en.wikipedia.org/wiki/Saw-tooth_roof

The sentence says saw-tooth roofs were most common from the mid-19th century to the mid-20th century, and frames that whole period as one “when electrification of factories was not yet common.” That timing is incorrect.

Credible historical sources show that factory electrification was already widespread decades before the mid-20th century:

• The Smithsonian’s National Museum of American History states that in U.S. manufacturing, electricity provided less than 5% of primary horsepower in 1899, 50% by 1919, and 75% by 1929.
• A U.S. government historical overview reproduces a diffusion chart showing factories at about 53% electrified in 1919, 78% in 1929, and 86% in 1939.
• The 1929 Census of Manufactures reported that approximately 80% of machinery in manufacturing establishments was electrically driven in 1929.

So while the statement might fit part of the mid-19th century or even the very early electrification era, it is not accurate to extend it through the mid-20th century. By the 1910s–1930s, electrification of factories was already common.

The claim says night work in factories was “typically lit by oil lamps and candles.” That is not accurate for much of the 19th century industrial period.

Evidence from museum and heritage sources shows that gas lighting became a standard factory light source long before electric lighting took over:

• The Smithsonian’s National Museum of American History says that by the late 1850s most cities, factories, schools, theatres, and shops were lit by gas.
• Historic England notes that providing mills with gas lighting allowed them to operate at night, replacing the need to light them by oil lamps or tallow candles.
• Historic England also describes one of the earliest surviving gasworks as having been installed specifically to light a worsted spinning mill, showing that factory gas lighting dates back to the early industrial period.

So candles and oil lamps were certainly used earlier on, but describing night work in factories as typically lit by them is misleading because gas lighting had already become widespread in factories well before electric light became dominant.

The statement identifies Saltaire Mills (founded 1851) as the “first documented example” of the saw-tooth / north-light weaving shed. That is contradicted by architectural history sources describing the type earlier.

Two independent sources point to earlier documented examples:

1. A scholarly article on textile mill architecture states that in Britain, after weaving became a factory industry during the 1820s, it was usually done in a separate mill building, the weave shed, and that these sheds were single-storey buildings with a sawtooth or north-light roof.
2. A heritage assessment of Pennine Lancashire weaving sheds says Blackburn had very early weaving sheds, and lists Brookhouse Mill (1830), Nova Scotia Mill (1833), and George Street West Mill (1834) among the earliest examples.

Because documented north-light/saw-tooth weave sheds are attested at least by the 1830s, the Saltaire sheds of 1851 cannot accurately be called the first documented example.

The article dates Melbourne’s Central Telephone Exchange to “approximately 1919.” Available historical records place the building noticeably earlier.

• An Australian Government Gazette from 1909 already refers to the “Power Plant for Central Telephone Exchange” in Melbourne, showing the exchange project was underway by 1908–1909.
• The City of Melbourne’s Hoddle Grid Heritage Review says the Central Exchange manual switchboard was installed in the Lonsdale Street Central Telephone Exchange building in 1911 and that the former Central Telephone Exchange had occupied the site since 1910.
• A period account reproduced online states that the new exchange building had been completed by January 1911.

Those sources contradict an approximate construction date of 1919. A date around 1909–1911 is consistent with the evidence.