Short answer
Home additions get expensive when new structure has to tie into old structure. Foundation, roof, engineering, utilities, and occupied-home protection matter.
Cost drivers
What moves the number.
Tie-ins drive cost
Foundation, roof, exterior wall, structural, HVAC, plumbing, and electrical tie-ins make additions more complex than raw square footage suggests.
Second story is a different animal
Stairs, seismic work, temporary protection, and roof reconstruction can push a second-story addition into custom-home territory.
Get structure reviewed early
A cheap concept that ignores engineering is not a bargain. It is deferred pain.
Planning ranges
Use ranges until scope is real.
| Line item | Planning range | Why it moves |
|---|---|---|
| Simple addition | $330-$500+/sq ft | Usually lower structural and utility disruption. |
| Complex addition | $500-$850+/sq ft | Second story, kitchen/bath scope, seismic, or tight access. |
| Soft costs | 9%-18%+ | Architecture, engineering, title 24, permits, and plan check. |
FAQ
Fast answers.
Is this a contractor bid?
No. It is a planning estimate that helps you understand the likely budget range before drawings, engineering, city review, and contractor pricing.
Why is the range wide?
Early construction budgets should be ranges because site conditions, structural scope, utility work, finishes, permits, and contractor availability can move the number fast.
Do I need to enter contact information?
No. The estimate appears first. Contact information is only for saving the estimate or asking for a local review.
