ADU Builders in Richardson - Plans, Permits & Build, One Fixed Price

Fast, Reliable ADU Builders Across Richardson

If you’re weighing an accessory dwelling unit in Richardson, the first thing to know is that this city’s zoning rules will shape your project before a single drawing gets approved. Detached ADUs here cap at 800 square feet or 50% of your primary home’s conditioned floor area, whichever is smaller, and most single-family districts require either alley access or a 10-foot side setback. That’s not a hurdle; it’s just the reality of building in Richardson, and it’s exactly the kind of detail our ADU Builders team works through every week. We’re the ADU company of the Kingswell family, led by Russ Delmar, and we’ve been scoping, pricing, and building ADUs across Richardson since 2010. Call (361) 204-4652 for a written estimate before you commit to anything.

Call (361) 204-4652

ADU Construction in Richardson

ADU Construction in Richardson means building a secondary dwelling on a lot that already has a primary home, and it’s one of the most cost-effective ways to add livable square footage without buying new land. In Richardson specifically, the city’s zoning ordinance sets hard caps on detached ADUs: 800 square feet or 50% of the primary dwelling’s conditioned floor area, whichever is smaller. For a 2,400-square-foot house, that 50% figure is 1,200 square feet, so the 800-square-foot cap governs. For a 1,400-square-foot house, the 50% figure is 700 square feet, and that lower number becomes your ceiling. We see this catch Richardson homeowners off guard regularly, especially when they’ve already picked a prefab plan online that’s wider than the city allows.

Construction costs in Richardson for a detached ADU typically run $180 to $320 per square foot, depending on finish level and site conditions. A 700-square-foot unit lands between $126,000 and $224,000. A full 800-square-foot build runs $144,000 to $256,000. Those are line-item ranges that include foundation, framing, mechanicals, drywall, flooring, and a basic kitchenette or bath, not just the shell.

The Permit Sequence That Slows Most Richardson Builds

Richardson’s Building Inspection Division reviews ADU plans against zoning, building code, and floodplain requirements in a specific order. We submit the site plan and architectural drawings first, then the structural and MEP drawings, then the floodplain development permit if the property is anywhere near Duck Creek. Miss the floodplain review and the city will stop your foundation work mid-pour. We’ve seen it happen to homeowners who tried to self-permit.

Foundation Work and Soil Conditions

Richardson sits on expansive clay soils in most neighborhoods, which means slab-on-grade ADU foundations need a geotechnical report before the city approves the footing plan. That report tells us how deep piers or beams must go to handle soil movement. Skipping it is a guaranteed rejection from the Building Inspection Division. Our crews coordinate the soil test as part of the estimate, so the price you see includes it.

Detached ADU in Richardson

A Detached ADU in Richardson is a standalone structure separate from the main house, and it’s the most common ADU type we build because it gives the homeowner a fully private unit instead of a converted garage or attached addition. Richardson’s rules for detached ADUs are stricter than for attached ones. You need alley access or a 10-foot side setback in most single-family districts, plus a 5-foot side-yard setback in some older neighborhoods like Cottonwood Heights. Those setbacks often shrink a standard prefab plan by a foot or two on one side, which means reworking the foundation layout before the permit gets approved.

Detached ADU costs in Richardson run $190 to $340 per square foot, slightly higher than attached or garage conversions because you’re building a full envelope from the ground up. A 600-square-foot detached studio lands between $114,000 and $204,000. An 800-square-foot one-bedroom with a full bath sits between $152,000 and $272,000. Prefab shells from brands like Boxabl or Plant Prefab can lower the framing cost, but Richardson still requires engineered drawings and an on-site footing inspection, so the city review time doesn’t shrink.

Site Prep and Setbacks in Cottonwood Heights

We built a 720-square-foot detached ADU off a rear alley in the Cottonwood Heights neighborhood, using a Tuff Shed shell upgraded with James Hardie siding and a mini-split system. The biggest variable was the required 5-foot side-yard setback that forced a narrower footprint and rework of the foundation plan before the permit was approved. The alley access helped, because Richardson counts alley-loaded lots differently than street-loaded lots when calculating setbacks. If your lot backs to an alley, you have more flexibility on the rear line.

What Richardson Inspectors Look At Closely

On a detached ADU in Richardson, our crew hits specific inspection points: footings after excavation, slab prep before pour, framing before drywall, rough-in for electrical and plumbing, and a final after the unit is complete. The Building Inspection Division also checks the ADU’s square footage against both the 800-square-foot cap and the 50%-of-primary-dwelling rule at plan review, not just at the end. If you’re over, that’s a zoning rejection, not a small correction. We verify that math before we submit anything.

Trusted Brands We Service in Richardson

Lodgewick ADU Dallas works hands-on with established ADU brands and materials suppliers, including Mighty Buildings, Boxabl, Plant Prefab, Tuff Shed, and James Hardie. We choose the brand that fits your Richardson lot, budget, and timeline, and we don’t push a prefab kit where a site-built structure makes more sense. For Richardson specifically, we keep a close eye on which prefab plans meet the city’s 800-square-foot cap and setback rules without triggering a variance. A Boxabl or Plant Prefab module that’s 19 feet wide won’t fit a lot with a 5-foot side-yard setback in Cottonwood Heights. We know that before you spend a dollar on drawings. If you have a brand in mind, we’ll tell you honestly whether it works on your specific Richardson lot, then put that answer in writing.

Common ADU Builders Problems We See in Richardson Homes

• Zoning rejections from square footage mistakes. A homeowner falls in love with a 900-square-foot prefab plan online, then Richardson’s Building Inspection Division rejects it because the cap is 800 square feet or 50% of the primary dwelling, whichever is smaller. Weeks of delay and a redesign fee follow.
• Foundation delays from missing geotech reports. Richardson’s expansive clay soils demand a geotechnical report before a slab-on-grade ADU foundation gets approved. We see homeowners try to skip it, and the city stops the footing inspection until the report is on file.
• Floodplain issues near Duck Creek. Properties within the mapped floodplain around Duck Creek need a floodplain development permit before construction starts. If you break ground without it, the city can halt work mid-foundation, and re-mobilizing a crew costs real money.
• Setback surprises in older neighborhoods. In areas like Cottonwood Heights, the 5-foot side-yard setback plus the 10-foot side setback in most single-family districts can shrink a standard ADU footprint by a foot or more on one side. The result is a narrower foundation than the plan you bought, and a change order if your builder didn’t catch it.

Pricing for ADU Builders in Richardson, TX

We Also Serve Cities Near Richardson

Our ADU Builders in Richardson team handles projects across the area, including Addison, Plano, Garland, and Rowlett. Each city has its own zoning quirks, and we know them well enough to flag the differences before you sign. If you’re a few minutes outside Richardson, the same written-price guarantee and 365-Day Done Right Promise apply. Call (361) 204-4652 and we’ll give you the straight answer for your specific lot.

FAQs About ADU Builders in Richardson