New Detached ADU in Arlington - Plans, Permits & Build, One Fixed Price

Fast, Reliable New Detached ADU Across Arlington

A new detached ADU in Arlington typically runs $185,000-$310,000 all-in, drawings through final inspection, and takes 7-11 months from signed contract to certificate of occupancy. The two numbers that move most in Arlington are foundation engineering for the city’s shrink-swell clay and whether you’re on city sewer or a septic system. Our team handles both from our Dallas-Fort Worth office, and every Arlington project includes a written price before any work starts. Call (971) 497-2402 and we’ll walk the lot with you, pull the plat, and give you real numbers instead of ranges.

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Why Ellery ADU Studio Is Arlington’s Preferred New Detached ADU Company

Most of the ADU work we see in Arlington comes from owners who started with a garage conversion and hit the city’s covered-parking replacement rule. That rule is real: Arlington requires you to preserve or replace covered parking when you convert a garage, which means adding a carport or reworking the driveway. For a lot of Arlington lots, a New Detached ADU in the backyard is actually the cheaper path once you run the numbers. We’ve done this math on 900+ ADUs since 2015, and we walk every Arlington property before we quote so you’re not surprised at permit review.

Nadia Ellery founded this studio on the principle that the drawings, the permit set, and the construction should be one contract at one written price. That matters in Arlington because the zoning review process here is exacting: lot coverage, rear setback angles, and the clay soil condition all get scrutinized. Out-of-town contractors routinely under-scope the foundation and eat the cost later, or worse, push it onto you as a change order. We don’t do change orders on scope we’ve already walked. Under Haven Standard Clause 5, the scope is locked at signing.

Our New Detached ADU Services in Arlington

Custom Built ADU in Arlington

A custom detached ADU on an Arlington lot gives you control over the roofline, the window placement, and the interior layout, but it also puts the soil condition front and center. Arlington sits on Blackland Prairie clay that expands when wet and shrinks when dry. A standard slab-on-grade will heave within two wet-dry cycles and crack the walls of a new build. We specify engineered piers or a post-tension slab on every custom ADU we do in Arlington, and that line item is in the written price before you sign, not discovered at excavation.

Prefab ADU Installation in Arlington

Prefab and modular systems from Abodu, Cover, and Dvele can shorten on-site construction time substantially, but Arlington’s foundation requirements don’t change just because the unit arrives on a truck. The unit still sits on Arlington clay, so the foundation scope remains the same as a site-built unit. What changes is crane access: many Arlington lots in older subdivisions like Sherwood Forest and Dalworthington Gardens have rear yards fenced in by mature oaks and narrow side yards that can’t clear a crane. We check truck and crane access before we quote a prefab install in Arlington, because a crane that can’t reach the pad turns a simple delivery into a multi-day lift.

Modular ADU in Arlington

Modular construction splits the difference between prefab and fully custom. The modules are built off-site and assembled on your Arlington lot, which reduces weather exposure during framing and gets you to dry-in faster. We still engineer the foundation for shrink-swell clay, and we still pull the same city permits. The advantage in Arlington is schedule predictability: with the rainy season in spring and summer heat indexes over 105°F, fewer days of outdoor framing means fewer weather delays and a faster path to your certificate of occupancy.

Studio ADU in Arlington

A studio ADU (300-500 square feet) is the most common detached build we do in Arlington, and it fits well on the larger lots in the city’s 1960s-1980s ranch subdivisions. These lots were platted wide, so a detached studio often clears setback requirements without a variance. The constraint is usually the septic system if you’re on one: Arlington has areas of the city that are still on septic rather than city sewer, and county health setbacks between a dwelling and a septic lateral are stricter than city zoning. We check which jurisdiction governs your address before we draw the siting plan.

1-Bed & 2-Bed ADU in Arlington

A 1-bedroom detached ADU in Arlington typically runs $210,000-$260,000, and a 2-bedroom runs $260,000-$310,000. The square footage drives the foundation cost, the HVAC load, and the panel capacity requirements. Most Arlington ranch homes from the 1960s and 1970s were built with 100-amp electrical service, and a new detached 2-bedroom with its own kitchen, laundry, and HVAC will almost always require a panel upgrade on the parent home before the city will sign off. We include that line item in the written quote when the existing panel tells us it’s needed.

Trusted Brands We Service in Arlington

We specify and coordinate prefab and modular systems from Abodu, Cover, and Dvele within the same single-contract design-build model we use for site-built ADUs. That means the unit selection, the foundation engineering for Arlington clay, the crane logistics, and the final connection are all one contract, one written price, one responsible party. If a module arrives out of square or a finish is damaged in transit, it’s our problem to fix, not a finger-pointing exercise between the factory and the builder. We also use James Hardie siding products on many Arlington custom builds for their handling of the city’s hot, humid summers without the warping we see in cheaper fiber cement.

Common New Detached ADU Problems We See in Arlington Homes

• Slab-on-grade foundations poured without engineered piers. Arlington’s black clay heaves within two wet-dry cycles, and a standard slab will crack walls and jam doors within the first two years. The fix after the fact is three times the cost of doing piers from the start.
• Detached units sited too close to septic laterals or wells. If your Arlington property is on septic, the county health department setback is 10 feet from any dwelling to the lateral line. A city zoning permit won’t catch this, but the county inspection will, and a failed inspection can force a full resite of the unit.
• Undersized HVAC in a freestanding unit. Arlington’s summer heat indexes regularly exceed 105°F, and a code-minimum mini-split can’t hold temperature in a unit with full sun exposure and no shared wall insulation. We size HVAC for the actual orientation of the unit on your lot, not a generic square-footage chart.
• Garage conversions that trigger the covered-parking replacement rule. Arlington requires that a converted garage be replaced with covered parking elsewhere on the lot. On many Arlington lots, the driveway rework and carport addition cost more than building a detached ADU in the rear yard in the first place.

We scoped a detached ADU on a 1970s ranch lot in the Sherwood Forest neighborhood, where the rear setback line angled sharply at the back corner. Our crew pulled the plat and found the only buildable footprint sat 18 feet from the existing septic lateral, so we sited the unit to keep the required 10-foot clearance and specified a post-tension slab with piers driven 12 feet to reach stable soil below the shrink-swell clay. The owner originally wanted a garage conversion, but Arlington’s covered-parking replacement rule meant a detached build was actually cheaper than reworking the driveway.

Pricing for New Detached ADU in Arlington, TX

We Also Serve Cities Near Arlington

While this page focuses on New Detached ADU in Arlington, our crews also work in Mansfield, Burleson, Cedar Hill, and Grand Prairie. Each of those cities has different zoning rules and soil conditions, but the same written-price guarantee applies. If you’re outside Arlington, call (971) 497-2402 and we’ll tell you honestly whether your project fits our schedule and our model.

FAQs - New Detached ADU in Arlington