Patent Publication Number: US-11643816-B2

Title: Roof panel, roof structure, and roof structure construction method

Description:
TECHNICAL FIELD 
     The present invention relates to a roof panel which forms a roof slope, a roof structure constituted by a roof panel which forms a roof slope, and a construction method of these. 
     BACKGROUND ART 
     Conventionally, some of sloping roofs are formed using roof panels each of which includes a plate material functioning as a base material for a roof finishing material and fixed to rafters spanned between horizontal base materials such as purlins (for example, Patent Literature 1 and Patent Literature 2). These roof panels are carried into a construction site in a state where the rafters and the plate materials placed and fixed on the rafters are integrated in advance in a factory. Accordingly, the respective members need not be lifted to a height of a roof and separately constructed, which improves workability. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: JP 10-46737 A 
         Patent Literature 2: JP 7-286394 A 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problems 
     Meanwhile, bearing force (horizontal bearing force) of entire roof structural surfaces of some wooden roof structures is secured by combining joining strength between purlins and rafters and joining strength between the rafters and a roofing board. However, according to roof panels described in Patent Literatures 1 and 2, adjacent roof panels are disposed on horizontal base materials in a state of alignment between joining portions of the respective roof panels in both horizontal and roof slope directions. In this case, joint positions of the roof panels weaken the structure, and reinforcements such as horizontal braces are highly likely to be required to secure sufficient horizontal strength of the entire roof. Alternatively, the joint positions of the roof panels may be disposed in a staggered manner. However, this arrangement complicates allocation of the roof panels and causes a problem of more complicated processes for construction. 
     On the other hand, for forming a large sloped roof having a large length, such as a roof having a large length between beams and a one-sided roof, wooden rafters sloped along a roof slope may be joined to each other. In this case, highly accurate construction is required by the necessity of accurate joining between joint portions of the rafters to form a smooth roof surface. It is extremely difficult, however, to accurately join the sloped long rafters with sufficient accuracy, and the construction accuracy depends largely on skills of builders. In this case, construction quality may differ depending on a construction site. 
     Accordingly, the present invention has been developed in consideration of the aforementioned problems. An object of the present invention is to provide a roof panel easily constructed while maintaining structural strength required for a roof, a structure using the roof panel, and a construction method of these. 
     Solutions to the Problems 
     A first roof structure according to the present invention is a roof structure comprising a plurality of horizontal base materials disposed in parallel to each other with a clearance left between each other, and so disposed as to produce a height difference that forms a roof slope, and a plurality of roof panels fixed on the horizontal base materials and spread side by side in a slope direction, wherein each of the roof panels includes a roofing board, and rafters fixed to a lower surface of the roofing board in parallel to each other with a clearance left between each other, and extending perpendicularly to the horizontal base materials, each of the rafters of one of the two adjacent roof panels in the slope direction includes a carry-out portion that projects from an edge of the roofing board, each of the carry-out portions is disposed between the rafters of the other roof panel and fixed to the roofing board of the other roof panel, a projection length of the carry-out portions is smaller than a distance between the adjoining horizontal base materials, and the carry-out portions and the other roof panel are fixed to the same horizontal base material. 
     In a second roof structure according to the present invention, the one roof panel is fixed to the horizontal base materials with the carry-out portions facing an upstream side, and the other roof panel is disposed on the upstream side of the one roof panel and fixed to the horizontal base materials. 
     In a third roof structure according to the present invention, the carry-out portions of the one roof panel and the rafters of the other roof panel are alternately disposed at equal intervals. 
     A fourth roof structure according to the present invention is the roof structure includes the three or more roof panels disposed side by side in the slope direction, wherein each of the roof panels located on a downstream side except for the roof panel located closest to a ridge side includes the carry-out portions that project toward the upstream side, and each of the carry-out portions is disposed and fixed between the rafters of the roof panel adjacent on the upstream side. 
     A fifth roof structure according to the present invention is the roof structure includes the three or more roof panels disposed side by side in the slope direction, wherein the roof panel on the upstream side includes the carry-out portions that project toward the downstream side, the roof panel on the downstream side includes the carry-out portions that project toward the upstream side, and the roof panel that is an intermediate roof panel located between the roof panel on the upstream side and the roof panel on the downstream side is disposed such that an upstream end and a downstream end of each of the rafters do not project from an edge of the roofing board. 
     A roof structure construction method according to the present invention is a roof structure construction method for constructing the roof structure according to any one of 1 to 5 comprising fixing the one roof panel to the horizontal base materials, and then disposing the other roof panel such that the roofing board of the other roof panel covers the carry-out portions of the one roof panel, and bringing ends of the roofing boards of the one roof panel and the other roof panel into abutment with each other; and driving a fixing tool into each of the carry-out portions from above the roofing board of the other roof panel to fix the one roof panel and the other roof panel. 
     A first roof panel according to the present invention is a roof panel comprising a first roofing board, and a plurality of first rafters fixed to a lower surface of the first roofing board in parallel to each other with a clearance left between each other, and projecting from at least one edge of the first roofing board, the roof panel being fixed to upper parts of a plurality of horizontal base materials disposed in parallel to each other with a clearance left between each other, wherein a projection length of a first projection portion included in each of the first rafters and projecting from an edge of the first roofing board is equal to or larger than an interval between the adjoining horizontal base materials. 
     A sixth roof structure according to the present invention comprises a plurality of horizontal base materials disposed in parallel to each other with a clearance left between each other and extending in an outrigger direction and the first roof panel, wherein the roof panel is fixed to the horizontal base materials with the first projection portions facing an upstream side. 
     A seventh roof structure according to the present invention comprises a receiving roof panel that includes a second roofing board disposed with one edge of the second roofing board abutting on one edge of the first roofing board and a plurality of second rafters fixed to a lower surface of the second roofing board in parallel to each other with a clearance left between each other, and disposed such that at least one end of each of the second rafters is disposed at one edge of the second roofing board, wherein the receiving roof panel is fixed to the horizontal base materials with one end of each of the second rafters disposed between the adjacent first projection portions. 
     An eighth roof structure according to the present invention comprises a second roof panel that includes a third roofing board disposed with one edge of the third roofing board abutting on the opposite edge of the second roofing board, and a plurality of third rafters fixed to a lower surface of the third roofing board in parallel to each other with a clearance left between each other, and disposed such that one end of each of the third rafters projects from one edge of the third roofing board, wherein the second roof panel is fixed to the horizontal base material located on a most upstream side in a state where a second projection portion included in each of the third rafters and projecting from an edge of the third roofing board faces a downstream side, and the receiving roof panel is fixed to the horizontal base materials in a state where the opposite end of each of the second rafters are disposed between the adjacent second projection portions. 
