The National, a former bank tower in Downtown Dallas, is today a luxury hotel and apartment building. Its transformation is something of a miracle — and an expensive one. The building’s reinvention cost half a billion dollars.

The building is a “testament to the possibilities of office conversions,” Kimberly Byrum and Jasmine Cracknell-Young, VPs of advisory at Zonda Home and Zonda Urban, write in Builder.

However, for projects like the National to come to fruition, the stars have to align on a number of factors — eight to be precise. They include: heritage status, building height, ceiling height, balconies, windows, elevators, parking, and uses.

“Any of these elements on their own isn’t likely to make or break a project, but if you start measuring the variables, you begin to see just how difficult it is to make the math work on a conversion,” they write.

Still, empty offices buildings are ripe for reinvention. That’s a lot of good, useable real estate. Developers who can make the math work in their favor can consider adding propane to help supplement natural gas, ensuring adequate supply. Clean-burning propane can fuel high-efficiency appliances such as condensing tankless water heaters and boilers, hydronic in-floor heating, and community amenities like fire pits and heated pools.

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