Cleaning services in
Downtown DC, DC.

Under the Height of Buildings Act of 1910 commercial streets here are capped at 130 feet, and even the tallest commercial building — One Franklin Square, 210 feet at the tips of its two ornamental towers — keeps its occupied roof at that limit, so the residential stock is horizontal rather than tall: condominium and apartment floors inserted above and behind offices, a population that grew from about 4,000 in 1990 to 8,449 in 2010, all of it on hard-paved blocks where spring pollen off the avenues, humid-summer condensation and winter road salt arrive by elevator on shoe soles instead of across a yard.

This is the nation's third-largest central business district, built on the 1930s Federal Triangle buildings — the Herbert C. Hoover Building that headquarters Commerce, the Robert F. Kennedy Building that headquarters Justice, the Internal Revenue Service Building, the National Archives and the Federal Trade Commission's Apex Building — on the lobbying, law firm, trade association, advocacy group and think tank concentration along K Street, and on the Penn Quarter and Chinatown blocks around Capital One Arena at 601 F Street NW, all within the DowntownDC business improvement district's 140 blocks and one square mile, with the separate 43-block Golden Triangle running west of 16th Street NW.