     A second roof structure construction method according to the present invention is the roof structure construction method using the roof structure according to any one of 6 to 8 comprising fixing the roof panel to the horizontal base materials with the first projection portion of each of the first rafters facing the upstream side, bringing one edge of the second roofing board into abutment with one edge of the first roofing board from above, and fixing the receiving roof panel to the horizontal base materials with one end of each of the second rafters disposed between the first projection portions, and fixing the second roofing board to the first projection portions. 
     A third roof structure construction method according to the present invention is the roof structure construction method comprising bringing one and the other edges of the second roofing board into abutment with the one edge of the first roofing board and the one edge of the third roofing board from above, respectively, after the second roof panel is fixed to the horizontal base materials located on the most upstream side with the second projection portion of each of the third rafters facing the downstream side, fixing the receiving roof panel to the horizontal base materials with one end of each of the second rafters disposed between the first projection portions and with the opposite end of each of the second rafters disposed between the second projection portions, and fixing the second roofing board to the first projection portions and the second projection portions. 
     Advantageous Effects of Invention 
     According to the first roof structure of the present invention, one of the two roof panels adjacent to each other in the slope direction includes the carry-out portions which are the rafters projecting from the edge of the roofing board. Each of the carry-out portions is disposed between the rafters of the other roof panel and fixed to the roofing board of the other roof panel. Accordingly, the roof panels are joined to each other by joining the rafters of the one roof panel and the roofing board of the other roof panel. As described above, the carry-out portion of each of the rafters projecting from the one roof panel is disposed between the rafters of the other roof panel. In this manner, an interval between the rafters at the joint positions between the roof panels decrease. Therefore, workability improves without the necessity of joining ends of the rafters of the respective panels as conventionally required. In addition, structural strength produced by the rafters increases. Moreover, the joining portions of the roofing boards and the joining portions of the rafters are not aligned with each other in each of the panels. This configuration can supplement structural weaknesses. In addition, required horizontal strength as the whole roof structural surface can be secured by maintaining the joining strength between the rafters and the roofing board. Furthermore, the projection length of the carry-out portions is smaller than the length of the adjacent horizontal base materials, and the carry-out portions and the other roof panel are fixed to the same horizontal base material. Accordingly, the roof panels can be easily handled while minimizing the projection length of the carry-out portions without lowering the joining strength between the respective roof panels. 
     According to the second roof structure of the present invention, the one roof panel is fixed to the horizontal base materials with the carry-out portions facing the upstream side. The other roof panel is disposed on the upstream side with respect to the one roof panel, and fixed to the horizontal base materials. In this case, during construction, the one roof panel disposed on the downstream side is initially fixed onto the horizontal base materials, and then the other roof panel on the upstream side is fixed onto the horizontal base materials. Accordingly, work is performable while facing the upstream side, which improves workability. 
     According to the third roof structure of the present invention, the carry-out portions of the one roof panel and the rafters of the other roof panel are alternately disposed at equal intervals. Accordingly, joining strength between the roof panels can be equalized. 
     According to the fourth roof structure of the present invention, the roof structure includes the three or more roof panels disposed side by side in the slope direction. In addition, each of the roof panels on the downstream side except for the roof panel closest to the ridge side has the carry-out portions each projecting toward the upstream side, and the carry-out portions are arranged and fixed between the rafters of the roof panel adjacent on the upstream side. Accordingly, an increase in the roof size can be handled by arranging the plurality of roof panels in the slope direction. 
     According to the fifth roof structure of the present invention, the roof structure includes the three or more roof panels disposed side by side in the slope direction. The roof panel on the upstream side includes the carry-out portion that projects toward the downstream side. The roof panel on the downstream side includes the carry-out portion that projects toward the upstream side. The roof panel that is an intermediate roof panel located between the roof panel on the upstream side and the roof panel on the downstream side, and is configured such that an upstream side end and a downstream side end of each of the rafters do not project from an edge of the roofing board. In this manner, a large roof can be formed by arranging a plurality of the roof panels in the slope direction. 
     According to the roof structure construction method of the present invention, the one roof panel is fixed to the horizontal base materials, and then the other roof panel is disposed such that the roofing board of the other roof panel covers the carry-out portions of the one roof panel. The ends of the roofing boards of the one roof panel and the other roof panel are brought into abutment with each other. The fixing tools are driven into the carry-out portions from above the roofing board of the other roof panel to fix the one roof panel and the other roof panel to each other. In this manner, the respective roof panels are easily joined to each other, which improves workability. 
     According to the first roof panel of the present invention, the one end of each of the first rafters projects from the edge of the first roofing board to form the first projection portion. Accordingly, an interval between the rafters of the respective panels can be reduced by setting the roof panel on the horizontal base materials with the first protrusion portions facing in the roof slope direction, and bringing a roofing board of a composite panel which includes a roofing board widely spread and rafters integrated with each other into abutment with one edge of the first roofing board, and by fixing the composite panel to the horizontal base materials with the rafters of the composite panel disposed between the adjacent first rafters. Therefore, workability improves without the necessity of j oining ends of the rafters of the respective panels as conventionally required. In addition, structural strength of the joining portions of the rafters increases. In addition, the joining portions of the roofing boards of the respective panels and the joining portions of the rafters are not aligned with each other. Accordingly, structural strength required for the roof can be maintained by supplementing structural weaknesses. Furthermore, the projection length of the first projection portions is equal to or greater than the interval between the adjacent horizontal base materials. Accordingly, the roof panel can be stably set on the upper parts of the horizontal base materials. 
     According to the sixth roof structure of the present invention, the roof panel is fixed to the roof horizontal base materials with the first projection portions facing the upstream side. Accordingly, an interval between the rafters of the respective panels can be reduced by bringing a roofing board of a composite panel which includes a roofing board widely spread and rafters integrated with each other into abutment with one edge of the first roofing board from the upstream side, and fixing the composite panel to the horizontal base materials with the rafters of the composite panel disposed between the adjacent first rafters. Therefore, workability improves without the necessity of j oining ends of the rafters of the respective panels as conventionally required. In addition, structural strength of the joining portions of the rafters increases. Moreover, the joining portions of the roofing boards and the joining portions of the rafters are not aligned with each other in each of the panels. This configuration can supplement structural weaknesses. In addition, required horizontal strength as the whole roof structural surface can be secured by maintaining the joining strength between the rafters and the roofing board. 
     According to the seventh roof structure of the present invention, the one edge of the second roofing board is disposed in abutment with the one edge of the first roofing board, and the receiving roof panel is fixed to the horizontal base materials with the one end of the second rafter disposed between the adjacent first projection portions. In this case, the interval between the one end of the second rafter and the first projection portion can be reduced. Therefore, workability improves without the necessity of joining ends of the rafters of the respective panels as conventionally required. In addition, structural strength of the joining portions of the rafters increases. Moreover, the joining portions of the roofing boards and the joining portions of the rafters are not aligned with each other in each of the panels. This configuration can supplement structural weaknesses. In addition, required horizontal strength as the whole roof structural surface can be secured by maintaining the joining strength between the rafters and the roofing board. 
