Calculation methodology
The complete baseline, escalation, and regional adjustment model, shown without black-box scoring.
Two data layers, one visible result
The baseline records hold dated material, labor, permit, and disposal inputs. Monthly index snapshots adjust material and labor direction. A ZIP-derived OEWS wage multiplier then adjusts labor only.
material = baseline rate × quantity × (1 + material index delta)
labor = baseline rate × quantity × (1 + labor index delta) × regional multiplier
subtotal = material + labor + permit + disposal
range = subtotal × explicit low/high multipliers
Range tiers
Commodity and well-defined scopes use a 1.40× to 1.70× spread. Standard installed systems use 1.60× to 2.00×. High-variance scope projects use 2.00× to 2.50× at most, then expose scope depth so the user can recalculate a narrower band. Technical formula tools do not receive a cost spread. The complete before-and-after rule is recorded in the range audit.
Numeric provenance
Every default quantity, base rate, allowance, and range multiplier resolves to a named source_id. Public sources support wage selection, input-price movement, and automated plausibility validation. The exact legacy base-period values are separately labeled as locked HomeCostTotals model inputs; they are not represented as verbatim government or university figures. Each calculator prints the value, identifier, and derivation beside its calculation record.
Automated publication
Estimates on this site are produced by an automated model. Baseline rates are escalated using published federal price and wage indices on a scheduled refresh. No individual estimate is reviewed by a person before publication.
Publication gate
A calculator is indexable only when its record passes automated validation, every numeric field resolves to a registered provenance identifier, citations resolve, arithmetic is internally consistent, and its index series are verified. Failed refreshes retain the last valid snapshot.
Limitations
Indices track input-cost direction rather than local retail prices. OEWS wages exclude contractor overhead and scarcity. Every result remains a planning estimate.