium density fiberboard (MDF) which has low water absorption.

[0012] Medium-density fiberboard (MDF) is a wood-based board formed by hot-pressing wood fibers with adhesive, resulting in low water absorption. Furthermore, roofing underlayment materials made of MDF, which has a relatively high density and few voids, offer significantly higher nail-hole waterproofing than sheathing made of plywood or other materials, thanks to the adhesion of the wood fibers coated with a water-resistant adhesive to the nails driven in to install the roofing underlayment. Furthermore, an adhesive layer is provided between the underside of the waterproof sheet and the top surface of the sheathing, ensuring close contact with the nails driven in to install the roofing underlayment. This significantly improves nail-hole waterproofing compared to sheathing made of staples or other fasteners. Therefore, even when using roofing underlayment materials with the waterproof sheet pre-attached to the sheathing in a factory, rainwater does not seep into the sheathing through the nail holes, preventing water absorption and deformation (thickness expansion, warping, twisting) of the sheathing. This also prevents mold growth and decay of the sheathing.

[0013] In addition, in roof underlayment materials in which a waterproof sheet of the same size as the top surface of the sheathing board is attached to the top surface of the sheathing board so that it covers the entire top surface, the joints between the roof underlayment materials are not covered by the waterproof sheet, so there is a risk that rainwater will seep into the interior through the joints of the roof underlayment materials and cause leaks.

[0014] Therefore, in the first invention, the sheathing board is made of a medium-density fiberboard containing a water-repellent agent, rather than a simple medium-density fiberboard.

[0015] By incorporating a water-repellent agent into the medium-density fiberboard used as sheathing, the contact angle of water with the surface of the medium-density fiberboard becomes greater than 90 degrees (it has water repellency). Therefore, even if rainwater seeps in through the joints of the roofing underlayment and reaches the joints of the sheathing, the rainwater turns into droplets with a contact angle greater than 90 degrees on the end grain surface of the sheathing, and the droplets act as plugs, preventing further penetration. In other words, according to the first invention, the water-repellent properties of the sheathing can prevent rainwater from seeping into the interior through the joints of the roofing underlayment, even without covering the joints with a waterproof sheet or waterproof tape, thereby preventing leaks.

[0016] The second invention is characterized in that, in the first invention, the sheet body is formed to the same size as the upper surface of the sheathing board and is adhered to the upper surface of the sheathing board so as to cover the entire upper surface of the sheathing board.

[0017] In the roof underlayment of the second invention, the entire top surface of the sheathing boards is covered with a waterproof sheet body of the same size. With this roof underlayment, the waterproof sheet can be easily installed along with the sheathing boards by simply fixing multiple roof underlayments onto the rafters supporting the roof with their butt ends abutting. Therefore, the second invention allows even unskilled workers to easily and satisfactorily install roof structures, helping to alleviate the recent shortage of craftsmen. Furthermore, while it is common for a roofer other than the sheathing installer to apply a waterproof sheet to the sheathing boards after installation, the second invention prevents the sheathing boards from getting wet even if it rains after installation, eliminating the need for a roofer other than the sheathing installer to come to the construction site to perform the waterproofing after installation.

[0018] The third invention is characterized in that, in the first invention, the sheet body is formed to the same size as the upper surface of the sheathing board and is adhered to the upper surface of the sheathing board at a position offset in at least one of the vertical and horizontal directions.

[0019] In the roof underlayment of the third invention, a waterproof sheet body of the same size as the top surface of the sheathing board is adhered to the top surface of the sheathing board at a position offset in at least one of the vertical and horizontal directions.

[0020] If the sheet body is adhered to the top surface of the sheathing board at a position offset in one vertical direction (first vertical direction), for example, the edge portion of the top surface of the sheathing board in the second vertical direction, which is the opposite vertical direction to the first vertical direction, is not covered by the sheet body and is exposed, and at the end portion of the top surface of the sheathing board in the first vertical direction, the sheet body protrudes from the end of the sheathing board in the first vertical direction. With this type of roof underlayment, during construction, the protruding portion of the waterproof sheet body of each roof underlayment is placed on the exposed portion of the top surface of the sheathing board of the adjacent roof underlayment, and both roof underlayments are fixed to rafters or the like, so that the joint between the two roof underlayments is covered by the waterproof sheet body of one of the roof underlayments.

[0021] Furthermore, when the sheet body is adhered to the top surface of the sheathing board at a position offset in one of the vertical directions (first vertical direction) and one of the horizontal directions (first horizontal direction), the edge portion of the top surface of the sheathing board in the second vertical direction and the edge portion of the top surface of the sheathing board in the second horizontal direction opposite the first horizontal direction are exposed and not covered by the sheet body, and at each end of the top surface of the sheathing board in the first vertical direction and the first horizontal direction, the sheet body protrudes from each end of the sheathing board in the first vertical direction and the first horizontal direction, respectively. With this roof underlayment, during construction, the protruding portion of the waterproof sheet body of each roof underlayment is placed on the exposed portion of the top surface of the sheathing board of the adjacent roof underlayment, and the two roof underlayments are then fixed to rafters or the like, so that the joint between the two roof underlayments is covered by the waterproof sheet body of one of the roof underlayments.

[0022] As described above, according to the third aspect of the present invention, the infiltration of rainwater into the interior of the room through the seams of the roof underlayment can be prevented not only by the water-repellent properties of the sheathing boards but also by the fact that the seams are covered by the waterproof sheet itself, thereby further reducing rain leakage.

[0023] The fourth invention is characterized in that, in the first invention, the sheet body is formed to be larger than the upper surface of the sheathing subfloor, covers the entire upper surface of the sheathing subfloor, and is adhered to the upper surface of the sheathing subfloor so as to extend beyond one side or two adjacent sides of the upper surface of the sheathing subfloor.

[0024] In the roof underlayment of the fourth invention, a waterproof sheet body larger than the top surface of the sheathing board is adhered to the top surface of the sheathing board so as to cover the entire top surface of the sheathing board and extend beyond one or two adjacent sides of the top surface of the sheathing board. With this type of roof underlayment, during construction, the portion of the waterproof sheet body that extends beyond the sheathing board in each roof underlayment is placed on the top surface of the adjacent roof underlayment (the waterproof sheet body is overlapped), and both roof underlayments are fixed to rafters or the like, so that the joint between the two roof underlayments is covered by the waterproof sheet body of one of the roof underlayments.

[0025] As described above, according to the fourth aspect of the present invention, the infiltration of rainwater into the interior of the room through the seams of the roof underlayment can be prevented not only by the water-repellent properties of the sheathing boards but also by the seams being covered by the waterproof sheet itself, thereby further reducing rain leakage.

[0026] The fifth invention is a roof structure of a building comprising a plurality of roof underlayments and a plurality of roof covering materials attached above the plurality of roof underlayments, characterized in that the roof underlayments are roof underlayments according to any one of the first to fourth inventions.