     According to the eighth roof structure of the present invention, the one edge of the third roofing board is disposed in abutment with the opposite edge of the second roofing board, and the receiving roof panel is fixed to the horizontal base materials with the opposite end of the second rafter disposed between the adjacent second projection portions. Accordingly, even in a case of a large roof, the necessity of joining the ends of the respective rafters at a construction site is eliminated by combining the respective roof panels, which improves workability. 
     According to the second roof structure construction method of the present invention, the one end of each of the second rafters is disposed between the adjacent first projection portions exposed from the first roofing board after the roof panel is set on the horizontal base materials. Accordingly, the necessity of joining the ends of the first rafters and the second rafters at a construction site is eliminated, which improves workability. 
     According to the third roof structure construction method of the present invention, the roof structure can be constructed only by dropping the receiving roof panel between the roof panel and the second roof panel from above after the second roof panel is fixed to the horizontal base materials on the most upstream side for positioning of the upstream side. Accordingly, workability improves. In addition, both the ends of the second rafter are disposed between the first projection portions and between the second projection portions, respectively, which are projection portions exposed from the first and third roofing boards. Accordingly, the necessity of joining the ends of the respective rafters at a construction site is eliminated, which improves workability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view showing a whole structure of a roof structure according to a first embodiment. 
         FIG.  2    is a perspective view showing a structure of the one roof panel. 
         FIG.  3    is a perspective view showing a structure of the other roof panel. 
         FIG.  4    is a view illustrating a state that the one roof panel is fixed to the horizontal base materials according to a construction method of the roof structure. 
         FIG.  5    is a view showing a state before the rafters of the one roof panel are fixed to an outrigger. 
         FIG.  6    is a view showing a state after the rafters of the one roof panel were fixed to the outrigger. 
         FIG.  7    is a view showing a state that the rafters of the roof panel are fixed to the purlins. 
         FIG.  8    is a view showing a state that the joining fixing tools are driven between the carry-out portions of the one roof panel by disposing the rafters of the other roof panel. 
         FIG.  9    is a view illustrating a state that the one rafter joining tools are driven into the purlins by penetrating the roofing board and the rafters. 
         FIG.  10    is a view illustrating a state that the other roof panel is fixed to the horizontal base materials according to a roof structure construction method. 
         FIG.  11    is a view illustrating a state that a roof structure was completed according to a first embodiment. 
         FIG.  12    is an exploded view illustrating a whole structure of a roof structure according to a second embodiment. 
         FIG.  13    is an exploded view illustrating a whole structure of a roof structure according to a third embodiment. 
         FIG.  14    is a perspective view showing a roof structure according to a forth embodiment. 
         FIG.  15    is a perspective view showing a roof panel according to a forth embodiment. 
         FIG.  16    is a perspective view showing a roof panel comprising the reinforcing rafters according to a forth embodiment. 
         FIG.  17    is a perspective view showing a receiving roof panel according to a forth embodiment. 
         FIG.  18    is a perspective view showing a condition that a roof panel is spanned on the horizontal base materials according to a forth embodiment. 
         FIG.  19    is a perspective view showing a condition that a receiving roof panel is spanned on the horizontal base materials according to a forth embodiment. 
         FIG.  20    is a perspective view showing a state before the first rafters are fixed to the outrigger according to a forth embodiment. 
         FIG.  21    is a perspective view showing a state that the first rafters were fixed to the outrigger according to a forth embodiment. 
         FIG.  22    is a perspective view showing a state that the second rafters are set on the purlins according to a forth embodiment. 
         FIG.  23    is a plan view showing a roof structure according to a forth embodiment. 
         FIG.  24    is a plan view showing a condition that a plurality of the roof panels and the receiving roof panels were spanned on the horizontal base materials to a forth embodiment. 
         FIG.  25    is a plan view showing a roof structure comprising a plurality of the roof panels according to a modification of a forth embodiment. 
         FIG.  26    is a perspective view showing a condition that a receiving roof panel is set between a roof panel and a second roof panel according to a fifth embodiment. 
         FIG.  27    is a plan view showing a roof panel according to a fifth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     A roof structure according to a first embodiment of the present invention will be hereinafter described with reference to the respective drawings. For example, a roof structure  11  of the present embodiment is a roof structure  11  having a slope, such as a gable roof, a one-sided roof, and a hipped roof. For example, the roof structure  11  is a type supported by a roof frame of a wooden structure, but may be a type partially or entirely supported by a steel roof frame. As shown in  FIG.  1   , the roof structure  11  includes a plurality of horizontal base materials  2  parallel to each other with a clearance left between each other, and perpendicular to a slope direction, and a plurality of roof panels  40  fixed onto the horizontal base materials  2 . 
     The horizontal base materials  2  are a plurality of long wooden materials. The horizontal base materials  2  are supported by not-shown pillars or posts, and extend in the horizontal direction. The plurality of horizontal base materials  2  are parallel to each other, and have such a height difference that the horizontal base materials  2  on an upstream side are located high, and that the horizontal base materials  2  on a downstream side are located low. The horizontal base materials  2  are disposed along a roof slope. According to the example shown in the figure, the horizontal base materials  2  are constituted by an outrigger  21  disposed on the most downstream side, a ridge  22  disposed on the most upstream side, and three purlins  23  disposed between and in parallel to the outrigger  21  and the ridge  22 . The number of the respective horizontal base materials  2  and the intervals between the respective horizontal base materials  2  are calculated and determined by structural calculation in consideration of factors such as a roof shape, a climate of each region, and a load acting on the roof. For example, a horizontal distance between the adjacent purlins  23  of the horizontal base materials  2  may be set in a range from 1000 mm to 1500 mm. Note that the arrangement of the horizontal base materials  2  in  FIG.  1    is presented by way of example. The type and shape of the horizontal base materials  2 , and the number of the purlins  23  are not particularly limited. 
     As shown in  FIGS.  1  and  5   , the outrigger  21  and the ridge  22  are long wooden members each having a rectangular cross section. A rafter stand  24  for receiving the rafters  5  of the roof panel  40  described below is fixed to an upper surface of each of the outrigger  21  and the ridge  22 . Each of the rafter stands  24  includes groove-shaped notches  25  formed at positions where the respective rafters  5  are fixed, and each configured such that a bottom surface has a slope equal to the roof slope. As shown in  FIG.  6   , a lower side of the rafter  5  is inserted into the notch  25 , and the rafter  5  is fixed to the outrigger  21  or the ridge  22  in a state where a lower surface of the corresponding rafter  5  come into contact with a bottom surface of the notch  25 . While  FIGS.  5  and  6    each show a joining portion between the outrigger  21  and the rafter  5 , a joining portion between the ridge  22  and the rafter  5  has a similar configuration as shown in  FIGS.  4  and  10   . 
