Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
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AfterFast, Reliable Home Additions & ADU Across Missouri City
A detached ADU in Missouri City typically costs $90,000 to $220,000, while a garage conversion runs $30,000 to $80,000. Most homeowners we work with in the 77459 and 77489 zip codes need two things before anything else: clarity on which county actually governs their property, and a straight answer on what Sienna’s HOA will and won’t approve. That is where we earn our keep. Call (877) 610-1318 and Tom or one of his sons will walk you through what applies to your specific parcel before you spend a dime.
We have been building Home Additions & ADU projects across Missouri City long enough to know that a house on one side of Sienna Parkway can need a completely different permit path than a house three blocks away. The Harris County and Fort Bend County line cuts right through this city, and it trips up out-of-town contractors every single week.
Why Barrett & Sons Construction Is Missouri City’s Preferred Home Additions & ADU Company
Barrett & Sons Construction has been owner-operated since 1998, and Tom Barrett is the name on the truck. When we build a room addition off your Quail Valley ranch or convert a garage into a junior ADU in Sienna, Tom or one of his sons is on site most days. Not a project manager you have never met. The person who shook your hand at the estimate is the person who will answer when you call about a change order.
Our Missouri City customers tell us the same thing over and over: they got burned by a company that quoted one price on the phone and handed them a different bill at the door. That is exactly why every scope item, every allowance, and every price change at Barrett & Sons arrives as a written change order before work proceeds. The permit inspector works for you, not for me. That is why we like him.
We answer our own phones. 24 hours a day, 7 days a week, a live person picks up. No voicemail box, no out-of-state call center. If you are calling about a home addition in Missouri City, you get a person who knows what a Sienna HOA submittal looks like.
Our Home Additions & ADU Services in Missouri City
ADU Design & Permitting
If your Missouri City property sits in Fort Bend County, your ADU permit application does not even get accepted until the HOA signs off first in most Sienna neighborhoods. We handle that sequence in the right order. We prepare the architectural drawings, pull the correct county permit, submit to the HOA design committee when required, and manage every inspection through final sign-off. One of the most common calls we get is from a homeowner who pulled a Harris County permit for a house that is actually in Fort Bend County. The application sat rejected for three weeks before they called us.
Garage Conversion ADU
A garage conversion in Missouri City runs $30,000 to $80,000 depending on whether you are adding a full kitchen or a kitchenette, a full bath or a three-quarter bath, and how much trenching the plumbing rough-in requires. In the older 77489 neighborhoods, those 1970s and 1980s slab foundations have been moving on Beaumont clay for decades, which means slab penetrations need a closer look before we cut. In Sienna, the garage conversions we do almost always need HOA design review for any exterior change, even something as simple as replacing a garage door with a wall and window.
New Detached ADU
A new detached ADU in Missouri City generally runs $90,000 to $220,000. The spread is wide because of what the county and the HOA require. In a Sienna parcel, you may be required to match roof pitch, exterior materials, and even paint palette to the main house. In the older Quail Valley sections, your biggest cost driver is usually foundation work on expansive clay soil and the flood elevation certificate that Oyster Creek-adjacent parcels frequently trigger. We have built enough of these to give you a line-item estimate that reflects your actual lot, not a generic price from a brochure.
Junior ADU & Interior Conversion
A junior ADU, or an interior conversion of an existing bedroom or bonus room into a self-contained living space, is often the fastest path to rental income or multi-generational living in Missouri City. These projects usually stay within the existing building envelope, which means fewer exterior changes and fewer HOA triggers. But do not assume that means no permit. A kitchenette and a full bath still require plumbing, electrical, and mechanical permits, and in Fort Bend County, the inspector will check egress, smoke detection, and ventilation before signing off.
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 Missouri City
When we build a Missouri City addition or ADU, we install materials you can look up. KraftMaid cabinets, Cambria countertops, Kohler and Moen fixtures, Andersen windows. For exterior hardscapes that often accompany a detached ADU, we work with Belgard and Techo-Bloc. You will not find a mystery brand off the back of a van on our job sites. We stock local parts and order direct from our supplier partners, which keeps lead times predictable even when the Sienna HOA delays approval by three weeks.