[0027] In the fifth invention, a roof structure comprising roofing materials and roof underlayment is constructed using roof underlayment in which a waterproof sheet is pre-attached to the sheathing boards in a factory or the like. Therefore, simply laying multiple pieces of the roof underlayment on rafters or the like allows the waterproof sheet to be installed along with the sheathing boards. Furthermore, there is no risk of the waterproof sheet wrinkling or tearing. Furthermore, an adhesive layer is interposed between the waterproof sheet and the sheathing boards, eliminating any gaps and preventing rainwater from seeping in between. Therefore, according to the fifth invention, even non-experts can easily install a roof structure with a good finish.

[0028] In addition, in the roof structure of the fifth invention, the sheathing is made of a roof underlayment composed of medium-density fiberboard containing a water-repellent agent, so even if nails to install the roof underlayment are driven from above the waterproof sheet, rainwater does not seep into the sheathing through the nail holes, so there is no risk of the sheathing absorbing water and deforming (expanding in thickness, warping, twisting), and mold growth and rotting of the sheathing can be suppressed. Furthermore, the water-repellent properties of the sheathing can prevent rainwater from seeping into the interior through the joints of the roof underlayment, even without covering the joints with a waterproof sheet or waterproof tape, thereby suppressing leaks. [Effects of the Invention]

[0029] As explained above, according to the present invention, a roof underlayment material is used in which a waterproof sheet is pre-attached to the top surface of the sheathing board in a factory, etc., thereby eliminating the process of laying the waterproof sheet at the construction site. Furthermore, since a medium-density fiberboard containing a water-repellent agent is used for the sheathing board, it is possible to prevent decay of the sheathing board and leakage of rainwater. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a cross-sectional view of the gable side showing a part of the roof structure of the building according to the first embodiment. [Figure 2] FIG. 2 is a partially enlarged view of FIG. [Figure 3]FIG. 3 is a cross-sectional view of the flat side showing a part of the roof structure of the building according to the first embodiment. [Figure 4] FIG. 4 is an explanatory diagram of a method for installing a roof underlayment for the roof structure of the first embodiment. [Figure 5] FIG. 5 is an explanatory diagram of a method for installing a roof underlayment for a roof structure according to the second embodiment. [Figure 6] FIG. 6 is an explanatory diagram of a method for installing a roof underlayment for a roof structure according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are merely preferred examples in nature and are not intended to limit the scope of the present invention, its applications, or its uses.

[0032] First Embodiment of the Invention As shown in FIG. 1, the roof structure 1 is formed by placing a plurality of roofing materials 10, . . . , 10 in order on a plurality of roof underlayment materials 20, .

[0033] -Roof structure configuration- As shown in Figures 1 to 3, the roof structure 1 comprises a plurality of roofing materials 10,...,10, a plurality of roof underlayment materials 20,...,20, and a plurality of insulating materials 30,...,30. The plurality of roofing materials 10,...,10 are installed on a plurality of roof underlayment materials 20,...,20, and the plurality of roof underlayment materials 20,...,20 are installed above a plurality of rafters 2,...,2 arranged at intervals in the rafter truss of the building. A plurality of gypsum boards 3,...,3 are attached to the lower end surfaces of the plurality of rafters 2,...,2. In Figure 1, reference numeral 7 denotes a fascia board, reference numeral 8 denotes a flashing, reference numeral 9a denotes a ridge wrap, and reference numeral 9b denotes a ridge ventilation member.

[0034] In this embodiment 1, a metal roofing material made of a folded rectangular metal plate is used as the roofing material 10. Note that the roofing material 10 is not limited to a metal roofing material, and may be clay roofing tiles, cement roofing tiles, asphalt shingles, decorative slates, etc.

[0035] The roof underlayment 20 comprises sheathing boards 21 and a waterproof sheet 22, and is attached to a plurality of rafters 2, ..., 2. The detailed configuration will be described later, but the roof underlayment 20 is formed by adhering the waterproof sheet 22 to the top surface of the sheathing boards 21 before construction in a factory or the like. The roof underlayment 20 is fixed to the plurality of rafters 2, ..., 2 with nails or the like (not shown), so that the sheathing boards 21 and the waterproof sheet 22 are constructed as a single unit.

[0036] The heat insulating material 30 is made of rock wool and is provided between each of the plurality of rafters 2, ..., 2. The heat insulating material 30 is formed so that its height is lower than the height of the plurality of rafters 2, ..., 2. Therefore, below the roof underlayment material 20, an air passage 40 is formed that extends along the rafters 2 from the eaves 6 side to the ridge beam 5 side.

[0037] With the above-described configuration, in the first embodiment, the roof structure 1 is configured as a so-called insulated roof structure in which the heat insulating material 30 is provided on the roof side, not on the ceiling side.

[0038] <Detailed composition of roofing materials> As described above, in the present embodiment 1, the roofing material 10 is a metal roofing material made of a bent rectangular metal plate. Specifically, in the present embodiment 1, the roofing material 10 is made of Galvalume Steel Plate (registered trademark). The roofing material 10 is attached to the upper surface of the roof underlayment 20 with screws 4 driven into the roof underlayment 20. Note that the roofing material 10 is not limited to Galvalume Steel Plate (registered trademark), and may be a metal roofing material made of a copper plate, a galvanized steel plate, an aluminum plate, a stainless steel plate, or the like.

[0039] As shown in FIG. 3, the roofing material 10 includes a main body portion 11, a first engaging portion (seam) 12, a second engaging portion (seam) 13, a support leg portion 14, and a fixing portion 15.

[0040] The main body 11 is the portion of the rectangular metal plate that constitutes the roofing material 10 excluding both widthwise ends, and is a generally flat portion that extends in the longitudinal direction of the roofing material 10 and covers the top of the roof underlayment 20 when attached to the roof underlayment 20. The main body 11 has step portions 11a at both widthwise ends that become lower as they move from the ends to the middle. As a result, the middle portion of the main body 11 in the widthwise direction has a shallower recessed shape that is lower than the both widthwise ends. The step portions 11a formed at both widthwise ends of the main body 11 suppress longitudinal deflection.

[0041] The first engagement portion 12 is formed by a portion of the width direction of the metal plate that constitutes the roofing material 10, and extends in the longitudinal direction of the roofing material 10. The first engagement portion 12 is formed in a shape that protrudes upward on one side of the main body 11 in the width direction (the right side in Figure 3) and engages with the second engagement portion 13 of the adjacent roofing material 10.