     As shown in  FIGS.  1  and  7   , a rafter receiver  26  which has an upper surface sloped in accordance with the roof slope is fixed to a side surface of each of the purlins  23  on the downstream side by a nail  27 . A lower surface of each of the rafters  5  of the roof panel  40  comes into contact with an upper surface of the rafter receiver  26  to stabilize a sloped state of each of the rafters  5  along the roof slope and fix the rafter  5  and the purlin  23 . 
     The roof panel  40  is a composite panel formed beforehand in a factory by fixing roofing boards  6  made of plywood and the rafters  5  each constituted by a square timber using fixing tools  43  constituted by screws or nails. A plurality of the roof panels  40  are spread side by side in the slope direction to form the roof slope, and roofing materials such as not-shown asphalt roofing and roof tiles are laid on the roofing boards  6  of the roof panels  40 . According to the first embodiment, two types of roof panels  40   a  and  40   b  are provided as the roof panels  40 , and disposed such that the roof panels  40   a  and  40   b  abut on each other in the slope direction. The roof panels  40   a  as one type of the roof panels  40  are disposed on the downstream side, while the other roof panels  40   b  as the other type are disposed on the upstream side. 
     As shown in  FIG.  2   , the one roof panel  40   a  has the roofing board  6 , and a plurality of the rafters  5  fixed to the lower surface of the roofing board  6  in parallel to each other with a clearance left between each other. The roofing board  6  is structural plywood having a thickness of 12 mm, and has a rectangular shape having a width of 2000 mm or smaller and a length of 3000 mm or larger and 4000 mm or smaller. The roof panel  40   a  in this size can be lifted by a crane and placed at a predetermined position without any problem during construction, and can be easily transported. The rafters  5  are fixed to the roofing board  6  by a plurality of the fixing tools  43  such as nails driven from above the roofing board  6 . The one roof panel  40   a  has carry-out portions  53  which are projecting portions of the rafters  5  from an edge of the roofing board  6 . A projection length L of the carry-out portions  53  in the first embodiment is 500 mm. The projection length L of the carry-out portions  53  is smaller than at least a distance between the adjacent purlins  23 . In addition, the projection length L of the carry-out portions  53  is equal to or larger than a length sufficient for fixing the carry-out portions  53  to the roofing board  6  of the other roof panel  40   b  by driving joining fixing tools  44  such as nails. For example, each of the joining fixing tools  44  is a thick iron round nail having a length of 50 mm. The roof panels  40  are joined to each other with joining strength necessary or larger by driving the three joining fixing tools  44  from above the roofing board  6  of the other roof panel  40   b  into each of the carry-out portions  53  of the rafters  5 . When the projection length of each of the carry-out portions  53  is 500 mm or more, the three joining fixing tools  44  can be driven from above the roofing board  6  to the carry-out portion  53  with an appropriate distance left between each other. 
     Efficient construction work is achievable with easy handling of the one roof panel  40   a  during construction by setting the projection length of the carry-out portions  53  to the minimum projection length L required for joining the roof panels  40  to each other as described above. 
     In addition, the one roof panel  40   a  has the rafters  5  projecting from a downstream edge of the roofing board  6 . The projecting portion of the rafter  5  toward the downstream side is fixed to the outrigger  21 . As shown in  FIGS.  5  and  6   , reference ink  54  is marked on a side surface of the rafter  5  at a position in contact with the outrigger  21  to equalize projections of eaves. A projection width of the rafters  5  of the roof panel  40   a  from the roofing board  6  is determined by a projection size of roof eaves. Note that each of the rafters  5  of the roof panels  40  other than the roof panel  40   a  provided on the most downstream side does not project from the roofing board  6  toward the downstream side. 
     Each of the rafters  5  of the one roof panel  40   a  has a length enough to be spanned over the outrigger  21  and the two purlins  23 . The length of the rafters  5  of the one roof panel  40   a  is not limited to this length, but may be a length enough to be spanned over the three or more purlins  23 . 
     An interval between the adjacent rafters  5  of the roof panel  40  is preferably 500 mm or smaller in accordance with positioning standards for the horizontal base materials  2  specified in “Allowable stress design of wooden frame construction method housing (2017 version)”. In addition, the plurality of rafters  5  are preferably provided at equal intervals in consideration of allocation easiness and workability, but are not necessarily required to be provided at equal intervals as long the interval is 500 mm or smaller. 
     The other roof panel  40   b  included in the roof panels  40  and disposed on the upstream side is a composite panel which includes the roofing board  6  and the rafters  5  integrated beforehand in a factory, similarly to the one roof panel  40   a . As shown in  FIG.  3   , the other roof panel  40   b  has the roofing board  6 , and a plurality of the rafters  5  fixed to the lower surface of the roofing board  6  in parallel to each other with a clearance left between each other. Each of the rafters  5  is connected and fixed to the roofing board  6  by a plurality of the fixing tools  43  driven from above the roofing board  6 . The rafters  5  of the other roof panel  40   b  are aligned with the edges of the roofing board  6  without projecting from both edges of the roofing board  6 . 
     As shown in  FIGS.  1  and  8   , the roofing board  6  of the other roof panel  40   b  is disposed on the carry-out portions  53  of the one roof panel  40   a , and covers the carry-out portions  53  from above. The carry-out portions  53  of the one roof panel  40   a  and the rafters  5  of the other roof panel  40   b  are arranged to overlap each other when viewed from the side. The carry-out portions  53  are disposed between the rafters  5  of the other roof panel  40   b . The carry-out portions  53  of the one roof panel  40   a  and the rafters  5  of the other roof panel  40   b  are alternately disposed at equal intervals. In this manner, joining strength between the roof panels  40  is equalized to reduce an excessive load applied to a certain part when the carry-out portions  53  of the one roof panel  40   a  are fixed to the roofing board  6  of the other roof panel  40   b.    
     The joining fixing tools  44  constituted by three nails are driven into each of the carry-out portions  53  of the one roof panel  40   a  at intervals of 150 mm from above the roofing board  6  of the other roof panel  40   b  to join the carry-out portions  53  of the one roof panel  40   a  and the roofing board  6  of the other roof panel  40   b . Moreover, as shown in  FIG.  9   , one rafter joining tool  55  penetrates the roofing board  6  of the other roof panel  40   b  and the carry-out portion  53  of the one roof panel  40   a , and is driven into the purlin  23  at a position where the carry-out portion  53  is disposed to join the carry-out portion  53  of the one roof panel  40   a  and the purlin  23 . Joining strength between the carry-out portion  53  of one roof panel  40   a  and the roofing board  6  of the other roof panel  40   b  produced by the three joining fixing tools  44  is equal to or higher than joining strength between the carry-out portion  53  of the one roof panel  40   a  and the purlin  23  produced by the rafter joining tool  55 . 
     According to this configuration, the one roof panel  40   a  and the other roof panel  40   b  can be integrated with each other as the whole roof panel  40  without joining the respective rafters  5 , which increases structural strength. 
