A backyard cottage is a detached ADU: a complete dwelling on the same lot as the main house. In San Antonio, it can be up to 800 sq ft or half the size of the main house, whichever is larger, with an overall ceiling of 1,600 sq ft. It is usually the most expensive ADU type because nothing is reused.
How tall can a cottage be?
The city's ADU page sets detached ADUs at a maximum of two stories and 25 feet as of October 2026. That leaves room for a loft or a full second floor on many lots.
How close to the property line?
As close as 3 feet from the side and rear lines, but with conditions: eaves cannot reach within 3 feet of the line, and the wall must be fire-rated if it is within 5 feet. The city itself suggests 5-foot side and rear setbacks to avoid those measures. We usually design to 5 feet unless the lot is tight.
Does it need parking?
Only if it is larger than 800 sq ft, in which case one dedicated off-street space is required. Staying at or under 800 sq ft removes that requirement.
Can it have its own meters?
Yes. San Antonio lets an ADU have separate meters or share the main house's. Separate CPS Energy and SAWS service costs more up front but makes billing a tenant simpler.
What does a cottage cost?
One San Antonio guide, updated October 2026, estimates $80,000 to $150,000 for construction and about $95,000 to $170,000 all-in. Utility connections alone can run $5,000 to $20,000 by the same estimate. Details are in the cost guide.
What can change the plan?
- Soil. Clay soils common in the region shrink and swell, so the foundation is engineered for the site.
- Trees. Mature live oaks and their roots often decide where the slab can go.
- Drainage and floodplain. Lots near creeks may carry extra review.
- Deed restrictions. A subdivision covenant can forbid a second dwelling regardless of city zoning.