By Kathleen Lavallee, Product Manager, LightBox
At the recent ASTM meetings in Dallas, I had the opportunity to sit in on the E1528 Transaction Screen session, where participants discussed whether the definition of “adjoining properties” should be updated to address additional scenarios and reduce ambiguity in the current language.
What stood out was how much of the discussion focused on edge cases. Not the obvious adjacencies, but the real-life scenarios that environmental professionals (EPs) are faced with that fall into the grey areas: properties separated by easements, questions around what constitutes “public,” or how a “thoroughfare” should be interpreted.
Listening to the conversation around adjoining properties during the E1528 committee meeting reinforced many of the challenges we had to address while developing our adjoining property technology. LightBox engineers require defined logic. The system has to account for real-world permutations. That means accounting for every possible boundary condition, every exception, and every scenario that might arise in practice.
It was notable to see a working session slide at the ASTM meeting that outlined potential updates to the definition, closely mirroring the same questions our team spent months debating, often in consultation with clients. The industry is still working toward greater clarity, but the underlying challenge is already very real in day-to-day project work.
E1527-21 and the Expanding Scope of Adjoining Property Research
ASTM first published the E1527 standard for Phase I Environmental Site Assessments (ESAs) in 1993, establishing the framework EPs use to identify recognized environmental conditions (RECs) during commercial real estate due diligence. The standard has been revised several times, most recently in 2021 (E1527-21).
One of the more notable recent updates affected the language surrounding historical research on adjoining properties. While the practical impact was minimal for most historical sources, the revision more significantly raised the bar for city directory research.
Under the prior version of the standard (E1527-13), references to adjoining properties appeared primarily in the Site Reconnaissance section. Past uses of adjoinings were typically documented if they were observed during the site visit or identified through interviews or records review. Uses in the surrounding area were often captured only to the extent they surfaced during research on the subject property.
E1527-21 raised that expectation.
The standard calls for reviewing the four primary historical sources, often referred to as the “Big Four,” for adjoining properties when those sources are already being used for the subject property and provide relevant coverage:
- Aerial photographs
- Fire insurance maps (Sanborn maps)
- Local street directories (city directories)
- Historical topographic maps
If any of these sources are used for the subject property but not reviewed for adjoinings, the environmental professional must explain that decision in the report.
The implication is clear. Adjoining property research is no longer incidental. It is part of a more structured and defensible historical analysis.
Why City Directories Create a Practical Constraint
For three of the Big Four sources (i.e., aerials, topographic maps, and fire insurance maps), expanding the review to adjoinings is typically manageable. These resources generally capture multiple properties and surrounding areas, often in a single image or map, making adjoinings visible during the normal course of research.
Not so for city directories.
These records are historically organized by street address and published in individual volumes by year. Identifying historical occupants for adjoining properties often requires reviewing multiple addresses across multiple streets, years, and books, significantly increasing the number of pages that must be examined.
In practice, expanding the scope to include several surrounding streets can quickly turn into a time-intensive process. Until now.
Ushering in a New Era for City Directory Research
The digitization of historical city directories has fundamentally changed what is feasible.
LightBox’s investment in technology tools and digitization of decades of city directories enables EPs to access occupant data directly within LightBox Live. Geolocating historical occupants on a map makes it significantly easier to identify relevant properties that once required manual review of physical books or static records. Integrated tools for searching, sorting, and filtering streamline what was previously a time-intensive, manual process.
Additional curation, including machine learning and proprietary datasets developed through years of historical research, helps categorize records associated with higher-risk historical uses such as gas stations or dry cleaners.
The result is a more scalable approach to adjoining property research. What once required significant manual effort can now be completed more efficiently, while also reducing the likelihood of missed information.
Supporting More Complete Adjoining Property Research
As E1527-21 places greater emphasis on identifying past uses of adjoinings, the expectation for thoroughness has increased. At the same time, the definition of what qualifies as an adjoining property continues to evolve through industry discussion and interpretation.
Improved access to digitized, searchable city directory data helps EPs navigate both challenges. It supports a more complete view of surrounding property use while giving teams the ability to scale their research without proportionally increasing time and cost.
The outcome is not just efficiency. It is a more complete and defensible understanding of potential environmental risk, aligned with the realities of how projects are scoped and reviewed today.
