What price air?

The air you breathe is free; all the rest has a price. Coming up with that price, however, is difficult.

Without comparables to guide them, appraisers in the Triangle use all kinds of calculations to compute the value of Triangle air.

Some equations involve figuring out how much is allowed to be built on a site -- and how much income that make-believe building could produce -- then subtracting that value from what's already there.

Others are looking to comparable air-rights sales in growing cities, such as Charlotte, as a guide. But that can be tricky.

"In Charlotte, if you're up on the 30th floor of the building facing west, you can see the mountains," said Cody Jetton, a Cary appraiser. "But here, what do we have? Would people in office buildings be willing to pay more [for a view]? I doubt it."