Yuko TAAGE 1, Osamu GOTO 2, Hirokazu YAMAMOTO 3, Masaki TAMURA 4 1 INTRODUCTION BACKGROUND

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1 A STUDY FOR A HIGH QUALITY PRESERVATION SYSTEM OF KOKERA ROOFING USED IN TRADITIONAL WOODEN ARCHITECTURE PART 1 : THE ANALYSIS OF THE LIFE CYCLE PROPERTIES OF KOKERA ROOFING Yuko TAAGE 1, Osamu GOTO 2, Hirokazu YAMAMOTO 3, Masaki TAMURA 4 ABSTRACT: One type of traditional wooden architecture uses Kokera roofing in Japan. These Kokera are made from natural stands of Japanese cedar, and other evergreen trees. These trees are traditionally over 100 years old before they are used. Although recently, natural stands of Japanese cedar forests and also the numbers of 100 year old Japanese cedars has been decreasing rapidly. We researched all existing National Government buildings in Japan using information collected from the Agency for Cultural Affairs. The results of our research show Kokera roofed buildings. Many the National Government buildings use Kokera roofing. Material demand and the Kokera roof life cycle relationship needs to be reconsidered. The cost of materials needs to be reduced otherwise we fear that the future of Kokera roofing may not continue. KEYWORDS: Shingle, Roof, Traditional architecture, Life cycle 1 INTRODUCTION 123 In Japan, we can often see traditional wooden architectures that are considered as important sociocultural assets. One type of wooden architecture uses Kokera roofing. These Kokera are made from natural stands of Japanese cedar, and other evergreen trees. These trees are traditionally over 100 years old before they are used. Although recently, natural stands of Japanese cedar forests and also the numbers of 100 year old Japanese cedars have been decreasing rapidly. The cost of Kokera roofing has risen dramatically that it has become too expensive as a roofing option. We fear that this traditionally historical past of Japanese culture and the skill involved in making Kokera will disappear. Therefore it is necessary to develop social and technical systems to promote the preservation of Kokera roofing reasonably. The results of our study will help preserve this traditional Japanese craft of Kokera roofing. 2 BACKGROUND 2.1 KOKERA In Japan Kokera is typically made from Sawara cypress or Japanese cedar (Called sugiin in Japanese). The standard size of a typical traditional type of a Kokera roofing board is about 300mm in length, 80 to 120mm in width and 3mm in thickness. The width may vary depending on the trunk s diameter. There are 4 points for optimal Kokera. From here on, the word Kokera will be used instead of shingle. 1 Yuko TAAGE, Graduate Student, Faculty of Eng., KOGAKUIN University, JAPAN. dm09044@ns.kogakuin.ac.jp 2 Osamu GOTO, Prof., Faculty of Eng., KOGAKUIN University, JAPAN. Dr. Eng. ogoto@cc.kogakuin.ac.jp 3 Hirokazu YAMAMOTO, Prof., Graduate School of Frontier Sciences, the University of Tokyo, Dr. Ag. yama@uf.a.u-tokyo.ac.jp 4 Masaki TAMURA, Associate. Prof., Faculty of Eng., KOGAKUIN University, JAPAN. Dr. Eng. masaki-t@cc.kogakuin.ac.jp Fig.1: Manufacturing steps of Kokera

2 Photo 2: bundled together Photo 1: Manufacturing steps of Kokera 1. No knots. 2. Straight wood. 3. Easily dividable. 4. Long lasting. Sawara cypress and Japanese cedar are ideal suitable for Kokera. Fig.2: plane of Kokera roofing Fig.3: section of Kokera roofing 2.2 Manufacturing of Kokera Manufacturing of Kokera is done in steps as shown in Figure 1. The following dimensions are typical for making Kokera in Akita prefecture. 1) Tamawari : The logs are sawed into 242mm in length. 2) Oowari : Tamawari is divided through the center into eighths. 3) Itawari : A hatchet is used to cut perpendicularly into the grain making 36mm thick boards. 4) Sengake : A Sengake is used to smooth the rough cut end of the board. 5) Kowari : The board is divided into eight Kokera. 6) One Kokera is called Zaku in Akita prefecture. The final product is bundled together in a specific size. Zaku are placed side by side to a length of 600mm and stacked 40 boards high. This is one bundle. This final Kokera has many names depending on it is thickness and the region where it is used. For example, a thickness of 3mm is called Kokera in some areas and Zaku in others. A thickness of 4 to 6mm is called Tokusa. A thickness of 10mm is called Tochi. 2.3 Roofing procedures Refer to Fig2 and Fig3. The eaves board is made from chestnut trees and 2 layers are used. The edge of the eaves boards overhang the sheathing roof board by 30 mm and are secured with metal nails. The first layers of Kokera overhangs the eaves board by 6mm and are secured to the eaves with metal nails. The second layers Table1: outline the conditions for our research Research data Forest data Reseach topics research matter National important cultural properties in the 47 prefec tures of Japan, listing as 2,344 premises with 4,272 buildings as of 2 December I selected only buldings with Kokera roofing designated as a national cultural property. Forest reserves in each prefecture. 1 The number of important cultural buildings using Kokera roofing. 2 The percentage of land in each prefecture with conifers. 3 Percentage of natural stand of cedar, artificially grown cedar, natural stand of cypress and manmade grown cypress in each prefecture in comparison with the total land area of Japan.

