At an open house Thursday for Plan Santa Barbara, city planning staff helped curious locals navigate the massive General Plan and environmental impact report documents.

The housing and land-use elements are the only ones fully available in draft form, as is the entire EIR and associated maps. Thursday’s open house was held at the Santa Barbara Central Library’s Faulkner Gallery.

There are 17 principal land-use and zoning change areas within the city, as well as a new recommended average residential density for multifamily, mixed-use, commercial and industrial designations, which is calculated by the number of average size units that can fit into a volume of space.

So, the smaller the average unit size, the greater the density.

For each area, the target unit size is about 1,000 square feet, enough to accommodate two bedrooms — the most highly demanded unit type in 2009. The purpose is to encourage smaller, affordable units while allowing flexibility for larger units, which helps subsidize the cost of the smaller units, according to the draft land-use element.

In a medium-high density residential area, densities range from 15 to 25 dwelling units per acre, depending on unit size. A high-density residential area is recommended to have a range of 27 to 34 dwelling units per acre.

The EIR was put together by the local office of AMEC Earth and Environmental Inc. and offers four growth alternatives to consider.

There are trade-offs with each alternative, planner Barbara Shelton said. The document includes comparisons between the various alternatives, which are Plan Santa Barbara’s proposed policies (through the General Plan update), keeping existing policies, lower growth and additional housing.

The existing policies and lower-growth alternatives “partially” meet the project’s environmental objectives, while the additional growth model meets “all” of them, according to the EIR draft summary.

Considering only residential growth to 2030 for each of these alternatives, Plan Santa Barbara and the “no project” existing policy option expect 2,795 net new homes within the city, and 403 within the city’s sphere of influence. The draft EIR assumes 2,000 new homes for the lower-growth alternative, and 4,360 for the additional housing option.

For nonresidential growth to 2030, policy limits assume 2 million net new square feet within the city for Plan Santa Barbara, about 2.29 million for the “no project” alternative and 1 million for the lower-growth and additional housing alternatives.

All of the documents and maps are available on the city’s Web site dedicated to the project, or in hard copy or digital form at the Planning Division office, 630 Garden St. They will also be available for review at the main library branch at 40 E. Anapamu St. and the Eastside branch at 1102 Montecito St.

Public comments will be accepted until May 17 via phone, e-mail, letter, fax, in person or at a public hearing. Hearings will be held April 28 and May 6 in the Council Chambers at City Hall, 735 Anacapa St.

— Noozhawk staff writer Giana Magnoli can be reached at gmagnoli@noozhawk.com.