In the morning one side of the house is going to be really hot, in the afternoon the other side of the house is going to be really hot, and it becomes difficult to balance out the swinging loads. There are many things which must be considered when talking about house plans designs. If you have a lot of glass on those sides, you’re going to have heat gain any way you cut it. Often people don’t have the ability to say, “on this fifth-acre lot I want to rotate the house 90 degrees.” But if you’re early in the process and you haven’t picked a lot yet, don’t even consider lots that face East or West unless there are numerous trees on site, instead look for a lot that faces North or South.