[0042] Specifically, in this embodiment 1, the first engagement portion 12 has a first linear portion 12a in the shape of a rectangular flat plate extending upward from one end of the main body 11 in the width direction, a protruding portion 12b that extends from the upper end of the first linear portion 12a toward the inside in the width direction of the roofing material 10, then bends diagonally upward to the outside in the width direction and extends diagonally upward, and a second linear portion 12c in the shape of a rectangular flat plate extending downward from the upper end of the protruding portion 12b in parallel to the first linear portion 12a. The first engagement portion 12 is formed into a single-whiskered arrow shape that protrudes toward the inside in the width direction by the first linear portion 12a, the protruding portion 12b, and the second linear portion 12c.

[0043] The second engagement portion 13 is formed by a portion of the width direction of the metal plate that constitutes the roofing material 10, and extends in the longitudinal direction of the roofing material 10. The second engagement portion 13 protrudes upward on the other width direction side of the main body 11 (the left side in FIG. 3) and covers over the first engagement portion 12 of the adjacent roofing material 10, thereby being formed in a shape that engages (seam-joints) with the first engagement portion 12 of the adjacent roofing material 10.

[0044] Specifically, in this first embodiment, the second engagement portion 13 has a rectangular, flat, straight portion 13a extending upward from the other end of the main body 11 in the width direction, a protruding portion 13b extending diagonally downward from the upper end of the straight portion 13a outward in the width direction, then bending toward the inside of the roofing material 10 in the width direction and extending approximately perpendicular to the straight portion 13a, and a terminal portion 13c bending diagonally downward from one end of the protruding portion 13b outward in the width direction and extending diagonally downward. The second engagement portion 13 is formed into a single-whisker arrow shape that protrudes outward in the width direction by the straight portion 13a, the protruding portion 13b, and the terminal portion 13c. The second engagement portion 13 is formed into a single-whisker arrow shape that is slightly larger than the first engagement portion 12 so as to cover the first engagement portion 12.

[0045] The support leg 14 is formed from a portion of the width direction of the metal plate that constitutes the roofing material 10, and extends in the longitudinal direction of the roofing material 10. The support leg 14 extends downward from the lower end of the second straight portion 12c of the first engagement portion 12 (at the same height as the lower end of the first straight portion 12a), and is a portion that supports the first engagement portion 12. The support leg 14 is formed in the shape of a rectangular flat plate whose length (length in the direction perpendicular to the plane of the paper in FIG. 3) is equal to that of the second straight portion 12c of the first engagement portion 12.

[0046] The fixing portion 15 is formed from a portion of the width direction of the metal plate that constitutes the roofing material 10, and extends in the longitudinal direction of the roofing material 10. The fixing portion 15 extends outward in the width direction from the lower end of the support leg portion 14, has a flat portion that abuts against the roof underlayment 20, and is fixed to the roof underlayment 20. The fixing portion 15 is formed in the shape of a rectangular flat plate that is equal in length to the support leg portion 14 (the length in the direction perpendicular to the plane of the paper in Figure 3). As described above, the fixing portion 15 is fixed to the roof underlayment 20 with the screws 4 that are driven into the roof underlayment 20.

[0047] With this configuration, the roofing material 10 is installed on the roof underlayment material 20 by simply fixing the fixing portion 15 to the roof underlayment material 20 with the screws 4, covering and engaging the second engaging portion 13 of the roofing material 10 adjacent to the first engaging portion 12, and engaging the second engaging portion 13 so as to cover and engage the first engaging portion 12 of the adjacent roofing material 10.

[0048] <Detailed composition of roof underlayment> 1 to 3, the roof underlayment 20 includes a sheathing board 21 and a waterproof sheet 22. In the first embodiment, the sheathing board 21 is configured to be both moisture-permeable and waterproof to prevent decay of the sheathing board 21. In addition, an air passage 40 that communicates with the outdoors is provided between the sheathing board 21 and the heat insulating material 30.

[0049] [Noji board] The sheathing board 21 has a density (g / cm 3 ) is 0.7 or more and less than 0.85. In this embodiment, the density is 0.79 g / cm 3 A medium density fiberboard with a thickness of 9.2 mm is used as the sheathing board 21.

[0050] The medium-density fiberboards constituting the sheathing boards 21 contain an adhesive with excellent water resistance. In the first embodiment, the sheathing boards 21 are made of medium-density fiberboards containing a urea-melamine co-condensation resin adhesive. The adhesive used for the medium-density fiberboards is not limited to the urea-melamine co-condensation resin adhesive, and may also contain diphenylmethane diisocyanate, phenol resin, or the like.

[0051] (water repellency) The sheathing board 21 is configured so that the contact angle of water with the upper surface is greater than 90 degrees. Specifically, in the first embodiment, when forming the medium-density fiberboard that constitutes the sheathing board 21, a water-repellent agent such as paraffin, silicone resin, or fluororesin is added in an amount necessary to make the surface of the medium-density fiberboard water-repellent (so that the contact angle of water at any point on the surface is greater than 90 degrees).

[0052] From the viewpoint of excellent water repellency, the surface of the sheathing board 21 is preferably configured so that the contact angle of water is 110 degrees or more, and more preferably so that the contact angle of water is 120 degrees or more.

[0053] (Water absorption rate) The sheathing boards 21 are configured to have a water absorption rate of 15% or less. Preferably, the sheathing boards 21 are configured to have a water absorption rate of 13.6% or less, and more preferably, to have a water absorption rate of 13.2% or less.

[0054] Here, the water absorption rate is determined by measuring the weight (m1) of a test piece that has reached a constant weight in an environment of 65±5% relative humidity in accordance with the water absorption thickness swelling rate test specified in JIS A5905, placing the test piece in water at 20±1°C, immersing it for 24 hours, removing the test piece, and measuring its weight (m2). The water absorption rate is calculated from the difference in weight of the test piece before and after immersion in water (the difference in weight of the test piece before and after immersion (m2 - m1) divided by the weight m1 before immersion, and multiplying this value by 100).

[0055] As described above, in medium-density fiberboards containing a water-resistant adhesive, the wood fibers are coated with the adhesive, which makes it difficult for water to penetrate between the wood fibers, resulting in a low water absorption rate. Therefore, by using a water-resistant adhesive to form the medium-density fiberboards that make up the sheathing boards 21 and adjusting the blending ratio, the water absorption rate of the sheathing boards 21 can be set to the desired level, which in this embodiment is 15% or less (preferably 13.6% or less, more preferably 13.2% or less).

[0056] The water absorption thickness expansion test was conducted on 12 mm thick structural plywood (cedar) and structural plywood (surface layer larch, core layer cedar) that are commonly used as conventional sheathing boards, and the water absorption rates were calculated to be 82% and 61%, respectively. This shows that the water absorption rate of the sheathing board 21 of this embodiment 1 is significantly lower than that of conventional sheathing boards.

[0057] (Breathability) The moisture permeability resistance of the sheathing board 21, measured in accordance with the cup method specified in JIS A1324, is 1.2 m 2 Specifically, in the first embodiment, the moisture permeation resistance of the sheathing board 21 is set to be less than 1.2 m 2The element size (size, diameter, length of wood fibers) of the medium density fiberboard that constitutes the sheathing board 21 is adjusted so that the modulus of elasticity is less than s·Pa / μg.

