Multifamily development requires large buildings and parking lots that are fundamentally incompatible with low impervious cover and tree preservation.
Attached garages are what allow single-family homes to be so efficient when it comes to impervious cover. The cars are parked inside the building, with living space above and around it within a door of the parking space. It’s extremely compact, and with proper minimum setbacks in the code you eliminate a lot of pavement.
The average apartment requires 2.2 parking spaces. The average house requires 2.5. Multiply that out by 100 units and you’ve got 220 versus 250, but by having garages the driveways can be shortened to only 2 have room for 2 spaces. Now you’ve got 4 spaces’ worth of parking for the impervious cover of 2, so the parking requirements for single-family are more than twice as efficient while being lower in absolute terms.
A parking space requires about 100 square feet of IC, so for a 100-unit complex you’re looking at 22,000 square feet of IC just for the parking spaces. Plus another 1500 for ADA spaces. Throw in drive aisles (which due to emergency vehicle access are just as wide as a SF road) and that number more than doubles. Also put in fire lanes, hammerheads/turnarounds, etc and you’re quickly looking at 150,000 square feet of pavement just for the parking lot, plus the extra road lanes and decel lanes required to support its traffic impact.
The thing about SF roads is that they serve multiple purposes. They provide access to the site, as well as emergency vehicle access, fire lanes, etc. They also can do storm water detention under the roads to limit the required off-site detention, so they don’t have to clear-cut as large of an area for detention and water-quality facility as an apartment complex does.
So the road, drive aisle, emergency access, fire lane, storm sewer, and more can all be combined in a lower-density area in a manner that combines to decrease the per capita environmental impact.
There’s no additional ADA requirements because every parking space has open space on at least 1 side and they’re all close enough to the houses that reserving empty parking spaces for ADA isn’t required. And half the parking spaces are inside the house. And the occupancy rate of SF houses is half-again higher than an apartment, but with fewer drivers per capita (higher percentage of multiple-child households in SF).
You can’t just look at building sizes and get the full picture of a development’s impact.