Plan 61718UT Review: A Two-Story 616 Sq Ft ADU Stacked Over a Two-Car Garage

One note before you commit: ADU eligibility in the U.S. is governed by local zoning, not state or federal code. A plan that drops cleanly onto a Nashville lot may not be permissible on an Atlanta one even four miles away. Confirm your municipality's ADU ordinance (size cap, setback rules, owner-occupancy, parking minimums) before you buy the construction documents.

Floor Plans

Main Level (Garage)

Second Floor (Living)

The main level dedicates a 23'-4" x 19'-9" two-car garage with a half bath tucked at the rear. That placement lets the garage and stairwell function as a guest entry without anyone tracking through the upstairs apartment to find the powder room. The stair runs straight up to the second floor, where the layout opens into a single-volume living core. The kitchen at 8'-6" x 12'-7" wraps an L of counters along the stair wall and flows directly into the 8'-6" x 9'-8" dining area and the 8'-11" x 11'-7" living room. There is no hallway between any of those zones; every square foot is doing visible work, which is the right move at 616 sq ft. The bedroom suite is 10'-11" x 13'-5" (respectable for the size class) and is buffered from the social zones by the laundry closet and the 5'-8" x 10'-7" full bath. From a styling standpoint, the upstairs reads as one room with three functional zones, which gives you flexibility on furniture but demands restraint on color and finish (more on that further down).

Exterior Elevations

The base renderings present a gable-front volume with a secondary roof plane sheltering the garage bay, the textbook carriage-house silhouette. A large upper window grouping is centered above the garage door, which is the primary daylight source for the apartment's social core. Smaller rectangular windows on the side elevation serve the entry stairwell, bath, and bedroom. The elevation drawings confirm a straightforward rectangular massing with modest overhangs and predictable construction. That matters when you are pricing this with a builder, because there is no architectural complexity adding cost. The scale is appropriate for rear-yard placement on a single-family parcel or for a side-yard infill where height limits permit two stories but width is constrained.

Interior Renderings & Finish Direction

The interior renderings show a restrained, contemporary palette: full-height white shaker cabinetry, dark quartz counters, stainless appliances in a single linear run, and dark wood-look flooring throughout. Recessed can lighting handles uniform overhead illumination. The living area carries pale grey walls, white trim and white plantation shutters, which is the right call for 616 sq ft; deeper wall colors compress the perceived volume and you cannot afford that here. From a styling perspective, this is a smart base palette to layer against. We would add one warm element (a brass pendant over the dining area, an unlacquered brass bath sconce, or a butter-yellow upholstered banquette in lieu of dining chairs) to break the cool grey-white tension and make the apartment feel warm rather than rental-grade. The dark floors photograph well in listing photos but will show every speck on a Saturday morning; if this unit is going on Airbnb, consider a slightly lighter wood-tone laminate to reduce daily upkeep.

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Pros & Cons

Pros

The strongest argument for this plan is the stacking. Putting the living quarters directly over the garage is the gold standard for ADU footprint efficiency: it preserves yard space and satisfies the strictest lot-coverage rules, because the building occupies no more ground than a garage would on its own. The size works in its favor as well. At 616 sq ft heated, the unit lands inside most municipal ADU size caps (typically 600–1,200 sq ft), so it clears the most common zoning hurdle out of the gate, before any conversation about setbacks or height.

Upstairs, the open-concept level eliminates hallway circulation, which keeps every one of those 616 square feet productive. The upstairs laundry closet sits next to the bedroom, the right adjacency for a single occupant or a couple. Downstairs, the ground-floor half bath lets the garage and stairwell serve guests without anyone walking through the private apartment.

The garage itself is generous for this size class. The 23'-4" x 19'-9" two-car bay accommodates two full-size vehicles plus modest perimeter storage, which is rare in a plan this small. The predictable rectangular massing also keeps construction cost down and reduces variance between builder bids, a practical benefit when you are pricing a secondary structure on a fixed budget.

Trade-Offs in Plan 61718UT

The largest limitation is the stair. With stair-only access to the living quarters, this plan is disqualified for buyers prioritizing aging-in-place and for mobility-impaired residents, and no amount of finish work changes that. The single-bedroom configuration also limits occupancy flexibility, so the unit does not work for households that need two private sleeping zones.

