Addition or ADU: Which One Makes Sense for Your Property?
Both add square footage. They behave very differently for permits, cost, and resale. Here is how I help clients decide.
A client last month asked whether to add a 400 sq ft room or build a 400 sq ft detached ADU. Same square footage, very different projects. Here is how I walk through the decision.
When an addition wins
Pick an addition when the space is for your family long term, the lot is tight, and you want the house to function as one home. Additions tie in with existing HVAC and plumbing more easily.
When an ADU wins
Pick an ADU when you want rental income, need a separate living space for aging parents or adult kids, or want resale flexibility. ADUs are also friendlier under current state law.
Cost comparison
Additions run 350 to 550 per square foot. ADUs run 275 to 425. ADUs are often cheaper per square foot because they are independent and do not require tying into existing systems.
Permit comparison
ADUs have protected review timelines under state law. Additions follow standard plan check with no timing mandate.
For a deeper look at ADU permits in SB County, read our post on the ADU permit process.
Home Additions
Room additions, second stories, and bump outs that look like they were always there.
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