By Peter Grant And Robbie Whelan

Investors are pouring money into buying and developing senior housing, medical-office buildings and other health- care-related properties, a class of commercial real estate that has been outperforming almost all others since the recession.

The country's aging population and recovering economy, as well as major changes taking place in the economics of health care, are fueling demand for more space.

Investors are gravitating to health-care real estate in part because it held up well during the downturn. Since 2007, health-care real-estate investment trusts have outperformed all other property types except for manufactured homes and self-storage facilities, according to the National Association of Real Estate Investment Trusts.

Investors also are betting the Affordable Care Act will translate into millions more visits to doctors by patients who are getting insurance for the first time. Last year, health-care-focused REIT shares produced total returns of 35.5% , including dividends, Nareit said.

The strong performance and new money flowing into the sector are signs that many investors want to stick with properties that are more recession-resistant. The memory of the pain suffered by owners of office buildings, stores, hotels and many other types of property still runs deep.

Health-care property "has a stability factor that's very attractive," says John Sweet, chief investment officer of Physicians Realty Trust, a real-estate investment trust that went public in 2013 at $11.50 a share. It traded recently at about $17.25.

Sales and construction activity have been surging. In all, about $5 billion in medical-office buildings were sold last year in the U.S., a record, up from $4.3 billion in 2013, according to John Smelter of the real-estate firm Marcus & Millichap. About 8 million square feet of new medical-office buildings were delivered, up from 7 million in 2013, but far short of the more than 26.5 million square feet delivered in 2008, Mr. Smelter said.

Medical-related housing--ranging from apartment complexes that exclude younger people to nursing facilities with 24-hour-a-day care--also is experiencing a boom. Sales transactions involving senior housing and nursing facilities rose to $17.4 billion in 2014 from $14.8 billion in 2013, according to the National Investment Center for Seniors Housing & Care, a Maryland nonprofit organization that tracks investment in the senior-housing real-estate sector.

Construction of assisted-living facilities, which provide more care than regular apartments but less care than nursing homes, is running at more than twice the amount of 2008 to 2011. There were 11,268 units under construction at the end of 2014, compared with the long-term average of 5,450 units under construction each quarter between the end of 2008 and the end of 2011.

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Graying America, Health-Care Overhaul Boosts Medical Properties