3 of Kokera are 15mm back of the first and are not secured. The third and fourth layers are placed 24mm from back each. From the fifth layer on, they are all placed 30mm back. Each layer is staggered to cover the spaces the boards. Starting with the third layer, bamboo nails are used to secure the Kokera. The fourth layer is not secured, but the fifth layer is secured. Securing is done with every other layer starting with the third layer. These bamboo nails are about 36mm in length and they are heated in a skillet before using. With several layers of Kokera to hit these bamboo nails through, the head of the nails are crushed. Using such force is an important step which helps secure the Kokera. 3 RESEARCH 3.1 Evaluation of area characteristics of Kokera We researched all existing national treasure and important cultural property buildings in Japan using information collected from the Agency for Cultural Affairs. These are historical buildings which are designated by the National Government. We also researched data from the Forestry agency on natural stand and manmade forest areas throughout Japan. Table 1 outlines the conditions for my research; nationally important cultural properties and the significance of the ratio of forestry in Japan. Table 2 are the results of our research on Kokera roofed buildings and significant conifers forest in all 47 prefectures. Many national treasure buildings and important cultural property buildings use Kokera roofing. The number of buildings with Kokera roofing are shown by each prefecture in 1. 2 shows the percentage of land in each prefecture covered with evergreens. 3 is divided into four categories of forest. These percentages reflect the amount land covered with Japanese cedar and Hinoki cypress three in comparison with the total land area of Japan. The prefectures with many Kokera roofed buildings have or had a large area of cedar or cypress forests. This data is 2008 data. We forests were when these buildings were constructed. The main materials for Kokera are Sawara cypress and Japanese cedar. There are no manmade forests of Sawara cypress in Japan. The number of natural Stands of Sawara cypress had decreased so dramatically that the Forestry Agency has no data on their numbers. According to Kenichi Murata the architecture rush or building boom of the Asuka period ( ) and Nara period ( ) consumed large quantities of Japanese cypress causing near depletion levels especially in the Kinki\ area of Japan. Therefore we can see the regional differences of forests and how the supplies of certain trees were used in building construction within that region. As supplies of certain trees decrease, we see a change in architecture to adjust to less supply or use of a different raw material. We believe the raw material for Kokera was determined Table 2: Kokera roofed buildings and significant conifers forest in all 47 prefectures. National treasure Important Cultural Properties 1Kokera roofing 2The percentage of conifer Natural stand Japanese cedar Manmade Japanese cedar 1 Hokkaidou 0 56(25) % 0.04% 0.53% 2 Aomori-ken 0 67(30) % 3.64% 2.85% 0.06% 0.002% 3 Iwate-ken 1(1) 34(23) % 1.53% 3.98% 0.28% 0.07% 4 Miyagi-ken 4(3) 41(19) % 1.39% 2.34% 0.18% 0.15% 5 Akita-ken 0 55(24) % 22.89% 6.11% 0.09% 0.001% 6 Yamagata-ken 1(1) 38(28) % 3.40% 2.78% 0.10% 0.002% 7 Fukushima-ken 1(1) 45(32) % 2.49% 4.01% 2.74% 0.62% 8 Ibaraki-ken 0 49(31) % 0.45% 1.29% 0.37% 0.98% 9 Tochigi-ken 9(6) 153(31) % 0.15% 1.79% 0.66% 1.74% 10 Gunma-ken 0 60(21) % 0.41% 2.37% 0.80% 