Accessory Dwelling Unit (ADU) projects in Austin, Texas demand architectural drawings that knit together dense code references, precise site documentation, and meticulously detailed construction standards. Every sheet-site plan, section, electrical, or note page-must align with Austin’s evolving adoption of national model codes, from the 2021 IRC/IBC and IECC to 2020 NEC, 2021 UPC, and the City’s own granular Land Development Code (LDC) amendments. Austin’s plan reviewers at the Development Services Department (DSD) routinely flag site dimensioning, incomplete fire assemblies, and missing energy compliance as the top hurdles. Their routine redlines and intake rejections follow clear code citations, which are exacting and fiercely enforced. From SF-3 setbacks to fire ratings under Section R302 to R-values in IECC Climate Zone 2, assembling compliant ADU drawings is an exercise in detail and discipline at every stage.

Detailing Austin-Specific Zoning Compliance and Impervious Cover Calculations on ADU Site Plans

Zoning documentation and site plan accuracy are foundational in Austin, where the Land Development Code (LDC) shapes ADU configuration, placement, and overall building envelope. Austin’s ADU allowance is tightly constrained by zoning district overlays, impervious cover maximums, protected tree overlays, and highly prescriptive setback controls-not just for code compliance, but permit eligibility. Typical City of Austin plan review checklists put LDC Chapter 25-2-774 at the center of ADU site design, and deviations are common sources of DSD redline and rejection.

LDC Chapter 25-2-774 and Site Dimensional Controls

In the SF-3 (Family Residence), SF-5 (Urban Family Residence), and SF-6 (Townhouse/Condo Residence) districts, setbacks and maximum building dimensions must be explicitly dimensioned and labeled on the site plan. For SF-3 lots-the vast majority of central Austin infill-the basic site parameters are:

  • Front setback: 25’
  • Side setback: 5’
  • Rear setback: 10’ (may be reduced to 5’ if the ADU is ≤1 story/<15’ tall per Section 25-2-555(D))
  • Height restriction: 35’ overall

SF-5 and SF-6 districts allow similar yard dimensions, but with nuanced differences: SF-6 (for townhome/condo) allows 0’ side setback for attached buildings and reduces front setbacks to 15’. All three districts limit the ADU’s total area using both a hard cap and a percentage-of-lot-size test, as per Section 25-2-774(C)(5): “The total gross floor area of a secondary unit may not exceed the lesser of 1100 square feet or 15 percent of the lot size.” The second story is further limited to 550 sq ft. Each dimension must be hashed out on-site plans with callouts-no “typical” notes, only actual scaled dimensions and area tabulations.

A sample drawing call-out for the ADU setback would look like:

  • (Site Plan-A-101) DIMENSION: 'PROPOSED ADU WALL TO REAR P.L. (5’-0”) TYP. (See 25-2-555(D))'
  • (Calculated Area Table): 'ADU 1st Floor GFA = 850 SF; 2nd = 550 SF; Total = 1,100 SF; Lot = 7,200 SF; Allowed Max = 1,080 SF. Compliant? NO. Revise.' (common redline)

Plan reviewers consistently cite missing or erroneous area calculations for ADU maximum size, especially when the second-floor restriction is not separately tabulated. A compliant plan set will delineate these areas explicitly in its site data block, matching each value directly to code text and dimensional site evidence.

Impervious Cover Calculations: Accuracy, Not Estimation

Impervious cover-defined as any surface that disallows water infiltration, including roofs, paved walks/drives, and contiguous decks-has an outsized influence on ADU feasibility. SF-3 limits total impervious cover to 45% of the lot area; SF-5 and SF-6 allow 55%. Calculations must be itemized on a dedicated “IMPERVIOUS COVER TABLE”-samples from accepted plan sheets often look like this:

  • Building 1 (Primary Residence): 1,800 SF roof
  • Building 2 (ADU): 1,050 SF roof
  • Driveway/Parking: 700 SF
  • Walkways: 180 SF
  • Total Impervious Cover: 3,730 SF / 8,000 SF lot = 46.6% (NONCOMPLIANT-redline triggers: “Revise site plan to reduce impervious surfaces or provide variance approval.”)

A compliant plan not only itemizes each category but notes “Total impervious cover limited to 45% of lot (25-2-492)” and graphically identifies every impervious area on the site plan itself.

Tree Protection Plan Integration

Heritage and protected trees (≥24” and 19” DBH, respectively) must be surveyed and their “critical root zones” (CRZ) diagrammed. Drawings must show:

  • Exact species, DBH, and canopy spread
  • CRZ boundary (typically 1’ radius per 1” DBH)
  • Distances from new construction, with notes such as: “PROPOSED ADU 19’ FROM 28” LIVE OAK CRZ-TREE PROTECTION FENCING REQUIRED (see Sheet L-200 for details and Section 25-8-604).”

