Maryland ADU cost-scope guide
The headline quote is not the project budget.
A builder, modular company or kit supplier can quote one real piece of an ADU project and still leave major site, utility, permit or finishing work outside that number. The useful question is not “Is this quote cheap?” It is “Exactly what scope does this quote buy?”
The structure, kit or factory-built module.
The building plus some foundation, set or installation work.
Design, site, utilities, permits, construction, closeout and exclusions resolved.
Turn a headline quote into a scope check
This does not guess what missing work will cost. It tells you how many major cost categories are still unresolved before you compare the quote with another proposal.
Optional. The tool does not add invented allowances to this number.
Read the written proposal and mark every category that is excluded or unclear.
Where ADU budgets usually expand
These are scope layers, not universal add-on amounts. A project may need all, some or none of them.
Feasibility & design
Zoning verification, survey, architecture, engineering and agency revisions can exist outside a construction quote.
Site & foundation
Excavation, grading, drainage, stormwater, retaining, access and foundation conditions are parcel-specific.
Utilities
Water, sewer, electric service, panels, meters and trenching depend on distance, capacity and utility requirements.
Private systems
Well or septic review can create health-department, reserve-area or system-capacity work before construction proceeds.
Factory delivery
For modular projects, the factory-built unit can be only one part of the job; transport, set, foundation and on-site connections remain separate work.
Permits & review
Application fees, building permits, local approvals and correction cycles are separate from the act of drawing or building.
Allowances & finishes
Cabinet, fixture, flooring, appliance and lighting allowances can make two proposals look comparable when they are not.
Restoration & closeout
Driveway, landscaping, disturbed-area repair, punch list, final inspections and closeout can remain after the structure is standing.
What Maryland’s official process tells us
The strongest evidence for cost escalation is not a statewide dollar average. It is the amount of project work that exists outside a headline structure price.
Modular does not eliminate site work
Maryland’s Building Codes Administration says modular units are factory-regulated, but local officials still oversee installation and on-site work including foundations, component assembly, utility connections and site preparation. That is why a factory price should not automatically be treated as an all-in ADU price.
Howard County requires property work
Howard County’s ADU application requires a plot plan showing size and setbacks. For a newly constructed ADU, the plan must also demonstrate adequate water conveyance so runoff does not harm neighboring properties or existing stormwater facilities.
Permitting is its own scope
Montgomery County’s residential permit process separates application/payment, plan submission, review, corrections and final fee payment. Its guidance also notes that a municipality may require additional permission. Those steps are not the same thing as a contractor’s construction scope.
Normalize every quote before comparing price
Two totals are not comparable until the scope behind them is comparable.
| Ask the bidder | What you are trying to learn |
|---|---|
| “What exactly is excluded from this total?” | Make exclusions explicit instead of assuming “turnkey” means the same thing across companies. |
| “Who pays for survey, engineering and agency revisions?” | Separate design/preconstruction scope from field construction. |
| “Does site work have a fixed scope or allowance?” | Identify whether grading, drainage, excavation or foundation surprises can become change orders. |
| “What utility distance and service assumptions are built in?” | Expose assumptions behind trenching, panels, meters and utility coordination. |
| “For modular, is freight, crane/set and foundation included?” | Distinguish factory module price from delivered/installed project scope. |
| “Which permit and government fees are included?” | Separate permit management from the actual third-party fees and approvals. |
| “What finish allowances are written into the contract?” | Find low allowances that can predictably create later upgrades. |
| “What remains after substantial completion?” | Capture restoration, punch list, final inspection and closeout work. |
Do not turn one Maryland homeowner’s $300,000 project into a statewide benchmark.
Individual ADU stories are useful for discovering where homeowners get surprised, but they are not statewide pricing data. This guide deliberately separates scope evidence from price evidence. Use written local bids and our editable budget tool for your actual project.
Primary and supporting sources
- Maryland Department of Labor — What is a Modular and Manufactured Home?
- Maryland Department of Labor — Industrialized/Modular Buildings General Description
- Maryland Department of Labor — Modular Building Site Procedure
- Howard County — ADU Application
- Montgomery County DPS — Residential Accessory Structure Permit Process
Last reviewed: September 7, 2026. Planning information only. Costs vary by property, jurisdiction, utility conditions, design and contractor scope.