Inside the apartment, the compromises are about space. The compact L-shaped kitchen offers limited counter and prep space, and serious cooks will feel the constraint. The living room dimensions require disciplined furniture selection; oversized sectionals will not fit cleanly. Guest access to the upstairs full bath crosses the bedroom, because the bath opens only off Bed #1, which can feel awkward depending on the household routine.

Finally, there is no exterior balcony or upstairs outdoor space. The rooftop ADU experience some buyers expect is not in this plan as drawn, so anyone who wants a deck off the living level should raise it with a designer before the drawings go out for permit.

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Who This Plan Is For

The plan fits multi-generational families first: those who want a private in-law suite separated from the main house but kept on the same lot. It suits long-term-rental investors in markets with active ADU rental demand just as well, because the layout reads as a true one-bedroom apartment, not a studio compromise, and tenants notice the difference. The same qualities serve adult children launching independently who want to stay close to the family parcel during the early-career phase.

For remote-work professionals, the unit offers a separate residential structure that can serve as a home office with a full kitchen and bath. Empty nesters downsizing on the same lot can move into it and plan to convert the main house into the rental or sell it later. And for property owners with deep rear lots in Charleston, Nashville, Atlanta, or Charlotte, where ADU ordinances permit detached structures of this footprint, it is a straightforward candidate to price out.

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Regional Fit & 2026 Build-Cost Context

Because the fate of Plan 61718UT depends on the local ordinance, the market notes below pair each city with three things: the facade direction from the eight further down that we would specify there, a realistic 2026 turnkey build cost for the 616 sq ft heated apartment plus the 576 sq ft garage, and the zoning or code overlays a builder will have to work through.

Charleston, SC is where we would build the Modern Farmhouse (#1), with a turnkey allowance of $245,000–$370,000. The City of Charleston ADU ordinance (2020) allows accessory units in most single-family zones up to a 1,200 sq ft cap; construction follows IRC 2021 with ASCE 7-22 wind loads at a 130 mph design speed, and a parcel inside a mapped flood zone needs a raised foundation set by its FIRM panel. Savannah, GA suits the Cottage Craftsman (#5) at $235,000–$355,000. Carriage houses and ADUs are allowed in many of its residential districts on the same IRC 2021 and ASCE 7-22 base, though setbacks get tighter on parcels bordering the Historic District.

Nashville's wooded lots point to the Moody Modern Rustic (#3), budgeted at $240,000–$365,000 turnkey in Nashville, TN. Detached ADUs (DADUs) have been broadly permitted there since the 2017 zoning reform, capped at 700 sq ft or 25% of the main house, and the upper apartment needs IRC 2021 framing, IECC climate zone 4A insulation and a Manual J load calculation so the HVAC is not oversized for such a small volume. Atlanta, GA pairs with the Transitional Stone Accent (#2) at $225,000–$340,000; a 2018 city ordinance opened single-family residential zones to ADUs with a 1,000 sq ft limit and an owner-occupancy requirement, and the energy baseline drops to IECC climate zone 3A under IRC 2021.

Charlotte's older neighborhoods suit the Cottage Craftsman (#5), and a Charlotte, NC build should carry $230,000–$350,000. Its UDO 2023 (Unified Development Ordinance) is more generous toward ADUs than the code it replaced, but the rules still shift by district, so check yours before buying drawings; the build itself falls under IRC 2021 and IECC climate zone 4A. Naples / Ft. Myers, FL is the costliest market here at $280,000–$420,000 for the Organic Modern (#8). ADU rules there vary by municipality, and Collier County allows guest houses only with deed restrictions on rental. FBC 7th Edition with ASCE 7-22 puts the coast in a 170+ mph wind zone, which means impact-rated glazing on every opening.

In the Washington DC metro, the Ultra-Modern Minimalist (#7) fits the infill lots best, at $285,000–$425,000 turnkey. DC ZR 2016 permits ADUs in most residential zones, the code base is IRC 2021 with IECC climate zone 4A, and if the unit may one day house an older parent, specifying ICC A117.1 accessibility details at the ground floor costs far less now than as a retrofit.

