I am about to buy a house in Santa Clara, CA county that has an ADU. As of today ADU has guest house and an operational garage.

Seller is convinced that 990 sqft guest house in the ADU was built legally together with the main house under the same permit. Hence seller is counting guest house square footage in legal livable area.

However, I called county assessor and he told me that total living area for the property is only 4,180 sqft. This number exactly matches the main house and nothing else. Assessor also told me that property has 1,976 sqft garage. He said that they receive information from building department and permits while possible get seldom lost.

So, seller agent sent me this permit back from 1985, which I believe was issued at the time main house was built. He claims that this permit proves that 990 sqft guest house is permitted, because

  1. "residence" in "residence+att garage" in his opinion refers to guest house and not to the main home.
  2. seller claims that bathroom in ADU shows up on blueprints. And there would not be sole bathroom without guesthouse.


However, I am still unconvinced that guest house was introduced under this permit, because:

  1. "residence" on this permit could actually still refer to the main home.
  2. assessor does not have any information about this guest house at all.
  3. it feels strange that guest house was introduced together with the main house but assessor did not know anything about living area beyond the 4,180 sqft.
  4. if guest house is permitted then on this permit I expected to see number ~990 sq ft. OR
  5. if I would subtract garage size (1,976 sqft as per assessor) from what I believe is the total ADU size (2,683 sqft), then I am left with only 707 sqft. So how could 990 sqft guest house be squeezed in a 707 sqft area?

How can I make sure that guest house is permitted? Does this permit in any way prove whether guest house was built with permit?

Update #1: Saw blueprints and it clearly shows that what they call as "Guest house" is actually labeled as "Work shop". If my understanding is correct, then Workshop does not count towards "legal livable area", but yet they still included it.

  • 1
    Call the county and ask them providing the information you just provided, note get ready for a tax hike once they realize it is not being taxed.
    – Ed Beal
    Sep 1, 2020 at 7:09
  • 2
    Perhaps I'm reading it wrong but I don't see anything about an ADU listed on the permit. There seem to be two parts, "Residence + ATT Garage" and "Garage + Work, Shop, Truck Storage". I'd interpret that as a detached garage, not a dwelling unit. That part may have been converted into a dwelling unit at some later time but this permit doesn't show it. So that conversion and use is likely unpermitted. You might consult with a lawyer familiar with real estate before you spend your money.
    – jwh20
    Sep 1, 2020 at 9:56
  • 2
    Why not go to the planning department and request a copy of the blueprint. The permits would not have been issued without the drawings. Also seller, claims the ADU is on the plan, so ask the seller for the plan showing the ADU. Sep 1, 2020 at 13:50
  • @EdBeal They'll get a tax hike anyway due to Prop 13. Sep 1, 2020 at 15:47
  • @Harper-ReinstateMonica that is not unconditionally true. See escape clauses based on relative selling price of sold house if buyer is selling & buying, and/or if buyer is > 65 Sep 1, 2020 at 17:43

2 Answers 2


Very easy to resolve. Have seller put in writing that the ADU was legally permitted when built. He has put you on notice with "seller is 'convinced' that it was legally built." If you accept that statement, you are making the purchase "as is" based on what he believes, not factual evidence.

Only if he puts it in writing that the ADU is legally built would he bear responsibility for misleading you if you later have an issue with the "ADU".

Ways to validate if ADU was built with a permit.

Go to the planning department and request a copy of the blueprint. The permits would not have been issued without the drawings. Also seller, claims the ADU is on the plan, so ask the seller for the plan showing the ADU.

Edited based on additional information:

The "guest house" was originally built as a "workshop". Later converted into livable space, “ADU”, conversion most likely done without a permit. So your underlying questions has been answer.

Per your added comment, “If my understanding is correct, then Workshop does not count towards "legal livable area", but yet they still included it.”.

I do not believe there is a California law that regulates how a home's square footage must be calculated. Livable space needs to meet certain requirements, i.e., heat, ceiling height, etc.”, The bottom line is you are purchasing the “ADU” feature “As Is”. Whether you believe the seller should include it as part of the "livable" space is your opinion. Even if the seller removes the footage as part of the livable space, the price would still be the same.

  • Indeed blueprint is the document to prove legality of "guest house". I just saw it and it clearly indicates that what they call as "guest house" is actually "work shop". I believe "Work Shop" should not count towards listing's "legal livable area" even if it visually appears like a bedroom with kitchen and bathroom.... Sep 2, 2020 at 2:58

This seems to be more of a legal problem than a "DIY" problem. My advice would be to have your offer to purchase contingent on seller providing clear and unassailable proof that the converted garage is fully permitted - whether from historic records or by going thru a new permitting request.
And, as comments say, get yourself an attorney experienced in real estate law to make sure you do not get financially committed to anything unapproved.

My opinion is that any real estate agent who failed to get this cleaned up before listing the property in the first place should lose his licence (or at the very least specifically state in the listing that the out- building in question may not be legal to occupy).

  • The seller in disclosure stated "guest house remodeled without permits". After I removed all contingencies seller secretly amended disclosure to "guest house remodeled and built without permits" and asked me to acknowledge it with rest of documents. From my position this is bait&switch. From their position they think they properly disclosed unpermitted work even if guest house was included in legal living area on the listing. I guess the fact that they tried to pull a quick one on me by showing main house permit as proof for legality of guest house actually work against them. Sep 2, 2020 at 22:19
  • Will get attorney, but wondering if it is acceptable in CA to include unpermitted living area in listing. Or if it has to match tax records with county. Sep 2, 2020 at 22:21
  • These are new questions subject to debate and Discussion. You should ask these new questions in legal. Seller has now provided a "Full Disclosure", You are getting hung up on "livable space". As stated before, the seller has set his price. Just for ref, a Palo Alto condemned property, "900 sf", sold for >$4m a few years back. Sep 3, 2020 at 13:20

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