Maryland ADU costs are difficult to compare because builders, modular companies and kit suppliers often quote different scopes. A $25,000 kit, a $180,000 factory-built module and a $275,000 turnkey contractor proposal may all describe very different amounts of work. This guide separates those scopes, shows what Maryland-area companies actually publish, and gives you two planning tools: an editable budget calculator and a contractor-bid completeness checker.
This page does not claim a single Maryland-wide average. Instead, it uses published Maryland builder ranges as context and keeps the calculator assumptions visible and editable. County rules, site conditions, utilities, septic/well constraints, finish level and project delivery method can change the final number substantially.
Last verified: September 6, 2026. Cost figures are planning references, not bids. Always compare written contractor proposals and confirm what each price includes.
Quick answer: what do Maryland ADUs cost?
| Project type | Published Maryland planning ranges we found | Important scope warning |
|---|---|---|
| Conversion / interior ADU | Makara publishes roughly $50,000–$150,000 for conversion ADUs. Karma publishes about $75,000–$150,000 for garage conversions and $80,000–$200,000 for basement conversions. | Existing-condition work, egress, insulation, HVAC, plumbing and electrical upgrades can dominate the budget. |
| Attached ADU / addition | Makara describes attached ADUs around $100,000–$200,000, with a broad $100–$250/sq-ft range. Karma publishes roughly $100,000–$250,000. | Foundation, roof tie-in, structural work and utility routing can make an addition behave more like a custom project than a simple room addition. |
| Detached site-built ADU | Makara publishes roughly $150,000–$300,000, while Karma publishes about $120,000–$300,000+ and roughly $180–$400/sq ft for DC-suburb conditions. | Site development, grading, foundation, utility runs, stormwater, access and septic/well can sit outside headline construction numbers. |
| Modular / prefab | Karma publishes roughly $150,000–$200,000 for modular ADUs. PurBilt publishes broader Maryland modular-home figures around $150,000–$400,000 installed, which are not ADU-specific. | Factory price is not the same as all-in site cost. Foundation, transport, crane/set, utility work, permits and site restoration may be separate. |
| High-end custom | Makara says larger/high-finish ADUs can exceed $300,000. Design Build Remodeling Group of Maryland says many of its ADU/guest-quarter projects range from $150,000 to $1 million depending on size and customization. | Luxury accessibility, elevators, large additions, premium finishes and major existing-home remodeling can push the project far beyond basic ADU ranges. |
What Maryland builders actually publish
Published cost pages are useful only when you read the scope behind them. The table below preserves that distinction instead of blending every number into one misleading “average.”
| Source | Published cost information | How we use it |
|---|---|---|
| Makara ADU | Overall ADUs roughly $60,000–$225,000; larger/high-end projects can exceed $300,000. Separate Maryland article says hard costs are often 70–80% and soft costs 20–30% of total. | Useful for understanding hard vs. soft cost structure and broad local project ranges. |
| Makara by type | Conversions roughly $50,000–$150,000; detached roughly $150,000–$300,000; attached often $100,000–$200,000. | Useful as a Maryland builder-published type comparison, not a guaranteed quote. |
| Karma Construction Group | Basement $80,000–$200,000; garage $75,000–$150,000; attached $100,000–$250,000; detached $120,000–$300,000+; modular $150,000–$200,000. Design/engineering/permitting roughly $8,000–$25,000; detached utility connections roughly $5,000–$15,000. | Useful for editable planning allowances and for identifying commonly separated soft/utility costs. |
| UP Craftsmen | Publishes an average Maryland ADU range around $250,000–$300,000. | Shows that turnkey local design-build pricing can sit materially above basic construction-only ranges. |
| Winthorpe Design & Build | Publishes examples around $342,000 for a 1,200-sq-ft detached ADU, $180,000 for an 800-sq-ft over-garage ADU, and $200,000 for an 800-sq-ft attached ADU; also warns site development/driveway work can add significantly. | Useful evidence that site work and project configuration can overwhelm simple $/sq-ft assumptions. |
| Maryland Department of Planning (2023 task-force presentation) | Cited about $150/sq ft as an average Maryland home-construction figure, excluding land, permit fees, excavation and other costs. | Historical context only. We do not use this older, non-ADU-specific figure as a 2026 ADU price baseline. |
Maryland ADU planning budget calculator
Build an editable planning budget
The defaults are planning allowances chosen to sit within published Maryland builder ranges. Change every field to match your project or written quotes.
Important: this calculator does not automatically add county permit fees, impact fees, sprinkler requirements, financing, temporary housing, landscaping, unusual grading, rock excavation, utility-company charges, septic upgrades or premium finishes unless you enter them. The 2026 Maryland legislative record also contains proposals that were not enacted; do not assume fee exemptions from proposed HB 1538.
