When I first became interested in rehabbing older houses, I stumbled on the private, nonprofit Philadelphia Architectural Salvage Ltd., which had a warehouse a couple blocks from Girard College.

On occasion, I would accompany the employees on salvaging missions, typically houses that had been condemned by the city, which authorized the expeditions.

By the time the salvagers arrived, the houses were in sorry shape and stripped of anything valuable. One house we went into back in 1991 had a tree growing through the kitchen roof, and the living room ceiling was sagging deeply.

As we were leaving, a neighbor stopped by, not to question what we were doing there, but hoping that the city was doing something about the abandoned house.

We had to disappoint him, although we all understood his concern, since his property values were being affected.

Experience shows that one abandoned house, for whatever reason, affects the real estate values of the rest of the block, street, and neighborhood.

This isn't just a Philadelphia phenomenon. Suburban communities, too, have empty houses, vacated for a variety of reasons - such as the foreclosure crisis, from which the real estate industry is still extricating itself.

Blight is blight, whether urban or suburban.

"Blight to Bright: A Comprehensive Toolkit for Pennsylvania" is a manual, recently released by the Housing Alliance of Pennsylvania, that offers communities and neighborhoods a way of turning vacant properties to productive use.

It is a lengthy treatise, considering the problem it is tackling, but the statistics are worthy of presenting here. You can read it at http://goo.gl/RgzstZ.

There are 300,000 abandoned properties throughout Pennsylvania. Besides being eyesores, they create significant costs for government, make communities less safe, and deter investment.

A 2010 study by May 8 Consulting said Philadelphia's blighted properties cost the city $21 million a year to maintain, including providing police and fire protection, pest control, and waste cleanup.

More police and fire protection is needed for vacant properties than for occupied ones because they are often the sites of crime, arson, or accidental fires.

Many are tax delinquent, to the tune of $2 million each year.

"The greatest financial cost is the $3.6 billion in lost household wealth as vacant properties reduce the value of each nearby property by an average of $8,000," the manual states.

It doesn't matter how well you care for your property. If there is a blighted, vacant property next door, you suffer.

A study by the Reinvestment Fund this year of the anti-blight Windows and Doors Program found that the effort increased the value of surrounding properties by millions of dollars.

Under the program, the city fined the owners of long-term vacant structures that had openings not covered by functioning windows and doors.

Properties that complied with the citations created $74 million in sales prices for surrounding properties.

The increased value resulted in $2.34 million in additional transfer-tax revenue to the city, the Redevelopment Fund found.

The "Blight to Bright" manual also cites studies by Penn showing that eliminating blight through greening or redevelopment increases surrounding property values by up to 30 percent in certain neighborhoods, reduces gun-related violence, and improves the health and exercise habits of residents while easing stress.