Use these Maryland ADU planning tools before you commit to design, financing, prefab deposits or construction. Each tool answers a different feasibility question and shows where local verification is still required.
Start with the question you need to answer
1. How large could my ADU be?
Use the Maryland 75% ADU Size Calculator to compare Maryland Planning’s recommended measurement method with verified county-specific methods such as Howard County’s exterior-footprint rule.
2. Will septic or private well conditions complicate the project?
Use the Septic & Well Readiness Checker to identify whether records review, Health Department review, reserve-area verification or more complex site work may be needed.
3. What should I budget?
Use the Maryland ADU Cost Calculator & Bid Comparison Tool to build an editable planning budget, download a CSV and compare the scope completeness of up to three contractor bids.
4. How does an ADU compare with assisted living for an aging parent?
Use the Maryland ADU vs. Assisted Living Cost Planner to compare cash outlay using your own ADU budget, in-home care needs and a verified Maryland assisted-living benchmark. It keeps housing and care costs separate instead of assuming an ADU replaces care services.
5. What are my current county rules?
Use the Maryland County ADU Rules Tracker to separate enacted local rules from transition measures and legacy code.
Rule-friction checklist: what can make a permitted ADU harder to execute?
A local ordinance can technically allow ADUs while still adding cost, delay or uncertainty. Before spending on plans, use the County Rules Tracker and local code to answer these questions:
- Approval path: Is the ADU administrative/by-right when standards are met, or does it require a special exception, hearing or other discretionary approval?
- Parking: Is additional off-street parking required, and are there waivers or location-based exceptions?
- Owner occupancy: Must the property owner live in the main dwelling or ADU?
- Utilities: Are separate water/sewer taps, meters or connection fees required, or can services be shared?
- Lot and dimensional limits: Do minimum lot size, setbacks, lot coverage, height or another local cap reduce the practical buildable area?
- Rental use: Are long-term rental, short-term rental, licensing or occupancy rules relevant to how you plan to use the ADU?
Why we track these: a Maryland Department of Planning-hosted 2021 Smart Growth webinar by land-use attorney/planner Donald Elliott identified parking, discretionary approval and new utility/tap requirements among the recurring forms of ADU regulatory friction seen around the country. The webinar is expert commentary, not Maryland law; our county pages use current statutes, ordinances and official local records for actual requirements. View the webinar background.
These are planning tools, not permit determinations, engineering calculations, lender approvals or contractor recommendations. Verify property-specific requirements with the relevant local authority before acting.