HELOCs are not available because they are residential loans guaranteed by individuals and what you seek is a type of commercial loan or credit line which are available to seasoned companies with proven financial track record.

In San Diego at the current rates for a purchase loan (which has better rates than an ADU additions) at high LTV, I show 1% does not cash flow on a sustained basis.  

Quote from @Juan Ruben Cortez: I believe the funding fee is 0.5% of the remaining loan balance, plus maybe another $500 - $1,000 in lender fees. 

Quote from @Noah Bacon: Hi Robert,Stessa and RentRedi provide different benefits and features.

I bought a 3/2.00 home in Tampa, FL in April 2022 for $245k at a 4.75% interest rate, I still owe $210K on the loan, my RE agent thinks it could sell for $280k ($70k in equity).

You can't decide which one to choose based on the minimal information you provided.

I can say from having taught classes on these loans that your contractor will be the biggest key to your success.

Be sure to check out the free tools BP provides to help analyze deals you may have and also market insights.

There are mortgage recast calculators online or you can reach out to your lender.P+I payment will go from 2155 to ~1800 given the numbers you provided.

I know many landlords set a credit score threshold around 580-600 for Section 8 tenants since the program provides a rental guarantee.