Fast, Reliable New Detached ADU Across Southlake
A new detached ADU in Southlake typically runs $285,000 to $410,000 all-in, from survey and soil testing through final inspection, with the foundation engineering on expansive black-clay soil accounting for a meaningful share of that range. We design, permit, and build the unit under one contract at one written price, so the number you approve before we start is the number you pay when the certificate of occupancy is issued. If you’re weighing a detached ADU on a Timarron, Stone Lakes, or Monticello lot, call (971) 497-2402 and ask for the written price on your specific property.
We’re Ellery ADU Studio, a design-build practice founded in 2015 and led by Nadia Ellery. We work across Southlake consistently, and our crews know precisely what the city’s permit office asks for and what the HOAs layered over these subdivisions will reject. That dual-approval reality, documented below, is the single most common reason Southlake ADU projects stall.
Why Ellery ADU Studio Is Southlake’s Preferred New Detached ADU Company
Most ADU projects in Southlake don’t fail on the construction site. They fail at the permit desk or the HOA Architectural Control Committee review, usually because the contractor treated the HOA’s written approval as a formality rather than a parallel jurisdiction. We’ve completed hundreds of ADUs across the DFW metro since 2015, and the Southlake pattern is consistent: the projects that move cleanly are the ones where the HOA packet, the city permit set, and the soil report are prepared in that order, not discovered in that order.
Homeowners in Southlake consistently tell us the same thing: they expected the city permit to be the hard part, and the HOA turned out to be the real gatekeeper. We’ve handled enough Timarron and Stone Lakes projects to know which CC&R clauses trip review, how to phrase the application so the board sees an attached-family-living asset rather than an unknown structure, and when to pull the soil report early so the foundation design in your permit set matches what the HOA already approved. Ask Nadia about the specific approval sequence for your subdivision when you call (971) 497-2402.
Every project includes the Haven Standard: a written price before work starts, a documented photo record on every visit, and a 365-Day Done Right Promise in writing. If the finished ADU is not built to the permitted drawings, we make it right. That clause matters more in Southlake than most places, because a stop-work order from an HOA or a foundation re-engineer mid-project is exactly the kind of disruption a written scope protects you from.
Our New Detached ADU Services in Southlake
Custom Built ADU
A custom-built detached ADU on a Southlake estate lot gives you full control over the footprint, roofline, and interior finish so the new structure reads as an extension of the main house rather than an addition bolted on. On the half-acre to two-acre lots common in Timarron and Stone Lakes, we typically see custom ADUs between 700 and 1,200 square feet, often designed as a one-bedroom with a full kitchen and a private entrance for an aging parent. Because these projects are designed from the foundation up, the soil report and an engineer’s foundation letter happen before the HOA review, which keeps the timeline coherent.
Prefab ADU Installation
Prefab systems from Abodu, Cover, and Dvele can cut on-site construction time by months, but in Southlake the prefab route introduces a specific wrinkle: the HOA packet often triggers a design review on a structure the manufacturer has already fixed. We coordinate the system within our single contract, meaning we specify the model, prepare the Southlake-appropriate foundation for the black-clay soil, and manage the HOA filing so the review committee sees exactly what’s coming. A prefab ADU in Southlake typically lands between $260,000 and $340,000 delivered and installed, before site-specific foundation work.
Modular ADU
Modular ADUs built off-site and set in place are increasingly common on Southlake lots where the main home’s garage is too tightly integrated to convert and the owner wants a predictable build timeline. The foundation is still site-built and still subject to the same expansive-soil engineering requirements as any other detached structure, so we don’t treat a modular unit as a shortcut on the geotech work. We handle the entire sequence: soil testing, pier-and-beam or post-tension design, the HOA filing, and the setting and finishing of the unit.
Studio ADU
A studio ADU in Southlake is the most popular starting point for homeowners who want a rental or a long-term guest suite without the plumbing and square footage of a full one-bedroom. In Southlake’s current market, expect $210,000 to $280,000 for a well-finished 500 to 600 square foot studio with a kitchenette and a full bath. That range assumes the HOA packet clears on the first pass and the soil report doesn’t force a deep foundation redesign, which is where a written price and a careful pre-file review keep your number stable.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Southlake
When a Southlake client wants a prefab or modular ADU, we specify and coordinate systems from Abodu, Cover, and Dvele within the same single contract that covers the site work, foundation, and finish. For custom-built ADUs, James Hardie siding is our default exterior spec because it holds up to North Texas sun and hail seasons without the maintenance burden of wood. We maintain direct supply relationships for these systems and materials, so a Southlake project doesn’t wait on a third-party distributor to restock.
Common New Detached ADU Problems We See in Southlake Homes
- HOA stop-work orders after the city permit is already issued. Timarron’s Architectural Control Committee operates independently of the city permit office, and its early-1990s CC&Rs define “accessory structure” in language that predates modern ADU law. Contractors who file for a city permit without first getting written HOA approval routinely get stopped mid-foundation and have no legal path forward until the board reviews plans, which can take months.