[0058] As described above, medium-density fiberboards containing adhesives with excellent water resistance have a low water absorption rate. However, in this embodiment, by adjusting the element size (size, diameter, and length of wood fibers) of the medium-density fiberboards that make up the sheathing board 21, it is possible to achieve a moisture permeation resistance of 1.2 m / s even if the water absorption rate is 15% or less. 2 It is possible to construct a sheathing board 21 with a low compressive strength of less than ·s·Pa / μg.

[0059] In addition, the moisture permeability resistance of 12mm thick structural plywood (cedar) and structural plywood (surface larch, core cedar) that are commonly used as roofing boards, measured in accordance with the cup method specified in JIS A1324, is 11m 2 s·Pa / μg and 13m 2 ·s·Pa / μg. This shows that the moisture permeation resistance of the sheathing board 21 of the first embodiment is significantly lower than that of the conventional sheathing board, that is, the moisture permeation performance is significantly higher.

[0060] [Tarp] As shown enlarged in FIG. 2, the waterproof sheet 22 has a sheet body 22a and an adhesive layer 22b formed on the lower surface of the sheet body 22a.

[0061] In the first embodiment, the sheet body 22a is made of a modified asphalt roofing material, which is a fiber sheet impregnated with asphalt containing synthetic rubber and coated thereon. Note that the sheet body 22a is not limited to a modified asphalt roofing material. The sheet body 22a may be made of an asphalt roofing material, which is a fiber sheet impregnated with asphalt containing no synthetic rubber and coated thereon, a polymer roofing material (such as "Roof Lamitect Z" manufactured by Seiren Co., Ltd.), or a moisture-permeable waterproof sheet having moisture permeability (moisture permeation resistance conforming to JIS A6111).

[0062] In the first embodiment, the sheet body 22a is formed to have the same size (same length and width dimensions) as the upper surface of the sheathing board 21 so as to cover the entire upper surface of the sheathing board 21 without excess or deficiency.

[0063] The adhesive layer 22b is formed by applying or transferring an adhesive to one surface of the sheet main body 22a (the surface that will be the underside during construction). In the first embodiment, the adhesive layer 22b is formed from an adhesive obtained by adding a tackifier to an asphalt-based adhesive. The adhesive layer 22b may be formed using any adhesive as long as it has sufficient adhesive strength to adhere the sheet main body 22a to the upper surface of the sheathing board 21. Furthermore, examples of tackifiers that can be added to the asphalt-based adhesive include butyl rubber and styrene-butadiene rubber. As asphalt-based adhesives have weak adhesive properties, adding a tackifier in this manner makes it possible to form an adhesive layer 22b with sufficient adhesive strength.

[0064] In the present embodiment 1, the adhesive layer 22b is formed by applying or transferring an adhesive to the entire surface of one side (lower surface) of the sheet main body 22a so as to cover the entire surface of the one side (lower surface) of the sheet main body 22a. In other words, the waterproof sheet 22 has a lower surface formed of the adhesive layer 22b.

[0065] In the roof underlayment 20 of the present embodiment 1, a sheet body 22a having the same size as the upper surface of the sheathing board 21 as described above is adhered to the upper surface of the sheathing board 21 by an adhesive layer 22b formed on the entire lower surface of the sheet body 22a, thereby covering the entire upper surface of the sheathing board 21. In the roof underlayment 20 of the present embodiment 1, one waterproof sheet 22 is adhered to the upper surface of one sheathing board 21, that is, the sheathing boards 21 and the waterproof sheets 22 are provided in a one-to-one correspondence.

[0066] -Roof structure construction method- The roof structure 1 is constructed as follows.

[0067] First, insulating material 30 (bagged rock wool) is filled between multiple rafters 2, ..., 2 spaced apart in the truss of a building, and fixed to the lower end surface (inner surface) of each rafter 2 with staples.After that, multiple gypsum boards 3, ..., 3 are pressed against the lower end surfaces (inner surfaces) of the multiple rafters 2, ..., 2, and each gypsum board 3 is nailed to the multiple rafters 2, ..., 2 with screws or the like.

[0068] Next, multiple roof underlayments 20,...,20 are installed above multiple rafters 2,...,2 spaced apart in the roof truss of the building. Specifically, as shown in FIG. 4 , multiple roof underlayments 20,...,20 are laid on the multiple rafters 2,...,2 with their end faces facing each other, and each roof underlayment 20 is fixed to the multiple rafters 2,...,2 with nails, screws, or the like. Because the roof underlayment 20 has a waterproof sheet 22 adhered to the top surface of the sheathing boards 21 before installation, simply installing the multiple roof underlayments 20,...,20 installs the sheathing boards 21 and the waterproof sheet 22. Therefore, while in the past, the waterproof sheet 22 was installed after the sheathing boards 21 (two installation steps), using the above-mentioned roof underlayment 20 allows the sheathing boards 21 and the waterproof sheet 22 to be installed in a single installation step. Furthermore, by using the roof underlayment 20, the waterproof sheet 22, which is prone to being blown up by the wind and which may wrinkle or tear during construction, can be attached to the top surface of the sheathing boards 21 in advance at a factory or the like, rather than being laid at the construction site. Therefore, there is no risk of the waterproof sheet 22 wrinkling or tearing, and the adhesive layer 22b is interposed between the sheet body 22a of the waterproof sheet 22 and the sheathing boards 21, so no gaps are formed, and rainwater does not seep into the gaps.

[0069] Furthermore, in this embodiment 1, the insulating material 30 used is thinner than the thickness of the rafters 2. Therefore, by installing the insulating material 30 and the roof underlayment material 20, an air passage 40 is automatically formed between the insulating material 30 and the roof underlayment material 20, extending from the eaves edge 6 side toward the ridge beam 5 side.

[0070] After the multiple roof underlayments 20, ..., 20 have been installed in the above manner, the roofing materials 10, ..., 10 are laid. Specifically, each roofing material 10 made of a flat decorative slate is placed in a predetermined position on the multiple roof underlayments 20, ..., 20, and fixed with screws 4 driven from above each roofing material 10 toward the roof underlayment 20. In this way, the multiple roofing materials 10, ..., 10 are laid in order.

[0071] After installing the multiple roofing materials 10, ..., 10 in the manner described above, a gutter 8 is provided on the eaves 6 side of the multiple roofing materials 10, ..., 10, while a ridge wrap 9a and a ridge ventilation member 9b are provided on the ridge beam 5 side of the multiple roofing materials 10, ..., 10.

[0072] The roof structure 1 is constructed in the manner described above.

