As we start to produce the grading plans and drainage plans in Los Angeles under the new Low Impact Development requirements, we have a much better sense of what's involved.
While wrapping my head around the increased sizing for the different mitigations, I decided to take a rough size increase for planter boxes and rain barrels. For a 1500sqft impervious improvement (mainly new roof), we are sizing approximately 1.4 times the size of what these devices used to be. Previously we would be able to use 8 55-gallon rain barrels (440 gallons total), now we need 11.5 55-gallon rain barrels (630 gallons). Previously we could use 52 square feet of raised planter boxes, now we would be required to use 75 square feet of raised planter boxes. On Single Family Residential we were already using up valuable real estate before, now we have even more constraints to work with.
The above picture shows the breakout of a remodel project with a new roof. A mix of planter boxes and rain barrels are being used. I have been told that with the new LID requirements that they will be a bit relaxed on enforcing everything as we get used to the changes. Not only were their increases, there are now new setback requirements, sizing widths, and a bunch of other things. The hardest part may be that rain barrels now require the landscaping zone to be within 25 feet of the barrels along with being 1/3 the size of the gallons being capture.
As always we look forward to the challenge and have quite a few complicated hillside projects that I am trying to hide as much of the Low Impact Design as possible. We have about 2 years before the next change occurs.