Roofing in Bangladesh

Bangladesh occupies most of the delta of the Ganges, Brahmaputra and Meghna rivers, one of the wettest and most flood-prone inhabited regions on earth. For centuries its houses were roofed with thatch on bamboo frames, bent into a curve that later gave the world the bangla roof. Today the country is a land of corrugated metal: about three-quarters of households live under tin (corrugated iron, or "CI sheet") roofs.

Climate and hazards

The country is low-lying, hot and humid, with heavy monsoon rain. River and flash floods are frequent, and the coastal belt along the Bay of Bengal is exposed to tropical cyclones and storm surges. A roof here must shed intense rain, resist wind uplift during cyclones and be light enough for houses built on mud plinths or bamboo frames. Bangladesh also lies close to active seismic zones; the 1897 earthquake, for instance, destroyed the towers of the Kantanagar temple in Dinajpur.

Roofing history

The alluvial soil of the delta provides clay but almost no building stone. Traditional dwellings were of earth, bamboo and timber, roofed with straw, reed, grass or palm leaf. Their curved ridges and drooping eaves helped rain run off quickly.

In the medieval period, mosques were built of burnt brick. The Historic Mosque City of Bagerhat, founded in the 15th century by the general Ulugh Khan Jahan and inscribed by UNESCO as a World Heritage Site, includes the Shait Gumbad Mosque, one of the largest mosques of its kind, built of baked brick.

From about the 16th century, builders in Bengal translated the curved thatched hut roof into brick and terracotta for temples and mosques. These forms, the do-chala, char-chala and at-chala, are known together as Bengal or bangla roofs, and they were taken up by Mughal and Rajput builders across northern India. Temples in the ratna style added towers above a curved-cornice roof.

In the colonial and modern periods, corrugated galvanised iron sheet replaced thatch on most rural houses, while flat reinforced concrete slabs became standard in cities.

Traditional and vernacular roofs

• Chala roofs: thatched hut roofs with two (do-chala) or four (char-chala) curved slopes on a bamboo frame, the model for the masonry bangla roof.
• Jhupri: the simplest shelters, with walls and roofs of straw, bamboo, palm leaves or polythene, still used by 0.57% of households in 2023.
• Kutcha houses: earth, bamboo and mat houses, now usually roofed with tin.
• Terracotta temples: brick temples with curved chala roofs or ratna towers, decorated with carved terracotta panels.

Roofing today

The Bangladesh Bureau of Statistics' Socio-Economic and Demographic Survey 2023 found that about 74% of households have tin (CI sheet) roofs and about 25% have cement (concrete) roofs. More than half of households (55.85%) live in kutcha, or non-brick, houses made largely of earth, bamboo and mats, rising to about 70% of rural houses and more than 77% in Mymensingh division; in Dhaka division the share was about 38%. Cement or concrete walls were reported for 49.84% of houses.

Corrugated sheet roofs are cheap and light but conduct heat readily into the rooms below.

Codes, standards and regulation

The Bangladesh National Building Code (BNBC) was first prepared in 1993, without legal force, and gained a legal basis through a gazette in 2006. The revised BNBC 2020 was published in the official gazette on 11 February 2021. It provides for a Bangladesh Building Regulatory Authority of five members to implement the code and act against violations, though about two years after the gazette the authority had still not been formed.

Notable roofs

• Shait Gumbad Mosque, Bagerhat (15th century): large multi-domed brick mosque in a UNESCO World Heritage city.
• Kantanagar Temple, Dinajpur (1704-1752): nine-towered (navaratna) terracotta temple whose towers fell in 1897.
• Gunjanth Siva Temple, Jessore (1740): an at-chala temple with two tiers of curved roofs.
• Gobinda Temple, Puthia (first half of the 19th century): a five-towered (pancharatna) temple.

Local roofing terms

• chala (Bengali): roof slope
• do-chala: two-sloped curved roof; jor-bangla, a pair of joined do-chala roofs
• char-chala: four-sloped curved roof
• at-chala: eight-sloped, two-tier curved roof
• ratna: tower or pinnacle on a temple roof
• jhupri: makeshift hut of straw, bamboo, palm leaf or polythene
• kutcha: non-permanent house of earth, bamboo or mat

Sources and gaps

The roof figures are as reported in the press from the BBS survey. Data on roofing manufacturers and on cyclone-resistant roof standards: published information is limited.