The Commerce Department Monday reports September new-home sales. Economists estimate they slowed to an annualized pace of 455,000 units from 460,000 in August. Three years ago the pace was at about 1.2 million.

Friday brought news of a surprising gain in home resales in September. But up to 40% of home resales these days are foreclosures or "short sales," in which the mortgage balance is higher than the home's value, according to the National Association of Realtors. Such sales drag down the prices of other homes and pull more mortgage-holders underwater.

This phenomenon has led to an oddly bifurcated housing market, in which existing-home sales have built a bottom, while new-home sales haven't stopped drilling their way to the center of the earth.

"New homes have never decoupled from existing homes" before, as "most people that buy a new home have to sell an existing home first," says Ivy Zelman, CEO of Zelman & Associates Housing Research. She expects new-home sales of just 410,000 next year, the worst pace in a quarter-century.

This decoupling may be because many of the people buying foreclosed homes -- maybe 50% in some markets -- are investors. Some will rent the houses until the market recovers, further hurting demand for home purchases.

Until new-home sales find their own bottom, housing won't begin to heal.

How Low Can Prices in New York Go?

The buzz in the commercial-property world is whether things will get as bad as they were in the real-estate "depression" of the early 1990s. A new report coming out Monday from Portfolio & Property Research suggests they might.

Portfolio & Property Research is expected to release a revised forecast Monday that shows 17.6% of New York metro area offices will be empty by the middle of next year. That's the same level as in 1991, when New York tycoons were going broke in a New York minute.

It's troubling news for already battered New York-area office landlord SL Green Realty, which reports results Monday. Analysts are expecting funds from operations -- a common REIT measure -- to come in at $1.41 a share, compared with $1.25 a year ago, according to SNL Financial.

SL Green is also a big lender to other landlords, both from its own balance sheet and through its ailing spinoff, Gramercy Capital Corp., in which SL Green has a 22% stake.

Investors are looking for clarity on the roughly $840 million in loans SL Green made from its balance sheet, as many are mezzanine positions in undisclosed properties.

The company says it plans to provide more detail on a Tuesday conference call and discounts the vacancy forecast, pointing out that SL Green's portfolio is mostly in Manhattan, where vacancies are lower -- and rents are higher -- than the regional average.

Write to Mark Gongloff at mark.gongloff@wsj.com and Alex Frangos at alex.frangos@wsj.com