Jeremy Hobson: A study out this morning from the National Trust for Historic Preservation finds retro-fitting an old building almost always saves more energy than framing up a new one — even if the new building is eco-friendly.

From the Marketplace Sustainability desk, Eve Troeh reports.

Eve Troeh: Say you want to build a downtown apartment complex with a cafe and shops. You add solar panels, recycled floors, insulated windows.

But, if you tear down an existing building to do it, it’ll take decades to get any “green” benefit, says Patrice Frey at the National Trust.

Patrice Frey: Up to 80 years for a new, efficient building to compensate for the environmental impacts that occur during the construction process.

Frey says city planners should think about all the energy wasted before they let developers tear down buildings.

But the real estate market is moving that way on its own, says Rob Melnick at Arizona State. He says developers are nervous to gamble on new construction, but they like the idea of sprucing up property with an energy-efficient retrofit.

Rob Melnick: You know to protect what you have, and really to provide building efficiencies at a lower, short-term cost.

Because developers do know people want green buildings. Buyers will pay more for them, and renters will stay in them longer.

I’m Eve Troeh for Marketplace.