A housing development under contruction in Denver, Colorado. Getty Images

The steady rise in home prices is so far showing no boundaries, and that is turning up the heat on some already overheated housing markets. Home prices rose 7 percent nationally in September, compared with September 2016, a higher annual increase than was seen in August, according to CoreLogic, a real estate data firm. As a result, 48 percent of the nation's top 50 housing markets are now considered "overvalued," up from 46 percent in August. A market is considered overvalued when home prices are at least 10 percent higher than the long-term, sustainable level. For the top 100 markets, 36 percent were considered overvalued.

"A strengthening economy, healthy consumer balance sheets and low mortgage interest rates are supporting the continued strong demand for residential real estate," said Frank Martell, president and CEO of CoreLogic, in a statement. "While demand and home price growth is in a sweet spot, a third of metropolitan markets are overvalued and this will become more of an issue if prices continue to rise next year as we anticipate," he said. Las Vegas, Denver, Los Angeles, Miami and the New York-New Jersey metropolitan area are all considered overvalued. By comparison, these pricey markets, Boston, San Francisco and Chicago, are considered at-value, based on long-term price sustainability. San Francisco is one of the most expensive markets in the nation, but higher incomes can support it. High housing demand and low supply are continuing to fuel prices. Both are weighing on consumer sentiment. After matching an all-time high in September, homebuyer and seller sentiment dipped in October, according to a monthly index from Fannie Mae. The share of respondents who said now is a good time to sell a home decreased 8 percentage points compared with September, and the share who said that now is a good time to buy a home fell 6 percentage points in the survey, Fannie Mae found.

Seasonality a factor

Fannie Mae's chief economist, Doug Duncan, attributed this decline to seasonality. "The modest decrease in October's Home Purchase Sentiment Index is ... a shift we expect at this time of year moving out of the summer home-buying season," said Duncan. While seasonality is certainly a factor in sentiment, the dynamics of today's market may finally be taking their toll as well. Real estate agents nationwide are reporting increased frustration among buyers who either can't find a home that suits their needs, or, more likely, can't afford one that does. They are also concerned that mortgage rates, which have remained stubbornly low all year, may start to rise in the coming months, dampening affordability. Meanwhile, sellers are worried that they may not be able to find another home to buy. Even if they can sell their home quickly, they need to live somewhere. They are also starting to see price pushback in the market, especially in areas that are overheated. While home prices continue to soar, rents, which had been overheating, are now cooling. CoreLogic's single-family rent index is up just 3 percent annually, less than half that of home prices. While homeownership generally has been considered cheaper than renting, that is shifting quickly. Owning a home and building equity just narrowly outpaces renting a comparable property and investing in stocks and bonds, an index from Florida Atlantic University shows. Four cities — Miami, Pittsburgh, Portland, Oregon, and Seattle — are beginning to look better for renting, according to the FAU report. Only Detroit, New York and St. Louis trended more toward ownership, according to the report.

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