Some area homeowners will notice that their property values have increased when they open their new real estate assessment notices this week.

The Fairfax County Department of Tax Administration started mailing more than 350,000 real estate assessment notices to Fairfax County taxpayers Tuesday.

Alexandria ZIP code area properties on average increased 0.38 percent, from $367,948 in 2011 to $369,362 in 2012. The ZIP code area is essentially any property with a mailing address of “Alexandria, Va.” That includes areas around Kingstowne, Rose Hill, Huntington, Belle Haven, Fort Hunt and Mount Vernon.

“Property owners are cautioned against assuming that any percentages reported here have been applied to any individual assessment. The percentages are only shown as a measure of the change in mean value for a large group of properties from one year to the next,” the Fairfax County website warns.

Across Fairfax County, almost 41 percent of residential properties increased in value, and 34 percent had no change for 2012, the county said in a statement.

Values are as individual as the property. One home may decrease while the one next door increases, particularly if improvements are made to the latter home.  According to Fairfax County, “The assessed value of properties may change for a variety of reasons. Among these are appreciation and value declines (i.e., equalization changes); and, structural changes (additions, remodeling), rezonings, and land divisions (i.e., growth). A combination of these factors can apply to the same property.”

Other things to know:

Property tax bills and stormwater bills are based on every $100 of assessed value of your property. The proposed county budget released Tuesday calls for no property tax rate increase and a 1-cent increase in the stormwater rate.

Fairfax County is also mailing real estate tax notices for commercial properties this week. Existing commercial properties increased in value by 8.21 percent, led by apartment buildings and high-rise office buildings.

Both residential and commercial real estate in Fairfax County for 2012 totals approximately $200.3 billion. This is an increase of approximately $6.34 billion, or 3.27 percent from the 2011 assessment base, the county said.

If you have questions about your assessments or want to appeal them, contact the Department of Tax Administration (DTA) at 703-222-8234.

Administrative appeals can be filed with DTA if citizens believe their assessment is not equitable in comparison with similar properties, or if they believe their assessment exceeds fair market value. Appeals may be made In writing to the Real Estate Division of DTA or online through DTA’s website at www.fairfaxcounty.gov/dta/realestatetax_home.htm.

DTA requests that appeals be filed by April 6, 2012.

McLean Patch Editor Bobbi Bowman contributed to this report.