The resurgence of the Boston housing market since the beginning of the year has been the talk of these and other real estate pages for the past 10 months. But perhaps unnoticed in the excitement over the overall return to form has been the exceptional strength of the condominium market, particularly in Boston.

Condo sales gains have outpaced the considerable rises on the single-family side of the ledger for the last six months by significant margins. September was no exception: While single-family sales were up 8.1 percent last month, condo sales surged 23 percent.

 “If you look at historical cycles, we’ve come through the darkest hours and now we’re on a growth pattern,” said Robert Byrne, senior vice president at Otis and Ahearn in Boston. “There are small projects going on all around town.”

In the downtown Boston core, sales in the third quarter were up a mere 7.2 percent over last year’s strong fall. But some of the trendier, outlying neighborhoods have seen surprising surges this year, with condo sales in Charlestown up 39.5 percent over the past three months compared with the same period last year. Condo sales for the quarter were up 41.7 percent in Dorchester, 34 percent in Jamaica Plain and 64.8 percent in South Boston, where the number of sales jumped to 267 from 162 during the same three-month period last year.

South Boston in particular is ground zero for the collision of two trends: Falling interest rates and rising rents.

Michael Sylvia, broker/owner of The Terrier Group in South Boston, said, “What’s driving the market at that lower price range is that rent-versus-buy scenario. People find [they] can rent this apartment for $2,500, or buy it for $375,000, for 5 or 10 percent down, and be paying $2,100 all-in. The rent versus buy scenario has become a lot more appealing, and financing has gotten a lot easier.”

Tight Inventory

High rents have also been a boon for investors.

“There’s such a thirst for investment properties because inventory is so tight. Here in South Boston, we have so much industrial land that’s primed for residential development, so that’s what’s driving that – [the desire for] new construction with parking,” Sylvia said.

There are certainly many potential investors out there with cash on hand to make the leap. Though down from this time last year – when cash purchases made up nearly half of condo sales – 38.5 percent of third-quarter condo sales this year were cash.

“There wasn’t a lot of leveraging, there wasn’t a lot of bad debt, and now we’re at a point where there’s a lot of money in the market,” Byrne said. “Coming out of the recession, you’ve got a lot of people who had put off establishing a household, and rent has been going up 10 percent a year for the last couple of years.”

The rise in demand has been enough to inspire some maiden flights from Mayor Menino’s favorite bird – the crane – but “they’re still not online yet, and that’s pushing rents up,” Byrne said.

It’s also squeezing inventory. “We have really tight inventory. We have only two and a half months of inventory in the downtown market right now. There’s a lot more demand than supply at the moment,” said Michael DiMella, a broker at Charlesgate Realty in Boston.

That tightness has helped stabilize condo prices. In a year when the median price for single family homes has dropped almost 1.6 percent year-to-date, including a 4.5 percent drop in September, condo prices have held steady, up about 1.5 percent year to date, and flat last month, with September 2012’s $275,000 median a tick less than September 2011’s $275,450. Earlier this year, condo prices even briefly exceeded single family prices, the first time that’s happened since The Warren Group began tracking that data.

What remains to be seen is whether the demand can be sustained, or whether increasing buyer frustration drives renters back into the arms of their landlords for another season.

“Sellers are a little bit behind in terms of reacting to the market right now. Some may have this notion of waiting for higher prices,” DiMella said. “It’s causing a lot of buyer frustration right now, because they’re missing out on these multiple offer situations – not just one or two offers, but five, six, seven offers in some cases.”

But brokers seem confident.

“I just think people really believe the worst is over,” said Sylvia.