WASHINGTON – U.S. home prices posted a robust gain in August — another sign that the American housing market remains strong despite economic fallout from the coronavirus pandemic. The S&P CoreLogic Case-Shiller 20-city home price index, released Tuesday, showed that home prices climbed 5.2% in August from a year earlier, accelerating from a 4.1% gain in July. Phoenix (up 9.9% from August 2019), Seattle (up 8.5%) and San Diego (7.6%) posted the biggest gains. The 20-city index excluded prices from the Detroit metropolitan area index because of delays related to pandemic at the recording office in Wayne County, which includes Detroit. And the Commerce Department reported that home building rose 1.9% in September on a surge in construction of single-family homes.