[0073] -Roof structure characteristics- <Ventilation path characteristics> As described above, in this embodiment 1, the insulating material 30, which is thinner than the thickness of the rafters 2, is provided between each of the multiple rafters 2. Therefore, simply by installing the insulating material 30 and the roof underlayment material 20, an air passage 40 is formed between each insulating material 30 and the roof underlayment material 20, extending from the eaves edge 6 side toward the ridge beam 5 side.

[0074] In the ventilation channel 40, the end on the eaves edge 6 side serves as the inlet 40a, and the end on the ridge beam 5 side (the end of the ridge ventilation member 9b provided between the ridge wrapping 9a and the roofing material 10) serves as the outlet 40b, and outdoor air flows from the inlet 40a to the outlet 40b. Therefore, even if indoor moisture passes through the insulation material 30 and reaches the underside of the roof underlayment material 20 (the underside of the sheathing boards 21), condensation is unlikely to occur on the underside of the roof underlayment material 20. Furthermore, even if condensation does occur on the underside of the roof underlayment material 20, the condensed water is evaporated by the air flowing through the ventilation channel 40 into water vapor, which flows together with the air from the eaves edge 6 side to the ridge beam 5 side and is quickly discharged to the outdoors through the outlet 40b. Therefore, deterioration due to decay of the roof underlayment material 20 can be prevented.

[0075] <Waterproof> In the roof structure 1 of the first embodiment, a medium-density fiberboard having a density of 0.7 or more but less than 0.85 and a water absorption rate of 15% or less is used as the sheathing boards 21. By using such a medium-density fiberboard with a low water absorption rate as the sheathing boards 21, the waterproofing of the roof underlayment 20 is improved compared to when structural plywood is used as the sheathing boards.

[0076] <Water-repellent for nail holes in roof underlayment> In the roof structure 1 of the present embodiment 1, by using medium-density fiberboard, which has a relatively high density and few voids, as the sheathing boards 21, the nail hole waterproofing ability of the roof underlayment 20 is dramatically improved compared to when structural plywood is used as the sheathing boards. It is thought that the nail hole waterproofing ability of the roof underlayment 20 is dramatically improved because the wood fibers coated with a water-resistant adhesive adhere to the screws 4 driven in to install the roof underlayment 20.

[0077] Furthermore, in the present embodiment 1, one surface (the upper surface facing outdoors) of the sheathing board 21 is covered with a waterproof sheet 22 having an adhesive layer 22b. Therefore, even if nail holes are made in the waterproof sheet 22 to drive screws 4 from above when the roof underlayment 20 is installed, the adhesive of the adhesive layer 22b adheres to the screws 4, and thus the waterproof sheet 22 has a significantly improved ability to stop water from entering the nail holes.

[0078] As described above, the roof structure 1 of the first embodiment uses a roof underlayment 20 in which a waterproof sheet 22 having an adhesive layer 22b is adhered in advance in a factory or the like to one side (the upper surface facing outdoors) of a sheathing board 21. Therefore, compared to conventional roof structures in which a waterproof sheet without an adhesive layer is fixed to the upper surface of the sheathing board by stapling with a tacker or the like, the nail hole waterproofing ability of the sheathing board and the waterproof sheet is dramatically improved.

[0079] <Water-stopping at joints> In conventional construction methods for installing waterproof sheets on sheathing boards at construction sites, after the sheathing boards have been attached to the exterior (top) sides of rafters, etc., the waterproof sheets are typically attached so as to cover multiple sheathing boards as a whole and so that adjacent waterproof sheets overlap. Furthermore, the waterproof sheets are secured in place by driving staples into the boards using a stapler or similar. According to this conventional construction method, the joints between the sheathing boards are covered with the waterproof sheet, preventing rainwater from seeping in through the joints.

[0080] In contrast to this, the roof structure 1 of the present embodiment 1 uses the roof underlayment 20 in which the waterproof sheet 22 is adhered to one side (top surface) of the sheathing boards 21 before construction, as described above. This makes construction of the roof structure 1 easier, but since the waterproof sheet 22 cannot cover the joints of the sheathing boards 21, there is a concern that rainwater may seep in through the joints of the roof underlayment 20.

[0081] Therefore, in the roof structure 1 of the first embodiment, the sheathing boards 21 of the roof underlayment 20 are made of medium density fiberboard (MDF), which has low water absorption. Medium density fiberboard is a wood board formed by hot pressing wood fibers together with an adhesive, and has a low water absorption rate. Therefore, even if rainwater seeps in through the joints of the roof underlayment 20 and reaches the sheathing boards 21, the sheathing boards 21 will not absorb water and deform (expand in thickness, warp, twist) or develop mold.

[0082] Furthermore, in the roof structure 1 of the present embodiment 1, the medium-density fiberboards constituting the sheathing boards 21 of the roof underlayment 20 contain a water-repellent agent, so that the contact angle of water with the surface is greater than 90 degrees (water-repellent). Therefore, even if rainwater seeps in through the joints of the roof underlayment 20, the rainwater turns into droplets on the end grain surfaces of the sheathing boards 21, with a contact angle of greater than 90 degrees, and the droplets act as stoppers, making it difficult for the rainwater to further seep into the joints of the roof underlayment 20.

[0083] -Effects of the first embodiment- In this embodiment, the roof underlayment 20 is a waterproof sheet 22 of the same size as the sheathing board 21 adhered to the top surface of the rectangular sheathing board 21 before construction. Therefore, simply laying the roof underlayment 20 on the rafters 2 supporting the roof allows the waterproof sheet 22 to be installed along with the sheathing board 21. Therefore, by using the roof underlayment 20, the work of laying the waterproof sheet 22 at the construction site, which is prone to being torn by wind and may wrinkle or tear during construction, can be eliminated. Furthermore, by attaching the waterproof sheet 22 to the top surface of the sheathing board 21 in advance at a factory, etc., the waterproof sheet 22 is prevented from wrinkling or tearing. Furthermore, the adhesive layer 22b is interposed between the waterproof sheet 22 (sheet body 22a) and the sheathing board 21, preventing gaps from forming. Therefore, rainwater does not seep into the gap between the waterproof sheet 22 and the sheathing board 21. Therefore, by using the roof underlayment material 20, even an unskilled person can easily construct the roof structure 1 with a good finish.

[0084] Incidentally, when using roof underlayment 20 in which waterproof sheets 22 have been previously adhered to sheathing boards 21 in a factory or the like, the screws 4 for installing the roof underlayment 20 are driven from above the waterproof sheet 22, so that the nail heads are positioned above the waterproof sheet 22, and nail holes are also formed in the waterproof sheet 22. Therefore, when using the above roof underlayment 20, there is a concern that rainwater will seep into the sheathing boards 21 through the nail holes and cause the sheathing boards to rot.

[0085] Therefore, in the roof underlayment material of the first embodiment, the sheathing boards 21 are made of medium density fiberboard (MDF) which has low water absorption.