0.67% 11 Saitama-ken 0 41(24) % 1.01% 0.70% 0.78% 12 Chiba-ken 0 51(28) % 0.03% 1.10% 0.01% 0.37% 13 Tokyo-to 1(1) 99(67) % 0.40% 0.48% 0.12% 0.32% 14 Kanagawa-ken 1(1) 66(54) % 0.08% 0.48% 0.29% 0.69% 15 Niigata-ken 0 72(33) % 3.88% 3.45% 0.02% 0.002% 16 Toyama-ken 3(1) 50(19) % 2.98% 1.18% 0.12% 0.01% 17 Ishikawa-ken 0 73(42) % 0.48% 1.91% 0.02% 0.11% 18 Fukui-ken 2(2) 31(25) % 0.35% 2.15% 0.40% 0.14% 19 Yamanashi-ken 2(2) 89(49) % 0.70% 0.63% 2.25% 1.52% 20 Nagano-ken 10(5) 141(82) % 1.06% 1.28% 43.15% 2.21% 21 Gifu-ken 3(3) 88(49) % 1.22% 2.67% 27.42% 7.72% 22 Shizuoka-ken 0 94(32) % 0.97% 2.16% 2.18% 5.47% 23 Aichi-ken 0 115(76) % 0.01% 1.22% 0.15% 2.35% 24 Mie-ken 3(3) 35(21) % 0.59% 2.00% 1.19% 4.44% 25 Shiga-ken 23(22) 232(181) % 1.57% 0.85% 0.91% 0.97% 26 Kyouto-fu 60(48) 586(287) % 9.59% 1.46% 2.52% 1.86% 27 Oosaka-fu 8(5) 162(97) % 0.15% 0.12% 0.17% 0.40% 28 Hyougo-ken 14(11) 211(102) % 2.33% 2.98% 1.77% 4.07% 29 Nara-ken 71(64) 374(261) % 0.22% 2.56% 0.27% 2.67% 30 Wakayama-ken 7(7) 121(76) % 0.61% 2.46% 0.76% 6.57% 31 Tottoti-ken 1(1) 32(15) % 2.09% 1.58% 0.18% 1.05% 32 Shimane-ken 2(2) 74(23) % 1.32% 1.85% 0.28% 2.14% 33 Okayama-ken 2(2) 138(55) % 1.01% 0.95% 0.21% 4.36% 34 Hiroshima-ken 12(7) 112(62) % 2.76% 1.16% 0.49% 3.50% 35 Yamaguchi-ken 3(3) 58(36) % 0.21% 3.10% 0.04% 4.72% 36 Tokushima-ken 0 37(17) % 0.04% 2.93% 0.02% 1.03% 37 Kagawa-ken 2(2) 37(26) % 0.03% 0.07% 0.29% 38 Ehime-ken 3(3) 114(45) % 0.27% 2.73% 1.36% 4.89% 39 Kouchi-ken 1(1) 46(19) % 4.02% 4.03% 2.35% 7.99% 40 Fukuoka-ken 0 55(37) % 0.34% 1.89% 0.27% 2.50% 41 Saga-ken 0 16(13) % 0.19% 1.05% 0.18% 1.26% 42 Nagasaki-ken 3(3) 43(31) % 0.09% 0.83% 0.20% 2.99% 43 Kumamoto-ken 5(1) 76(29) % 1.03% 4.21% 0.65% 5.60% 44 Ooita-ken 4(2) 35(29) % 0.77% 4.47% 0.70% 2.82% 45 Miyazaki-ken 0 16(9) % 2.33% 5.72% 1.09% 2.99% 46 Kagoshima-ken 0 19(10) % 19.88% 3.26% 2.20% 4.65% 47 Okinawa-ken 0 36(20) % 0.04% 0.002% 3Comparison with the total land area of Japan Natural stand Hinoki cypress Manmade Hinoki cypress 計 262(214) 4272(2344) 423 1% 100.0% % % 99.68% Fig.4: sheathing roof board Fig.5: buildings built by century and sheathing roof board

4 by which evergreen was in abundance in that region. In Aomori-ken, Hiba wood was used instead of Japanese cedar or cypress. 3.2 History of Kokera The conventional method of Japanese architecture used plant materials for its structures and the roofing used Kokera tree bark and thatch. Mr. Takashi Harada researched a book written in 1197 titled Tounomineryakki. During 1180 to 1190, Kokera roofing was first used in constructing Housyakudou and Nanindou. Horryuji temple, constructed in 1284 and located in Nara, has the Zushi buildings with Kokera roofing. The Zushi building enshrines the figure of shotokutaishi. Kokera roofing was common on temples and shines, teahouses and Sukiya style buildings. Kokera roofing was also popular in residential homes until the Edo period ( ). During the Edo period, kawara tiles became popular. Kokera roofing has a short life cycle and needs to be replaced regularly. Because of this, researching early knowledge of Kokera roofing materials and how roofing was done is difficult. So we decided to look at building roof base sheets for answers. The data in Fig 4 and Fig 5 are from a construction and repair report on 32 important cultural buildings in Kyoto involving work on sheathing roof board. Fig4 shows the different materials used in these 32 buildings. These 32 building currently have tile roofing. It is safe to assume that the material