How accurate are the County Assessor’s Records on your San Carlos home?

October 7, 2009

If I asked you to describe the basic specifications of your home (square footage, number of bedrooms and bathrooms, and lot size) could you do it?  Sure you could.  But the real question here is this: Would your answer be correct?   How would you know?  It all depends on where you get your information.  Let's take a look at where most people get information about their homes…

The County Assessor's Records.

Probably the most common source of information about our homes resides in the San Mateo County Assessor's Records.   When a home is listed on the Multiple Listing Service, the specifications of the home are most often taken from the Assessor's records.  Why?  Convenience and impartiality.  Generally speaking, when the County Assessor's data is used as the source of specifications,  the seller (and their agent) can't be held liable if the Assessor's data turns out to be inaccurate (disclaimer time:  I'm not a lawyer, nor do I play one on TV.  So take this as a general guideline.  Be sure to consult a real estate attorney if you have additional questions on this. )   So if the Assessor's records are being used as the default, how accurate are they?

“Reliable, but not guaranteed accurate.”

Over time, the real estate industry's dependence on the County Assessor's Records has led to a mythical notion that these records are somehow the “legal” or “official” description of the home, and therefore they're 100% accurate.   In reality, they're neither.  The Assessor's Office will be the first to tell you that the specifications they keep on our homes are for taxation purposes only.   From those three words,  you can safely assume that they aren't going to fret over whether the square footage of your home is accurate down to the square foot.    So this means there may be a discrepancy between what the County believes your home is, and what you do.

Where do most of the discrepancies show up?  Bedroom/bathroom count, and square footage of the home.    To understand why this happens, you first need to know how the County gets information on your home.   In incorporated areas like San Carlos, they rely heavily on outside sources — primarily the City building department.     As a matter of course, the County gets copied on permits where work is completed for home modifications, so at least in theory they're kept “in the loop.”    But if there's a mistake in the translation of the permit, OR the homeowner had work done without getting required permits, you can see how disconnects can happen.

Buyer Beware.

When you're looking at a home on the MLS,  how can you tell if the seller's specs (square footage and bedroom/bath count) actually correlate with what the County has on file?  The answer is that you can't — short of running down to the County office and pulling the record on the home, it's not readily obvious to you.    The public version of the MLS doesn't quote the source of the information.  However, the agent-version of the MLS does contain this data, and any Realtor worth his or her salt should be automatically cross-checking this information to confirm the source of the information.   On top of that, the seller (and their agent) are required to be forthcoming in their disclosure documents if they're stating the home is different from what is recorded in the County records.  Does it always happen?  No, and that's why you need to be aware as a buyer and ask that question of your agent.

Why does it matter?

Why should you care about a discrepancy in the County records?  There are two key reasons why you should:

  1. Value.  Square footage and bedroom/bath count have a direct correlation on the value of a home, even if the square footage is equal.  For example, a 4BR/3BA home is generally worth more than a 3BR/2BA house of the same size.   Bedroom count is especially critical, and it's important to remember this:  A bedroom isn't a bedroom unless the City/County says it is.   The seller cannot randomly refer to any room in the home as a “bedroom” — in San Carlos there are very specific guidelines on what is required for a room to be recognized as a bedroom.
  2. Liability:  As we discussed earlier, discrepancies in the specs may arise due to un-permitted work that was done to the home.  The buyer generally takes on that liability when they purchase the home, so it's important to fully understand what you're inheriting.

Remember that you may be a buyer today, but at some point in the future you'll be a seller — and it's important for you to know up front how you'll be able to represent your home.

How to find out.

It's not the end of the world if the seller's claims don't match the County records.  Figuring out why is simply a matter of a little detective work.  The records that are kept at the City and County level are all accessible to the public.   Regardless of whether you're a buyer or a seller, it's not a bad idea to check both — especially if the home has been modified.    Ultimately, if you're going to ask for changes to be made to the records, allow yourself plenty of time.


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  1. Michael on October 7, 2009 at 1:51 pm

    According to county records, our home is missing a half bath and over 400 square feet; all original to the house when it was built in 1985; no other structure was here previous to it being built.

