Roofing in Japan

In traditional Japanese architecture the roof is the dominant element, often making up about half of a building's visible mass. Deep, gently curved eaves project well beyond the walls, shading verandas and giving interiors their characteristically soft light. Japan developed an unusually wide range of roof coverings, from grass thatch and cypress bark to thin wooden shingles and fired clay tile, and the skills to make and maintain them are recognised by UNESCO as intangible cultural heritage.

Climate and hazards

Japan has heavy summer rain, a typhoon season, deep snow on the Sea of Japan side and in the mountains, and frequent earthquakes. Steep thatched roofs such as those of Shirakawa-go are designed to shed snow; deep eaves protect timber walls from rain; and widely reported tile damage in earthquakes and typhoons has driven both lighter roof coverings and mechanical fixing of tiles. Dense timber towns made fire a constant danger, which pushed cities toward tiled, non-combustible roofs.

Roofing history

Prehistory. Pit dwellings of the prehistoric periods were roofed with grass, and thatch remained the roof of ordinary rural houses into the 20th century.

Shrines. The Ise Grand Shrine preserves one of the oldest Japanese roof forms, shinmei-zukuri, with a thatched reed roof, chigi finials and katsuogi billets on the ridge. Its buildings are rebuilt every 20 years in the Shikinen Sengū; the first ceremonial rebuilding took place in 692 under Empress Jitō, and the present buildings date from 2013, the 62nd rebuilding.

Arrival of tile. Fired clay tiles came with Buddhism. In 588 the Korean kingdom of Baekje sent craftsmen, including four tile makers, to build Asuka-dera, the first full Buddhist temple in Japan. The Kondō of Hōryū-ji has a tiled hip-and-gable (irimoya) roof, and its 7th-century pagoda is among the oldest wooden buildings in the world. The tile technology itself descends from the tile tradition that developed in China under the Western Zhou and later spread to Korea and Japan.

Heian and medieval periods. Heian-period aristocrats roofed their mansions with layered cypress bark (hiwadabuki) rather than tile, and builders developed the "hidden roof" (noyane), a separate structure above the visible ceiling that allowed a steeper outer pitch and better drainage. Temples such as Kinkaku-ji and Ginkaku-ji use roofs of very thin split-wood shingles fixed with bamboo nails. In Kyoto in the late Heian and Muromachi periods, town roofs were clad in thin shingles held down with stones.

Edo period. Distinctive farmhouse (minka) styles, including gasshō-zukuri, matured. Urban townhouses (machiya) and storehouses (dozo) moved from thatch and shingle to clay tile for fire protection, and the udatsu, a wall projecting above the roofline, served as a firebreak and status symbol.

Modern era. In the 20th century most thatched houses were re-roofed, and clay tile was joined by metal sheet and later fibre-cement and coated-steel products.

Traditional and vernacular roofs

• Kayabuki - grass thatch, usually miscanthus (susuki) or reed; farmhouses (nōka) were mostly hipped (yosemune) and thatched.
• Gasshō-zukuri - very steep "praying hands" thatched roofs of Shirakawa-go and Gokayama, with attic floors used for silkworm rearing.
• Hiwadabuki - layered hinoki cypress bark, on shrines, palaces and temples.
• Kokerabuki - thin wooden shingles of cypress fixed with bamboo nails.
• Kawarabuki - clay tile; the traditional pan-and-cover form is hongawarabuki. Ridges carry onigawara (ogre tiles) or shachi fish ornaments, and eaves end in circular tiles.
• Roof shapes - kirizuma (gable), yosemune (hip), irimoya (hip-and-gable) and hōgyō (pyramidal).

Roofing today

Clay kawara remains common on detached houses, but lighter coverings have gained ground: coated steel and zinc-aluminium-coated sheet, and fibre-cement slates. Lighter roofs reduce seismic forces on timber frames, and modern tile practice fixes tiles with screws, wires or clips rather than bedding them in clay. Apartment and commercial buildings mostly have flat concrete roofs with membranes.

Codes, standards and regulation

The Building Standards Act (Act No. 201 of 24 May 1950) sets national minimum standards for building sites, structure, equipment and use. Its Article 22 lets authorities designate areas where roofs must be covered with non-combustible materials to stop fire spreading between buildings; Yokohama, for example, applies the designation across the whole city. Stricter roof rules apply in fire-prevention districts.

Industry

Kawara production is concentrated in traditional centres such as Sanshū (Aichi) and Sekishū (Shimane).

Notable roofs

• Ise Grand Shrine - thatched shinmei-zukuri roofs rebuilt every 20 years.
• Hōryū-ji, Nara - tiled Kondō and 7th-century pagoda.
• Historic Villages of Shirakawa-go and Gokayama (UNESCO, 1995) - gasshō-zukuri thatch.
• Kinkaku-ji and Ginkaku-ji, Kyoto - thin wooden shingle roofs.

Local roofing terms

• yane (屋根) - roof
• kawara (瓦) - roof tile; onigawara - ogre ridge tile
• kayabuki (茅葺) - thatch
• hiwadabuki (檜皮葺) - cypress-bark roofing
• kokerabuki (柿葺) - thin-shingle roofing
• noki (軒) - eaves

Sources and gaps

Market data, roof-material statistics and further manufacturer data for Japan: published information is limited.