used in the sheathing roof board was also used as the finishing material on the roof at the time of its construction. The construction and repair report confirms that many buildings once had Kokera roofing and were changed to tile or cooper roofing. We speculate there are two reasons for this change. One is that it was difficult to obtain Kokera materials. The second was to avoid the possible spread of fire due to wood roofing. In recent years these tiled roofed buildings are changing back to Kokera roofing using the heart wood of Sawara cypress. 4 LIFE CYCLE ASSESSMENT OF KOKERA We did extensive research on repairs works of national treasure and important cultural properties and only came up with 10 buildings with records of changing the Kokera roofing. With these records, we determined the life span of Kokera roofing. The buildings that had been re-roofed with tiles are not included. The buildings listed below have Kokera roofing with records of re-roofing. Also refer to table3. a: Kumano- okutera jinjya shrine Honden (in Aomori) b: Hakusan jinjya shrine Honden c: Hongwanji temple hiunkaku (in Kyoto) d: Nin-naji temple Ryoukakutei (in Kyoto) e: Ohjyougokurakuin Aidadou (in Kyoto) f: Gyokurinin Saan (in Kyoto) g: Murouji temple Kondou (in Nara) h: Murouji temple Mirokudou (in Nara) i: Okadera temple syoin (in Nara) j: Fuwa hachimanguu Honden Looking at this table you can see that, Okadera temple (letter g ), at one point had a life span of only 9 years compared to the longest span of 64 years for Kumano-okutera jinjya shrine (letter a ). The roofing of the Okadera temple was covered with corrugated iron causing this short life span. The average Kokera life span of these 10 buildings is Photo 3: Honganji temple a b c d e f g h i j Building name Kumano-okuteru jinjya shrine (Honden) Hakusan jinjya shirne (Honden) Hongwanji temple hiunkaku Nin-naji temple rinsyuntei Oujyou-gokurakuinamidadou Gyokurinin (saan) Okadera temple (syoin) Murouji temple (mirokudou) Murouji temple (kondou) Fuwa hachimanguu(honde n) year built year Photo 4: Nin-naji temple Table.3 Life span of the Kokera roof Peri od Change roof Change roof Change roof Change roof back side only front side only dismantled rebuilt Change roof Part of the roof repairs for restoration of fire Cheange roof Change roof Change roof Change roof Change roof Change roof Change roof Change roof Change roof Change roof Change roof Change the eaves of the east side overed the north roof with corrugated iron Covered the south and west roof with in the corrugated iron Change roof Change roof Change roof dedismantled rebuilt Change roof Change roof Change roof Change roof Change roof Change roof Change roof Change roof detail

5 28.2 years. If the span of years changing the Kokera is too long, water damage can occur and rot the beams of the building. In these cases, the building was dismantled and rebuilt with the same materials plus replacement parts. In addition, there are times when natural disaster also called for the repairing of Kokera roofing. Given that, a life span of 25 years or so can be said as being reasonable. Kumano-okutera jinjya shrine of 64 years Kokera life span is unusually long and we assume that the roof was changed once or even twice during that time. 5 MAINTENANCE AND MANAGEMENT COST OF KOKERA Fig.5 shows the changes in the Sawara materials cost of for re-roofing, total re-roofing costs and price fluctuation. We used the consumer price index (CPI) data of 2009 as our base of 100% and calculated the CPI fluctuations