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NatureInterface > No.01 > P032-033 [Japanese]

One Day with Chrono-Bit -- Seiko Epson Corporation


Eaves & Pent Roofs


There are many new building sites for houses in my neighborhood. These were probably good purchases, as the price of land is about half what it was at the top of the bubble economy. When I spent some time looking them over, I found that these new houses did not have pent roofs with windows, and besides that, there weren't any houses with eaves. It is natural that concrete houses do not have eaves or pent roofs, but even wooden houses do not have them these days.

In the beginning, in ancient times, people didn't distinguish between eaves and pent roofs. After the Meiji era, eaves were known as the portion of a roof that extended beyond the external walls, whereas the pent the pent roof was known as everything above the windows.

Almost all Japanese old houses have long eaves, in some cases as long as 1.8 meters. Eaves play various roles. First, they keep rain off the windows and doorways. In the old days, not everyone in Japan had glass, so usually Syoji, a window made of paper, was used. Syoji windows did not stand up well to rain. Oiled paper was stronger, but its availability also was limited. When rain was heavy, people used storm doors. In any case, one of the primary roles of both eaves and pent roofs was to keep rain out. Another role was to protect walls and mudsills from rain. Of course, loam does not stand up well to rain, and walls made of wood siding will be damaged or they will leak rain. Loam is the weakest, and damp loam brings white ants. And in snowy districts, the absence of eaves or pent roofs would allow snow to strike windows or open corridors directly.

The pent roofs also stop sparks from entering the house in case of fire, and they serve as a means of emergency escape from the second floor. On the other hand, pent roofs give thieves a footing for climbing into the house, a negative role.

But the biggest purpose of eaves and pent roofs is to block the sunlight in the summer. The Japanese words "Hisashi" and "Hizashi" closely resemble each other, and it seems that these words may have the same origin. In Japan, the sun is at an angle of about 75 ”ėto 80 ”ėat noon in the middle of June and early summer. But that is also the rainy season, so the sunlight is not strong. Rather, the period after mid-August is the problem, when the heat of summer lingers. Eaves stop sunlight until 60 ”ėnot only at noon but also in the afternoon. Eaves of about 90 cm keep direct rays away from walls and windows to a height of around 2 meters, whereas pent roofs, 60 cm is needed to keep direct rays off of ordinary windows. Commonly, with pent roofs, 30 cm are used, but these don't cover all of the windows, but only about half.

On the other hand, in December, the sun is about at an angle of 30 ”ėto 35 ”ė. At this time, eaves 90 cm long will keep sunlight off from only around 40 cm to 50 cm of the opening parts, allowing sunlight to penetrate deeply into the rooms. Long eaves are found not only on private houses in Japan but also in other countries. Singapore's ancient rows of stores and houses on streets had roads running through the buildings so people could stay out of the sun and out of the rain. There were also grand verandas with flowers and pent roofs to keep direct rays away from the second floor. These were built in the shape of a bird, similar to the Japanese style, called Ganmoku-tsukuri (bird's shape), as found in the snow zone. I have also seen these buildings in Taiwan, Thailand and many other tropic areas.

Today, as I walked the streets of Singapore, I was able to see a few these buildings; people have come to take modern apartments in the suburbs and, in the center area, modern buildings have been taking the place of old ones. In Singapore, I don't see men walking in the daytime, for the sun is high, shade is scarce and the roads reflect rays back into the air, making the streets too hot to walk in.

Some of the problems of keeping the elements out have been solved. Glazed windows keep the rain out, their aluminum frames are durable, and at least storm doors aren't needed anymore. Many foundations are concrete rather than wood, and external walls use noncombustible sidings, which stand up well to the rain. These modern materials have made eaves and pent roofs unnecessary.

Early concrete apartment buildings erected by the Japan Housing Corporation still used wood sashes, which had made lots of eaves. And old buildings had many pent roofs as well as windows that were caved away from the outside of walls.

Summer's hot weather is solved by air cooling. Today, most families are not in their houses in the daytime, because of the changing lifestyle, so they don't care about the sun's rays. In the cities, the desire to have sunshine come into one's home may be more important than keeping the sun out. Therefore, eaves and pent roofs may not necessary in cities.

And laws, such as the Building Standards Act, include a standard measure for effective lighting size for hygienic sake. In case neighboring houses are very close together, eaves will be short because long eaves and pent roofs may interfere with the sunshine a neighbor might otherwise receive. There are several other laws that prevent house owners from constructing eaves and pent roofs. Besides, in the tightest areas, eaves take away from needed open space, which is a problem.

If we use pent roofs, on the other hand, a bow window will be better from the point of view of the law and such a window's size is not the floor size. Fortunately, in Japan, a washing and drying area is necessary, and a second-floor veranda is standard equipment for our houses now. Most of the verandas have eaves, which are also eaves for the first floor, so that they the tradition of eaves remains in Japan. But pent roofs are few.

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