Mighty Buildings ADU Design & Permitting Nationwide

Mighty Buildings ADU Design & Permitting: The San Antonio Owner’s Guide

Mighty Buildings ADU design and permitting in San Antonio typically runs $8,500 to $18,000 for the full design set, structural documentation, and permit package, depending on lot conditions, utility tie-ins, and how much of the Mighty Buildings engineering is already in hand. Most owners call us after they’ve hit a wall: they bought or are buying a Mighty Buildings unit, got told by the city that the standard factory drawings aren’t enough, and now need a stamped local set before anything gets delivered. We carry the design and permitting workload from survey to approved permit, and we’ve done it enough times in San Antonio that we know exactly which drawing revisions Bexar County and the City of San Antonio will flag first.

Call (430) 258-2928

Here’s the thing most people don’t realize until they’re in it: a Mighty Buildings unit is a panelized prefab system, which means the factory engineering is excellent, but it doesn’t automatically satisfy local wind-load, floodplain, or foundation requirements that San Antonio’s reviewers check against your specific lot. That’s where a local design and permitting package becomes the difference between a unit sitting in a warehouse and a unit getting bolted to a foundation. Troy Eastman puts the design and permit number on paper before any drafting hours get billed. That’s just how we work at Benson ADU San Antonio.

Which Mighty Buildings Models This Applies To

We’ve built design and permit packages for every Mighty Buildings lineup currently shipping in Texas: the Mighty House series (studio, one-bedroom, and two-bedroom layouts), the Mighty Mods accessory units, and the larger Mighty Duo and Mighty Family configurations. The design and permitting work applies the same way regardless of model: we take the factory engineering package, adapt it to San Antonio’s adopted building codes, and produce the stamped architectural, structural, and MEP sheets the city wants to see.

Here’s the compatibility gotcha most owners don’t know until it’s too late: Mighty Buildings’ standard drawings assume California-grade seismic detailing, not Texas-grade wind uplift. San Antonio is in a 110 mph wind zone, and the city’s reviewers will look specifically for uplift anchors, shear wall nailing patterns, and roof-to-wall connections that match Texas wind requirements. If you submit the factory set untouched, it gets rejected. If you submit our local set, it passes. We also handle the foundation plan, which Mighty Buildings does not provide beyond general recommendations. San Antonio soils – especially in the clay-heavy neighborhoods on the north and east sides – need a foundation design that accounts for expansive soil movement. We spec and stamp that locally.

We’re an independent design and build firm, not affiliated with Mighty Buildings, which means we can recommend the right fix without pushing a factory line. We also work with Abodu, Cover, Dvele, and Boxabl units, so if you’re comparing brands, we can tell you how the permit path differs before you commit to a purchase.

Signs Your Mighty Buildings ADU Design & Permitting Package Is Failing

• The permit desk kicked your factory drawings back. This is the most common failure. The city wants Texas structural stamps, local wind-load calcs, and a foundation plan. Mighty Buildings’ factory set doesn’t include those. That’s not a product defect, but it stops the project cold.
• You’ve been told you need a variance and you don’t know what that means. A setback is the distance between your ADU and the property line. San Antonio’s zoning code has specific setback rules for accessory structures, and if your lot is narrow or oddly shaped, the standard placement won’t pass. A variance is a formal request to bend that rule. It takes weeks and a hearing. We write the variance request right the first time.
• Your HOA is asking for documents you’ve never heard of. Some San Antonio HOAs require design review, elevation drawings, and even landscape plans before you can pull a city permit. If you’re mid-purchase and the HOA just threw a binder of requirements at you, your design package is incomplete.
• The utility connection plan doesn’t match your actual lot. Mighty Buildings units need water, sewer or septic, and electrical service delivered to the ADU footprint. If your lot has an existing sewer line in the wrong place or an electrical panel that’s already maxed out, the design has to account for that before the unit arrives.
• You bought the unit first and now the lot doesn’t work. This happens more than you’d think. The Mighty Buildings unit you fell in love with doesn’t fit the buildable area of your San Antonio lot once setbacks and easements are applied. We do feasibility checks before you’re stuck with a unit that can’t be placed.

DIY or Call Us?

You can absolutely pull your own permit in San Antonio. The city will let you be your own contractor and submit your own drawings. Here’s the honest math: if you’ve never produced a stamped structural drawing set or answered a plan review comment, you’ll spend 8 to 12 weeks going back and forth with the permit desk, and every resubmission costs money. If you hire us, the design and permit package is done in one pass, usually 4 to 6 weeks from survey to issued permit, because we already know what the reviewers in San Antonio flag. This is not a safety issue like a gas line or a high-tension spring – nobody gets hurt filing a bad permit application. But it is a budget issue, because a rejected permit adds time, and time adds carrying costs on a unit you already bought. If you want to run the permit yourself, we’ll cheer you on. If you want it done right the first time, call (430) 258-2928 and Troy Eastman will give you a flat number for the whole package.