ADU rules in Burnet County

Texas counties have no general zoning power, and no subchapter of the county zoning chapter (Local Government Code ch. 231) reaches Burnet County, so unincorporated Burnet County has no use table, density limit or one-house-per-lot rule. The Commissioners Court adopted its Subdivision and Development Regulations under LGC ch. 232, subchapters A and E (orders of January 11, 2011), and the subchapter E rule-making power expressly may not regulate the use of property, the number of buildings on a tract or the number of residential units per acre (LGC §232.101(b)). A detached second dwelling therefore faces no county prohibition: it needs a 911 address, a county building (development) permit and a septic permit (from the county, or from LCRA near the lakes), the same steps as any new residence. Platting applies only when land is divided, so building a second home on an existing tract does not trigger a plat (Regulations Art. 1 §2(D)).

Nothing in the county's orders treats an attached unit, a garage apartment or an internal conversion differently from other residential construction, and the same §232.101(b) bar on regulating residential use and unit counts applies. The septic system is the practical gate: a permit is required to alter or extend an on-site sewage facility (Health and Safety Code §366.051(a)), and TCEQ sizes systems by bedrooms and floor area, so a unit with its own bedrooms usually means a modified or new system designed for the combined flow. TCEQ's rules count detached buildings "routinely used only by members of the household" as part of the single family dwelling, while a unit occupied by a separate household adds its own dwelling flow. Inside LCRA's lake zones any floor-plan change, even a remodel within the existing footprint, needs LCRA floor-plan review, and an LCRA permit to operate ends automatically if the structure is enlarged beyond the size the system was approved for (LCRA OSSF Rules §10.08).

Burnet County sets no maximum size for any dwelling, and LGC §232.101(b)(3) bars the county from regulating "the size of a building that can be constructed on a particular tract of land" through its subdivision rules. Size matters instead through the septic design: TCEQ's Table III flows step up with bedrooms and floor area (225 gallons per day, or 180 with water-saving fixtures, for a one- or two-bedroom dwelling under 1,500 sq ft), and the site must hold a drainfield sized for every dwelling it serves plus the required setbacks. In a mapped flood hazard area the lowest floor must sit at least one foot above the base flood elevation (Flood Damage Prevention Order Art. 5 §B(1)). In the Colorado River watershed area mapped under LCRA's Highland Lakes Watershed Ordinance, a project that creates more than 10,000 sq ft of impervious cover or disturbs more than one acre needs an LCRA development permit; smaller residential projects proceed on a written notification.

No Burnet County order requires the owner to live on the property, either at application or afterward: the Subdivision and Development Regulations (with their flood, septic, manufactured home rental community and groundwater appendices), the On-Site Sewage Facility Order and the hotel occupancy tax regulation contain no owner-occupancy, owner-residence or homestead condition. The county could not add one through its subdivision powers, since LGC §232.101(b)(1) bars regulating "the use of any building or property for business, industrial, residential, or other purposes." Texas has no state ADU statute that adds or forbids such a rule. Private deed restrictions can impose occupancy terms, but the Regulations leave their enforcement to the subdivider and lot owners (Art. 1 §2(E)).

Burnet County has no parking requirement for a house or a second dwelling; its regulations set road, drainage and frontage standards for subdivisions, not on-site parking. Access is the only related control: the 911 office will not assign a new address off a county road or TxDOT road until the precinct commissioner (on the county's Road Access Permit, which fixes culvert size at a site meeting) or TxDOT has approved the driveway. Address numbers are assigned from the driveway and structure locations, so the address request for a second dwelling must show where it sits relative to the driveway and lot lines.

Every step is administrative, with no hearing: first a 911 address (14 to 21 business days), then a county building permit (Class A outside the flood hazard area, $25 with no structural inspections; Class B inside it, $400 with an elevation certificate or engineer's letter and pre-pour and final floodplain inspections), then the septic permit ($250 for most systems, $400 for aerobic) based on a licensed site evaluator's evaluation and the installer's design. Burnet County permits and inspects every septic system regardless of tract size (OSSF Order §10(A)), and the state exemption for large tracts would not cover a tract with two dwellings anyway, since it requires the single family dwelling to be the only dwelling on the tract (30 TAC §285.3(f)(2)). Within 2,200 feet of Lake Buchanan, Inks Lake, Lake LBJ or Lake Marble Falls, and 2,000 feet of Lake Travis, LCRA is the septic permitting authority instead ($260 conventional, $410 professionally designed). The Commissioners Court acts only on appeals, variances and land divisions.

Burnet County has no rental registration, short-term rental permit or minimum-stay rule for unincorporated areas; its only short-term rental regime is the county hotel occupancy tax, levied at 5% on rooms "outside the city limits of Marble Falls, Burnet, and Bertram" and reported and paid quarterly, with occupants of 30 or more consecutive days exempt. Tax Code §156.001(b) makes a short-term rental a "hotel" for both the 6% state tax and the county tax under Tax Code ch. 352. Renting out two or more manufactured-home spaces on one tract makes it a manufactured home rental community that needs an engineered infrastructure development plan approved by the Commissioners Court (Regulations Appendix F). Selling an ADU separately means dividing the land, which the Regulations treat as a subdivision requiring a plat unless a statutory exemption applies, and the definition expressly includes a condominium or multi-family scheme.