[0086] Medium-density fiberboard is a wood board formed by hot-pressing wood fibers with an adhesive, and has a low water absorption rate. Furthermore, in a roof underlayment 20 in which sheathing boards 21 are constructed from medium-density fiberboard, which has a relatively high density and few voids, the wood fibers coated with a water-resistant adhesive adhere to the screws 4 driven to install the roof underlayment 20, resulting in significantly improved nail-hole waterproofing compared to sheathing boards made of plywood or other materials. Furthermore, an adhesive layer 22b is provided between the underside of the waterproof sheet 22 (sheet body 22a) and the upper side of the sheathing board 21, which face each other. This allows the adhesive of the adhesive layer 22b to adhere to the screws 4 driven to install the roof underlayment 20, resulting in significantly improved nail-hole waterproofing compared to when the waterproof sheet 22 is fastened to the sheathing board 21 with staples or the like. Therefore, even if a roof underlayment material 20 in which a waterproof sheet 22 has been previously adhered to the sheathing boards 21 in a factory or the like is used, rainwater does not seep into the sheathing boards 21 through the nail holes, so there is no risk of the sheathing boards 21 absorbing water and deforming (expanding in thickness, warping, twisting), and it is also possible to prevent mold from growing and causing the sheathing boards 21 to rot.

[0087] In addition, in a roof underlayment 20 in which a waterproof sheet 22 of the same size as the upper surface of the sheathing board 21 is attached to the upper surface of the sheathing board 21 so as to cover the entire upper surface, the joints between the roof underlayment materials 20 are not covered by the waterproof sheet 22, so there is a risk that rainwater will penetrate into the interior through the joints of the roof underlayment materials 20, causing leaks.

[0088] Therefore, in the roof underlayment material of the first embodiment, the sheathing board 21 is made of a medium-density fiberboard containing a water-repellent agent, rather than a simple medium-density fiberboard.

[0089] By incorporating a water-repellent agent into the medium-density fiberboard used as the sheathing boards 21, the contact angle of water with the surface of the medium-density fiberboard becomes greater than 90 degrees (the medium-density fiberboard has water repellency). Therefore, even if rainwater seeps in through the joints of the roof underlayment 20 and reaches the joints of the sheathing boards 21, the rainwater turns into droplets with a contact angle greater than 90 degrees on the end grain surface of the sheathing boards 21, and the droplets act as stoppers, preventing further penetration of the rainwater. In other words, according to the first embodiment, the water-repellent properties of the sheathing boards 21 prevent rainwater from seeping into the interior through the joints of the roof underlayment 20 without covering the joints with a waterproof sheet, waterproof tape, or the like, thereby preventing leaks.

[0090] Furthermore, in the roof underlayment 20 of this embodiment 1, the entire upper surface of the sheathing boards 21 is covered with the sheet body 22a of the waterproof sheet 22 of the same size. With this roof underlayment 20, the waterproof sheet 22 can be easily installed together with the sheathing boards 21 simply by fixing multiple roof underlayment materials 20, ..., 20 onto the rafters 2 supporting the roof while abutting their butt surfaces. Therefore, according to this embodiment 1, even an unskilled person can easily install the roof structure 1 with a good finish.

[0091] Furthermore, in this embodiment 1, the roof structure 1, which includes roofing materials and roof underlayment, uses roof underlayment materials 20, ..., 20 in which waterproof sheets 22 are pre-attached to sheathing boards 21 in a factory or the like. Therefore, simply laying multiple roof underlayment materials 20 on rafters 2 or the like allows the waterproof sheets 22 to be installed along with the sheathing boards 21. Furthermore, there is no risk of the waterproof sheet 22 wrinkling or tearing. Furthermore, the adhesive layer 22b is interposed between the waterproof sheet 22 and the sheathing boards 21, eliminating any gaps, preventing rainwater from seeping into the gaps between the waterproof sheet 22 and the sheathing boards 21. Therefore, this embodiment 1 allows even non-experts to easily install the roof structure 1 with a good finish, which can contribute to resolving the recent shortage of craftsmen. Furthermore, normally, after the sheathing boards 21 are installed, a roofing contractor other than the installer of the sheathing boards 21 will attach a waterproof sheet 22 to provide weather protection. However, according to this embodiment 1, even if it rains after the sheathing boards 21 are installed, the sheathing boards 21 will not get wet directly, so after the sheathing boards 21 are installed, there is no need for a roofing contractor other than the installer of the sheathing boards 21 to come to the construction site to provide weather protection.

[0092] Furthermore, in the roof structure 1 of this embodiment 1, the sheathing boards 21 are made of roof underlayment material 20 composed of medium-density fiberboard containing a water-repellent agent, so even if the nails 3 for installing the roof underlayment material 20 are driven from above the waterproof sheet 22, rainwater does not seep into the sheathing boards 21 through the nail holes, so there is no risk of the sheathing boards 21 absorbing water and deforming (expanding in thickness, warping, twisting), and mold growth and rotting of the sheathing boards 21 can be suppressed. Furthermore, the water-repellent properties of the sheathing boards 21 prevent rainwater from seeping into the interior through the joints of the roof underlayment material 20 even without covering the joints with a waterproof sheet, waterproof tape, or the like, thereby suppressing rain leaks.

[0093] Second Embodiment The roof structure 1 of the second embodiment is obtained by changing a part of the configuration of the roof underlayment 20 in the roof structure 1 of the first embodiment.

[0094] As shown in Figure 5, in the roof underlayment 20 of embodiment 2, a sheet body 22a of a waterproof sheet 22 having the same size as the upper surface of the sheathing board 21 is adhered to the upper surface of the sheathing board 21 at a position offset in the vertical and horizontal directions.

[0095] Specifically, the sheet body 22a is adhered to the top surface of the sheathing board 21 at a position offset both in one vertical direction (first vertical direction D1) and one horizontal direction (first horizontal direction D3). By adhering the sheet body 22a in this offset manner, an edge portion x1 in a second vertical direction D2, which is the vertical direction of the top surface of the sheathing board 21 opposite the first vertical direction D1, is exposed and not covered by the sheet body 22a, and at the end of the top surface of the sheathing board 21 in the first vertical direction D1, the sheet body 22a protrudes in the first vertical direction from the end of the sheathing board 21. In addition, an edge portion x2 in a second horizontal direction D4, which is the horizontal direction of the top surface of the sheathing board 21 opposite the first horizontal direction D3, is also exposed and not covered by the sheet body 22a, and at the end of the top surface of the sheathing board 21 in the first horizontal direction D3, the sheet body 22a protrudes in the first horizontal direction D3 from the end of the sheathing board 21.

