Great Boston Fire of 1872

The Great Boston Fire began at about 7:20 p.m. on 9 November 1872 in the basement of a warehouse at 83-87 Summer Street and was contained around midday on 10 November. It destroyed 776 buildings across about 26 ha (65 acres) of downtown Boston, including much of the financial district. It is one of the best-known examples of roofs helping a fire to spread.

The role of mansard roofs

The Second Empire style, with the mansard roof as its central feature, was popular in the United States and Canada between about 1865 and 1900; Boston's Old City Hall (1862-1865) is an example. Many Boston commercial buildings had brick or stone walls but wooden framing and timber-built mansard roofs. The first warehouse's wooden mansard caught fire, and flames passed from rooftop to rooftop along the street. Combustible roofs above masonry walls allowed fire to travel across the district.

Conditions in Boston

Boston had no strictly enforced building code in 1872. Its fire service had installed the world's first telegraph-based fire alarm boxes in 1852, but this could not offset combustible construction. The fire came only a year after the Great Chicago Fire of 1871.

Aftermath

• 1873: Boston fire chief John Damrell founded the National Association of Fire Engineers, which identified flammable materials and excessive building height among key fire-safety concerns.
• 1874: Damrell resigned as chief engineer, and Boston began replacing its water mains.
• 1877: Damrell became Boston's building commissioner.
• 1884: he petitioned for a more formal building code.
• 1892: Boston set formal limits on building height and area, then unique among American cities.
• 1905: the National Board of Fire Underwriters published the first standardised US National Building Code.

Lessons for roofing

The fire showed that a roof is part of a building's fire defence. Combustible roof structures on otherwise masonry buildings let fire travel across a city. The code reforms that followed in Boston, and the national building code of 1905, reflected this lesson.