ADU vs house extension - appreciation/equity

[Rene Schmitz]

Hey -

Originally I was planning to add an extension to an existing house in San Mateo (2BD, 1BA, 820sqft). Doubling the size of the kitchen, master bedroom with en-suite bath and walk-in closet, adding approx. 700 sqft.

Required investments seem to be around 328k plus permits.

- approx. 18k design, architecture, structural engineering

- Permits (?)

- Labor, demo, foundation, rough materials etc. 260k

- Labor, finished materials 50k

Looking at ADU options prefab or stick build, we could add 500 to 700sqft for like 200k to 250k saving at least 70k in investment.

Thoughts? Especially considering future sale of property and appreciation?

Thanks!

René