What is the McMansion Ordinance in Austin?

Subchapter F of the Austin Land Development Code — adopted by Ordinance 20060309-058 in 2006 and known as the McMansion Ordinance — governs residential additions on parcels inside the Urban Roadways Network, which covers most of central Austin between Highway 290, Loop 360, MoPac, and the eastern edge of the original city grid. Any second-story addition or substantial first-floor expansion in that zone interacts with the rule.

Three controls do most of the work. Floor-to-Area Ratio under 25-2 Subchapter F Article 2.4 caps gross floor area at 0.4 of lot area, with a sliding-scale FAR bonus that rewards garage placement, smaller second-floor footprints, and certain family-friendly area exclusions. The tent-plane control (Article 2.6) projects a 45-degree plane upward from a 15-foot side-setback datum line; any building mass that punches through that plane requires a redesign or a Subchapter F Modification through the Residential Design and Compatibility Commission. Side-wall articulation under Article 2.7 forces breaks in long second-story walls to soften the visual impact on neighbors.

Because Subchapter F operates as an overlay on top of base zoning (SF-3 in most central Austin neighborhoods), it stacks with other constraints: impervious cover under 25-8-63, compatibility setbacks under 25-2-1051 if the parcel is near non-SF zoning, and the McMansion-Plus heritage-tree protections under 25-8-622. A typical second-story addition on an SF-3 lot has to satisfy all four simultaneously, and the binding constraint is rarely the one homeowners expect.

The HOME Phase 1 ordinance (20231207-001) loosened minimum lot size and unit count but did not repeal Subchapter F — the tent plane and FAR cap still control on existing single-family lots. HOME Phase 2 modified some compatibility provisions but again left F intact. Plan against F first, then layer HOME bonuses.

The practical authoring tactic: have your designer run a tent-plane analysis (a simple sectional drawing through the worst-case side wall) before any site plan or interior layout work begins. Most failed Austin second-story additions failed at the tent plane, and reshaping the roof to clear the plane usually cascades back through every other dimension on the project.