Missing these dimensions is among the most common DSD rejection causes. Any encroachment or tree removal must be justified and mitigated using City-approved methods, all described in detail on both the site and landscape sheets.

Common City of Austin Redlines and Required Site Plan Details

  • “Incorrect or missing setback dimension. Show all required setbacks measured from property lines to new construction.” (DSD Plan Review Checklist)
  • “Impervious cover area not provided or exceeds allowable limit. Provide calculations in tabular form.”
  • “Tree survey missing or incomplete. Identify all protected trees per LDC 25-8.”
  • “Maximum ADU area not calculated for second story/total, or not shown in plan data block.”

Drawing-Sheet Conventions and Required Plan Data Blocks

Austin reviewers expect to see on the cover and/or site plan: a north arrow and scale (graphic and numeric), legend for line types and symbols, table of zoning data, impervious cover table, tree inventory, and dimension chains pulled from property lines to each structure, all match-linked to the site’s legal plat. Incorporation of benchmarks, legal addresses, and registered surveyor’s information is required whenever property lines are not self-evident. Every code/callout must reference the relevant LDC, such as "SEE LDC 25-2-774 FOR TWO-FAMILY USE STANDARDS."

Drafting Fire-Resistive Assemblies and Egress Compliance for Austin ADUs

Safety in ADU design pivots on clearly-dimensioned and code-cited assemblies for fire separation, egress, and life safety alarms. Austin requires full, prescriptive compliance with the 2021 International Residential Code (IRC) as adopted and amended, with particular scrutiny given to wall/floor assemblies (R302), emergency opening dimensions (R310), and alarm placement (R314, R315). DSD reviewers will flag even minor ambiguities, rooting comments and rejections in specific Sheet/Detail omissions.

1-Hour Fire-Resistive Assemblies (IRC R302.1, R302.3)

When an ADU sits within 5’ of any lot line, exterior walls must achieve a 1-hour fire-resistance rating per IRC 2021 R302.1. Where an ADU abuts or is attached to the primary unit, separation between units is governed by IRC R302.3-“Dwelling units in two-family dwellings shall be separated by wall and/or floor assemblies having not less than a 1-hour fire-resistance rating.” Austin currently follows these requirements without relaxation for detached/attached status.

Plan sets must illustrate the fire-rated assembly in section and provide a “Fire-resistive wall legend,” typically as:

  • Typical Detail Callout-A-501:
    "1HR RATED WALL PER IRC R302.1: (2) 5/8” TYPE ‘X’ GYP EACH SIDE 2x4 WD STUD @ 16” OC, ROCKWOOL BATTS, CAULK ALL PENETRATIONS WITH FIRE-CAULK. RATED WALL CONTINUES TO UNDERSIDE ROOF SHEATHING. JOINTS STAGGERED. SEE UL DESIGN U305 OR GYPSUM ASSOC. GA-1HR."
  • Dimension: Continuous, unbroken, full-height wall on both plan and section, with all wall types keyed to their rating in the partition schedule.

For projections/eaves, “No projections permitted less than 2’ from property lines (R302.1 & City of Austin amendment).” Interrupting this assembly with an unrated window or door within a 3’ zone (typically) will generate DSD comments.

Egress Windows: Dimensions and Labeling (IRC R310.1 & R310.2)

Every ADU sleeping room requires at least one emergency escape/rescue opening per R310.1, culled from R310.2 minimums:

  • Net clear opening: 5.7 square feet
  • Minimum clear opening height: 24 inches
  • Minimum clear opening width: 20 inches
  • Maximum sill height above floor: 44 inches

On floor plans and window schedules, dimensions must be explicit:

  • Window Keynote on A-201: "Egress window at all bedrooms-3'-0"W x 4'-0"H, 5.7 SF clear open, 42" sill (see R310.2). Window Schedule: U-Factor/SHGC tags included per IECC."

Plan review comments will cite “window schedule does not indicate which windows meet emergency egress requirements. Mark all egress windows with code reference and dimensions.” Floor plan graphics should use a window symbol note and a data bubble referencing the schedule.

Smoke and Carbon Monoxide Alarms: Placement and Interconnection (IRC R314, R315)

The 2021 IRC, as locally amended, mandates smoke alarms in each sleeping room, outside each sleeping area, and on every story, interconnected and hard-wired with battery backup (R314.3, R314.6). Carbon monoxide alarms are required “outside of each sleeping area in the immediate vicinity of the bedrooms” when gas appliances or an attached garage is present (R315.3), also hard-wired/interconnected.

