Fast, Reliable New Detached ADU Across Keller
A new detached ADU in Keller typically runs $190,000-$310,000 all-in, from engineer-stamped drawings through final inspection. That’s the number most Keller homeowners need first, and it’s the number we write down before any work starts. If you’re weighing a backyard casita for aging parents who want to stay in the Keller ISD zone, or a rental unit behind a home you bought between 2015 and 2022, we can walk you through what your specific lot will actually require. Call (971) 497-2402 and we’ll put a written price on it.
We know Keller’s housing stock because we’ve spent years working through it: the large-lot subdivisions around Bear Creek Park, the three-car-garage floor plans off Keller Parkway and Johnson Road, the cul-de-sac lots in Hidden Lakes where rear setbacks run fifty feet deep or more. Those setbacks matter for a detached ADU. They give you room to build. But Keller’s clay soil and its inspection requirements will shape what that build costs, and we’d rather tell you that now than surprise you later.
Why Ellery ADU Studio Is Keller’s Preferred New Detached ADU Company
We’re a design-build studio, not a contractor juggling a designer. The drawings, the permit set, and the construction are one contract at one written price. That structure matters in Keller, where detached ADU permits hit a specific wall: the structural engineer’s letter. Keller building inspectors require written confirmation that any bonus room over a three-car garage meets residential live-load criteria before they’ll issue an ADU conversion permit. We get that letter before we pull the permit, not after an inspector stops the job. Under Haven Standard Clause 5 (No Surprises), that engineering review is priced into your contract at signing, not billed as a change order when the inspector asks for it.
Nadia Ellery founded this studio in 2015, and every Keller project we’ve run since has followed the same sequence: written price, documented photo record, engineering first. We don’t promise “fast” in a way that skips the structural step. We promise the sequence will be right. Keller homeowners who’ve had a neighbor’s detached ADU stall at permitting tend to call us second. The ones who call us first don’t stall.
Our New Detached ADU Services in Keller
Custom Built ADU
A custom detached ADU in Keller means designing to your lot’s specific setbacks, drainage, and tree canopy, then building it from the slab up. This is where Keller’s Blackland Prairie clay becomes the central line item. A properly engineered post-tension slab with extended grade beams adds $20,000-$30,000 to a ground-up project here. We don’t quote around it. We quote it. The alternative is slab movement and cracked walls within two seasons, which we’ve seen on Keller properties where someone tried to save that money on the front end.
Prefab ADU Installation
For homeowners who want a faster build and a factory-controlled envelope, we specify and coordinate prefab systems from Cover, Dvele, and Boxabl within the same single contract. Here’s what that means in Keller: the prefab manufacturer handles the module, but we handle the site work, the foundation engineering, the utility tie-in, and the Keller permit set. A prefab unit doesn’t exempt you from the clay soil problem. The slab under it still has to be engineered for Keller’s shrink-swell Vertisols. We run that calculation before the factory even starts production.
Modular ADU
Modular ADUs in Keller fall between custom and prefab: factory-built sections assembled on-site, with more layout flexibility than a fully prefab box and a shorter site schedule than stick framing. We’ve found modular works especially well on the one-third-acre lots in older Keller subdivisions where crane access is tight but not impossible. The permitting path is the same as site-built, which means the structural engineering letter still applies if you’re placing the unit over or adjacent to an existing garage structure.
Studio ADU
A studio ADU, 400-600 square feet, is the most common detached unit we permit in Keller. Single bath, kitchenette, one open living space. In Keller’s market, a well-built studio casita runs $160,000-$210,000 when the soil work and utility tie-in are priced honestly. That’s the number buyers are willing to pay for a rental that clears $1,400-$1,600 a month in Keller’s rental market. Our job is to make sure the numbers on your permit set match the numbers in your contract.
1-Bed & 2-Bed ADU
For Keller families building an in-law suite for parents, a one-bedroom or two-bedroom detached ADU is the typical ask. These run $210,000-$310,000 depending on footage, finishes, and how far your utility lines have to run from the main house. On larger Keller lots, distance is the quiet cost driver. If your water and sewer tie-in point is 80 feet from the ADU slab, that’s trenching, backfill, and grade work you won’t see on a speculative quote. We survey it during design and price it in writing before the contract is signed.
What happens when you call
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A real person answersNo phone trees - you reach a local pro.
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You get an upfront price rangeHonest numbers before anyone is dispatched.
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A background-checked tech heads outLicensed & insured, dispatched right away.
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You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Keller
We specify and coordinate prefab and modular systems from Cover, Dvele, and Boxabl for Keller projects. That means we handle the structural coordination, the foundation engineering, and the Keller permit set while the factory builds your unit to spec. You don’t get handed off to a manufacturer’s installer who’s never pulled a Keller permit. You get one contract, one written price, and one team accountable for the result. Under Haven Standard Clause 1, that price is written before any work begins, on every project, no exceptions.
Common New Detached ADU Problems We See in Keller Homes
- Slab movement on untreated clay. Keller sits on expansive Blackland Prairie Vertisols that swell in wet seasons and shrink in drought. A detached ADU built on a standard slab will crack within two seasons. We see this repeatedly on Keller properties where a previous owner tried to save $20,000 on the foundation.
