San Marin Apartments

Kaufman and Broad Inc. wanted to construct thirty eight-unit apartment buildings for eventual sale to an investor. The site was located in a rapidly growing suburban community in the northern section of Marin County, close to the City of San Francisco. The site had been previously zoned for two hundred and forty units. However, the city had reserved approval rights both for plan and density prior to construction and had indicated that a portion of the land was unbuildable because of unstable soil on the hillside. The city felt that substantial grading would be unacceptable. Also, the city required that view corridors to the top of the hill from the street at its base and adjacent to the site be preserved. The city zoning, resulting in a total of 240 units, was based upon a gross density of 12 units per acre. If the net density substantially exceeded that figure due to leaving the unbuildable land in open space, the City would insist on a reduction in the 12-unit/acre densities. Two other planning firms retained by Kaufman and Broad, Inc. to develop a site plan consistent with city and community requirements failed and the decision was made to use the CARLA process.

A geophysical survey utilizing seismic resistivity ground testing was used to analyze the homogeneity of the geological formation of the upper part of the site to determine what parts, if any, were unbuildable. The results of this procedure indicated to the city that geological mapping by the U.S. Department of Mines as applied to the site was not accurate. The computerized drainage analysis and slope analysis indicated that the flat land at the base of the hill would not drain satisfactorily unless fill were placed in this area. Information from the computerized slope analysis permitted the correct planning units to be selected for testing not only in terms of units required to fit existing slopes but also to suit the new slopes which would result from the filled land.

In order to test net density, the Planning Unit Analysis program tested to determine the ideal density of 232 units. Since the Massing of Alternate Configuration program can accurately predict density changes as units are rotated on natural slopes, Willis and Associates Inc. was able to identify site locations where views from units towards the adjacent creek and surrounding hills would be maximized. This process enabled the planner to preserve the view corridor from the street to the adjacent ridgeline while retaining optimum development density.

Grading proposals by the prior two planners were rejected by the city due to lack of detailed substantiating data. The computerized cut and fill analysis enabled the planner to reduce earth movement by 20 per cent and provided a scaled map which caused the city to recognize that the proposed earth movement did not have excessive environmental impact.

In the end the San Marin Apartments consisted of 224 units of two-story rental apartments and condominiums with 11 units per acre in gross density and 14 units per acre in net density. The amenities include tennis courts, recreational center, swimming pool, and children’s play area.