  • Electrical Plan Keymark-E-101: S = SMOKE ALARM (HARDWIRE, BATTERY BACKUP); C = CO ALARM. Place legend with: "Smoke and CO alarms per IRC R314 & R315; interconnected, AC-powered with battery backup; locate as shown."

Missing these symbols or failing to note interconnection/hard-wiring is a near-certain initial rejection. DSD reviewers often comment: “Show all alarm locations per IRC R314/R315 and indicate wiring method as interconnected, hard-wired, with battery backup.”

Fire and Egress: Drawing-Sheet and Code Citation Essentials

  • Wall Section (A-501/A-502): Partition legend shows all fire-rated and unrated wall types, keyed directly in plan.
  • Reflected Ceiling Plan: Shows all alarm placements graphically, with cut-sheets or schedule table showing device type.
  • Window Schedule: Indicates type, clear opening, U-factor, SHGC, and egress code compliance.
  • Plan General Note: “All penetra­tions in fire-rated walls and assemblies to be sealed with approved firestopping material per R302.4.”

Structural Specification and Detailing for Austin ADU Foundations and Framing

Foundation and framing details must address both Austin’s expansive soil conditions and the city’s wind loading requirements as declared in the 2021/2024 IRC (Chapters 4-Foundations, 5-Floors, and 8-Roof-Ceiling Construction), with local DSD amendments that often set a higher bar for performance and clarity. Engineering studies and structural plans are mandatory for new ADUs, and redlines often track incomplete structural calculations, “generic” details not responsive to Austin soils, or omission of hold-downs/shear bracing for wind events up to 140 mph (ASCE 7-16 basic wind speed).

Foundation Design: Slab-on-Grade and Pier-and-Beam Best Practices

ADU plans must specify foundation system selected per geotechnical or pre-engineered guidelines. Austin DSD accepts:

  • Slab-on-grade: 4” reinforced slab on compacted fill with #4 @ 12” OCEW; edge beams min 12” x 24” with (2) #5 continuous bottom steel. Post-tensioning or additional beams required on high plasticity soils per Building Criteria Manual §4.4.5.4.
  • Pier-and-beam: Isolated or continuous piers min 12” dia, 24” deep, #4 verticals with #3 ties @ 18” oc; grade beams (2) #4 T&B. Crawl space vented 1 SF per 150 SF area.

Detail callouts:

  • "FOUNDATION-SLAB-ON-GRADE PER IRC R402, POST-TENSION IF SOILS CLASS PI > 40 (See Geo Report #5201). All reinforcing per schedule, see S-101."
  • "PIER REINFORCEMENT: #4 VERT @ 12” OC W/ #3 TIES. GRADE BEAM: (2) #4 TOP, (2) #4 BOTTOM."
Include all footing dimensions, depth below grade, and location of all reinforcement in both plan and section (see S-101/S-201).

Framing and Shear Wall Detailing: Dimensioned and Fully Scheduled

Floor, wall, and roof framing must reference species, grade, and spacing. Use souther yellow pine, #2 or better, as standard unless otherwise engineered. Lumber schedule should be keyed on framing plans:

  • S-102: “Studs: 2x4 SYP #2 @ 16” OC unless otherwise noted. Floor joists: 2x10 SYP #2 @ 16” OC. Rafters: 2x8 SYP #2 @ 16” OC.”

Shear wall and lateral bracing per IRC 602.10 and ASCE 7-16:

  • Shear Wall Table-S-103: “Shear Wall: 7/16” OSB, nailed 6” OC at edges, 12” in field; hold-downs required at each end SW1-SW3, see details. Min wall: 4’ length, aspect ratio ≤2:1.”
  • All braced wall lines are dimensioned/located on plan view, with cross-references to “Shear Wall Assembly Detail 2/S-501.”

For Austin's location in the 140 mph wind speed zone (per ASCE 7-16), show all connections, nailing schedules, and wind anchors/straps per manufacturer’s ICC-ES report number on both plan and detail sheets.

Common DSD Redlines and Required Inclusion in Structural Sheets

  • “Provide lateral bracing/shear wall schedule and show locations on both foundation and framing plans.”
  • “Detail all hold-downs, anchor bolts, and uplift hardware per ASCE 7-16 wind loads (140 mph).”
  • “Dimension all framing members and specify species/grade on sections and schedules.”
  • “Include engineering for foundation suitable to expansive soils; generic slab details not accepted.”

