How much does it cost to add arond 500 sft to the existing 1200 house in san jose, CA area?

Asked by Pankaj, 95129 Thu May 24, 2012

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Kara Blader’s answer
Kara Blader, Home Owner, Salt Lake City, UT
Tue Aug 27, 2013
I was about to give you the estimate of ours but we also put in custom doors in Miami so it would probably be way off from your bid. If you're interested, though, we used this company and they did an incredible job.
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0 votes
Steven Ornel…, Agent, Fremont, CA
Thu May 24, 2012

In 1993, I acted as "owner/general contractor" in a fairly significant remodel. We tore off the entire roof, and with the exception of three, every wall down to the subfloor; gutted all the old electrical, HVAC, galvanized plumbing, drain/waste piping etc. We then added 1700sf and doubled the home's size.

Hear me on this topic: your cost can only be accurately determined based on the level of detail provided to the contractor bidding on your job!

Commit this inverse relationship to memory: Increased detail = reduced Change Order$ (not a good idea to travel down the reverse path).

If you are going to remodel definitely use an architect! I'm extremely pleased we didn't build what I had “cost-consciously” created on my home computer at the time. Also, start collecting your remodeling ideas (with pictures) so you can communicate exactly what you want to the Architect. Both you and the Architect will be pleased you did! A fantastic tool you can use to gather your “design thoughts” is – I certainly wish I had it back in 93! Figure on at least a year to “perfect” your remodel on paper and the corresponding budget (the legwork takes time).

Use LICENSED contractors when a task crosses over your “Do-it-yourself” comfort level of difficulty.…

Make sure to obtain a permit for the work. If you do not take this step an Appraiser will not be able to provide any value for the remodel, which could "blow-up" any future sale because this can affect the Buyer's financing in addition to making the Buyer wonder if the remodel was done per building code.

From your profile I assume you live in SJ. Here’s the main permitting site for San Jose for your reference:

Visit the SJ permit office to find out what you will need to provide them based on the scope of your project. Most of these offices are quite helpful in this regard. Ask about your "Property Line Set Backs". Just about every detached residential home has "setbacks" that bound the front, back, and side foundation foot prints of any remodel to a limited space (sometimes you can actually extend this about three feet if you cantilever a bay window). There may also be “Floor Area Lot Ratios” that effectively govern this as well. Bottom line: don’t let this scare you away from your project, just confirm details via the city permit department.

Moving forward to the completion of your remodel:

When a City or other governmental jurisdiction issues a building permit, they are required to notify the Assessor's office of that new permit. Santa Clara County, and all 15 cities within the county, are required to provide the County Assessor with copies of building permits. This notification is required since the Assessor is mandated to assess value added by new construction. Typically, this will manifest itself in you receiving a “Building Questionnaire/Statement Form” to fill out and return to the Assessors' Office which asks for details of the project. This is due to the fact that new construction that adds value to the property will generate a one-time supplemental assessment representing the market value of the new improvements. In your case, only the value of the new 500sf is added to your assessed value. Your property’s “base year assessed value” (structure and land) remain unchanged.

The timing/completion of the remodel also influences this reassessment as follows:

Each year, on January 1st, County Assessors determine the market value of all residential properties (however, each property’s value, and therefore its amount of tax, is controlled by Prop 13, which you can read about below) If the construction is ongoing on the first of the year, an estimate of the value of the partially complete construction is made and entered on the next assessment roll. When construction is complete, the base year assessed value is determined and a supplemental tax bill is issued for the difference between the value as of the date construction is completed, and the value that existed on the assessment roll.

"Estimating Property Taxes in CA"…

3 votes
charles butt…, Agent, san jose, CA
Thu May 24, 2012
Thank you, for your question Pankaj:

I recommend that you get bids from at least 3 licensed contractors. The amount of money that it will cost depends on what you want in the room addition.

Recently, one of my clients asked for bids for a 400 square foot room addition for his home. The bids that he received were in the range of $35,000 to $45,000.

Because the room addition that you are asking about is 100 square feet larger than the room addition that my client was looking for, I expect that your bids will be a bit more than that. Also, in the case of my client, the roof tie in, heating and cooling system, and the type of foundation desired were significant factors in the amount of the bids. I expect those will be significant factors in the case of your room addition as well. .

Thank you,
Charles Butterfield MBA
Real Estate Broker/REALTOR
American Realty
Cell Phone: (408)509-6218
Fax: (408)269-3597
Email Address:
2 votes
Julie Wyss, Agent, Los Gatos, CA
Wed Feb 19, 2014
Kitchens and bathrooms are the most expensive additions but a basic bedroom or dining room will cost about $50K total, give or take. Consider fees for your architect, permits, school tax (about $3/sq foot for additions 500+ sq feet) and contractor fees. Also, it is always wise to budget in a little extra for unforeseen expenses that always seem to pop up during a remodel.
1 vote
It is interesting what all the little costs can be from doing a home addition. I had some friends growing up that had their house under construction for at least six years. Would the length of time the project take factor into the cost of the addition?
Flag Fri Oct 24, 2014
The complexity of the proposed space can add tot he cost. If the roof line tie ins for the new room are complicated, this can also increase the cost, as can adding in large windows, fireplaces, etc. It is always wise to meet with an architect and/or contractor for an initial consultation to fully comprehend the cost implications.
Flag Wed Feb 19, 2014
Henry Coe, , California
Fri Sep 28, 2012
San Jose is certainly a more expensive place to add on - labor is a lot higher than many parts of the country. In addition to that the biggest cost driver is how will the room be finished/used. On the low end if this 500 sqft will be a 2 car garage then possibly you can build it for $100 a square foot..depending on who you hire, how much work you do yourself. if this new space will be a big kitchen and family room then it could easily cost $200k or even $300k depending on your taste.

