Guest presenter cites NPS guidance: substitute materials require case‑by‑case review, may reduce historic integrity

Guest presenter Deb Parcel summarized National Park Service guidance on substitute materials for historic exteriors and urged the commission to treat approvals on a case‑by‑case basis.

Parcel reviewed the difference between imitative materials (used from construction) and substitute materials (replacing original fabric) and emphasized that, "the integrity is always diminished when you use a substitute material," even when a substitute is appropriate. She noted substitute materials can nonetheless be acceptable in many circumstances — for example, when the original material is no longer available, when trade skills are lacking, when code or resilience considerations make replacement necessary, or when a modern product demonstrably outperforms the historic material.

Parcel walked through product‑specific considerations: dimensional and textural match, paintability, water absorption, thermal expansion behavior, warranty versus expected service life, abrasion resistance and repairability. She recommended documenting approval rationales in motions ("put that in your motion for approval why you're doing that") so future reviewers can understand the basis for decisions. Commissioners asked whether Indiana Landmarks could assist; Parcel confirmed that staff review and outside recommendations (Indiana Landmarks where appropriate) are part of a defensible review process and that some products with long track records are often preapproved.

Parcel closed by reminding members that the updated preservation brief is not a blanket approval for substitutes; each proposal must be assessed on the property and application in question.