- Bonus room over a three-car garage fails live-load review. Many 1990s Keller homes have bonus rooms over their garages that were framed for storage, not residential occupancy. Keller inspectors will stop a permit cold without a structural engineer’s letter confirming the joists can carry a bedroom. That letter takes 4-6 weeks to obtain, which is why we start it during design, not after permit submission.
- Utility tie-in exposes the main house. When we trench from a new detached ADU to a 1990s Keller home’s water and sewer lines, we sometimes find original cast-iron or polybutylene pipe that won’t pass current code. The tie-in triggers a main-house upgrade. We write allowances for this discovery into your contract, so the price doesn’t move without your written approval.
- Electrical panel at capacity. Keller homes built in the 1990s and early 2000s often have 150-amp or even 100-amp panels. A detached ADU with its own HVAC, water heater, and appliance load will push that panel over. We size the panel upgrade as a line item before construction, not as a surprise mid-build.
Pricing for New Detached ADU in Keller, TX
A new detached ADU in Keller runs $190,000-$310,000, with the biggest variables being soil engineering, utility distance, and whether the unit is a studio, one-bedroom, or two-bedroom. Here’s the line-item range we write into Keller contracts:
| Line Item | Keller Range |
|---|---|
| Design & permit set (including structural engineering) | $12,000-$22,000 |
| Post-tension slab with extended grade beams (expansive clay) | $20,000-$30,000 |
| Utility tie-in & trenching | $8,000-$18,000 |
| Construction (studio, 400-600 sq ft) | $90,000-$135,000 |
| Construction (1-2 bed, 600-900 sq ft) | $120,000-$200,000 |
| Electrical panel upgrade (if required) | $3,000-$6,000 |
These are Keller-specific numbers, not national averages. They reflect what we’ve written into recent Keller contracts for lots off Johnson Road, in Hidden Lakes, and around Bear Creek. Every project we quote includes the written price before work starts, per Haven Standard Clause 1. Call (971) 497-2402 and we’ll put the same specificity on your lot.
We Also Serve Cities Near Keller
Our New Detached ADU work extends across the northeast Tarrant County corridor. We’re actively permitting and building in North Richland Hills, Southlake, Haltom City, and Colleyville, with crews dispatched from our Dallas-Fort Worth office. If your project sits just outside Keller, the soil conditions, permit expectations, and pricing we’ve described here will be close, but not identical. We’ll tell you the difference in writing.
Serving Keller, TX - Our Local Coverage Area
We’re based in the Keller 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 Keller
Yes. Keller building inspectors require a structural engineer’s letter confirming existing floor joists meet residential live-load criteria before issuing an ADU conversion permit. This applies to bonus rooms over three-car garages built in the 1990s and early 2000s, which were often framed for storage loads. The letter typically takes 4-6 weeks to obtain. We start it during design, so it doesn’t hold up your permit. Call (971) 497-2402 and we’ll order the structural review for your specific garage.
Keller sits on expansive Blackland Prairie clay, so a detached ADU needs an engineer-stamped post-tension slab with extended grade beams. This typically adds $20,000-$30,000 to a ground-up project. Skipping it means slab movement and cracked walls within two seasons. We price this line item into every Keller contract from the first written quote. Call (971) 497-2402 for a foundation spec on your lot.
Keller ISD’s reputation means families stay put and aging parents move onto the property rather than out of the district. That drives demand for one-bedroom and two-bedroom in-law ADUs with full kitchens and accessible bathrooms, rather than simple studios. The unit becomes a permanent residence, not a short-term rental, which affects your plumbing, HVAC, and electrical load calculations. We design for that reality from day one. Call (971) 497-2402 and we’ll walk you through the multigenerational layout options.
Often yes. When we trench from the ADU to your main water, sewer, or electrical panel, we may uncover original pipe or undersized panels that won’t pass current code. The tie-in point is where old Keller construction meets new code, and that’s where upgrades surface. We write allowances for these discoveries into your contract, so you approve any change in writing before we touch it. Call (971) 497-2402 and we’ll review your existing utility layout before quoting.
Because the tie-in excavation reveals what the original builder actually installed, which often doesn’t match the permit record. A homeowner on Johnson Road found this when our crew opened the trench for a 2003 home’s sewer line and found the original line was shallower and older than the plans showed. Contractors who don’t write allowances for this discovery will fight the homeowner over the change order. We write the allowance in advance, and we price the change in writing before any work continues. That’s Haven Standard Clause 5. Call (971) 497-2402 for a quote that anticipates Keller’s reality.
Get Your Keller Detached ADU Priced in Writing
We’re Nadia Ellery’s team at Ellery ADU Studio, and we’ve designed, permitted, and built 900+ ADUs since 2015, every one with a written price before work started and a documented photo record when work was complete. If you already have an estimate from another builder, bring it in. We’ll give you a free second opinion. Call (971) 497-2402 and we’ll schedule the site walk, pull the soil report, and put your Keller detached ADU price in writing before you sign anything.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Keller, TX with written-price design-build ADU services since 2015.
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