How to finance an ADU?

[David Yee]

Hello. My primary residence has a large backyard that can easily fit an ADU. Based on some online calculators I used, I can probably get a HELOC of about $150k in 3 years time. It could cost up to $450k to build the ADU. What options do I have to get the necessary financing to fund the rest of the construction? I live in Poway, Ca which is part of San Diego county.

Thank you!