Documentation must include all lumber/connector specs, dimension every wall/joist/beam/column on sheets, and tie every assembly (plan, elevation, detail) to code: “SEE IRC R502.3 FOR JOIST SPAN; ALL FRAMING PER TABLE R602.3(1).”

MEP and Energy Code Compliance for Austin ADUs

Mechanical, electrical, plumbing (MEP), and energy code requirements for Austin ADUs are derived from UPC 2021, NEC 2020, IMC 2021, and IECC 2021, all with local DSD/utility amendments. Omission of fixture counts, GFCI/AFCI schedules, ventilation specs, or window/insulation performance are near-automatic plan review knockbacks; DSD as well as Austin Water and Austin Energy reviewers require this data on dedicated disciplines’ sheets and in project-wide general notes.

Plumbing: Fixture, Drain, and Vent Sizing (UPC 2021)

  • Fixture Counts: ADUs must include, at minimum, a single water closet, lavatory, tub/shower, and kitchen sink per UPC Table 422.1. Additional fixtures and washing machine are optional, but must be itemized in plumbing schedule on P-101.
  • Drain/Vent Sizing: Use fixture unit tables per Chapter 7 to size branch/stack, with complete isometric diagrams, pipe slopes, and all vent terminations labeled.
  • Common Redline: “Show all fixtures with total fixture-unit demand; size all drains and vents in schedule; provide waste and vent isometric.”
  • Backflow Prevention: All hose bibbs and irrigation valves require labeled backflow devices, per Austin Water amendments.

Electrical: Panel Schedules and Circuit Protection (NEC 2020)

  • Panel Schedule (E-201): Shows all loads, circuit numbers, breaker sizing, calculated demand/load summary. NEC 210.52 governs outlet spacing; 210.8 and 210.12 control GFCI/AFCI coverage.
  • GFCI: All kitchen, bath, laundry, outdoor, and garage circuits, plus outlets within 6' of sinks, must provide GFCI-the schedule must note “GFCI PER 210.8” with legend marking.
  • AFCI: All living, sleeping, hall, and stair circuits must be AFCI protected: "AFCI PER 210.12."
  • Common DSD Rejection: “GFCI and/or AFCI protection not indicated for all required circuits-label on schedule and floor plan.” Lack of circuit legends is a common intake fail.

Mechanical: Ventilation and Exhaust (IMC 2021)

  • Kitchen: All range/cooktops must vent to exterior-Section 505. Ducts shown in plan and isometric, with notation: “Range hood exhaust min 100 CFM to exterior, backdraft damper per IMC 505.”
  • Bathroom: 50 CFM intermittent / 20 CFM continuous (IMC 403.3.1.1); labeled on M-101: “Exhaust fan 80 CFM, 0.4 sones, ducted to exterior.”
  • Common Redline: “Provide mechanical schedule with fan make/model, CFM and sone rating; show all duct runs and terminations on plan and in section.”

Energy Efficiency: IECC 2021 (Climate Zone 2)

  • Insulation: Per IECC R402, walls R-13, ceilings R-38 (minimum). Wall sections must show insulation and cite R-values; callout: “Walls R-13 BATT, SEE IECC TABLE R402.1.2.”
  • Windows: Max U-factor 0.40, SHGC 0.25, shown on window schedule: “WIN-3: 3040, VINYL, U-0.30, SHGC 0.22, NFRC-LABELED.”
  • Energy Reports: COMcheck or REScheck required with each submission, showing compliance; sample note: “Provide completed IECC compliance report with plans. All insulation/window values must match report.”
  • Common Redline: “Missing insulation values in wall section/elevations; provide window U/SHGC data in schedule.”

Utility Company and DSD Coordination

  • Austin Water: Water meter sizing, backflow device location, sewer connection, and cleanout must be depicted on utility plan. “Water and wastewater notes per Austin Water Utility Standard Details-see W-101.”
  • Austin Energy: Panel location, service drop, and meter base shown per Building Service Planning Application (BSPA) approval. “All electrical service and meter per Austin Energy standards-submit BSPA.”
  • DSD: All disciplines' designs coordinated-no conflicting notes/dimensions between mechanical, electrical, and plumbing sheets; each must cross-reference specific local corrections.

Optimizing Plan Set Organization and General Notes for Austin ADU Permit Review

Plan set structure and the organization of general notes shape not just the permit review process, but the speed of approval, with Austin DSD reporting that the majority of initial rejections are due to omission or miscoding at the plan index/general notes stage. Every project must now be digitally submitted through Austin Build + Connect (AB+C), each file correctly named, signed, and indexed per DSD instructions.

