Retrofit  Cohousing is developed in existing housing by changing
the way the occupants of that housing relate - usually with new occupants
moving in to participate in the community.  Retrofiting the social relations
and not necessarily the structures.

One description of Retrofit cohousing
Retrofit Cohousing: How to begin by Kevin Wolf of N Street
May 2001 SF Gate articles from Carol Lloyd's column

Note, Oct 2007.  The links below have been around for a while.  There are other retrofit
cohousing community organizing efforts not listed here.
To find others search for "Retrofitting" in the Coho/US cohousing community index .
If you know of others not listed there, please encourage them to enter themselves there.
Note that not all communities that I would describe as "retrofit cohousing" use that term
or have that status in the directory.  The stages of development of retrofit cohousing are
much less well defined than for new construction cohousing.
Are retrofit cohousing communites ever "completed"?

Established Retrofit Cohousing Communities :
N Street Cohousing              Davis          California
On Going Concerns               Portland       Oregon
San Mateo Cooperative Community San Francisco Bay area, California
Temescal Creek Cohousing        Oakland        California
  Temescal Creek article Jan '05 See also the Cohousing Consultants web site for more about  Temescal Creek

something like Retrofit Cohousing:
Homewood Cohousing              Minneapolis    Minnesota
Terra Firma Drummond Cohousing  Ottawa         Ontario, Canada
5-plex at Halcyon Commons       Berkeley       California

Cohousing Consultants who specialize in retrofit cohousing in the
East Bay area of California

Discussion of retrofit cohousing on the Cohousing-L mailing list
can be found by seaching the 20,000+ archived messages.

For a related approach to building residential intentional community (among
folks who don't live so close together but still in the same area) see also
Neighbornets

One set historical roots for residential community building / cohousing
by Polly Allen / Neighborhood Housing Partnership:
_Building Domestic Liberty_

This page is maintained by Fred H. Olson fholson at cohousing.org
Retrofit Cohousing (This page)
The Cohousing Association of the United States (Coho/US)