     As shown in  FIG.  4   , according to a construction method of the roof structure, the outrigger  21 , the purlins  23 , and the ridge  22  are spanned on the not-shown pillars or posts to constitute a roof frame. Thereafter, the one roof panel  40   a  is disposed and fixed to the outrigger  21  and the two purlins  23  adjacent to the outrigger  21 . As described above, the one roof panel  40   a  is placed on the rafter stand  24  on the upper part of the outrigger  21  and the rafter receivers  26  fixed to the purlins  23  in a state where the carry-out portions  53  of the rafters  5  face the upstream side. Thereafter, as shown in  FIG.  5   , a downstream end of the rafter  5  is fitted into the notch of the rafter stand  24 . Subsequently, after the reference ink  54  and a downstream corner of the rafter stand  24  are aligned to equalize the protrusion width of the downstream end from the outrigger  21 , the rafter joining tool  55  as a long screw is driven from above to integrally connect and fix the downstream end of the rafter  5  and the outrigger  21  as shown in  FIG.  6   . At this time, the reference ink  54  is not hidden by the roofing board  6 . Accordingly, workability improves by easy alignment of the reference ink  54  with a predetermined position of the outrigger  21 . Then, as shown in  FIG.  7   , the rafter joining tool  55  as a long screw is driven from above the roofing board  6  into the purlin  23  at a portion in contact with the rafter receiver  26  while penetrating the rafter  5 . In this manner, the one roof panel  40   a  is fixed to the outrigger  21  and the purlin  23 . 
     Next, as shown in  FIG.  10   , the other roof panel  40   b  is disposed on the upstream side of the one roof panel  40   a , and placed on the rafter receivers  26  fixed to the purlins  23  and the rafter stand  24  on the upper part of the ridge  22 . At this time, a part of each of the rafters  5  on the downstream side is disposed between the carry-out portions  53  of the one roof panel  40   a , and the roofing board  6  of the one roof panel  40   a  and the roofing board  6  of the other roof panel  40   b  are brought into abutment with each other. Subsequently, by procedures similar to the procedures of the one roof panel  40   a , the upstream end of the rafter  5  is fitted into the rafter stand  24  of the ridge  22 , and the other roof panel  40   b  and the ridge  22  are integrally connected and fixed to each other from above the roofing board  6  using the rafter joining tool  55  as a long screw. Thereafter, as shown in  FIG.  9   , the rafter joining tools  55  as long screws are driven into the rafters  5  at the positions in contact with the rafter receiver  26  of the purlin  23  from above the roofing board  6  to fix the other roof panel  40   b  to the purlin  23  and the ridge  22 . 
     In this manner, as shown in  FIG.  8   , the roof panels  40  each fixed onto the horizontal base materials  2  constituted by the outrigger  21 , the purlins  23 , and the ridge  22  are connected to each other by driving the plurality of joining fixing tools  44  from above into positions where the roofing board  6  of the other roof panel  40   b  and the carry-out portions  53  of the one roof panel  40   a  are aligned with each other. Then, as shown in  FIG.  11   , each of the roof panels  40  is horizontally set by similar procedures, and an eave edge purlin  34  are fixed to eave side ends of the rafters  5  by screws. In addition, an eave edge roofing board  51  for eave edges is set at projecting ends of the rafters  5  from the eave edges and the upper parts of the eave edge purlins  34 . Finally, an end roofing board  52  is set between a gable-side edge of the other roof panel  40   b  located at a gable-side end of the roof surface and longitudinal edges of the purlin  23  and the ridge  22  to complete the roof structure  11 . 
     As described above, according to the roof structure  11  of the first embodiment, the interval between the rafters  5  of the roof panels  40   a  and  40   b  can be reduced by alternately disposing a part of the rafters  5  of the one roof panel  40   a  and the rafters  5  of the other roof panel  40   b . Therefore, structural strength of the joining portions of the respective rafters  5  can be raised without joining the ends of the respective rafters  5 . As a result, workability significantly improves. In addition, the joining portions of the roofing board  6  and the joining portions of the rafters  5  are not aligned with each other. Accordingly, the roof structure  11  to be provided can be easily constructed while maintaining structural strength required for the roof by supplementing structural weaknesses. 
     Second Embodiment 
     Next, a roof structure  12  according to a second embodiment will be described. Components similar to corresponding components of the roof structure  11  of the first embodiment are given the same reference numerals, and description of these components will be omitted. The roof structure  12  of the second embodiment includes the roof panels  40  having three types and disposed side by side in the slope direction. According to the present embodiment, each of two types of roof panels  40   c  and  40   d  except for a roof panel  40   e  closest to the ridge side has the roofing board  6  and the plurality of rafters  5 . The rafters  5  project from the upstream edge of the roofing board  6  to form the carry-out portions  53  as shown in  FIG.  12   . Each of the carry-out portions  53  has a projection length of 500 mm. 
     The roof panel  40   c  located closest to the eave side in the two roof panels  40   c  and  40   d  has the rafters  5  projecting from the downstream edge of the roofing board  6 . The projecting portion of the rafter  5  toward the downstream side is fixed to the outrigger  21 . The rafters  5  of the roof panel  40   d  located between the roof panel  40   e  closest to the ridge side and the roof panel  40   c  closest to the eave side do not project from the roofing board  6  toward downstream side. The carry-out portions  53  are provided only on the upstream side. In addition, the roof panel  40   e  closest to the ridge side has the same configuration as that of the other roof panel  40   b  in the first embodiment. The rafters  5  of the roof panel  40   e  do not project from both edges of the roofing board  6 , but are aligned with the edges of the roofing board  6 . 
     The roofing board  6  of the intermediate roof panel  40   d  is disposed on the carry-out portions  53  provided on the upstream side of the roof panel  40   c  closest to the eave side while covering the carry-out portions  53 . In addition, the rafters  5  of the intermediate roof panel  40   d  are disposed such that the carry-out portions  53  are sandwiched between the rafters  5 . The joining fixing tools  44  are driven into the carry-out portions  53  of the roof panel  40   c  closest to the eave side from above the roofing board  6  of the intermediate roof panel  40   d  to join the carry-out portions  53  of the roof panel  40   c  closest to the eave side and the roofing board  6  of the intermediate roof panel  40   d . In addition, the roofing board  6  of the roof panel  40   e  closest to the ridge side is disposed on the carry-out portions  53  provided on the upstream side of the intermediate roof panel  40   d  while covering the carry-out portions  53 . Moreover, the rafters  5  of the roof panel  40   e  closest to the ridge side are disposed such that the carry-out portions  53  are sandwiched between the rafters  5 . The joining fixing tools  44  are driven into the carry-out portions  53  of the intermediate roof panel  40   d  from above the roofing board  6  of the roof panel  40   e  closest to the ridge side to join the carry-out portions  53  of the intermediate roof panel  40   d  and the roofing board  6  of the roof panel  40   e  closest to the ridge side. The rafters  5  of the respective roof panels  40 , the outrigger  21 , the purlins  23 , and the ridge  22  are joined by the rafter joining tools  55  as long screws driven from above the roofing board  6  similarly to the first embodiment. 