Comprehensive General Notes Referencing Adopted Codes

A robust general notes section, typically on the cover (G-001) or first architectural sheet, must name the following enacted codes and amendments (as of July 10, 2025):

  • 2024 International Residential Code (IRC) with City of Austin amendments
  • 2024 International Building Code (IBC) where applicable
  • 2024 International Energy Conservation Code (IECC)
  • 2023 National Electrical Code (NEC)
  • 2024 Uniform Plumbing Code (UPC)
  • 2024 Uniform Mechanical Code (UMC)
  • City of Austin Land Development Code (LDC)

Sample general note:

  • "All work shall conform to the most recent City of Austin adopted codes and amendments, including: 2024 IRC, 2024 IECC, 2023 NEC, 2024 UPC/UMC, City of Austin LDC and Building Criteria Manual; see www.austintexas.gov/development-services/building-technical-codes."
  • "Project is an ADU (Accessory Dwelling Unit). All zoning, area, fire, foundation, MEP, and energy standards per LDC 25-2-774 and respective sections of applicable codes. Building is located in SF-3 zoning-see data block for specifics."
  • "All emergency egress and fire-rated assemblies per IRC R302, R310, City of Austin amendments. Windows, doors, and penetrations in fire-rated walls to comply with manufacturer’s listings and Table R302.1(1)."

Embedding Prescriptive Code References in Drawing Details

Every key detail, dimension, and specification should include explicit code cross-reference. For instance:

  • A-501 Wall Section: “1HR WALL PER R302.1-SEE PARTITION LEGEND. PENETRATIONS FIRESTOPPED PER R302.4.”
  • P-101 Plumbing Plan: “All drain and vent sizing per UPC 2021 Tbl 703.2(1) and 709.1.”
  • E-101 Electrical: “All circuits per NEC 2020 210.12 (AFCI) and 210.8 (GFCI) requirements.”

Plan reviewers expect to jump from plan graphic to code text without ambiguity. Including the code section on each relevant detail is an essential streamlining move, and missing code references are a top-quartile source of redlines and “See code section XX” responses.

Logical Sheet Index, Numbering, and Submission File Naming

Accepted sheet index convention (found on most approved Austin ADU submittals) is:

  • G-0XX: General, notes, code data, sheet index
  • A-1XX: Site and context plans
  • A-2XX: Floor plans and roof plan
  • A-3XX: Elevations
  • A-4XX: Sections, details
  • S-1XX: Structural plans, details, schedules
  • M-1XX: Mechanical layouts, schedules
  • E-1XX: Electrical layouts, schedules
  • P-1XX: Plumbing layouts, risers

File naming for AB+C digital submission follows: "A-101_SitePlan.pdf", "S-101_FoundationPlan.pdf", etc. Digital seals must appear in compliance with Texas Engineering Practices Act-and missing seals, PDFs with non-flattened layers, or inconsistent file names are among the most frequent causes for rejection at intake.

Common Intake Rejection Reasons and Required Detail

  • Plans not referencing City of Austin local amendments or showing adopted code years
  • Missing or incomplete site data block (setbacks, zoning, area tabulations, tree report)
  • Unsigned/sealed engineering or architectural sheets
  • Discrepant details or contradictory specifications between plan sheets
  • Insufficient drawing detail: lack of callouts for fire rating, window/insulation R-values, venting, or protected zones

Early correction by cross-referencing all code/code edition, verifying every table, sheet, and detail, and using a standardized indexing and naming system reduces the risk of iteration and keep application clocks running. Notably, Austin’s DSD process is almost entirely digital-hard copy submissions or scanned-for-signature documents will be outright rejected.

Standard Drawing-Sheet Call-Outs, Section and Detail Coordination

Every detail and section cut must be numbered and keyed directly to the index and referenced throughout, e.g., “See Section 1/A-401,” “See Detail 3/S-501.” Material, dimension, and assembly callouts must match across all sections, elevations, schedules, and notes. Conflict or omission drives iterative redlines, with DSD reviewers returning sheets for even minor discrepancies.

Conclusion

Plan sets for ADUs in Austin are measured as much by their cross-referenced compliance as by their construction clarity-every dimension, code citation, assembly detail, and material note forms a seamless chain of evidence that the project follows the city’s complex overlay of local zoning, national model codes, and digital submission requirements. The City’s DSD leverages powerful plan-review checklists and demands precision in every site metric, fire separation, foundation schedule, MEP schematic, and general/code note called out on drawing sheets. Consistency, specificity, and explicit code referencing remain the essential drafting tools for ADU approval in Austin.

Kingsway Drafting & Design delivers comprehensive, code-compliant residential plan sets and construction documentation trusted for quick city approvals across Texas.