Accessory Dwelling in Kentfield, CA – Marin County Planning and Building Code


We recently started a project on a beautiful mid century modern home in Kentfield, CA.   The owner is a professional designer and leader in the sustainability movement, so this will be a great one!

Before the fun of design and building begins, an initial planning report was written up by our design team and the findings were quite favorable.  Marin County gets a bad rep as their rules are actually right in line with most of the other cities around California.

Here are our findings for an accessory dwelling in Kentfield:

  • This house is in a R-1 or Residential Single Family zone.
  • The lot is about half an acre so lot coverage is not an issue
  • The maximum floor area ratio or “F.A.R.” is 30%.
  • The maximum size of an accessory dwelling is 750 square feet.
  • There is a very clear distinction between Building Area and Floor Area.  Building Area includes garages while Floor Area does not.
  • There is a 15′ height limit
  • The accessory dwelling can have a loft or mezzanine
  • The front setback is 25′
  • The side setback is 10
  • The rear setback is 10% of lot depth
  • Parking requirements are a bit tricky: There are two required for the main home and one per bedroom in the accessory dwelling. So three are expected. Kevin discussed a parking plan with John in land development and they can approve three spaces in the current driveway as long as the spaces are 8’6″ x 18’0″ minimum

Once we get into the permitting there will be some in depth review that might drive a Texan or New Hampshire Libertarian mad but it’s part of the deal for most projects in coastal California.

If the main home was under 4,000 square feet this will require a Major Design Review. This takes approximately 3 months to get approved. There is a provision to apply to encroach into a setback within the major design review so that may work out in the client’s favor. There is a slim chance that we can measure the home and confirm that the Floor Area of the home is under 4,000. A variance would be a very difficult process to pursue but that should be irrelevant. Planning approval is taking three months and building plan check is taking two months, so permitting time is a minimum of five months.

Permitting costs were quoted to be:

Planning/Zoning Permits:  Minor design review $1,440 and a major design review $3,500.  We anticipate the major design review.

Affordable Housing Fee:  There is an affordable housing fee of $10 per square foot or $10 x 500 sq ft for $5,000.

Building Permit Fees:  Estimate at $8,000.

Road Impact Fee: 1% of construction value so $1,500.

There is a school fee and a fire department permit fee that are both TBD.

The fees will be approximately $25,000 when all said and done.  A tough tax to pay but when you consider this is a new home in Marin that could rent for $3,000/month it’s a bit easier to stomach.

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