Looking for an addition contractor in San Mateo, CA? Describe your project once and up to three addition contractors who work in San Mateo and San Mateo County get back to you with a quote. It's free and there is no obligation.
San Mateo is home to about 103,006 people (2024 Census Bureau estimate), a shrinking community (−2.5% since 2020). With 8,489 people per sq mi, it is a densely built-up area. Growing families here often add space instead of moving.
San Mateo at a glance
- Population (Census Bureau estimate, 2024)
- 103,006 (−2.5% since 2020)
- Rank in California
- 71st of 482 cities and towns
- Land area
- 12 sq mi
- Population density
- 8,489 people per sq mi (densely built-up)
- Type
- City (San Mateo city)
- Main county
- San Mateo County
What to check before hiring in San Mateo
- Zoning: check San Mateo's setbacks, lot coverage and height limits first.
- License and permit: in California, additions are built by licensed contractors under a permit.
- Structure: second stories need an engineer to check the existing house.
- Price drivers: size, foundation, roof tie-in, plumbing and finishes.
Useful official resources
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ICC: International Code Council
Official information and guidance.
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NAHB
Official information and guidance.
Services available in San Mateo
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Room addition
Ground-floor addition with foundation, framing, roof and finishes.
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Second-story addition
New floor over the existing house, with structural engineering.
Frequently asked questions in San Mateo
How much does an addition cost in San Mateo, CA?
It depends on size, foundation and finishes. Describe your project: contractors who serve San Mateo reply with a quote.
How long does it take?
Often a few months, plus design and permits.
Does an addition raise property taxes?
Usually, since it increases the assessed value.
Which addition contractors will contact me?
Up to three independent addition contractors who serve San Mateo and the surrounding area, chosen for the service you need. Your details are shared only with your consent.
Source: U.S. Census Bureau, Population Estimates Program (Vintage 2024) and Gazetteer Files (public domain), imported on 10/31/2026. Figures describe the incorporated place or county as published; they are shown for information only.