Adding an ADU (Accessory Dwelling Unit) on your one-acre lot in Hawaiian Paradise Park is a total power move for your pocket. Since you already have the space, a detached unit could significantly boost your monthly cash flow and long-term equity.
In Hawaii County, these are often called "Ohana units." Given the rural nature of Keaau, demand for smaller, private rentals is high. You’re looking at a great way to turn underutilized land into a consistent paycheck.
| Build & Income Factors | Estimated Range |
| :--- | :--- |
| Estimated Build Cost | $150,000 - $225,000 |
| Potential Monthly Rent | $1,200 - $1,700 |
| Estimated Value Add | $90,000 - $140,000 |
| Annual Cash Flow Boost | $14,400 - $20,400 |
From a tax perspective, this is a major win. You can depreciate the new structure over 27.5 years, which helps shield that new rental income from the taxman. It’s like the government is helping you pay for the upgrade.
Just a heads-up on the logistics: since HPP relies on catchment water, you’ll likely need to expand your 10,000-gallon tank to support two households. Also, with the "extreme" flood risk noted in your report, building the ADU on post-and-pier (elevated) is a must to keep insurance costs from eating your profits.