Great thread. Had to reply.
Coming from Florida, the quicksand state, I really had very little information on basements. If you dig there, you find yourself on a fast track to life in a sink hole. I had lived in the Midwest as a small child, and only remember basements being for storage or pool tables--and of course the occasional flooding. Having moved to the mountains to cool off as an adult, rock and many natural springs in the area tended to prevent basements from being found as commonplace. For these reasons, when searching for my new home on the east coast and trying to determine how much space I would have to move the contents of my home, I needed to learn about the basement stuff. [Coming from acreage, a barn, and a three car garage really sucks.]
If you are a realtor in Southern Cali--well, it seems practical and logical to ask what these types of foreign "basement" structures entail--if for no other reason than to define for your clients how much more or less storage room they will have in their new Sunny homes! [Good call.]Here is what I have found out to the best of my ability through common conversation with realtors and exploration of potential new homes.
All basements have some element of the sub-terranian. The "Yankee basement", from everything I have found, appears to be akin to a "root cellar". Dark, musty places where your grandmother used to keep her canned goods--the typical "light bulb hanging from a string" concept seen in most scary movies comes to mind to describe the darkness. A sub-basement is one that is partially underground; think about in the movies when you see kids breaking into the ground level basement windows? That is probably what your clients are referring to; it might have a stairwell that comes down into the backyard ground for an enterance. A "walkout basement" is a basement that has some sort of a terraced enterance that is equal to ground level. Normally, this could be done when the lot ground levels are anything but flat. Instead, dirt may partially wrap around the structure (three sides perhaps).
Of course, I am no contractor. I may be dead wrong. I have my brokers license, but have not used it to any degree of profit--so technically, I am unqualified to answer. All my information comes from common discussions of houses and properties (as my family has been involved with the real estate industry for 50+ years).
Again, my thoughts on basements are about understanding storage and alternate recreational spaces--especially when a client is sacrificing space. Garage storage (as opposed to carport), basements, and attics all add usable storage value to a home. As a realtor, do not forget to include mention of these for calculation in cost; "Rent-It-Yourself" spaces for storage costs add up faster than you realize!
Best to all...
The longer I live, the more beautiful life becomes. ~~Frank Lloyd Wright