The reversal is a housing-mix finding, not proof that one property type adds or subtracts a fixed percentage of value.
In August 2026, Chicago's single-family ZHVI was 1.3% below its all-homes index. Five reviewed western suburbs had single-family indexes 2.9% to 15.7% above their all-homes indexes.
The contrast does not mean Chicago houses were discounted or Clarendon Hills houses carried a fixed 15.7% premium. It means the modeled populations differ.
The all-homes index contains a mix
An all-homes index can include several property types. The mix differs from one city to another. A single-family-only index removes some of that mix but still represents a broad range of houses.
When high-value attached homes are meaningful in one city, the relationship between the two indexes can differ from a suburb dominated by detached housing. The indexes do not pair otherwise identical homes.
Composition is not causation
To estimate the effect of property type, an analysis would need to control for location, square footage, age, lot, condition, renovation, parking, association costs, and other features. The public index comparison does none of that.
Its practical value is diagnostic. It tells a reader when a broad all-homes headline may not represent the property type under discussion.
Match the evidence to the decision
Use attached comparables for a condo or cooperative. Use single-family comparables for a house. Within either group, narrow the evidence to the relevant location, price range, size, condition, and time period.
The city indexes are a starting point for that process, not a shortcut around it.
Source and method: Zillow city all-homes and single-family ZHVI for August 31, 2026. Read the full six-city property-type study for exact figures and limits.