Methodology: Ranges cover the 616 sq ft heated apartment built to mid-builder-grade through low-architectural finish, plus the 576 sq ft two-car garage at standard finish, basic site work, utility connections from the main house, and standard permitting. ADUs run $30–75 per square foot higher than equivalent primary-residence per-sf rates due to the loss of construction economies of scale on small footprints. Land, demolition (if replacing an existing detached structure), separate utility meters, custom landscaping, impact fees, and high-end specification packages push above the upper bound. Ranges synthesized from the NAHB 2024 Construction Cost Survey, RSMeans 2026 City Cost Indexes, the AARP Backyard Cottages and Other Affordable Housing Options report, and reflect pricing for Q4 2025 to Q1 2026. Always verify your municipality's current ADU ordinance and confirm pricing with two local builders before locking a budget.

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Other Facade Directions Worth Styling

About the eight facades that follow: we drew them as design concepts to test how the Plan 61718UT footprint holds up under different exterior palettes. The plan publisher does not sell them as options and the drawings ship with the base elevation shown earlier, so building any of them means choosing the materials with your builder and an exterior designer.

1. Modern Farmhouse

For a back-lot ADU in Charleston, Mount Pleasant or Greenville, this is our first choice. White vertical board-and-batten covers both floors, the garage door and window frames are matte black, and a band of light stone wainscoting wraps the base at the garage corners to give the ground floor some weight. A slim black metal awning runs across the front between the two levels. White hydrangeas and upright grasses line the paved drive and the walk to the side door. It has the broadest appeal of the eight, photographs cleanly and should age well, because nothing about it chases a trend.

2. Transitional Stone Accent

For an Atlanta or DC-metro ADU sitting behind a more formal main house, we would push toward this transitional palette. A full-height stone veneer wraps one side, balanced by white vertical board-and-batten on the front. Integrated LED soffit lighting and modern sconces light the garage bay and entry path. Boxwood hedges and a geometric concrete driveway create a deliberate, manicured setting. This reads polished without going contemporary, which makes it a useful bridge for traditional-leaning neighborhoods.

3. Moody Modern Rustic

Nashville's wooded outer suburbs and the Asheville and Blue Ridge corridor are where this version belongs. Dark-stained vertical boards wrap the upper volume, and the garage front steps back as a painted white surround sitting on a low river-stone base. The yard goes minimal: gravel and moss with flat stepping slabs, a single Japanese maple by the entry and a few low ground lights. At dusk the warm window glow against the dark siding is the whole effect, and the colour lets the building settle into mature trees instead of standing out from them.

4. Desert Contemporary

Specify this version only for the truly arid markets (central Texas, Phoenix, the New Mexico exurbs), where the warm stucco, full stone side wall, and horizontal wood slat cladding around the garage bay read as native rather than imported. The black garage door grounds the warm material palette. The landscape carries the climate fit with agave, ornamental grasses, and gravel beds. Outside the dry climates, this palette feels off-key against humid-South vegetation and architectural context.

5. Cottage Craftsman

Horizontal lap siding paired with a full stone veneer on the side wall, exposed wooden brackets under the eaves, and a black garage door with divided-light window inserts. Rows of lavender soften the base, and a dark concrete driveway pulls the geometry tight. The Craftsman details nod to the carriage-house heritage without overwhelming the small footprint. This version suits Savannah, Charlotte's older neighborhoods (Dilworth, Plaza-Midwood), and any Southern parcel adjacent to a traditional craftsman primary residence.

6. Mountain Lodge

Charcoal board-and-batten siding above a heavy fieldstone base, with reclaimed-look wood carriage doors replacing the standard overhead garage door. Substantial timber brackets support the roof overhang, and evergreen shrubs with river rock bedding reinforce a rugged setting. This is for cooler-climate or rural mountain parcels such as Highlands NC, Cashiers, the Asheville foothills, or any Tennessee or Carolina lake property where a robust rustic presence belongs.

7. Ultra-Modern Minimalist

For a DC-metro infill lot or a design-forward Nashville backyard, we would draw it this way. Large-format smooth panels replace siding, a dark metal frame wraps the frosted glass-paneled garage door, and the roofline stays crisp with a concealed LED strip under the eaves. The landscaping holds the same line: clipped boxwood balls and topiary in Corten steel planters, with no loose or wandering planting. With the trim stripped away the building reads as a clean architectural volume, which will appeal to a narrower group of owners than the farmhouse or craftsman versions.