     According to the relationship between the roof panel  40   c  closest to the eave side and the intermediate roof panel  40   d  in the roof panels  40  of the present embodiment, the roof panel  40   c  closest to the eave side corresponds to “one roof panel” in the present invention, while the intermediate roof panel  40   d  corresponds to “the other roof panel” in the present invention. In addition, according to the relationship between the intermediate roof panel  40   d  and the roof panel  40   e  closest to the ridge side, the intermediate roof panel  40   d  corresponds to “one roof panel” in the present invention, while the roof panel  40   e  closest to the ridge side in the present invention corresponds to “the other roof panel”. 
     As described above, each of the roof panels  40   c  and  40   d  on the downstream side except for the roof panel  40   e  closest to the ridge side has the carry-out portions  53  each projecting toward the upstream side, and the carry-out portions  53  are disposed and fixed between the rafters  5  of the roof panel  40  adjacent on the upstream side. Accordingly, an increase in the roof size can be handled by arranging the plurality of roof panels  40  in the slope direction. While the three roof panels  40  are disposed side by side in the slope direction in the example presented in the second embodiment, the four or more roof panels  40  may be disposed side by side in the slope direction. In this case, a plurality of the intermediate roof panels  40   d  in the present embodiment are disposed between the roof panel  40   e  closest to the ridge side and the roof panel  40   c  closest to the eave side. 
     Third Embodiment 
     Next, a roof structure  13  according to a third embodiment will be described. Components similar to corresponding components of the roof structures  11  and  12  of the first and second embodiments are given the same reference numerals, and description of these components will be omitted. The roof structure  13  of the third embodiment includes the roof panels  40  having three types and disposed side by side in the slope direction similarly to the second embodiment. According to the present embodiment, a roof panel  40   h  on the upstream side and closest to the ridge side has the carry-out portions  53  projecting from the roofing board  6  toward the downstream side. Moreover, a roof panel  40   f  on the downstream side and closest to the eave side has the carry-out portions  53  projecting from the roofing board  6  toward the upstream side. Furthermore, a roof panel  40   g  which includes the rafters  5  having upstream and downstream ends projecting from the edges of the roofing board  6  is disposed between the roof panel  40   h  on the upstream side and the roof panel  40   f  on the downstream side. 
     The roofing board  6  of the intermediate roof panel  40   g  is disposed on the carry-out portions  53  projecting toward the upstream side of the roof panel  40   f  on the downstream side, and covers the carry-out portions  53 . The rafters  5  of the intermediate roof panel  40   g  are disposed such that the carry-out portions  53  are sandwiched between the rafters  5 . The joining fixing tools  44  are driven into the carry-out portions  53  of the roof panel  40   f  on the downstream side from above the roofing board  6  of the intermediate roof panel  40   g  to join the carry-out portions  53  of the roof panel  40   f  on the downstream side and the roofing board  6  of the intermediate roof panel  40   g . In addition, the roofing board  6  of the intermediate roof panel  40   g  is disposed on the carry-out portions  53  projecting toward the downstream side of the roof panel  40   h  on the upstream side, and covers the carry-out portions  53 . The rafters  5  of the intermediate roof panel  40   g  are disposed such that the carry-out portions  53  are sandwiched between the rafters  5 . The joining fixing tools  44  are driven into the carry-out portions  53  of the roof panel  40   h  on the upstream side from above the roofing board  6  of the intermediate roof panel  40   g  to join the carry-out portions  53  of the roof panel  40   h  on the upstream side and the roofing board  6  of the intermediate roof panel  40   g.    
     As described above, according to the roof structure  13 , the necessity of applying complicated processing to the ends of the rafters  5  to join the rafters  5  with each other as conventionally performed is eliminated by alternately arranging a part of the respective rafters  5 . Accordingly, workability greatly improves even in a case of a large roof having a long length. In addition, the joining portions of the roofing board  6  and the joining portions of the rafters  5  are not aligned with each other. Accordingly, the roof structure  13  to be provided can be easily constructed while maintaining structural strength required for the roof by supplementing structural weaknesses. Moreover, the intermediate roof panel  40   g  is dropped from above after determining a most downstream position and a most upstream position using the roof panel  40   f  on the downstream side and the roof panel  40   h  on the upstream side. Accordingly, deviation of the roof panels  40  around the eaves and ridges is avoidable. 
     Fourth Embodiment 
     A roof structure  1  according to an embodiment of the present invention will be hereinafter described with reference to the respective drawings. The roof structure  1  shown in  FIG.  14    is a structure mainly used for a slope roof having a wooden structure, and includes a plurality of the horizontal base materials  2  disposed in parallel with each other with a clearance left between each other and extending in an outrigger direction, a roof panel  3 , and a receiving roof panel  4  disposed on the upstream side with respect to the roof panel  3 . 
     As shown in  FIG.  14   , the horizontal base materials  2  are a plurality of long members disposed substantially parallel to each other with a clearance left between each other while producing a height difference along the roof slope, and extending in the outrigger direction while supported by not-shown pillars and posts. The roof panel  3  and the receiving roof panel  4  are placed on the upper parts of the horizontal base materials  2 . According to the example shown in the figure, the horizontal base materials  2  are constituted by the outrigger  21  disposed on the most downstream side, the ridge  22  disposed on the most upstream side, and a plurality of the purlins  23  disposed between and in parallel to the outrigger  21  and the ridge  22 . An interval L 1  between the respective horizontal base materials  2  is calculated and determined by structural calculation in consideration of a roof shape, a climate of each region, a load acting on the roof, and the like. For example, a vertical distance between the purlins  23  may be set approximately in a range from 1500 mm to 2000 mm. Note that the arrangement of the horizontal base materials  2  in  FIG.  14    is presented by way of example. The type and shape of the horizontal base materials  2 , and the number of the purlins  23  are not particularly limited. 
     As shown in  FIGS.  14  and  18   , a rafter stand  2   a  for receiving first rafters  32  and second rafters  42 , which will be described below, is fixed to each of the upper surfaces of the outrigger  21  and the ridge  22 . A notch  2   b  having a substantially triangular cross-sectional shape as shown in  FIG.  20    is formed in the rafter stand  2   a  at each point of contact with the rafters  32  and  42 . Moreover, as shown in  FIGS.  18  and  22   , a rafter receiver  23   a  having a trapezoidal cross section and an upper surface sloped in accordance with the roof slope is fixed to the downstream side surface of each of the purlins  23  using a fixing tool A such as a screw and a nail. In this manner, the respective rafters  32  and  42  can be placed in a stable manner. 
