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Home Addition Cost Calculator for Orange County
Home additions in Orange County generally run $325 to $640 per square foot depending on type and finish level, before design, engineering and permit fees. A garage conversion is the least expensive path per square foot; a second story is the most, because the existing foundation and framing usually need reinforcement.
Your project
Common on second story additions. A structural engineer determines whether this is required.
Estimated range
$220,500 to $385,000
What makes up this range
- 500 square feet at $325 to $520 per square foot$198,250 to $317,200
- Design, engineering and plan check$5,500 to $18,000
- Permits and city fees$2,500 to $12,000
- Added bathroom$14,000 to $38,000
Worth knowing
- Second story additions usually require the existing foundation and framing to be evaluated by a structural engineer for the added load.
- Setbacks, lot coverage and height limits vary by city, and HOA architectural review adds time in planned communities.
This is an estimate for planning purposes only, not a quote. Real pricing depends on your specific site conditions, material selections and city requirements. We provide a written itemized proposal after walking the space.
Get a written quoteRead the full home additions guideAnswers
Frequently asked questions
How long does a home addition take in Orange County?
Plan on six to eighteen months from first consultation to final inspection. Design and engineering take four to twelve weeks, plan check often runs six to sixteen weeks with corrections, and construction itself is typically three to six months depending on size.
Do I need a structural engineer for an addition?
Almost always for a second story, and frequently for a single story addition that removes existing walls or spans a large opening. Cities require stamped structural calculations for anything beyond simple prescriptive framing. Budget for it in your design phase.
Is an addition or an ADU the better choice?
An addition expands your existing living space and is best when you need more room in the same household. An ADU is a separate legal dwelling with its own kitchen and entrance, which suits rental income or independent multigenerational living. ADU permitting is often faster.
What limits how big my addition can be?
Setbacks from your property lines, maximum lot coverage, floor area ratio and height limits, all set by your city zoning code. HOA architectural review adds another layer in planned communities. These are checked before design begins.
Next step
Turn your estimate into a real number
An estimate is a starting point. We walk the space, confirm what is actually involved, and send a written itemized proposal so you know exactly what you are buying.
Licensed and insured. Written scope before work begins. Weekly progress updates with photos.
What happens next: we reply the same business day, schedule a walkthrough, then send your written proposal.