Lack of updates

Threat to value: Low to medium; usually, at least 10%

An oversupply of homes right now means that buyers can be picky — and they definitely are. Rather than seeing the potential in an outdated kitchen and bathroom, a buyer will just move on to another home that won't require as much work and vision.

"If you don't have granite countertops, someone wants to know what's wrong."   The same goes for new appliances and a modern kitchen and bathroom, "Fortunately, you can fix this easily. For between $5,000 and $8,000, you can install those granite countertops, update the light fixtures and add fresh paint and carpet. You'll likely get a return of $15,000 to $20,000 when it is time to sell.

 Bad floor plan

Threat to value: Medium to high; up to 25%

"An open floor plan is huge,"  "If you've got a long hallway, and all the bedrooms are off that hallway, no buyer I've shown homes to has ever wanted a house like that."

Appraisers  consider odd floor plans when appraising homes. One home, priced at more than $2 million, had an unusual floor plan with only a back stairway and no formal foyer, he says.

"The market would have probably accepted that in '06 or '07," he says. "Now buyers are more critical. Everybody hates the fact that there's not this big, easy access upstairs."

Appraisers classify that as a functional problem and determine value based on the market. A bad floor plan reduce an appraised value by as much as 25% compared with similarly sized homes.


Foreclosures

Threat to value: Varies

Generally, the many foreclosures on the market are bringing down home values, but it's difficult to quantify their effects.

According to a 2009 Harvard University and Massachusetts Institute of Technology  study, a home's value drops by 1%, on average, if it is within roughly 250 feet of a foreclosed home. That study was based on 1.8 million home sales in Massachusetts from 1987 to 2009.

But Rick Sharga, senior vice president at RealtyTrac, a foreclosure-data firm, says a single foreclosure on your street probably won't affect your home's value.

"Sometimes, the only way to sell a nonforeclosure property is to price it as if it were in foreclosure," Sharga says. "There is a certain point where the volume of foreclosure properties is so high that it takes the rest of the market down with it."

A home surrounded by foreclosures will lose value because an appraiser will use those homes as comparables, Downs says.

The lesson? If you're in an area that's saturated with foreclosures, and you don't absolutely need to sell, don't.


Major systems and structures

Threat to value: Medium to high; up to 20%

"A buyer wants to be able to walk in and say, 'I could move right in." Realtors have  seen major system and structure issues kill potential deals in high-end neighborhoods. "Have an inspection done before you list your house and fix the major things."

A roof that needs to be replaced could knock 15% off the value, she says. A heating and air-conditioning system that needs repairs could cut the value by as much as 20%, and an electrical-system problem is probably somewhere between 8% and 10%


Swimming pool

Threat to value: Varies

Depending on your market, a swimming pool or other water feature may boost or lower your home's value — and its appeal.

If you live in a hot climate where many homes have a pool, it's definitely an expected feature that will add value.

In regions where pools aren't common, though, buyers may not want the hassle of maintaining a pool they didn't want in the first place. Those buyers may not consider buying your home, particularly if they have young children and are concerned about safety. 

NO GARAGE

Threat to value: Varies; usually about $5,000 per stall

A garage definitely adds value to a home, and the key is to have the right-size garage for the home and the neighborhood.

"If I have a one-car garage in a 1,200-square-foot home in a starter neighborhood, there's a big premium for that."  "If I have a one-car garage in a half-million-dollar home, that's a functional problem."

The added value for a garage varies greatly by neighborhood, but Wiley and Downs say that a good rule of thumb is $5,000 per stall.

Allergens

Threat to value: Low to medium; up to 15%

Downs says a little mold under a sink killed two contracts with one home.

"(The potential buyers) could have easily gotten rid of it," she says. "But they just backed out, didn't even ask for money or for it to be fixed. If (people have) an allergy, they're going to run."

Possible problems also include cigarette smoke and pet dander. No matter how many times you clean your home, you can never really get rid of Fido.