    Our former home in San Mateo, according to county records, had a lot that was over 1,100 square feet larger than it really was, also original to the home.

    It is a mystery how such basic information that so many rely upon is so often wrong.

  2. iamnoone on October 7, 2009 at 4:59 pm

    What about areas below grade? I was told that Fannie Mae/County Assessor appraisal guidelines do not allow below grade areas to be counted in the square footage/bedroom count. The definition of below grade includes any area with any part of any wall below grade.

  3. Chuck on October 7, 2009 at 5:03 pm

    Great question, and one that you should probably pose to the City Planning Dept in San Carlos. I know they don’t count basements as part of the square footage, but I don’t know about the rules for rooms partially below grade.

  4. Sharon on October 7, 2009 at 5:35 pm

    Just a general question on unpermitted work. Five years ago, we spent $50k on some remodeling. We never would have been able to afford a modest kitchen and bathroom remodel with permits. Even with home equity financing, we were determined not to remodel with debt financing. We either had the money in savings or not.
    What is your general philosophy regarding remodels done without permits from the sellers persepective as well as from an agent?

  5. Chuck on October 7, 2009 at 6:16 pm

    Hi Sharon,

    Thanks for your question — first of all, I’m interested in understanding how much of a cost difference there was in your bedroom and bathroom projects both with and without permits. Was the difference solely due to the permit costs?

    To answer your question, from an agent’s perspective I generally like to see permits done where they’re required. Buyers tend to get anxious when they encounter remodel projects that were done without permits, so it puts them more at ease when they know the required permits have been obtained. Obviously there are limits to this – people generally don’t stress too much if you’ve just done cosmetic repairs such as replacing a cabinets and counter-tops.

    That being said, there’s so much work that has been done around here with permits that it’s really not that big of a deal when you go to sell it. It’s all part of living in a community where homes were originally built in the ’40’s and ’50’s.

    Thanks for your comment,


  6. Sharon on October 7, 2009 at 9:37 pm


    Using licensed contractors with permits, we got a total remodeling cost that ranged from $130K-$170K. There was no plumbing,structural or major electrical upgrade needed. I understand these construction companies carry major overhead, hence the job quote is higher.

    Using licensed solo contractor who didn’t want to hassle with the city’s inspector’s whims, we got two nice bathrooms and a kitchen for $50K. It won’t compete with those nice fancy houses, but it’s allowed me to send one son to grad school and a daughter to med school.

    I guess it’s a matter of perspective.

  7. Chuck on October 8, 2009 at 12:35 pm

    Wow….that’s a HUGE difference in price!

    Just expanding a bit more on the permit perspective…I think people are far less concerned about the permit status if the work that has been done doesn’t change the overall specs of the home (square footage, bedroom/bathroom count.) I don’t know if your remodel project changed the specs of your home, but many projects that I come across were simply an updating of an older home — kitchens, bathrooms, bedrooms. Buyers in general are far less concerned about permit status in this situation. The issue comes into play much more when the seller is claiming additional bedrooms and square footage aren’t in the Assessor’s records.

    Thanks for sharing your info!


  8. Jane on February 4, 2010 at 11:54 pm

    Hi Chuck,

    I’m about to undergo a major remodeling project and our surveyor’s measurements indicate that our house is approx 995 sf. However, the county assessor lists our square foot as 1290. Any thoughts on why the assessor actually has our square foot as larger than it really is?

  9. Chuck Gillooley on February 5, 2010 at 12:07 am

    Hi Jane,

    Wow.. that’s certainly a rarity. Usually it’s the other way around — the recorded square feet is usually smaller. Since the County often pulls their data from the respective City records, you might want to go down to the San Carlos Building Department and ask to see what permits or plans (if any) they have recorded on your home. That might be the source of the discrepancy. Other than that, just be sure your surveyor did indeed measure each room and didn’t miss anything. I can also look at the tax records online if you wish — just send me a private email with your address.

    I’d love to know what you find out.

    Thanks for writing in..


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