The costs most likely to disappear from a headline price
A bid can look inexpensive because the contractor is pricing a narrower scope. Before comparing totals, identify whether each proposal includes the same work.
| Cost bucket | What to look for in the proposal | Why it matters |
|---|---|---|
| Survey / site plan | Boundary/topographic survey, existing conditions, setbacks, easements and recorded constraints. | A missing survey can delay zoning feasibility and redesign the footprint later. |
| Architecture / engineering | Architectural drawings, structural, civil, energy, mechanical/electrical/plumbing and revisions. | “Plans included” may not mean every discipline or agency revision is included. |
| Permits / agency fees | Who prepares applications, responds to comments and pays government/utility fees. | Permit management and permit fees are separate concepts. |
| Foundation / grading | Excavation, slab/crawlspace, retaining, export/import, drainage and stormwater. | This can be one of the largest lot-specific variables for detached units. |
| Utilities | Water, sewer, electric, gas, meters, panels, trenching and utility-company coordination. | A short utility run and a service upgrade are completely different budgets. |
| Septic / well | Health Department review, perc/site evaluation, reserve area, upgrades or separate systems. | Private utilities can change both feasibility and cost. Use our septic/well checker first. |
| Prefab delivery / crane | Freight, escorts, crane, staging, set crew, weather delays and access preparation. | A factory module price is not automatically a landed and installed price. |
| Finish allowances | Cabinets, counters, appliances, tile, plumbing fixtures, flooring and lighting allowance values. | Low allowances create predictable change orders later. |
| Site restoration | Driveway, fencing, landscaping, drainage repair and disturbed-area restoration. | Often omitted from “construction complete” proposals. |
| Closeout | Final inspections, punch list, certificates, warranties, manuals and lien releases. | The project is not finished simply because the building is standing. |
Compare up to three Maryland ADU contractor bids
Bid completeness scorecard
Enter the total price and mark what each written bid explicitly includes. A high score does not mean the contractor is better; it means the scope is easier to compare.
Use this as a question generator. Read the exclusions, allowances, payment schedule, change-order language, warranty and licensing information in the actual contract before signing.
The prefab price trap: four prices that are not interchangeable
- Kit price. A structural/material package. It may exclude foundation, labor, mechanical/electrical/plumbing, finishes and permitting.
- Factory module price. The completed or partially completed factory-built unit before site-specific work.
- Delivered/set price. Factory unit plus freight, crane or set crew—but not necessarily foundation, utilities or local permit work.
- Turnkey project price. The closest concept to all-in cost, but “turnkey” still needs a written inclusions/exclusions schedule.
Our Maryland ADU Builder & Prefab Comparison explains the state modular-approval distinction and shows why a retail brand name or kit price should never substitute for a model-by-model Maryland approval check.
Before you sign an ADU construction contract
- Compare identical scope. Normalize the bids before choosing the lowest total.
- Verify Maryland licensing and the contracting entity. Confirm the name on the contract matches the licensed entity.
- Separate allowances from fixed prices. Ask what happens if the allowance is exceeded.
- Confirm design responsibility. Identify who owns drawings, engineering revisions and permit responses.
- Write down utility assumptions. Do not leave panel upgrades, trenching, meters, sewer/water connections or septic work as verbal assumptions.
- For prefab, confirm factory vs. site scope. Delivery, crane, foundation and local site work should be explicit.
- Review payment milestones. Tie payments to defined deliverables, not vague percentages of “progress.”
- Read change-order language. Know markup, approval process and how hidden conditions are handled.
- Confirm completion standard. Final inspections, certificate/occupancy approvals, punch list, warranty documents and lien releases should be addressed.
- Keep a contingency. A tight lot, old utility service or poor soils can change the budget after design starts.
What this calculator intentionally does not automate
We do not automatically assign county multipliers, permit fees, impact fees, sprinkler costs or septic costs because those can depend on the exact property, project type, utility provider and current local rules. The calculator is designed to make assumptions visible—not hide them inside a “Maryland average.”
We also do not treat proposed legislation as enacted law. For example, Maryland HB 1538 proposed utility-fee, parking, development-fee and tax changes in 2026, but the official General Assembly record still lists the bill as in the House, not enacted. Do not build a budget around those proposed exemptions.
Primary and company-published sources
- Maryland Department of Planning — ADU program
- Maryland Department of Planning — 2023 ADU Task Force presentation
- Maryland General Assembly — HB 1538 status
- Makara ADU — Maryland ADU cost guide
- Makara ADU — cost by ADU type
- Karma Construction Group — Maryland ADU rules, permits & costs
- UP Craftsmen — Maryland ADU FAQ
- Winthorpe Design & Build — ADU examples and published costs
Before pricing a project, confirm the rule set in our Maryland ADU Guide, check your county in the County Rules Tracker, calculate the preliminary size ceiling with the 75% Size Calculator, and use the Septic & Well Readiness Checker if the property is not on public utilities. If the project will be financed rather than paid entirely from cash, compare equity and renovation-loan structures in our Maryland ADU Financing Guide.