As a building enclosure consultant and professional engineer practicing in the building restoration and preservation space, I am frequently reminded that our greatest technical risks rarely stem from what we see—but from what we assume. Exploratory openings, also referred to as probes or inspection openings, remain one of the most effective tools available to reduce uncertainty during investigations and design, particularly for existing and historic buildings.
This point was reinforced for me recently while attending a continuing education event hosted by the Association for Preservation Technology New England (APTNE). The discussion centered on balancing preservation ethics, constructability, and risk—an intersection where exploratory openings play a critical, and often undervalued, role.
Non-destructive testing, archival research, and visual surveys are essential first steps in any investigation. However, in restoration work, they are rarely sufficient on their own. Legacy construction methods, undocumented repairs, concealed deterioration, and material transitions behind finished surfaces often lead to issues that need to be visually confirmed.
Exploratory openings allow the design team to verify assumptions about:
- Wall and roof assembly configurations.
- Moisture management strategies (or lack thereof).
- Structural interfaces and load paths.
- Hidden deterioration mechanisms.
When properly planned, documented, and repaired, these openings provide disproportionate value relative to their cost. In my experience, even a small number of well-located probes can dramatically improve confidence in both repair design and construction pricing.
The importance of early investigation aligns directly with the well-known MacLeamy Curve, which illustrates that the ability to influence project outcomes is highest early in the design process, while the cost of changes increases exponentially as a project progresses. While MacLeamy was first using the curve to discuss the benefits of BIM modeling,
In restoration projects, exploratory openings shift critical decision-making forward—when changes are least expensive and most impactful. They allow teams to:
- Identify scope-driving conditions early
- Reduce or eliminate redesign during construction
- Reduce contingency inflation driven by unknowns
- Improve alignment between drawings and field conditions
Put simply, probes help redistribute risk from construction—where it is costly and adversarial—back into design, where it can be managed deliberately and collaboratively.
For those unfamiliar, a concise overview of the MacLeamy Curve can be found here:
In the context of historic buildings, exploratory openings are not only practical—they are consistent with preservation best practices. The Secretary of the Interior’s Standards for the Treatment of Historic Properties emphasize minimal intervention, reversibility, and informed decision-making.
Exploratory openings support these principles by:
- Allowing repair strategies to be based on verified conditions rather than conjecture
- Reducing unnecessary demolition driven by uncertainty
- Helping distinguish between original fabric and later alterations
- Informing targeted, surgical repairs instead of broad replacement
When probes are thoughtfully located and carefully restored, they respect historic fabric while enabling responsible stewardship.
The full standards and guidance are available through the National Park Service:
Despite their benefits, exploratory openings are sometimes resisted due to concerns over cost, disruption, or owner perception. These concerns are understandable—but often misplaced.
From a cost standpoint, probes are typically inexpensive compared to change orders, delays, and disputes arising from concealed conditions. From an operational standpoint, they can usually be phased, limited in size, and coordinated to minimize disruption. And from an owner’s perspective, transparency about why probes are recommended—and what risks they mitigate—often reframes them as prudent investments rather than optional extras.
As engineers and building enclosure professionals, we have an obligation to base our designs on evidence rather than assumptions. Exploratory openings are one of the few tools that allow us to directly observe the true condition of existing assemblies. In restoration work especially, they bridge the gap between theory and reality.
My takeaway from recent continuing education—and from years of practice—is simple: projects that embrace early, strategic investigation tend to experience fewer surprises, more accurate pricing, and better long-term outcomes.
In a discipline where uncertainty is unavoidable, exploratory openings remain one of the most effective ways to manage it—early, responsibly, and in alignment with both sound engineering judgment and preservation ethics.
Kevin M. Duffy
Principal
Duffy Engineering