[0096] In embodiment 2, as shown in Figure 5, during construction, the portion of the sheet body 22a of the waterproof sheet 22 of each roof underlayment 20 that protrudes beyond the sheathing board 21 is placed on the exposed portion of the upper surface of the sheathing board 21 of the adjacent roof underlayment 20, and both roof underlayments 20, 20 are fixed to rafters 2, etc., so that the joint between the two roof underlayments 20, 20 is covered by the sheet body 22a of the waterproof sheet 22 of one of the roof underlayments 20.

[0097] Specifically, for two vertically adjacent roof underlayments 20, 20, the exposed portion of the upper surface of the roof underlayment 20 on the first vertical direction D1 side (edge ​​portion x1 in the second vertical direction D2) of the waterproof sheet 22 of the sheet body 22a of the roof underlayment 20 on the second vertical direction D2 side is placed on top of the sheathing board 21 (end portion y1 in the first vertical direction D1 of the sheet body 22a), and both roof underlayments 20, 20 are fixed to rafters 2 etc. with screws 4. In addition, an adhesive layer 22b is also formed on the underside of the protruding portion of the sheet body 22a of the waterproof sheet 22 that protrudes from the sheathing board 21 (the end y1 of the sheet body 22a in the first vertical direction D1). Therefore, simply by placing the protruding portion y1 of the roof underlayment material 20 on the second vertical direction D2 side on the exposed portion x1 of the upper surface of the roof underlayment material 20 on the first vertical direction D1 side, the protruding portion y1 is adhered to the exposed portion x1 and will not be rolled up by the wind.

[0098] Furthermore, for two roof underlayments 20, 20 adjacent in the horizontal direction, the exposed portion of the upper surface of the roof underlayment 20 on the first horizontal direction D3 side (edge ​​portion x2 in the second horizontal direction D4) of the sheet body 22a of the waterproof sheet 22 on the roof underlayment 20 on the second horizontal direction D4 side (end portion y2 in the first horizontal direction D3 of the sheet body 22a) is placed on top of the roof underlayment 21, and both roof underlayments 20, 20 are fixed to rafters 2 etc. with screws 4. In addition, an adhesive layer 22b is also formed on the underside of the protruding portion of the sheet body 22a of the waterproof sheet 22 that protrudes from the sheathing board 21 (the end y2 of the sheet body 22a in the first horizontal direction D3).Therefore, simply by placing the protruding portion y2 of the roof underlayment material 20 on the second horizontal direction D4 side on the exposed portion x2 of the upper surface of the roof underlayment material 20 on the first horizontal direction D3 side, the protruding portion y2 is adhered to the exposed portion x2 and will not be rolled up by the wind.

[0099] Thus, according to the roof underlayment 20 of the second embodiment, during construction, the portions y1, y2 of the main body 22a of the waterproof sheet 22 of each roof underlayment 20 that protrude beyond the sheathing board 21 are placed on the exposed portions x1, x2 of the upper surface of the sheathing board 21 of the adjacent roof underlayment 20, and the two roof underlayments 20 are then fixed to the rafters 2 or the like, so that the joint between the two roof underlayments 20 is covered by the main body 22a of the waterproof sheet 22 of one of the roof underlayments 20. Therefore, infiltration of rainwater into the interior through the joint between the roof underlayments 20 is prevented not only by the water-repellent properties of the sheathing board 21 but also by the fact that the main body 22a of the waterproof sheet 22 covers the joint. Therefore, the roof underlayment 20 and roof structure 1 of the second embodiment can further prevent rainwater from leaking.

[0100] Third Embodiment The roof structure 1 of the third embodiment is obtained by changing a part of the configuration of the roof underlayment 20 in the roof structure 1 of the first embodiment.

[0101] As shown in Figure 6, in the roof underlayment material 20 of embodiment 2, a sheet body 22a of a waterproof sheet 22, which is larger than the upper surface of the sheathing board 21, is adhered to the upper surface of the sheathing board 21 so as to cover the entire upper surface of the sheathing board 21 and extend beyond two adjacent sides of the upper surface of the sheathing board 21.

[0102] Specifically, the sheet body 22a is formed in a rectangular shape with vertical and horizontal dimensions larger than those of the top surface of the sheathing board 21. The sheet body 22a protrudes from each end of the top surface of the sheathing board 21 in the first vertical direction D1 and the first horizontal direction D3, while the sheet body 22a and the sheathing board 21 are aligned at each end of the top surface of the sheathing board 21 in the second vertical direction D2 and the second horizontal direction D4.

[0103] In embodiment 3, as shown in Figure 6, during construction, the portion of the sheet body 22a of the waterproof sheet 22 of each roof underlayment 20 that protrudes from the sheathing board 21 is placed on the top surface of the adjacent roof underlayment 20 (the sheet body 22a of the waterproof sheet 22 is overlapped), and both roof underlayment materials 20, 20 are fixed to rafters 2, etc., so that the joint between the two roof underlayment materials 20, 20 is covered by the sheet body 22a of the waterproof sheet 22 of one of the roof underlayment materials 20.

[0104] Specifically, for two vertically adjacent roof underlayments 20, 20, the portion of the waterproof sheet 22 of the sheet body 22a of the roof underlayment 20 on the second vertical direction D2 side that protrudes from the sheathing board 21 (the end y1 of the sheet body 22a in the first vertical direction D1) is placed on the end edge portion z1 in the second vertical direction D2 of the upper surface of the roof underlayment 20 on the first vertical direction D1 side, and both roof underlayments 20, 20 are fixed to rafters 2 etc. with screws 4. In addition, an adhesive layer 22b is also formed on the underside of the protruding portion of the sheet body 22a of the waterproof sheet 22 that protrudes from the sheathing board 21 (the end y1 of the sheet body 22a in the first vertical direction D1). Therefore, simply by placing the protruding portion y1 of the roof underlayment material 20 on the second vertical direction D2 side on the end edge portion z1 in the second vertical direction D2 of the upper surface of the roof underlayment material 20 on the first vertical direction D1 side, the protruding portion y1 is adhered to the end edge portion z1 and will not be rolled up by the wind.

[0105] Furthermore, for two roof underlayments 20, 20 adjacent in the horizontal direction, the portion of the waterproof sheet 22 of the sheet body 22a on the roof underlayment 20 on the second horizontal direction D4 side that protrudes from the sheathing board 21 (the end y2 of the sheet body 22a in the first horizontal direction D3) is placed on the edge portion z2 in the second horizontal direction D4 of the upper surface of the roof underlayment 20 on the first horizontal direction D3 side, and both roof underlayments 20, 20 are fixed to rafters 2 etc. with screws 4. In addition, an adhesive layer 22b is also formed on the underside of the protruding portion of the sheet body 22a of the waterproof sheet 22 that protrudes from the sheathing board 21 (the end y2 of the sheet body 22a in the first horizontal direction D3), so simply by placing the protruding portion y2 of the roof underlayment material 20 on the second horizontal direction D4 side on the edge portion z2 in the second horizontal direction D4 of the upper surface of the roof underlayment material 20 on the first horizontal direction D3 side, the protruding portion y2 is adhered to the edge portion z2 and will not be rolled up by the wind.

