Why do you need to estimate before starting any attached ADU construction
Attached ADU Construction Cost Calculator
How To Use Attached ADU Construction Cost Calculator Step By Step
This section is written so users can follow it inside the blog post while using the attached ADU construction cost calculator.
Step 1: Enter Your ADU Size
Start by adding your best estimate of square footage. If you’re not sure, use these rough guides:
- Studio: 350–500 sf
- 1 bedroom: 500–750 sf
- 2 bedroom: 750–1,000+ sf
Even if you guess, it helps the calculator produce a practical cost range.
Step 2: Choose the Finish Level
Pick Basic, Mid-Range, or High-End based on your goals. If you are building for long-term living, Mid-Range often matches what most homeowners choose.
If you plan to rent it out and want to control cost, Basic is a clean starting point.
Step 3: Select Your California Region
Choose the region that matches your project location. This adjusts the estimate for local California pricing patterns.
Step 4: Select the Attachment Type
Pick the option closest to your plan. This is one of the fastest ways to make the estimate feel “real” because structure and complexity affect labor.
Step 5: Set Bedrooms and Main Home Age
Select bedrooms and the main home’s age range. These inputs help the calculator reflect how hard it may be to connect systems and meet code.
Step 6: Choose Roof Integration
Select the roof tie-in complexity. If you’re not sure, choose Simple Tie-In first. You can always compare results by changing only this field.
Step 7: Optional Custom Labor Rate and Material Markup
If you have contractor feedback or local pricing, you can customize:
- Labor rate ($/hr)
- Material markup (%)
Leave them blank if you want the California average assumptions.
Step 8: Open Advanced Options (Only If Needed)
Advanced inputs are placed later to keep the main flow simple. Use them if you know your site has added challenges like tight access, major utility upgrades, or you want a bigger contingency.
Step 9: Click Calculate Attached ADU Cost
Once you calculate, review the total range and the breakdown. Then run “what-if” tests: change one variable at a time so you understand what drives cost.