From Curbed LA: http://la.curbed.com/archives/2008/05/mansionization.php
No love for the mcmansion today at City Hall. Homeowners crying foul showed up in impressive numbers from "negatively impacted" neighborhoods (Tarzana, Hancock Park, Studio City, Cheviot Hills) to beg the City to enact the mansionization ordinance, which would forbid homeowners from building big ugly boxes on their lots by restricting floor areas. Builders, realtors and homeowner representatives from other neighborhoods (South LA) showed up to voice opposition to the "one size fits all" approach that they say would screw up the whole city for the benefit of a few affected neighborhoods. In the end, the City Council voted unanimously to enact the Baseline Mansionization Ordinance. What it says:
"...the maximum residential floor area contained in all buildings and accessory buildings shall not exceed 25 percent of the lot area, except that when the lot is 20,000 square feet or greater, then the residential floor area shall not exceed 20 percent of the lot area or 5,000 square feet, whichever is greater."