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Matt Rourke, Associated Press
This June 6, 2013 photo shows passive homes in The Stables development in Philadelphia. These homes are built around the idea that houses can be airtight, super-insulated and energy efficient. The goal: a house that creates nearly as much energy as it consumes.

PHILADELPHIA — After decades of near silence, a passive voice is being heard in American architecture.

So-called passive houses, which have been around in Europe but never really caught on in the United States, are basically built around the idea of making houses airtight, super-insulated and energy efficient.

The goal is a house that creates nearly as much energy as it consumes. Think of being able to keep your house warm without a traditional big furnace, cool with no air conditioning unit.

Signature features often include thick outside walls and roofs, highly insulated windows and frames, and a super-efficient heating and cooling system.

Philadelphia firm Onion Flats has made passive low-income housing as well as high-priced luxury homes. They say these homes can be built on a budget.