For home builders, foreclosures and distressed sales remain a problem even after they are sold.

They become comparable sales to gauge value, reflecting decreased market values, forcing builders to shave prices or risk losing a deal. It is yet another problem - and one expected to last for some time - for the ailing sector searching for stability as the worst downturn in decades drags on.

"They don't need any of this incremental heartache," said Robert Curran, Fitch Ratings' lead home-building analyst. "It's like another shoe keeps dropping for them in terms of the challenges."

For months, builders have complained that foreclosures and short-sales - where the borrower unloads the house for less than what is owed - pose stiff competition because they can sell for steep discounts. The sector even finds itself competing with nearly-new product it built, which is pushing several builders, including KB Home (KBH), to alter product.

But, once a property sold, it may be used by appraisers to determine value. Most lenders now require that appraisals be based on sales closed within three months - instead of six-to-nine months, said Bill Garber, director of government and external relations with the Appraisal Institute. With distressed deal counts spiking, the comparative sales pool could more likely include a foreclosure, especially in boom-to-bust markets including Las Vegas, Phoenix and California's Inland Empire.

Back in the housing heyday, appraisers felt pressured by everyone from real-estate agents to consumers to inflate value estimates. But now, builders grumble appraisers are being conservative, or even, they fear, discounting the value to play it safe.

"The lenders that are using these appraisals [for] the amount they will loan, they were just burned by appraisers being too optimistic and liberal in the boom times, so they're going in the opposite direction," said David Ledford, senior vice president at the National Association of Home Builders. "It sort of contributes to a downward spiral in values."

Garber countered that appraisers, who are certified, "don't make the market, they simply point out what is transpiring."

Even so, both sides agree a main issue is that falling prices - dragged down by foreclosure sales - reflect battered markets. The latest S&P/Case-Shiller Home Price Index - which covers all nine U.S. census divisions - recorded a 19.1% decline in the first quarter compared to a year earlier. Since the 2006 peak, some markets have seen double-digit price erosion.

Builders also complain the comparisons don't take into account the added value of a new home. Foreclosures can be beat-up - missing pipes and appliances - and require a monetary investment and significant work to be livable.

"They are distressed sales," Curran said. "It's not reflective of the true cost of the house."

The Appraisal Institute's Garber said the appraiser simply asks what the property would sell for tomorrow in its current condition. When possible, sales within an existing neighborhood are used first. Adjustments downward are made for sales concessions such as free vacations or cash for upgrades. There are items, such as pools, that may not be worth as much as they cost to put in.

That has turned the appraisal process into a nail-biter for buyers and sellers. Should the appraisals come in below the contract price, lenders might not make up the difference - tens of thousands of dollars, in some cases. Buyers can either come up with more money, or ask the builder to reduce the price. Appraisals can be appealed or reordered. If that fails, the deal just might unravel.

Some builders are forced to search for different comparative sales that they consider a better match. "The best thing they can do is find the best comps, and that just takes more work on their part," said Eric Elder, a spokesman for Ryland Group (RYL), the nation's eighth-largest builder by annual closings.

Things only got more complicated last month with the Home Valuation Code of Conduct applying to mortgages that will be owned or guaranteed by government-backed mortgage companies Fannie Mae (FNM) and Freddie Mac (FRE) - which recently have been the bulk of new home loans.

The code prohibits selection and compensation of the appraiser by loan officers, mortgage brokers or real-estate agents. That has increased outsourcing the selection to third-party management companies, which may take some of the fee. Appraisers worry lenders are ignoring qualifications and hiring solely on cost, and there is concern that out-of-towners unfamiliar with the market aren't "geographically competent" to prepare a thorough appraisal.

"You risk having people unfamiliar with the marketplace having to determine value," Elder said. "It makes their job harder and then it makes the entire process more difficult."

The issue is expected to dog the building sector for some time. RealtyTrac this week released its May foreclosure report, saying the number of filings climbed nearly 18% from May 2008. It was the third straight month with the total number of properties slapped with filings topping 300,000.

Because the government is working to prevent homeowners from losing their homes, it is hard to predict the ultimate number of foreclosures. But Barclays Capital estimates new foreclosures started this year at 2.8 million, with 3 million expected in 2010.

Meanwhile, as interest rates climb and unemployment numbers remain escalated, more owners could be forced into short-sales or other desperate moves, prolonging the sector's pain.

"Everything's driving values in one direction, there's no counter-acting force," Ledford said.

-By Dawn Wotapka, Dow Jones Newswires; 201-938-5248; dawn.wotapka@dowjones.com

(James R. Hagerty and Ruth Simon contributed to this article.)