Clare Regez, a Wengen-based real estate agent, says apartment values here range from 8,000 Swiss francs to 15,000 Swiss francs ($7,980 to $14,964) per square meter, or around $725 to $1,360 a square foot, depending on the location, views and construction quality.

Mr. Hysinger considered setting up a hedge to guard against any change in currency values but ultimately decided to take out a franc-based mortgage for half the apartment’s cost, to minimize the risk. As it turned out, the franc has nearly doubled in value against the dollar during their eight years of ownership, giving the Hysingers an added benefit.

The Hysingers became Swiss residents in 2004, but when they bought the apartment they were subject to the Lex-Koller-Friedrich law, which strictly circumscribes real estate purchases by foreigners. Nonresidents can buy only one apartment with a maximum of about 200 square meters of living space, and only in tourist areas, like Wengen, St. Moritz and Davos. In addition, any nonresident who wants to buy must get one of the handful of purchase permits that the Swiss federal government divides among the cantons each year.

Ms. Regez said there were almost always enough permits to go around in Wengen. But in the neighboring canton of Valais, home to Crans Montana and Zermatt, the government temporarily halted new permits last year because of overbuilding, said Paul Sidebottom, the director of Alpine Switzerland, a luxury real estate brokerage based in Valais.

In the decade before the Hysingers bought in Wengen, its real estate values had stagnated. In fact, they paid the same price for the apartment as the prior owner had 10 years before. But in 2000, the local government in Lauterbrunnen changed the regulations to allow 66 percent of the livable space in chalets to be owned by nonresidents, double the previous allowable amount. (Only 37 percent of the Swiss own their own homes, according to Credit Suisse. Ownership rates are among the lowest in Europe.)

The loosened rules helped stimulate the construction and real estate market in Wengen, leading to a period in which property values rose 15 to 20 percent a year.