Maine ADU ROI: Long-Term Rental vs Short-Term Rental
A Place 400 sqft ADU runs $110K to $135K fully installed. As a self-managed short-term rental in Old Orchard Beach, payback runs about 5 years. As a Portland long-term rental, or a property-managed Old Orchard Beach STR, payback lands closer to 7 years with far less operator effort. The best path depends less on which market is "stronger" and more on how many operating hours you actually want to take on, and on whether your town allows the strategy you have in mind. Several Maine towns now restrict short-term rentals.
Last updated: 2026-05-02 | Author: Place Buildings Editorial Team | Reviewer: Place Buildings Project Review Team
Three-scenario payback comparison: Place 400 sqft ADU
| Metric | Portland LTR | Old Orchard Beach STR (DIY) | Old Orchard Beach STR (managed) |
|---|---|---|---|
| Installed cost | ~$130,000 | ~$120,000 | ~$120,000 |
| Annual gross revenue | ~$22,800 | ~$36,000 | ~$36,000 |
| Annual operating costs | ~$4,700 | ~$12,300 | ~$19,500 |
| Net annual income | ~$18,100 | ~$23,700 | ~$16,500 |
| Simple payback | ~7.2 years | ~5.0 years | ~7.3 years |
| Cash-on-cash return | ~14% | ~20% | ~14% |
| Operator effort | Low (a few hrs/month) | 10 to 15 hrs/wk peak season | Low (a few hrs/month) |
Old Orchard Beach STR: seasonal revenue model
| Season | Weeks | Typical ADR | Occupancy | Revenue |
|---|---|---|---|---|
| Summer (Jun to Aug) | 13 | $275 to $325 | 75% to 85% | ~$21,900 |
| Shoulder (May, Sep to Oct) | 13 | $175 to $225 | 40% to 55% | ~$8,600 |
| Off-season (Nov to Apr) | 26 | $125 to $175 | 15% to 25% | ~$5,500 |
| Annual blended | 52 | Mixed | Mixed | ~$36,000 |
What ROI Actually Means for a Maine ADU
ROI on a backyard ADU is rarely a single number. Three things drive the result: how much the building costs to install on your specific lot, how much net income it can produce, and how much operating effort you are willing to take on. The Maine wrinkle is that local short-term rental rules can quietly remove options before the math even starts, so before modeling returns, confirm what your town allows.
A Place 400 sqft ADU runs $110,000 to $135,000 fully installed in Maine, depending on site complexity. We use that anchor throughout this guide. For a deeper installed-cost breakdown by line item, see our ADU cost guide.
The Long-Term Rental Path
Long-term rental is the simpler path. A new 400 sqft ADU in Portland typically rents for $1,800 to $2,000 per month, anchored on the HUD Cumberland County Fair Market Rent for a one-bedroom plus a 10% to 25% premium for new construction. Year-round demand from Maine Medical Center, the University of Southern Maine, and the broader Portland professional workforce keeps vacancy low.
After 5% vacancy, a maintenance reserve, an insurance bump for landlord coverage, and a small property tax increase tied to the addition, a Portland LTR ADU typically nets around $18,100 per year. At a $130,000 installed cost (slightly higher than the OOB anchor below to reflect typical urban infill site work), that pencils to roughly a 7-year payback at about 14% cash-on-cash. The worked example is in the comparison table below.
Best fit: owners who want predictable monthly cash flow with minimal management overhead.
- Anchor rent on HUD Fair Market Rent for your county, then add a modest premium for new construction.
- Reserve 5% of gross for vacancy and roughly 8% of gross for ongoing maintenance.
- Budget $300 to $500 per year for a landlord insurance rider on top of homeowner coverage.
- Plan for a property tax assessment increase tied to the addition; it is real, and it shows up the year after completion.
The Short-Term Rental Path
Short-term rental is the higher-revenue path, but its viability depends almost entirely on your town. Maine collects a 9% lodging tax on stays under 28 days; the host collects it from the guest and remits it through Maine Revenue Services. The tax is a pass-through, so it does not reduce net income, but registration, monthly remittance, and recordkeeping are real administrative work.
Several Maine towns now restrict short-term rentals. The Portland registration program and zoning rules make non-owner-occupied STRs hard to permit in practice, which is why our STR worked example uses Old Orchard Beach rather than Portland. Bar Harbor caps non-owner-occupied STRs and ties licensing to year-round residency. Kennebunk, Ogunquit, and South Portland operate registration regimes with their own constraints. Most inland Maine has no special STR rules. These ordinances change frequently, so verify the current rules in your town before assuming Airbnb is on the table.
We model Old Orchard Beach because it is one of the few high-demand Maine markets where short-term rental remains broadly available, with strong summer ADR backed by tourism and beach access. The seasonal revenue model is in the second table below: roughly $36,000 in annual gross blended across summer, shoulder, and off-season.
