ADU / Granny Flat Build Cost Estimator
Formula
Total Cost = Construction + Permits + Design + Utilities + Landscaping | Cap Rate = (Annual Net Income / Build Cost) x 100 | Payback = Build Cost / Annual Net Income
Frequently Asked Questions
How much does it cost to build an ADU?
ADU costs vary widely: garage conversions ($50,000-$150,000), basement conversions ($40,000-$100,000), attached additions ($100,000-$250,000), and detached new construction ($150,000-$400,000+). The national average is roughly $150-$400 per square foot all-in.
Do ADUs increase property value?
ADUs typically increase property value by 20-30% of their construction cost, with some markets seeing even higher returns. The exact impact depends on local zoning, rental demand, and comparable sales with ADUs in your area.
What permits are needed for an ADU?
Permits required typically include building permits, electrical and plumbing permits, and sometimes separate utility connections. Many states have streamlined ADU permitting. California, Oregon, and Washington have been particularly ADU-friendly with reduced requirements and fees.
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