Posted by Kromey at 6:37pm Apr 8 '10putting the number of earth-sheltered homes in the US at around 6,000; other estimates I've seen go much higher, and I've seen some estimating as many as 50k. (Impossible to get a completely accurate number since there's no registry or anything, nor is it a census question.) Still a small number relatively speaking, though, and a lot of that has to do with the fact that this is an unusual type of architecture, and one that has a lot of prejudices against it (for example, the idea that these homes are dark and claustrophobic). If you add in earth-bermed homes (where you have earth piled up against 1 to 3 sides of the home, but not over the roof -- giving some of the same advantages), you can triple or even quadruple the number -- these are a lot more common.
A lot of earth sheltered homes are long in the east-west direction but short in the north-south direction, so that literally every single room in the house gets natural light (i.e. every room has windows on the southern exterior wall); some do similar but use skylights or other means of illuminating rooms on the northern side. Other homes make creative use of skylights, open spaces, mirrors, and even interior windows to get natural light into the northern rooms. The point being that if you want natural light in any given room in your earth-sheltered home, there's very likely a way to do it.
I need to find one particular page again, which showed several architectural experiments by one architect whose goal was specifically to get natural light into truly subterranean rooms - with pretty good results. Some methods he used: An inverted pyramid in an open courtyard in the center, which allowed windows facing outside (and thus letting in natural light) to a depth equivalent to 4 or 5 stories down (IIRC); skylights forming the roof of hallways, which had lights above them to serve double-duty as nighttime interior illumination and exterior security lighting; mirrors and skylights to create oversized periscope that literally gave office workers several floors below ground an exterior window view (although it suffered from odd perspective/parallax issues unless you were seated at your desk).
As for population density - you're right. It's easier to build up than it is to build down, even if you ignore the strong desire of most people to have natural light. So it's certainly not going to be replacing huge apartment complexes any time soon. Nonetheless, it is viable for people looking for their own homes or for small duplex-like situations.
A lot of earth sheltered homes are long in the east-west direction but short in the north-south direction, so that literally every single room in the house gets natural light (i.e. every room has windows on the southern exterior wall); some do similar but use skylights or other means of illuminating rooms on the northern side. Other homes make creative use of skylights, open spaces, mirrors, and even interior windows to get natural light into the northern rooms. The point being that if you want natural light in any given room in your earth-sheltered home, there's very likely a way to do it.
I need to find one particular page again, which showed several architectural experiments by one architect whose goal was specifically to get natural light into truly subterranean rooms - with pretty good results. Some methods he used: An inverted pyramid in an open courtyard in the center, which allowed windows facing outside (and thus letting in natural light) to a depth equivalent to 4 or 5 stories down (IIRC); skylights forming the roof of hallways, which had lights above them to serve double-duty as nighttime interior illumination and exterior security lighting; mirrors and skylights to create oversized periscope that literally gave office workers several floors below ground an exterior window view (although it suffered from odd perspective/parallax issues unless you were seated at your desk).
As for population density - you're right. It's easier to build up than it is to build down, even if you ignore the strong desire of most people to have natural light. So it's certainly not going to be replacing huge apartment complexes any time soon. Nonetheless, it is viable for people looking for their own homes or for small duplex-like situations.
I've seen estimates - Kromey