West Seattle is well known for its dazzling views of Mount Rainier, the Olympic Mountains, Puget Sound and downtown Seattle. But new buildings going up around the peninsula are obscuring portions of those resplendent vistas.

Legally speaking, home owners cannot protect views they've enjoyed for many years if new buildings block part of the field of vision As long as the new development is built within the height and mass limits allowed by zoning, it can block your view.

However the value of a house can be diminished if its view is obscured or lost.

When it comes to assessing the value of views from any particular property, King County assessors and private appraisers mostly rely on recent sales.

King County is divided into geographic areas. Property within each area is compared to similar properties sold recently in the same area, explained Stan Rowe, executive assistant to King County Assessor Scott Noble.

If you own a three-bedroom house in the Genesee Hill area or say Ballard's Loyal Heights neighborhood, its value is based on the average sale price for comparable three-bedroom houses in the same neighborhood over the last couple of years.

The King County Department of Assessments inspects all taxable property in the county every five years. Department inspectors also visit recently improved properties as they learn about them.

County tax assessors consider what can be seen from the property, Rowe said. Views of Mount Rainier, the Olympic or Cascade mountains boost value. So do views of downtown Seattle, Puget Sound, Lake Washington and Lake Sammamish.

When inspecting a property, King County assessors take in the views from the yard around the house rather than from the living room window. Their assessments depend partly on data but they also must use their discretion, Rowe said.

If there is a wide, unobstructed field of vision, the view is deemed "excellent." If about one-fourth of the view is blocked, it's considered a "good" view. If trees or something else blocks half of the panoramic view, it is deemed an "average" view, Rowe explained.

Another way the Department of Assessments determines the worth of views is by starting with the "base land value" of the property. That's the value of the land if it were vacant. Assessors then add 35 percent to the base land value if the view is rated "average," 50 percent if the view is "good," and 70 percent if the view is "excellent."

"View certainly is an important valuation characteristic," said Dave Goff, manager of the King County Board of Equalization. That's where property owners appeal when they disagree with what the county determines is the worth of their property.

Private appraisers use many of the same tools as tax assessors to determine the value of views.

"Typically we turn to the marketplace," said Gregor M. Strohm, an accredited senior appraiser in Oak Harbor and a member of the American Society of Appraisers, which accredits professional appraisers. "Here (on Whidbey Island), a good view can double the price of a lot."

Strohm carries a compass to precisely determine the scope of the view at a property. He also notes what can be seen in the view and figures out how permanent the view might be.

He also makes distinctions concerning where the viewpoint is located. A front yard view is less valuable than the view from a living room, dining room or breakfast nook, he said. By the same token, a bedroom view has less value than a living room or dining room view because people often are sleeping in the bedroom.

When determining the diminished value of a property that's lost its view, appraisers also check recent sale prices of similar homes with a view comparable to when it was unobstructed. Then they check sale prices of similar homes with similarly diminished views. It helps to compare the before and after scenarios, Strohm said.

"The appraisal of a property is more an art than it is a science," Strohm said. "In the end, it's the marketplace that sets the price."

To a large extent, house value is determined by personal interests and taste. A house might have a panoramic view, but one potential buyer might be swayed more by the design of the kitchen, said D. Lisa West, a broker at Windermere Real Estate's Fauntleroy office. Another person might decide to buy a house for its garden rather than for the view.

"If you buy a view property that's not right on the edge of a cliff, probably you should look at if every single tree in the neighborhood grows as tall as it can grow, and if every person on every lot goes up as high as they can go, do you still have a view, yes or no?" West said. "That's what happens to so many great views in so many neighborhoods in Seattle. They do change over time."

Tim St. Clair can be contacted at 932-0300 or timstc@robinsonnews.com