     The roof panel  3  is a composite panel which includes a roofing board and rafters integrated with each other beforehand in a factory, and includes a first roofing board  31 , and a plurality of first rafters  32  fixed to a lower surface  31   a  of the first roofing board  31  in parallel to each other with a clearance left between each other as shown in  FIG.  15   . The first field material  31  is constituted by structural plywood having a thickness of approximately 12 mm, and sized to have a width of approximately 2000 mm or smaller and a length of approximately 3000 mm to 4000 mm or smaller. The roof panel  3  in this size can be lifted by a crane without any problem and placed in a predetermined position during construction, and can be easily transported. Each of the first rafters  32  is connected and fixed to the first roofing board  31  by a plurality of fixing tools A driven from above the first roofing board  31 . One end of each of the first rafters  32  projects from one edge  31   b  of the first roofing board  31 . A projection length L 2  of a first projection portion  32   a , which is the foregoing projection portion, is equal to or larger than the interval L 1  between the adjacent horizontal base materials  2  shown in  FIG.  14   . In addition, an opposite end  32   b  of each of the first rafters  32  is a portion projecting from an opposite edge  31   c  of the first roofing board  31  and forming an eave, and is placed on the outrigger  21  as shown in  FIG.  14   . As shown in  FIG.  20   , reference ink  32   d  is marked on a side surface  32   c  of the opposite end  32   b  at a portion in contact with the outrigger  21  to equalize projections of eaves. A projection width of the opposite end  32   b  from the first roofing board  31  is determined by projections of eaves for each roof. Note that the opposite end  32   b  of the first rafter  32  does not project from the opposite edge  31   c  of the first roofing board  31  when the roof panel  3  is not set at the most downstream position. 
     As shown in  FIG.  14   , it is preferable that the roof panel  3  is fixed on the horizontal base materials  2  with the first projection portion  32   a  side of the first rafters  32  facing the upstream side, and that the total length of the roof panel  3  is at least twice to three times larger than the interval L 1  between the horizontal base materials  2 . For forming a roof having large projections of eaves as shown in  FIG.  16   , reinforcing rafters  33  may be provided adjacent to the opposite ends  32   b  of the plurality of first rafters  32  except for both ends to reinforce strength of the eaves. While not shown in the figures, each of the reinforcing rafters  33  has such a length that the opposite end of the reinforcing rafter  33  can reach the purlin  23  adjacent to the ridge  21  in a state where an edge of one end of the reinforcing rafter  33  is aligned with an edge of the opposite end  32   b.    
     An interval between the adjacent first rafters  32  is preferably 500 mm or smaller in accordance with positioning standards for the horizontal base materials specified in “Allowable stress design of wooden frame construction method housing (2017 version)”. In addition, the intervals between the plurality of first rafters  32  are preferably equal intervals in consideration of allocation easiness and workability, but are not necessarily limited to equal intervals as long as each interval is 500 mm or smaller. 
     Similarly to the roof panel  3 , the receiving roof panel  4  is a composite panel which includes a roofing board and rafters integrated with each other beforehand in a factory, and includes a second roofing board  41 , and a plurality of second rafters  42  fixed to a lower surface  41   a  of the second roofing board  41  in parallel to each other with a clearance left between each other as shown in  FIG.  17   . Each of the second rafters  42  is connected and fixed to the second roofing board  41  by a plurality of the fixing tools A driven from above the second roofing board  41 . One and opposite ends of each of the second rafters  42  are disposed at one edge  41   b  and an opposite edge  41   c  of the second roofing board  41 , respectively. Unlike the roof panel  3 , both ends  42   a  and  42   b  of the second rafter  42  do not protrude from the second roofing board  41 . As shown in  FIG.  14   , the receiving roof panel  4  is a panel overlapped on the upper parts of the first projection portions  32   a . It is preferable that the total length of the receiving roof panel  4  is at least twice larger than the interval L 2  between the horizontal base materials  2 . Note that the configuration of the second roofing board  41  and the interval between the second rafters  42  are similar to the configuration of the first field material  31  and the interval between the first rafters  32 . 
     Next, a construction method of the roof structure  1  will be described. First, as shown in  FIG.  18   , the roof panel  3  is spanned on the horizontal base materials  2  extended on not-shown pillars and posts. The roof panel  3  is placed on the rafter stand  2   a  at the upper part of the outrigger  21  and the rafter receivers  23   a  fixed to the purlins  23  in a state where the first projection portions  32   a  of the first rafters  32  face the upstream side. The opposite end  32   b  of the first rafter  32  is fitted into the notch  2   b  of the rafter stand  2   a  as shown in  FIG.  20   . Then, after aligning the reference ink  32   d  and a downstream side corner of the rafter stand  2   a  to equalize the projection width of the opposite end  32   b  from the outrigger  21 , the opposite end  32   b  and the outrigger  21  are integrally connected and fixed from above by a long screw B as shown in  FIG.  21   . At this time, the reference ink  32   d  is not hidden by the first roofing board  31 . Accordingly, workability improves by easy alignment of the reference ink  32   d  with a predetermined position of the outrigger  21 . Moreover, as shown in  FIG.  22   , the long screw B is driven from above the first roofing board  31  into the first rafter  32  at a portion in contact with the rafter receiver  23   a  to sequentially fix the roof panel  3  to the horizontal base materials  2 . 
     Subsequently, as shown in  FIGS.  14  and  19   , the receiving roof panel  4  is placed on the rafter receivers  23   a  fixed to the purlins  23  located on the upstream side with respect to the first roofing board  31 , and on the rafter stand  2   a  on the upper part of the ridge  22 . At this time, the one end  42   a  of each of the second rafters  42  is disposed between the adjacent first projection portions  32   a , and the one edge  41   b  of the second roofing board  41  is brought into abutment with the one edge  31   b  of the first roofing board  31 . Then, the opposite end  42   b  of each of the second rafters  42  is fitted into the rafter stand  2   a  of the ridge  22  by procedures similar to the procedures of the roof panel  3 . As shown in  FIG.  23   , the receiving roof panel  4  and the ridge  22  are integrally connected and fixed from above the second roofing board  41  by the long screws B, and the receiving roof panel  4  is fixed to the horizontal base materials  2  by driving the long screws B from above the second roofing board  41  into the second rafters  42  in contact with the rafter receivers  23   a.    
     In this manner, the roof panel  3  and the receiving roof panel  4  fixed onto the horizontal base materials  2  are connected to each other by driving a plurality of fixing tools A from above into positions where the second roofing board  41  and the first projection portions  32   a  of the first rafters  32  are aligned with each other as shown in  FIG.  23   . Then, as shown in  FIG.  24   , each of the roof panel  3  and the receiving roof panel  4  is horizontally set by similar procedures, and the eave edge purlin  34  are fixed to tips of the opposite ends  32   b  of the first rafters  32  by screws. In addition, the eave edge roofing board  51  for eave edges is set at the opposite ends  32   b  of the first rafters  32  projecting from the eave edges and the upper parts of the eave edge purlin  34 . Finally, the end roofing board  52  is set between a gable-side edge of the receiving roof panel  4  located at a gable-side end of the roof surface and longitudinal edges of the horizontal base materials  2  to complete the roof structure  1 . 
