In this age of the embarrassingly intimate personal disclosure, I think it is time to come clean about my own personal vice: I am obsessed with housing density. Obsessed.

Do not try small talk with me at a Christmas cocktail party because I am likely to start expounding on "units per acre," a topic which makes even public relations people scatter like confetti in a wind tunnel. I am, in fact, a housing nerd.

Boring or not, there is an urgent need to create attractive, medium-to-high-density neighborhoods for California's ballooning population. At the Rivermark subdivision in the city of Santa Clara, three of the largest homebuilders in the country - Lennar, Centex and Shea Homes - come surprisingly close to satisfying my density obsessions. Housing comes in six different "products," from "large-lot" single-family homes to town houses and apartments. One hundred units of affordable housing are included in Rivermark, as are a K-8 grade school, a public library, an 18-acre park and scattered pocket parks.

The 1,900-unit development fills about 152 acres formerly occupied by the Agnews State Hospital; Sun Microsystems has taken over the remaining 80 acres. The overall density of the project is 20 units per acre, which is at least twice the prevailing density in the surrounding neighborhoods. At its highest level, the density rises to 50 units per acre.

Rivermark has been praised as a progressive project for providing some New Urbanist-inspired architecture, affordable housing and open space. Architecture critic Alan Hess, however, seemed less impressed, describing Rivermark in the San Jose Mercury News as "just one more step in evolving and perfecting the art of suburbia." The project has "taken existing ideas and made them more sophisticated, more effective," according to Hess.

Rivermark is an uneasy amalgam of urban and suburban. Resisting the suburban label, master plan architect Mark Day rightly points out that the master plan has urban formality and urban densities. In fact, the project has a pedestrian orientation, houses with recessed garages and a combination of housing types and income levels - all plusses on the urban side of the score sheet.

What Rivermark fails to deliver, however, is a thoroughgoing urbanism. Like many master plans both urban and suburban, Rivermark is more or less a self-contained island. The site plan looks inward. Few streets connect Rivermark to the surrounding community beyond the arterial roads that define the four sides of the property and the existing Agnew Road. The retail portion of the project is a formula-driven "neighborhood center," all clumped together in its own realm. By falling back on formula, the developers have missed the opportunity to create a public shopping street stretched out along a boulevard. This failure to fully develop streets as public places is the most notable failure of the plan because urban character and coherence largely depend upon streets.

In a similar way, several large-scale multi-family developments are isolated in the northwest corner of the plan and situated on their own "super-blocks," rather than being arranged as more linear projects that front on a major street. There is, again, a lost opportunity to use streets to unite different housing types. And there is a failure to take full advantage of the library-school-park complex as a genuine public place. This is a set of civic buildings that needs to be played up as the res publica of this neighborhood, with a conspicuous courtyard. But the site plan, at least the way I am reading it, does not exploit this grouping to make it stand out dramatically from its neighbors. We need a public space to mark the public nature of these buildings.

Rivermark also raises the growing tension between the California imperative for the detached, single-family home and the drive to create greater housing density overall. Despite the many parks inside the Rivermark plan, Hess has written about the "claustrophobic" feeling of houses on very small lots, which I believe is the result of shoe-horning single-family homes into increasingly small lots. At least some of Hess's claustrophobia might be relieved by consolidating much of the housing into townhouses or courtyard housing, and arranging it along streets, while upping the number of parks and other spaces, such as esplanades that would run down the center of streets. This approach would have the dual effect of making the housing less claustrophobic, by replacing the sense of crowding with one of continuity.

Of course, many of the affluent young homeowners of Silicon Valley would rather live in a detached house, no matter how cramped, than in row housing. In this way, Rivermark is a case where California confronts the conflict between the traditional single-family home and the need to increase residential densities. Single-family housing remains a resonant symbol of independence and affluence, but the notion of "high-density" detached housing may have its limits. For all their virtues, the symbols of comfort at Rivermark - such as yards that are shrunk to postage-stamp size - may work against actual comfort.

To criticize the critic, I am probably failing to acknowledge that home building is a conservative, market-driven business, to which change comes very slowly, just as slowly as any change comes to society as a whole. I do not demonize homebuilders. Their goal is to promote urbanism only so far as it helps them build and sell houses. That is the narrow role of homebuilders in a free market economy.

Rivermark is praiseworthy for advancing certain ideas in home-building, and it is encouraging that the middle-of-the-road homebuilders are thinking in progressive ways because it is the middle-of-the-roaders who ultimately build our cities. We cannot complain entirely when we leave critical decisions in city making largely up to developers whose goals are only tangential to urban design. The making of neighborhoods that can grow into delightful places is the result of a larger public discussion, and in changing the tastes of the housing "consumer."

For the time being, Rivermark is the better mousetrap. But as the boring housing nerd at the Christmas party will tell you, sometimes better is not good enough.