up to The cost of changing a roof in 2009 was also my base of 100%. The price fluctuation has a gentle rising curve. The material cost of Sawara roofing usually remained at about 35% of total costs. But at the beginning of the Heisei period (1988), there was a sharp rise of material costs. There is no direct relation-ship the price fluctuation and the rising costs of Kokera roofing. The price fluctuation does increase naturally. It is inferred that the declining trend of natural stands of resources and the craftsman-ship skill of making Kokera not being encouraged are the causes of the rising costs. Therefore the preservation of Kokera roofing is difficult. Fig.5: Changing in cost of re-roofing a Sawara material, Kokera roof and change of price 6 CONCLUSIONS Kokera roofing has a life span of approximately 25 years and the trees used for Kokera roofing are 100 years old. Therefore maintenance costs and the life span of Kokera roofing does not correspond. There is a declining trend of natural stands of cedar and Sawara cypress resources. Material demand and Kokera roof life cycle relationship needs to be reconsidered. The cost of materials needs to be reduced or we fear that the future of Kokera roofing will not continue. Our research only covers important cultural properties, which is only a tiny portion of all existing Kokera roofed structures in Japan. Extensive research is needed to actually know the conditions of Kokera roofing in Japan. ACKNOWLEDGEMENT For this study, we show our gratitude to the many who contributed. Akio Kumagai of Kumagaya Sangyo company. The staff at the Agency for Cultural Affairs cultural assets division, and the many people who cooprated in our investigation. This research was supported in part by Grants-in-Aid for Scientific Research from Ministry of Education, Culture, Sports, Science and Technology JAPAN. REFERENCES [1] Takashi HARADA : Yane Hiwadabuki to Kokerabuki 2003 p [2] Kenichi MURATA : Dentou Mokuzou Kenchiku wo Yomitoku 2006 p.68 [3] Yonematsu SHIONO : Tewaza ni manabe Tuki no maki 2000 [4] Agency for cultural affairs : Kunishitei Bunkazaitou data base [5] Ministry of Agriculture, Forestry and Fisheries : Statistics of agriculture, forestry and fisheries 2003 [6] Ministry of Internal affairs and Communications Statistics Bureau : Consumer price Index [7] Aomori Prefectural Board of Education: Repair report of Important Cultural Properties Kumanookuteru jinjya honden [8] Kyoto Prefectural Board of Education: Repair report of Important Cultural Properties Ninwaji rinsyuntei, 1999 [9] Kyoto Prefectural Board of Education: Repair report of Important Cultural Properties Oujyougokurakuin-amidadou [10] Kyoto Prefectural Board of Education: Repair report of Important Cultural Properties National treasure Hongwanji-hiunkaku, 1967 [11] Kyoto Prefectural Board of Education: Repair report of Important Cultural Properties gyokurinin saan [12] Nara Prefectural Board of Education: Repair report of Important Cultural Properties Okadera syoin, 1989 [13] Nara Prefectural Board of Education: Repair report of Important Cultural Properties Murouji mirokudou, 1984 [14] Nara Prefectural Board of Education: Repair report of Important Cultural Properties murouji kondou, 1992 [15] Committee for repair of Fuwa hachimanguu Honden k: Repair report of Important Cultural Propertie Fuwa hachimanguu Honden, 1966 [16] ommittee for repair of Important Cultural Properties Hakusan jinjya Honden: Repair report of Important Cultural Properties Hakusan jinjya Honden, 1936