Maryland's ADU market is shaped by its proximity to Washington DC — Montgomery County and Prince George's County function effectively as DC suburbs with some of the highest housing costs on the East Coast. The state passed ADU preemption legislation in 2022, though implementation has been slower than in western states. Baltimore's urban core has an established accessory apartment tradition, and the state's diverse geography creates distinct markets from the DC suburbs to the Eastern Shore.
| Region / City | Base Cost / sqft | Permit Fees (est.) | Market |
|---|---|---|---|
| Montgomery County (close-in) | $300 – $420 | $22,000 – $40,000 | Very High |
| Prince George's County | $240 – $320 | $16,000 – $28,000 | High |
| Howard County | $260 – $340 | $18,000 – $30,000 | High |
| Baltimore City | $185 – $260 | $10,000 – $18,000 | Moderate |
| Baltimore County | $200 – $275 | $12,000 – $22,000 | Moderate-High |
| Annapolis / Anne Arundel | $220 – $295 | $14,000 – $24,000 | Moderate-High |
| Western / Eastern Shore MD | $160 – $230 | $8,000 – $15,000 | Standard |
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Calculate My Maryland ADU Cost →Montgomery County's close-in suburbs — Chevy Chase, Silver Spring, Takoma Park — have mature tree-lined lots well-suited for detached ADU construction. A 600 sqft detached ADU in close-in Montgomery County typically costs $230,000–$360,000. ADUs near Metro Red Line stations command $1,800–$3,000/month. Montgomery County has a streamlined ADU approval process for lots meeting standard criteria.
Baltimore's rowhouse and semi-detached housing stock is well-suited for basement apartment conversion. In Baltimore City, basement conversions typically cost $70,000–$150,000 — among the most affordable ADU options on the East Coast. Baltimore's below-market housing costs and improving neighborhoods in areas like Hampden, Remington, and Charles Village make basement ADU investment increasingly attractive.
Maryland's suburban housing stock has abundant attached garages. Conversion costs typically run $70,000–$150,000 depending on county and finish level. Montgomery County's stringent design standards add cost compared to other Maryland counties but also ensure quality that supports premium rents.
Maryland's large immigrant and multi-generational household population drives strong demand for in-law suites. Attached ADU additions typically cost $110,000–$220,000 in Maryland metros. Prince George's County and Montgomery County both have significant populations seeking multi-generational housing arrangements.
| Fee Type | Range | Notes |
|---|---|---|
| Building Permit | $4,000 – $10,000 | Based on project valuation |
| Forest Conservation Plan | $1,500 – $4,000 | Required in many MD counties |
| Stormwater Management | $2,000 – $5,000 | Required for impervious surface additions |
| Utility Connection | $4,000 – $12,000 | Sewer, water, electrical |
| Total Typical Range | $15,000 – $35,000 | Montgomery County; lower elsewhere |
Montgomery County has its own comprehensive ADU ordinance with specific design standards, setback requirements, and size limits that go beyond state minimums. The county offers a dedicated ADU review process and has staff specifically assigned to ADU applications. Pre-application meetings are strongly recommended — Montgomery County planning staff can identify potential issues before you invest in full architectural drawings.
Yes. Baltimore City allows ADUs in most residential zones under its Zoning Code. The city has an established tradition of basement apartments in its rowhouse neighborhoods. Baltimore's permit process can be slower than suburban counties — budget 4–6 months for permit review. Baltimore's relatively low housing costs make ADU ROI timelines longer than in the DC suburbs, but the city's ongoing revitalization creates improving rental market conditions.
State law prohibits localities from imposing owner-occupancy requirements that effectively prohibit ADUs. However, some Maryland counties had owner-occupancy requirements grandfathered before the 2022 law — check your specific county's current ordinance. Montgomery County eliminated its owner-occupancy requirement in 2021.
Properties within 1,000 feet of tidal waters (the Critical Area) in Maryland face additional development restrictions including limited impervious surface coverage. If your property is in the Critical Area, ADU construction may be restricted or require mitigation. Check your property's Critical Area classification with your county planning department before proceeding.
Maryland requires home improvement contractors to be licensed by the Maryland Home Improvement Commission (MHIC). Verify any contractor's MHIC license at mhic.maryland.gov before hiring. In Montgomery County, additionally verify that the contractor is registered with Montgomery County's Department of Permitting Services.
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