The most decision-shaping question for STR is who runs it. A self-managed STR keeps far more revenue, about $23,700 net annually after cleaning, platform fees, supplies, higher utility and wear costs, and an STR insurance rider, but it requires 10 to 15 hours per week during peak summer for guest communication, cleaning coordination, supply restocking, and turnover management. Hiring a property manager (typically 20% of gross revenue) drops the operator load to a few hours a month but cuts net income to about $16,500 per year, roughly tied with a Portland long-term rental.
- Maine collects 9% lodging tax on stays under 28 days; the host remits through Maine Revenue Services.
- Verify the STR ordinance in your town before committing. Portland, Bar Harbor, Kennebunk, Ogunquit, and South Portland all have active registration or restriction programs.
- Budget cleaning at roughly $120 per turnover and consumable supplies at $1,000 to $1,500 per year.
- Add an STR insurance rider (around $700/yr); standard homeowner policies usually exclude short-term rental.
- A 20% property manager removes operator effort but typically pulls STR returns roughly into line with long-term rental.
Worked Examples: Same Building, Three Operating Strategies
The tables above model a single Place 400 sqft ADU under three operating strategies. Installed cost differs slightly by market: about $130,000 in Portland, where urban infill often carries higher utility tie-in costs and tighter access; about $120,000 in Old Orchard Beach, where coastal residential lots often allow simpler site work. All assumptions are conservative; your actuals will vary with finish level, lot conditions, financing, and market timing.
Read across the comparison table: STR-DIY produces the highest absolute return at about a 5-year payback, but STR-managed lands close to Portland LTR once management fees are paid. The decision is less about which market is "better" and more about how many operating hours you actually want to put in. For a deeper payback walkthrough on a smaller footprint, see our 240 sqft case study.
- Net annual income figures are post-vacancy, post-maintenance reserve, and post-property tax bump.
- Cash-on-cash assumes all-cash purchase; financed deals will have a different return profile.
- Operator effort is often the most important comparison. STR-DIY is genuinely a part-time job in peak season.
- Lodging tax is collected from guests and remitted to Maine Revenue Services; it does not reduce net income but creates real recordkeeping work.
Need a property-specific answer?
We can map permitting, cost, and timeline to your lot before you commit.
Decision Framework
A few questions tend to settle the strategy quickly:
- Does your town allow non-owner-occupied STRs? If no, plan for long-term rental; that decision is made for you.
- Is your property within an easy drive of a tourism market with strong summer demand? If no, long-term rental is usually the realistic path.
- Are you willing to spend 10 to 15 hours per week on guest operations during peak season? If no, plan for long-term rental or hire a property manager.
- Do you need predictable monthly cash flow more than maximum return? Long-term rental fits.
- Are you optimizing for absolute return and willing to manage actively? An OOB-style self-managed STR is the highest-return path in this model.
Validate Against Your Property
Numbers in this guide are conservative anchors, not guarantees. Lot conditions, finish level, town ordinances, and rental market timing all shift the result. Try layouts in the Configure 3D tool, then Request a Free Property Feasibility Assessment when you want a town-specific permit and rental review for your address.
Frequently Asked Questions
Which strategy actually has the best ROI in Maine?
For a Place 400 sqft ADU, a self-managed short-term rental in a strong tourist market like Old Orchard Beach produces the shortest payback, roughly 5 years, but it requires real operator hours during peak season. Long-term rental in Portland and property-managed STR in Old Orchard Beach both land near 7-year payback with minimal effort. The highest return per hour of effort is usually long-term rental.
Can I run a short-term rental on a Portland ADU?
Generally not on a non-owner-occupied backyard ADU. The Portland short-term rental registration program and zoning rules limit non-owner-occupied STRs through caps and unit-type restrictions, so most ADUs in Portland are realistic only as long-term rentals. Verify the current ordinance before committing; the rules in Portland have tightened over recent years.
How much time does a short-term rental actually take?
For a self-managed STR, plan on 10 to 15 hours per week during peak summer for guest communication, cleaning coordination, supply restocking, and turnover management. Off-season effort drops considerably. Hiring a property manager (typically 20% of gross revenue) reduces this to a few hours per month, but it also cuts net income roughly to the level of a long-term rental.
Is the 9% Maine lodging tax paid by me or my guest?
The Maine 9% lodging tax is collected from the guest and remitted by the host to Maine Revenue Services. It is a pass-through, so it does not reduce your net income directly, but registration, monthly remittance, and recordkeeping create real administrative overhead that property managers usually fold into their fee.
Should I decide rental strategy before I build?
Yes. Layout, kitchenette specification, parking, entrance privacy, and storage decisions are much easier to get right when the operating model is locked in early. A unit designed for STR turnover (durable finishes, lockable owner storage, in-unit laundry) looks different than a unit designed for a long-term tenant. Plan the strategy first, then design backwards.
Sources
We refresh legal and compliance references regularly to keep guidance current.
Related Maine Guides
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