The Zilker Treehouse is a speculative design-build project, sited in South Austin's Zilker neighborhood. The original cottage dated from 1935, but had been marred by an ill-conceived addition and years of duplex zoning. The lot is triangular, and setbacks severely constrained the buildable area. The new addition has a relatively small footprint, but rises three stories into the live oaks and cedar elms surrounding the property to gain square footage and city views. While formally more modern than the cottage, the addition respects its context by stepping back from the street and exhibiting a similar material palette. An extensive interior remodel of the cottage results in a modern home with vintage charm.