Possibly the lowest-tech item on this list of tips is one of the most cutting-edge. But really, it's just that builders are remembering what our ancestors knew: Where you build matters as much as what you build. It's called passive design, and if architects use basic principles, the house itself will do a lot of the work when it comes to energy efficiency. For instance, a passive solar house doesn't use mechanical means to store solar energy. Instead, the placement of the house (on a north/south axis) and the requirement that the south face should receive sunlight between 8 a.m. and 3 p.m. during the winter means that natural processes can keep things warm or cool as needed.