Heritage Impact Assessment Calculator

Architectural impact is weighted at 30% versus just 10% for reversibility, reflecting that reviewers generally care most about direct, permanent alterations to character-defining features regardless of whether those changes could theoretically be undone later. A highly reversible change that still severely damages architectural character (weighted heavily) will still score as high-risk, while an irreversible but architecturally gentle change (reversibility weighted lightly) won't dominate the result on its own.

The five inputs are combined into a single weighted score out of 5, then bucketed into four tiers: minor below 1.5, moderate from 1.5 to 3, major from 3 to 4, and severe at 4 or above. The mitigation level output simply mirrors that same tier (0 through 3), so a major or severe result flags that avoidance, minimization, or mitigation measures will likely be required, not just recommended.

It's weighted lower than architectural impact, historical significance, and visual/setting impact because most heritage impact assessments deal with above-ground changes where subsurface disturbance either isn't a factor or hasn't been confirmed yet. If your project involves excavation near known or suspected archaeological resources, that 15% weight likely understates the real regulatory risk — a Section 106 or state review would evaluate archaeological impact on its own separate track regardless of what this combined score shows.

No. This tool is meant as a structured starting point for a SHPO consultation or Section 106 review, not a substitute for one — actual determinations of adverse effect weigh site-specific context, comparable precedent, and public input that a five-number weighted average simply can't capture. Even a minor score is worth confirming with a qualified preservation consultant before proceeding, especially on properties with contested or borderline significance.