For multi-family housing, dwellings can be grouped together based on what criteria?

The correct choice highlights the importance of grouping multi-family housing based on common materials or painting history. This criterion is essential because lead exposure risk assessments need to consider how lead-based paint was used in similar structures. Properties built around the same time often share similar construction materials and methods, which can influence the presence of lead hazards.

Grouping by common materials or painting history allows inspectors to assess risk more accurately. For example, if a series of buildings were constructed with the same paint techniques and materials, examining one property may provide insights into others in the same group, streamlining the inspection process and enhancing safety measures.

While other criteria such as location, year built, and number of units are relevant factors in different contexts, they do not provide as direct a correlation to the prevalence of lead-based paint hazards as the shared characteristics in materials and painting practices do. Knowing the specific history and materials helps focus remediation efforts effectively, making it a critical aspect of lead inspection practices in multi-family dwellings.