Common Home Additions & ADU Problems We See in Missouri City Homes
- Wrong-county permits. A block near the Harris/Fort Bend line can fall under either county’s jurisdiction. We have seen contractors pull a permit from the wrong authority, get rejected, and stall a job for weeks before the first wall is framed. We verify parcel jurisdiction on every estimate, for free.
- Sienna HOA stop-work orders. A homeowner orders custom windows or exterior paint without submitting to the Residential Design Committee, and the HOA hits them with a stop-work order. Materials sit in the driveway and the crew goes idle. We submit design review before we order a single item.
- Missing flood elevation certificates. On Oyster Creek-adjacent parcels and many 77489 homes, finished floor height has to clear FEMA’s base flood elevation. A room addition that starts without that certificate often gets flagged at rough-in. We pull the certificate first, not after.
- Builder-grade mechanicals that cannot carry the load. Sienna’s newer homes often have HVAC and electrical sized for the original footprint, not for a 400-square-foot addition. We check load calculations before we design, so you do not end up with a beautiful new room and a system that cannot heat it.
Pricing for Home Additions & ADU in Missouri City, TX
Here is what you can realistically expect to pay in Missouri City right now:
| Project | Missouri City Price Range |
|---|---|
| Home Addition | $45,000 - $130,000 |
| ADU Construction | $90,000 - $220,000 |
| Garage Conversion | $30,000 - $80,000 |
What moves the number? Foundation work on clay soil, flood elevation certificates on low parcels, HOA-mandated exterior materials in Sienna, and how far your plumbing and electrical need to run from the main structure. We give free estimates with written, line-item scope. Every allowance is on paper. Call (877) 610-1318 to schedule yours.
We Also Serve Cities Near Missouri City
Our crews work across Missouri City and the surrounding communities every week. That includes Stafford to the northeast, Fresno to the southeast, Sienna Plantation within our own service area, and New Territory just across the Brazos River. If you are anywhere nearby and wondering whether we make the drive, call and ask. If you are in the county, there is no trip charge.
Serving Missouri City, TX - Our Local Coverage Area
We’re based in the Missouri City 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 - Home Additions & ADU in Missouri City
Yes, if your home sits in Sienna or another master-planned community with a Residential Design Committee, HOA approval usually comes before the county will accept your permit application. In Sienna specifically, exterior elevations, roof pitch, and paint palette must be approved by the HOA before Fort Bend County processes the permit. Call (877) 610-1318 and we will tell you whether your specific parcel triggers this step.
It comes down to your exact parcel, not your mailing address. Some Missouri City streets split the county line. The simplest way is to check your property tax statement or call the county appraisal district, but we verify this on every estimate before we quote a single number. Pulling from the wrong county is the most common project killer we see.
It can, if the work is not permitted and inspected, or if the builder’s warranty excludes modifications by unlicensed contractors. Most Sienna builders require permitted work by a licensed contractor and signed inspections to keep the structural warranty intact. We pull permits and pass inspections on every eligible job, and our 90-Day Done Right Promise is written on the contract.
A detached ADU in Missouri City typically runs $90,000 to $220,000. The lower end assumes a junior ADU with a modest kitchenette and bathroom on a slab-heavy lot with no flood elevation complications. The upper end reflects a full one-bedroom unit with custom finishes, HOA-mandated exterior materials, and foundation work on expansive clay. Call (877) 610-1318 for a free, written estimate on your specific lot.
Not usually for a purely second-story addition, since the addition sits above the base flood elevation by definition. But if you are expanding the first-floor footprint in a flood zone, or adding a first-floor room on a pier-and-beam or slab home near Oyster Creek, you likely need one. We pull the certificate early so the county inspector does not flag your rough-in.
Call Barrett & Sons Construction for Your Missouri City Home Addition or ADU
If you are ready to price a room addition, garage conversion, or detached ADU in Missouri City, call (877) 610-1318. We will verify which county governs your parcel, tell you what the HOA requires if you are in Sienna, and give you a written line-item estimate. No surprise invoices at the end. Just a straight price from a company that has been doing this since 1998.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Missouri City since 1998.