the.com/mansard roof

means A roof with two slopes on each side — a steep lower one and a shallow upper one — that lets you tuck a full extra story under the roofline instead of wasting it as attic space.

from Named after François Mansart, a 17th-century French architect who popularized the style (his nephew-in-law Jules Hardouin-Mansart later spread it further). The enduring folk tale is that it caught on because French property taxes were once assessed by the number of floors visible below the roofline — so builders learned to hide a whole habitable story inside the roof itself, tax-free. That story is widely repeated and plausible-sounding, but it's the kind of tidy legend historians treat with suspicion rather than fact — the style's real popularity owes more to Mansart's practical, space-making design than to any confirmed tax dodge.