If you own a 1-to-4 family on Staten Island or in Brooklyn and you are looking at adding an Accessory Dwelling Unit (ADU) — whether a basement conversion, a garage conversion, or a backyard cottage — the financing landscape in 2026 looks different than it did even 18 months ago. Three programs stack, two cancel each other out, and one specific loan product is doing 80% of the actual closed deals my clients have used. Here is the full picture, in plain English, with the numbers that matter.
The five ways Staten Island and Brooklyn ADUs get financed in 2026
Every funded ADU on Staten Island or in Brooklyn in 2026 uses one or some combination of these five sources: a HomeStyle or 203(k) renovation mortgage, a HELOC against existing home equity, a cash-out refinance, the NYC Plus One ADU pilot program, or a private hard-money construction loan. Picking the right combination depends on three things — how much equity you have today, whether your unit will be income-generating, and how fast you need to close.
1. HomeStyle Renovation Mortgage (Fannie Mae)
This is the workhorse. A HomeStyle mortgage rolls the cost of the ADU build into the purchase or refinance, based on the after-renovation appraised value. So if your home is worth $750,000 today, you add a $150,000 legal basement ADU, and the new appraisal comes in at $920,000, you can borrow against that higher value. On a 2-family Staten Island house, projected ADU rental income can also count toward your DTI ratio — which means a tenant can effectively help you qualify for a bigger loan.
2. FHA 203(k) Standard or Limited
For first-time buyers and lower down-payment situations, the FHA 203(k) is a strong alternative to HomeStyle. The 203(k) Standard handles ADU builds up to roughly $250,000 in renovation; the Limited variant caps at $35,000 and is for cosmetic / non-structural work only. The trade-off versus HomeStyle: FHA mortgage insurance lasts the life of the loan, but the down payment requirement is 3.5%.
3. NYC Plus One ADU Program
The Plus One ADU pilot offers up to $395,000 in construction funding for one-unit homeowners adding a second legal unit. Eligibility is concentrated in specific zip codes (Staten Island’s South Shore and parts of North Brooklyn are in scope), and you must be the owner-occupant with household income at or below 165% of Area Median Income. Plus One funds cannot be stacked with HomeStyle — but they can be stacked with a HELOC for finish-out work.
4. HELOC against existing equity
The fastest path. If you have 30%+ equity, a HELOC from a Staten Island credit union (Northfield Bank, NYU FCU, Municipal CU) typically closes in 21-30 days with variable rates currently in the 8.5-9.5% range. Best for partial builds where you want to start work this quarter and refinance later.
5. Private hard-money construction loans
Last-resort speed money. 10-13% rates, 6-12 month terms, interest-only payments. Worth it only when you have a confirmed take-out exit (a permanent loan lined up after the build) and a project that bumps the appraised value by at least 1.7x the loan amount.
How to know which one is right for your specific situation
The fastest way to sort this out: run your numbers through the NYC ADU Income Calculator. Put in your address, the type of ADU you are considering, and the calculator returns projected monthly rent, after-renovation value lift, and breakeven timeline. Once you have that monthly rent number, you can run it through any of the five financing options above and see which one gives you the lowest monthly out-of-pocket cost.
The three financing mistakes I see most often
- Trying to stack HomeStyle and Plus One. Plus One funds are treated as a grant against project cost, which reduces the financeable amount on HomeStyle. You almost always come out worse using both than picking one.
- Forgetting that ADU rental income only counts at 75%. Whatever your projected rent is, lenders haircut it to 75% for vacancy / repairs in their DTI calculation. Build that into your model from day one.
- Closing the HELOC before getting the building permit. If your DOB filing is delayed (the median for an ADU in Staten Island is currently 4-7 months), HELOCs that funded too early get re-underwritten and rates jump. Time the HELOC draw to permit issuance.
What this means for selling later
A legally finished, COFO’d ADU on a Staten Island 1-family typically adds $180,000-$280,000 to the sale price and shaves 12-21 days off market time. On a Brooklyn 2-family, an income-generating basement ADU pushes the buy-side underwriting from “this is at my limit” to “I can comfortably afford this” — which is the difference between a 30-day offer-to-close and a 75-day contingency dance. Either way, the ADU is the highest-ROI improvement available right now under NYC zoning.
Ready to model your specific ADU build?
Run the numbers in the ADU Income Calculator, or text me at 917-905-2541 and I will tell you within an hour whether your situation is HomeStyle-best, Plus One-best, or HELOC-best — and which Staten Island or Brooklyn contractor you should be talking to first.
