The Greater Boston rental market has gone into overdrive seemingly overnight, with rents soaring and the number of available apartments plunging.

And what’s happening with apartments may very well prove to be a dress rehearsal for what’s in store for the battered home sales market once the long-awaited turnaround kicks in.

With frightening speed, we’ve gone from a rental market that was the sleepy safe haven of the Boston area’s perpetually overpriced housing market, to one where double-digit increases are taking hold.

One new survey, by Champagne, Ill.-based rental market data cruncher Cazoodle, claims an 18 percent spike in asking rents for apartments in Boston and its suburbs over the past year.

And the same combustible mix that is driving the escalation in rents is also present, but temporarily dormant, on the home sales side of the market, just waiting for a spark. It’s same old story of a sudden surge of demand colliding with a dearth of new construction.

“A couple of years ago, people had options,” said Arthur Horiatis of Tory Row Real Estate in Cambridge. “They could see five or six apartments before making a decision. Now they may see one, possibly two.”

“It’s been an extremely tight market,” he said.

Boom Times

The numbers from Cazoodle, a start-up launched at the University of Illinois in 2006, are particularly sobering.

The median asking rent for the Boston area skyrocketed in the past year to $1,902. Two-bedroom units experienced the biggest increase, with median rents now topping $2,000 – an increase of 21.4 percent in a year, Cazoodle reports.

Meanwhile, the number of available apartments has also fallen, putting added upward pressure on rents, notes Barry Bluestone, the Northeastern University economist.

“We are down to 4 percent vacancy rates,” noted Barry Bluestone, Northeastern University economist. “When it’s below 6 percent, you have escalating rents.”

So what’s behind the big jump in rents?

The demand right now is being driven in part by refugees from the battered housing market.

For starters, there are growing numbers of families pushed out of the homeownership market by foreclosure – which may explain the big spike in two-bedroom apartment rents.

But an important factor in Greater Boston is the rising number of young professionals opting to rent until home prices settle out.

The local boom in the biotech and high-tech industries is especially being felt in hot rental markets like Cambridge, Tory Row’s Horiatis said.

But demand is being met with a serious lack of supply. Rental construction in the Boston area has lagged for years, with investors interested in bankrolling luxury condos during the bubble years, not apartments.

While developers have put forth a flood of new apartment proposals, it will likely take two or three years before most finish construction and hit the market. That, in turn, has raised concerns that we could end up with an apartment glut given Greater Boston’s penchant for boom/bust real estate cycles.

In fact, if rents escalate at their current rate, many renters may soon start to reevaluate their decision to hold off buying a home or condo, which may start to suddenly look like the cheaper option.

It could be just the spark that gets home sales rolling again – though a stronger economy is also likely needed, as well, before that happens.

History Repeating

Regardless of what sparks the eventual, inevitable comeback in home sales, we could very well see a repeat of what is happening right now in the rental market.

The past few decades have seen steadily declining numbers of homes built across Greater Boston, with even that modest trickle drying up with the Great Recession.

Concerned about school costs, many towns have all but shut their doors to traditional, suburban-style subdivisions, limiting the number of bedrooms and encouraging the construction of over-55 communities.

There are already warning signs out there – even in the midst of an epic real estate downturn, half-decent homes in coveted towns like Lexington or Cambridge are continuing to spark bidding wars.

Greater Boston is likely to face a shortfall of 46,000 homes and apartments by the end of the decade, the Massachusetts Housing Partnership found in a recent report.

The lesson is not just that we could see the current spike in rents repeat itself with home prices – after all we’ve seen two big bubbles in the past 25 years.

But rather, there may be little or no warning time before the next spike in home prices occurs.

Unlike Florida or Arizona, we don’t have vast tracts of foreclosed subdivisions to burn through. Once demand picks up, it won’t take long to work through whatever surplus there is out there.

That will send home prices soaring – much like what we are seeing happening right now with rents.

Then we will all be wishing for the good old days of the real estate slump, when the median price of a home here in Massachusetts was just around $300,000.