The big drivers for figuring cost to add on are - where you live, how much work you will do (if any) yourself, complexity (plumping, electrical, roof, foundation), the design, and the materials/workmanship you select. And of course who you hire. Remodeling contractors each quote their own way so dont be suprised to see a 10 20 or even 30% difference between quotes. I have used the remodeling cost calculators at and they have helped me get a decent first estimate at the cost to remodel a kitchen or add on a bathroom or any number of other projects. Good luck
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1 vote
saaveri_11, Home Owner, San Jose, CA
Tue Jul 22, 2014
Hello Pankaj, Were you able to add a room? Could you please share with us how much it costed you? we are looking into adding a family room of ~400sqft. Thanks Hema.
0 votes
Guy Berry, Agent, San Jose, CA
Wed Jan 22, 2014
It depends. If you add something simple like a bedroom or family room the cost will be $100 to $150 per sq foot. If the add-on includes a bathroom, it will be much more. It also depends on your existing home. How easy will it be for the contractor to "tie in" the addition to the old house? Once you decide what you want to add and the cost, you need to ask an agent how much will this add to the value of my home. i have seen too many homeowners add space to their home and because of poor design or over improvement, they may have actually lost money

I suggest you start with an architect, not a contractor, who specializes in remodeling. Call Vadim Melik 408-390-4119. I am sure he would meet you with without charging for the first meeting. Once you decide what you want, he or i can give you the name of several contractors to bid the design you both decide on.
0 votes
Sallyswman, Home Buyer, Mountain View, CA
Mon Jan 20, 2014
Hi Pankaj,

I just moved in the same neighborhood 95129, same size house as u. thinking of a 500 aft addition too, plus remodeling the whole kitchen. do yours already? How long did it take? Any property tax increase?
0 votes
Leili Mortaz, Agent, Campbell, CA
Fri Jun 14, 2013
Dear Pankaj,

The estimates vary widely depending on what kind of finish you are looking for. There are flippers in the market now who claims they can do remodeling for less than $30 dollars per square feet which is awesome. But we have not seen the finishes to see what these home look like after they are remodeled.

Get as many estimates as possible and be weary of the lowest bidders.
0 votes
Alan Zapien, , San Jose, CA
Tue Jun 11, 2013
Hello Pankaj,

You are looking at an average price of 250.00 per square foot for standard finishes because your finishes dictate your cost.
If you have any questions feel free to give me a call
AL, with Al's Remodeling 408-391-2261 or
To see some ideas you can go to my web site at

Hopefully I answer your questions

0 votes
Ben, Home Owner, San Jose, CA
Thu May 2, 2013
Do not forget to include the cost of construction plans and city plan check fees and other taxes and fees.
0 votes
John Arendsen, Agent, Leucadia, CA
Thu Jan 24, 2013
Wow! Steve, you nailed it my friend. Best answer on this thread for sure. I don't think you left any stones unturned. Can I hire you as my contractor? Good job.
0 votes
Timber Creek…, Other Pro, Los Altos, CA
Thu Jan 24, 2013
$250 per square foot is the average for this area.
0 votes
John Arendsen, Agent, Leucadia, CA
Sun May 27, 2012
All the best to your new venture. Or should we say ADVENTURE!
0 votes
Pankaj, Home Buyer, 95129
Sun May 27, 2012
Thanks all of you. we are going to bid on the property and hope to get it.
0 votes
John Arendsen, Agent, Leucadia, CA
Sat May 26, 2012
The rule of thumb is that if you're talking bathrooms and kitchens you could be looking from $250/sf and up depending on your options i.e. appliances, floor, window, cabinetry, fixtures, etc. Kitchens are the most expensive rooms in the home followed by master baths then guest baths.

Now if you're talking bedrooms, living rooms etc. you could keep it at about $150 to 200/sf because there really isn't any plumbing and very little electrical. As Steve stated you're adding on not just remodeling. When you're expanding the footprint of your home it's all new construction and you're basically starting from scratch.
0 votes
Monica Goyal…, , Cupertino, CA
Thu May 24, 2012
Hi Pankaj,

As mentioned below, there is no flat fee for such addition. Best is to get a few estimates, talk to the city for permits and code requirements. Get a contractor who does good job according to code. If you want I can refer you some good contractors. Always get multiple bids, and check references. Remember that the cheapest bid is not always your best option.

Good luck!
Monica Goyal
0 votes
Ron Thomas, Agent, Fresno, CA
Thu May 24, 2012
That can vary a lot, depending upon what you are adding; a bathroom will cost a lot more than a bedroom. Also, if you have a wood floor (with a raised foundation) it will be easier and cheaper.

Ball park; $200/sqft, but that can be way off.

Get several estimates
0 votes
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