Fast, Reliable New Detached ADU Across Cedar Park
A new detached ADU in Cedar Park, TX typically costs $195,000-$285,000 all-in for a custom build, or $165,000-$235,000 for a prefab or modular unit, drawings through final inspection. That’s the written number you should expect to see on a real proposal, not a vague “call for a quote.” Ellery ADU Studio has been designing and building detached ADUs since 2015, and we work across Cedar Park every week. Call (971) 497-2402 and we’ll walk you through what’s actually feasible on your lot before you spend a dollar.
Here’s the thing about Cedar Park that most ADU write-ups miss: your lot might look flat and easy, but the Edwards Limestone under it changes everything. We know this because we’ve dug enough holes here. We’ll get into that below, along with the HOA review step that kills projects if it’s skipped, and the septic setbacks that matter on acreage outside city limits. This page is written for Cedar Park homeowners specifically. Read it before you talk to any builder.
Why Ellery ADU Studio Is Cedar Park’s Preferred New Detached ADU Company
We’re a design-build studio, not a general contractor who subs out the drawings and then blames the architect when something’s off. The permit set, the engineering, and the construction sit under one contract at one written price. That matters in Cedar Park because the city’s ADU ordinance is permissive on paper, but the real approval chain runs through HOA architectural review committees, county OSSF (On-Site Sewage Facility) permits on acreage lots, and the bedrock under your foundation. Splitting those across three companies is how budgets die. We keep it in one place.
Nadia Ellery founded the studio in 2015 and still reviews every Cedar Park permit set before it goes out. We’ve designed, permitted, and built 900+ ADUs since then, every one with a written price before work started. That’s Haven Standard Clause 1, and it’s not a marketing line. It’s the document you sign.
Our New Detached ADU Services in Cedar Park
Custom Built ADU
A custom detached ADU in Cedar Park runs $205,000-$285,000 depending on finish level, foundation type, and site access. On a standard 7,000 sq ft lot in Buttercup Creek or Forest Oaks, we’re typically designing a 1-bed or 2-bed unit between 600 and 900 sq ft. The Cedar Park-specific cost driver is the foundation: if we hit limestone at 12 to 14 inches, you’re on engineered piers or a thickened slab, and that adds 15 to 25 percent to the foundation line item versus a standard slab on grade in Pflugerville. We’ll know which camp you’re in before we quote, because we pull the county soil survey first.
Prefab ADU Installation
Prefab units from Cover, Dvele, and Mighty Buildings typically land in the $165,000-$235,000 range in Cedar Park once you add site work, foundation, and utility hookups. The factory number you see online is never the whole story. On Cedar Park acreage, the utility runs are the hidden line item: we’ve trenched 140 feet of electrical from a county road, and that alone can add $8,000-$12,000. We quote prefab with the same Haven Standard as custom: written price, no door-side upsells, no “the factory didn’t include” surprises.
Modular ADU
Modular ADUs built off-site and set with a crane generally run $180,000-$250,000 in Cedar Park, including the crane day, set, and finish work. One thing we flag early: modular is not automatically cheaper than custom, especially when your lot needs a 25-foot septic setback or pier drilling through shallow bedrock. We’re brand-fluent across Cover, Dvele, Mighty Buildings, and Boxabl, but we specify the system that matches your lot conditions, not whichever factory has the best Instagram ads. That’s the difference between a quote and a guess.
Studio ADU
A detached studio ADU (typically 400-500 sq ft, one open room, one bath, kitchenette) runs $150,000-$195,000 in Cedar Park. These are popular on the half-acre lots in the Buttercup Creek area and the unincorporated pockets west of the city, where a small studio can serve as a home office, guest quarters, or a rental that doesn’t trigger a full expansion of the septic system. If your lot is outside city limits, the county permit process applies, and we handle that end-to-end.
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 Cedar Park
We specify and coordinate prefab and modular systems from Cover, Dvele, and Mighty Buildings within the same single contract that covers your foundation, utilities, and finishes. We don’t just hand you a factory referral and walk away. When a Cover unit lands on a Cedar Park lot, we’re the ones setting it, hooking it up, and standing behind it. If a factory panel arrives damaged, we deal with the factory, not you. That’s the point of one contract.
Common New Detached ADU Problems We See in Cedar Park Homes
- Skipped HOA CC&R review. Most Cedar Park homes sit in master-planned communities like Twin Creeks, Walsh Ranch, and Forest Oaks. Pre-2010 deed restrictions often classify any detached secondary structure as a prohibited “outbuilding.” We pull the CC&Rs and HOA architectural guidelines before we spend a dollar on design. On a detached ADU, this is the single most common way projects die after fees are already spent.
