Mary Sibbet Copley Thaw, widow of William K. Thaw, commissioned this grand half-timbered house in 1901, according to a reference in The American Architect and Building

News of that year. The area was popular with Pittsburgh industrial moguls such as Andrew Carnegie and Charles Schwab, and it is not surprising that the Thaws would choose an architect well known to that set. George S. Orth (1843–1918) and his brother, Alexander Beatty Orth (1868–1920), formed their partnership in 1900, but George, while in solo practice, had already designed two houses for William Penn Snyder of Pittsburgh (
AL65).

The design of Elmhurst is often attributed to Stanford White, but research into the McKim, Mead and White archives disproves that assertion. The rumor persisted, however, and grew in dramatic license after 1906, when White was murdered by Mary's son, Harry K. Thaw, although that grisly coincidence did nothing to reveal the name of the architect of this house. The work was also mistakenly attributed to Beezer Brothers of nearby Altoona, especially when they designed buildings for Mary Thaw in Pittsburgh. However, the design can be credited to the Orth brothers, with contractors John H. Trimble and Brother of Allegheny, who were paid $75,000 in August 1901.

Its history aside, the Tudor Revival house is well designed and equally well appointed. Not only is the hand of the architects obvious in the house's siting and the design, it is also evident in the fittings and details, such as the heavy banisters, fine cabinetry, and oak woodwork. The first floor has four rooms with a slightly off-center central hall, and the upper floors are laid out to accommodate numerous guests and servants, with a fifty-foot-long corridor running parallel to the ridgepole. The main entrance has a heavy, 5 × 8–foot Dutch door that opens onto a porch overlooking a wide valley below. The estate includes a springhouse and timber-frame bank barn with two cupolas.