- Foundation redesigns driven by black-clay soil tests. Southlake’s expansive clay heaves dramatically between wet winters and 100°F-plus summers. A homeowner who budgets for a simple slab often receives an engineer’s letter requiring a pier-and-beam or post-tension design, and that change order can add $20,000 or more. When the HOA has already approved a different footprint, the redesign triggers a second HOA review, compounding the delay.
- Undersized electrical feeders in 1990s estate homes. Homes built roughly 1990 to 2015 in Southlake’s custom and semi-custom subdivisions often have detached garages with 60-amp aluminum feeders that were fine for a door opener and a workbench but cannot carry a full ADU subpanel. When we opened a 1998 Timarron home’s garage for conversion, the original feeder was rated for 60 amps, and the new one-bedroom unit required a 100-amp subpanel under current code.
- Failed waterproofing at the garage or pool-house interface. Many of the detached structures that make natural ADU candidates in Southlake, notably the bonus-room-over-garage and pool-house configurations, were originally built with waterproofing that’s now twenty-five to thirty years old. Once walls are opened, failed flashing and sill rot are common, and the repair is almost always a code-triggered upgrade, not a patch.
Pricing for New Detached ADU in Southlake, TX
Here are the real numbers we quote on Southlake projects. A custom-built one-bedroom ADU on a Timarron or Stone Lakes lot typically runs $310,000 to $410,000, drawings through final inspection. A studio ADU typically runs $210,000 to $280,000. A prefab or modular installation from Abodu, Cover, or Dvele typically lands between $260,000 and $340,000, not including foundation work specific to your soil report. Those ranges include the permit set, HOA filing support, the documentary photo record, and the written warranty. What moves the number is the foundation design your engineer requires after the geotech report, and whether the HOA review forces a resubmission. Both are knowable before you sign. Call (971) 497-2402 and ask us to put a written price on your specific lot.
We Also Serve Cities Near Southlake
We serve New Detached ADU in Southlake and the surrounding cities: Colleyville, Grapevine, Flower Mound, and Bedford. Each city has its own permit rhythm and HOA landscape, and the same one-contract approach applies. Read more about our full New Detached ADU process, or call (971) 497-2402 and ask for Nadia Ellery.
Serving Southlake, TX - Our Local Coverage Area
We’re based in the Southlake area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - New Detached ADU in Southlake
Yes. Timarron’s HOA Architectural Control Committee approval is required separately from and in addition to the city of Southlake permit, and the HOA’s authority runs parallel to the city’s. A city permit without written HOA approval leaves you exposed to a stop-work violation mid-project, and we’ve seen contractors pulled off half-built foundations in Timarron for exactly this sequence. We file the HOA packet before we pull the city permit, every time. Call (971) 497-2402 to have us review your specific lot and CC&R file before you spend anything.
Southlake’s expansive clay shrinks and heaves enough between seasons that a simple slab is often not what the engineer will stamp, and the cost difference is usually $15,000 to $25,000 for a pier-and-beam or post-tension design that won’t move with the soil. The soil report, which we commission early, tells you which foundation your specific lot requires before any HOA review or permit filing. That early report is what keeps the written price from moving later. Call (971) 497-2402 and we’ll walk you through what your parcel’s soil report is likely to require.
We usually find one of three things inside a 1990s Southlake build: aluminum branch wiring that doesn’t meet current code for a new dwelling unit, undersized headers over garage openings, or failed flashing at the existing structure’s junction with the ADU. Each of those is a code-triggered upgrade, not an optional repair, and the cost is typically $8,000 to $20,000 depending on scope. We write an allowance for these known unknowns into the contract at signing, and any surprise is priced in writing and approved by you before we touch it. Call (971) 497-2402 for an exact written price on your project.
No, because converting the garage changes its use from accessory to residential, and Stone Lakes’ CC&Rs, like Timarron’s, define accessory structures in terms that don’t automatically accommodate a dwelling unit. You need written approval from the HOA’s architectural review body before the conversion, and the filing should include the engineered drawings, the foundation note, and the proposed electrical service change. We prepare and file that packet as part of the same contract that builds the unit. Call (971) 497-2402 and ask for Nadia’s read on Stone Lakes’ current review posture.
The usual trigger is the feeder from the main panel to the detached structure. Most 1990s Southlake estate homes ran 60-amp aluminum feeders to detached garages, and a new one-bedroom ADU requires a 100-amp subpanel with copper feeders under current code, which typically costs $6,000 to $12,000 including the subpanel, trenching, and new conductors. The main panel itself may also need a service upgrade if the home is still on 150-amp service. We write that allowance into the contract so the number doesn’t move when the walls come open. Call (971) 497-2402 for a written price on your home’s specific electrical condition.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Southlake since 2015.