     As described above, according to the roof structure  1 , the intervals between the rafters  32  and  42  of the respective panels  3  and  4  can be reduced by alternately arranging a part of the first rafters  32  and the second rafters  42 . Therefore, structural strength of the joining portions of the respective rafters  32  and  42  can be raised without joining the ends of the respective rafters  32  and  42 . As a result, workability significantly improves. In addition, the joining portions of the roofing board and the joining portions of the rafters are not aligned with each other. Accordingly, the roof structure to be provided can be easily constructed while maintaining structural strength required for the roof by supplementing structural weaknesses. Moreover, while only the one roof panel  3  is used in the example shown in the figure, the receiving roof panel  4  may be fixed to the first projection portions  32   a  of the roof panel  3  located on the most upstream side in a state where the first roofing boards  31  of the plurality of roof panels  3  abut on and join each other as shown in  FIG.  25   . The number of the roof panels  3  can be adjusted according to the shape and size of the roof. 
     Fifth Embodiment 
     Next, a roof structure  6  according to an embodiment of the present invention will be described with reference to the respective drawings. Note that configurations identical to the configurations of the roof structure  1  are given similar reference numbers, and the same explanation is omitted. As shown in  FIG.  26   , the roof structure  6  includes a plurality of the horizontal base materials  2 , the roof panel  3 , the receiving roof panel  4 , and a second roof panel  7  disposed on the upstream side with respect to the receiving roof panel  4 . 
     As shown in  FIG.  26   , the second roof panel  7  as a composite panel which includes a roofing board and rafters integrated with each other includes a third roofing board  71  which has one edge  71   a  abutting on the opposite edge  41   c  of the second roofing board  41 , and a plurality of third rafters  72  fixed to a lower surface of the third roofing board  71  in parallel to each other with a clearance left between each other. Each of the third rafters  72  has one end projecting from the one edge  71   a  of the third roofing board  71 . A projection length L 3  of a second projection portion  72   a  corresponding to this projection portion is equal to or larger than the interval L 1  between the adjacent horizontal base materials  2  shown in  FIG.  14   . Note that the configuration of the third roofing board  71  and the interval between the third rafters  72  are similar to the configuration of the first roofing board  31  and the interval between the first rafters  32 . 
     Next, a roof structure construction method using the roof structure  6  will be described. First, the roof panel  3  is fixed to the horizontal base materials  2  by procedures similar to the corresponding procedures of the fourth embodiment. Then, as shown in  FIG.  26   , an opposite end  72   b  of the third rafter  72  is fitted into the not-shown notch  2   c  of the rafter stand  2   a  placed on the upper part of the ridge  22  with the second projection portion  72   a  facing the downstream side, and the third rafters  72  are placed on the rafter receivers  23   a  fixed to the purlins  23 . Then, the opposite end  72   b  and the ridge  22  are integrally connected and fitted to each other by driving the long screws B (not shown) from above. In addition, the second roof panel  7  is sequentially fixed to the horizontal base materials  2  by driving the long screws B (not shown) from above the third roofing board  71  into the third rafters  72  at portions in contact with the rafter receivers  23   a . At this time, note that the shape of the second roof panel  7  is adjusted such that the third rafters  72  are set on the horizontal base materials  2  substantially in such positions as to be aligned with the positions of the first rafters  32  in the outrigger direction, and that a separation distance between the first roofing board  31  and the third roofing board  71  is substantially equal to the length of the second roofing board  41 . 
     Subsequently, as shown in  FIG.  26   , the receiving roof panel  4  is placed on the rafter receivers  23   b  fixed to the purlins  23  located between the first roofing board  31  and the third roofing board  71 . At this time, the second rafters  42  are disposed such that the one ends  42   a  are located between the first projection portions  32   a  of the first rafters  32 , and that the opposite ends  42   b  are disposed between the second projection portions  72   a  of the third rafters  72 . The both ends  41   b  and  41   c  of the second roofing board  41  are brought into abutment with the one edge  31   b  of the first roofing board  31  and the one edge  71   a  of the third roofing board  72 , respectively. Then, similarly to the second roof panel  7 , the long screws B (not shown) are driven from above into the second rafters  42  at portions in contact with the rafter receivers  23   a  to fix the receiving roof panel  4  to the horizontal base materials  2 . 
     In this manner, the receiving roof panel  4  disposed on the horizontal base materials  2  are connected by driving the fixing tools A from above into the second roofing board  41  at positions where the first projection portions  32   a  and the second projection portions  72   a  are aligned with each other as shown in  FIG.  27   . Then, the eave edge roofing board  51 , the eave edge purlin  34 , and the end roofing board  52  are set by procedures similar to the corresponding procedures of the roof structure  1  to complete the roof structure  6 . 
     As described above, according to the roof structure  6 , the necessity of applying complicated processing to the ends of the rafters to join the rafters with each other as conventionally performed is eliminated by alternately arranging a part of the respective rafters  32 ,  42 , and  72 . Accordingly, workability greatly improves even in a case of a large roof having a large length. In addition, the joining portions of the roofing board and the joining portions of the rafters are not aligned with each other. Accordingly, the roof structure to be provided can be easily constructed while maintaining structural strength required for the roof by supplementing structural weaknesses. Moreover, the receiving panel  4  is dropped from above after determining a most downstream position and a most upstream position using the roof panel  3  and the second roof panel  7 . Accordingly, deviation of the respective roof panels around the eaves and ridges is avoidable. 
     The embodiment of the present invention is not limited to the embodiments described above, but may be appropriately changed without departing from the scope of the spirit of the present invention. 
     INDUSTRIAL APPLICABILITY 
     A roof panel according to the present invention is suitably applicable to formation of a sloped roof having a wooden structure. 
     DESCRIPTION OF REFERENCE SIGNS 
     
         
           1 ,  6 ,  11 ,  12 ,  13  roofing board 
           2  horizontal base materials 
           3  roof panel 
           31  first roofing board 
           31   b  one edge of the first roofing board 
           32  first rafters 
           32   a  first projection portion 
           4  receiving roof panel 
           41  second roofing board 
           41   b  one edge of the second roofing board 
           41   c  opposite edge of the second roofing board 
           42  second rafters 
           42   a  one end of each of the second rafters 
           42   b  opposite end of each of the second rafters 
           5  rafters 
           6  roofing board 
           40  roof panel 
           53  carry-out portions 
           7  second roof panel 
           71  third roofing board 
           71   a  one edge of the third roofing board 
           72  third rafters 
           72   a  second projection portion 
         L 1  the interval between the adjacent horizontal base materials 
         L 2  projection length of a first projection portion 
         L 3  projection length of a second projection portion