8. Organic Modern

Light vertical siding trimmed with natural wood at the rake boards and eaves, a warm wood garage door, and a neutral stone side wall. The landscape leans biophilic, with hostas, ferns, hydrangeas in structured beds, and a rain chain at the corner replacing a downspout. This direction emphasizes natural materials and soft greenery and reads as calm rather than performative. Strong fit for Naples / Ft. Myers, where organic modern is the dominant design vernacular for newer infill, and for any Lowcountry parcel with mature shade canopy.

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Frequently Asked Questions

Is Plan 61718UT zoning-compliant for an ADU in your municipality?

Likely yes for the major Southern coastal markets covered here, but you must confirm before purchasing the construction documents. The 616 sq ft heated footprint sits comfortably under most ordinance size caps (typically 600–1,200 sq ft), and the carriage-house silhouette over a garage is the form most cities permit. The variables that may disqualify it on a specific lot are: minimum lot size, required setbacks, owner-occupancy mandates, parking requirements, and historic-district overlays. Pull your zoning code or call your planning department before committing.

What rental income could this ADU realistically generate?

In 2026, a one-bedroom 616 sq ft detached ADU rents in the $1,400–$2,400/month range across the Southern markets covered above, with Charleston, Nashville, and Atlanta on the higher end of that band and Savannah and Greenville on the lower. Furnished short-term-rental rates run $90–$180/night depending on parcel proximity to demand zones, but local STR ordinances and HOA rules increasingly restrict short-term ADU rentals; verify before underwriting on Airbnb income.

Can this work as a primary residence rather than an ADU?

Functionally, yes for a single occupant or couple: the 616 sq ft delivers a real one-bedroom layout with a full kitchen, full bath, and laundry. Practically, most municipalities require ADU plans to be sited as accessory structures behind a primary residence, so building this as a standalone primary residence on a vacant lot may face zoning friction. Also, mortgage lenders treat detached ADU plans differently from primary-residence plans, which can complicate financing.

Does the upstairs-only living work for aging-in-place?

No. Stair-only access to the living quarters is the disqualifier. If the long-term goal is housing aging family members or planning for your own aging in place, look at a single-story ADU plan instead, or a stair-and-elevator-ready plan that allows future lift retrofit. The half bath at the garage level helps for occasional visits but does not solve the daily-living barrier.

What permit and impact fees should you budget on top of the build cost?

In the Southern markets covered above, expect $4,000–$15,000 in combined building permit, impact, and utility-connection fees for a detached ADU on an existing residential parcel. Charleston, Atlanta, and Nashville run on the higher end; Savannah and Charlotte on the lower. If you are tying into existing main-house utilities rather than running new meters, the utility line item drops significantly. Get a written fee schedule from your municipality before committing.

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Who Plan 61718UT Suits

Plan 61718UT is one of the cleaner two-story ADU options we've reviewed for buyers who need a real one-bedroom carriage-house unit with two parking bays underneath. At 616 sq ft heated it sits under the size caps discussed above, the upstairs layout has no wasted circulation, and the eight facade directions above let you anchor it convincingly to almost any Southern parcel. Just remember the zoning homework comes first, the construction documents come second. If you're comparing this against primary-residence plans in a similar size band, our review of the 1,677 sq ft vaulted-great-room modern farmhouse covers the next step up for buyers who could see this as a permanent home rather than an accessory unit. For an over-garage bonus-space comparison from the primary-residence side, our modern French country ranch with bonus over the garage uses the same stacked-over-garage logic in a larger primary-house context. And if you are evaluating the ADU specifically as a rental income property, the four-bedroom modern ranch duplex plan gives you the multi-unit alternative to compare against. Whichever path you go, this plan's headline feature is its discipline. If you want a no-wasted-square-foot ADU above two parking bays, it's worth a serious look.

Two newer comparisons clarify the same stacked-versus-ground-level decision. The 650 square foot carriage-house apartment review examines three included layouts above a two-car garage and an exterior stair, while the 816 square foot modern farmhouse ADU review keeps all living space on one level and devotes a full-width porch to outdoor use.