[0106] Thus, according to the roof underlayment 20 of the third embodiment, during construction, the portions y1, y2 of the waterproof sheet 22 main body 22a of each roof underlayment 20 that protrude beyond the sheathing boards 21 are placed on the edge portions z1, z2 of the upper surface of the adjacent roof underlayment 20, and the two roof underlayment 20 are then fixed to the rafters 2 or the like, so that the joint between the two roof underlayment 20 is covered by the waterproof sheet 22 (sheet main body 22a) of one of the roof underlayment 20. Therefore, infiltration of rainwater into the interior through the joint between the roof underlayment 20 can be prevented not only by the water-repellent properties of the sheathing boards 21 but also by the waterproof sheet 22 (sheet main body 22a) covering the joint. Therefore, the roof underlayment 20 and roof structure 1 of the third embodiment can further prevent rain leakage.

[0107] Other Embodiments In the above-described first to third embodiments, the adhesive layer 22b of the waterproof sheet 22 covers the entire one side of the sheet body 22a, but it may be formed partially or piecewise on one side of the sheet body 22a as long as the waterproof sheet 22 can be attached to the sheathing board 21 without rolling up or wrinkling. For example, a plurality of elongated adhesive layers 22b extending in the vertical direction (the length direction of the sheet body 22a) may be formed at regular intervals on one side of the sheet body 22a.

[0108] Furthermore, in the above-described first to third embodiments, the waterproof sheet 22 may be configured to have moisture permeability. Specifically, the sheet body 22a is configured from a moisture-permeable waterproof sheet having moisture permeability (moisture permeation resistance conforming to JIS A6111), and the adhesive layer 22b is configured to have moisture permeability by being formed, for example, from an adhesive solution containing an acrylic adhesive composition containing 5 to 60 weight percent (meth)acrylic polymer and polypropylene glycol, to which a crosslinking agent is added. By using such a moisture-permeable waterproof sheet 22, the roof underlayment 20 has excellent moisture permeability because the sheathing boards 21 to which the waterproof sheet 22 is attached are also made from medium-density fiberboard with excellent moisture permeability. By configuring the roof underlayment 20 to have such excellent moisture permeability, even if moisture due to condensation on the roofing material 10 or infiltrating rainwater reaches the roof underlayment 20, it can pass through the roof underlayment 20 and be discharged. This prevents deterioration of the roof underlayment 20 due to decay.

[0109] The adhesive forming the moisture-permeable adhesive layer 22b may contain a (meth)acrylic polymer containing a (meth)acrylic monomer having hydrophilicity, which is commonly used, as well as components such as hydrophilic additives and tackifiers that are commonly used in adhesives.In addition, the crosslinking agent may be an isocyanate resin, epoxy resin, metal chelate, etc. that are commonly used in acrylic adhesives, and further, a foaming agent may be added, or mechanical foaming may be performed like with an acrylic emulsion, etc., and any composition or coating method may be used as long as it can form an adhesive layer with the desired moisture permeation resistance.

[0110] Furthermore, in the above-described second and third embodiments, the roof underlayment 20 is used in which the sheet body 22a of the waterproof sheet 22 is adhered to the upper surface of the sheathing board 21 so as to extend beyond the sheathing board 21 both vertically and horizontally, but in each of the second and third embodiments, the roof underlayment 20 may be used in which the sheet body 22a is adhered to the upper surface of the sheathing board 21 so as to extend beyond the sheathing board 21 only vertically or only horizontally. For example, if the roof underlayment 20 is used in which the sheet body 22a is adhered to the upper surface of the sheathing board 21 so as to extend beyond the sheathing board 21 only in the direction in which rainwater flows (the direction of the roof flow), the joint between two adjacent roof underlayments 20, 20 in the direction of the roof flow is covered by the sheet body 22a of the waterproof sheet 22 of one of the roof underlayments 20, and therefore, rain leakage can be sufficiently suppressed. In this case, it is more preferable to configure the joint between the two roof underlayments 20, 20 so that it is covered by the sheet body 22a of the waterproof sheet 22 of the upper roof underlayment 20.

[0111] Furthermore, as mentioned above, in the above embodiment 1, decay and leaks of the sheathing boards 21 can be suppressed without waterproofing the joints of the multiple roof underlayment materials 20, ..., 20, but it is of course also possible to perform waterproofing treatment such as applying waterproof tape to the joints of the multiple roof underlayment materials 20, ..., 20.

[0112] In the above embodiments 1 to 3, an example has been described in which the roof underlayment material 20 of the present invention is applied to a roof insulation type roof structure 1, but the roof underlayment material 20 can of course also be applied to a ceiling insulation type roof structure in which the insulation material 30 is provided on the ceiling side rather than the roof side.

[0113] In the above-mentioned first embodiment, a roof structure constructed by the filling insulation method is described, but the present invention is also applicable to a roof structure constructed by the external insulation method. [Industrial Applicability]

[0114] The present invention is useful in roof underlayments and roof structures. [Explanation of symbols]

[0115] 1. Roof structure 10 Roofing materials 20 Roof underlayment 21 Field board 22 Tarpaulin 22a seat body 22b adhesive layer

Claims

1. A roof underlayment comprising a sheathing board and a waterproof sheet provided on the sheathing board, The sheathing board is made of rectangular medium-density fiberboard containing a water-repellent agent, The above waterproof sheet is A sheet body having a size equal to or larger than the top surface of the sheathing board; an adhesive layer provided between the lower surface of the sheet body and the upper surface of the sheathing board, which face each other; The sheet body is adhered to the upper surface of the sheathing board by the adhesive layer. A roofing underlayment characterized by:

2. The roof underlayment material according to claim 1, The sheet body is formed to the same size as the upper surface of the sheathing board and is adhered to the upper surface of the sheathing board so as to cover the entire upper surface of the sheathing board. A roofing underlayment characterized by:

3. The roof underlayment material according to claim 1, The sheet body is formed to the same size as the upper surface of the sheathing board and is adhered to the upper surface of the sheathing board at a position offset in at least one of the vertical and horizontal directions. A roofing underlayment characterized by:

4. The roof underlayment material according to claim 1, The sheet body is formed to be larger than the upper surface of the sheathing board, covers the entire upper surface of the sheathing board, and is adhered to the upper surface of the sheathing board so as to extend beyond one side or two adjacent sides of the upper surface of the sheathing board. A roofing underlayment characterized by:

5. A roof structure of a building comprising a plurality of roof underlayments and a plurality of roof coverings attached above the plurality of roof underlayments, The roof underlayment is a roof underlayment according to any one of claims 1 to 4. A roof structure of a building characterized by:

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