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Costs guide

Regional cost modifiers need dated evidence

Adjust a compatible baseline transparently and keep geography, source date, and coverage attached to the result.

Created 2026-08-02Author: not yet recordedQualified reviewer: not yet suppliedSubstantive review date: pending

Direct answer

A regional modifier is defensible only when it matches the cost category, geography, time period, and baseline methodology. It should never be inferred from a ZIP code alone or presented as a local contractor quote.

Planning workflow

  1. Choose a licensed or official baseline with a documented date and category coverage.
  2. Choose a regional series that measures a compatible concept rather than general inflation.
  3. Apply the modifier by category where evidence supports it and leave other categories unadjusted or unknown.
  4. Display the baseline, modifier, data date, geography, and remaining local gaps.

Formula or decision logic

Adjusted category cost = baseline category cost x regional index / baseline index, when both indexes are methodologically compatible. A national PPI measures price change, not the exact installed cost of one house in one ZIP code. Treat it as context or escalation evidence, not a turnkey local multiplier.

Worked planning example

If a licensed material series has regional index 112 and baseline index 100, a compatible $10,000 material category becomes $11,200 before other adjustments. Labor, site access, contractor availability, tax, fees, and project complexity remain separate because the material series does not measure them.

Open this starting state in AtriBuildUse the related calculatorReview Detached ADU concept

Limitations and review boundary

  • AtriBuild currently lacks an authorized production pricing baseline.
  • Official economic indexes are aggregate measures, not bids.
  • ZIP codes do not encode site conditions or contractor capacity.
Conceptual planning onlyAtriBuild does not provide architectural or engineering services, stamped plans, permit approval, code-compliance verification, contractor bids, or construction guarantees. Verify dimensions, assemblies, utilities, quantities, prices, permits, and safety decisions with qualified local professionals.

Primary sources

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