- Bid on a standard slab, then hit limestone. The Balcones Escarpment runs right under Cedar Park. Bedrock at 12 to 18 inches is normal, not rare. A contractor who bids a standard slab on grade will either eat the cost or come back with a change order. We core-sample before quoting, so the foundation line item in your written price reflects what’s actually under your grass.
- Undersized HVAC for the radiant heat. Cedar Park’s newer subdivisions are treeless. That means a 600 sq ft ADU can carry a cooling load you’d normally size for 1,000 sq ft. Rule-of-thumb sizing leaves tenants or family members baking from June through September. We oversize the system deliberately and show you the Manual J calc in the permit set.
- Septic and well setbacks ignored on acreage. Outside city limits, county OSSF rules govern. A detached ADU must sit at least 25 feet from drain field lines, and well-head clearances apply too. We pull the county permit and stake the setbacks before design locks. Jumping straight to a city-level understanding gets expensive fast.
Pricing for New Detached ADU in Cedar Park, TX
Here’s the range breakdown for Cedar Park, written plainly:
- Studio ADU (400-500 sq ft): $150,000-$195,000
- 1-bed detached ADU (600-750 sq ft): $185,000-$245,000
- 2-bed detached ADU (800-1,000 sq ft): $225,000-$285,000
- Prefab or modular unit, set and hooked up: $165,000-$250,000
The two biggest Cedar Park-specific cost variables are foundation type (limestone piers vs. slab) and utility run length on acreage. HOA fees and county OSSF permits add another $2,000-$5,000 depending on the community. Every project gets a written price before any work starts, per Haven Standard Clause 1. If you already have an estimate from another builder, bring it in. We’ll do a Free Second Opinion and tell you what’s missing. Call (971) 497-2402.
We Also Serve Cities Near Cedar Park
Our crews serve Cedar Park daily, and we work regularly in Leander, Round Rock, Pflugerville, and Cedar Park itself. If you’re on a half-acre in Leander or a newer lot in Pflugerville, the pricing and permitting reality shifts, and we’ll tell you how before you commit. For more on our New Detached ADU services across the region, that page has the full breakdown.
Serving Cedar Park, TX - Our Local Coverage Area
We’re based in the Cedar Park 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 Cedar Park
No, if your lot is outside Cedar Park city limits, the city permit does not apply. You’re under Williamson County jurisdiction, which means county OSSF (septic) permits, county building permits, and possibly well-head clearances. We pull the correct permit path before design starts, so you never get a city permit that the county then has to untangle. Call (971) 497-2402 and we’ll look up your specific parcel’s jurisdiction in about ten minutes.
A detached ADU must sit at least 25 feet from septic drain field lines and typically 50 feet from a well head, though exact setbacks depend on the county OSSF permit and your specific system. On a half-acre Buttercup Creek lot, that 25-foot line can remove a surprising amount of buildable area. We stake the setbacks and pull the OSSF permit before we quote a foundation, so your written price reflects where the ADU actually fits, not where the sales drawing hoped it would.
Maybe not. Cedar Park city code has been updated to be permissive on ADUs, but most of the city’s housing stock sits in HOA-governed communities like Butterfly Creek, Twin Creeks, and Walsh Ranch. Pre-2010 CC&Rs frequently classify any secondary detached structure as a prohibited “outbuilding.” The HOA review is not a formality; it’s the first billable step in any Cedar Park detached ADU project. We pull the deed restrictions and HOA architectural guidelines before we take a design deposit. Call (971) 497-2402 if you want us to check your HOA docs.
Because Cedar Park sits on the Balcones Escarpment, where shallow Edwards Limestone routinely stops excavation at 12 to 18 inches below the surface. That forces the foundation onto engineered piers or a thickened slab, adding 15-25 percent to the foundation line item versus a standard slab on grade. Pflugerville’s deeper clay soils don’t present this problem. Any Cedar Park foundation bid that doesn’t mention bedrock is a bid that hasn’t been thought through. Our written quotes include a soil evaluation before you sign.
Yes, if the lot has any slope toward the ADU, or if you have a septic drain field or well uphill, a grading and drainage plan is required. Even on the flats, we route a swale around the slab so water from the well head or neighboring lots can’t back-flood the foundation. It’s not optional when you’re on acreage; it’s part of the permit set. On our Buttercup Creek half-acre project, the grading plan was what prevented the uphill well from flooding the slab in a hard rain. Call (971) 497-2402 and we’ll tell you what your lot needs.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving Cedar Park and the surrounding area since 2015.