Has anyone ever heard of someone adding a basement under an existing Eichler? I live in Sunnyvale, CA.
I think if you use the "search" button at the top of this page you will find the topic of basements has come up before.
To my mind, it would not be cost-effective to raise a slab foundation to provide a basement. Unlike a wood framed/floored house which is somewhat flexible, a slab foundation is heavy and unlikely to lift without serious cracking (IMHO).
I grew up where basements were standard and I sorely miss the additional storage (not to say, the living) space they provide. However, I think you will find it is not a practical path for additional space in an Eichler. Upwards or outwards are really the only options, with outwards being the community preference.
I'd be happy to read other (more experienced) voices if I'm ill informed.
I would check with the City of Sunnyvale to see if adding a basement *under* an existing home is allowed. In some cities, it is not allowed. You might be able to add a basement under your yard, but not under your home.
Checked with my friend who'd been on the Sunnyvale planning commission for many years and he said Sunnyvale has no restrictions on adding basements and that basement square footage doesn't count as house square footage for the purposes of other restrictions.
Looked on the web and seems that the adding a basement to an existing slab foundation house can be done. The house+slab isn't lifted off the ground but rather the existing slab is demolished, temporary bracing is installed to keep the walls from collapsing, then the house is lifted and a new conventional foundation + basement is added underneath it.
Everyone who comments on this procedure says it's expensive and not for the faint of heart. However, the prospect of an Eichler with all that great storage space underneath is so tempting...
If demolishing the existing slab is necessary, the radiant heating system would have to be replaced; and so would the existing flooring (or re-installed over a new plywood surface.
Coming from the East Coast, basements are common and would only add $10-$20K to a new construction (basically excavation and concrete retaining walls) -- in Silicon Valley, basements are an oddity and only the Victorians seem to have them.
attempting to "add" a basement would damaging and wasteful. everything is anchired at a 50 year-old concrete slab. that slab is not intended to be propped up, rather rest on the ground. the anount of money needed to remove the slab, build a new structure of joists which would rest about a new basement structure would be astronomical. my advice would be to not harm the original structure and look for a basement elsewere. if the home is too small, find a larger one. much less pain :)