Source: https://guthlabs.ai/docs/instruments/roof-attic-insulation-r-value-calculator/

instrument / verified-clean

# Roof/Attic Insulation R-Value Calculator

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Inspectable records

[01**Overview**Purpose and lifecycle](<https://guthlabs.ai/docs/instruments/roof-attic-insulation-r-value-calculator/>)[02**Mechanism**Method and assumptions](<https://guthlabs.ai/docs/instruments/roof-attic-insulation-r-value-calculator/mechanism/>)[03**Implementation**Binding and validation](<https://guthlabs.ai/docs/instruments/roof-attic-insulation-r-value-calculator/implementation/>)[04**Qualification**Evidence and errata](<https://guthlabs.ai/docs/instruments/roof-attic-insulation-r-value-calculator/qualification/>)

## Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

**Area**: Everyday & Life

**Tranche**: tranche-7

**Evidence ID**: t7-082

**Ledger rows**: 1

No ledger note is attached.

## Review findings

The summation algorithm is standard for nominal stacked insulation layers, but the instrument needs a fixed, versioned material table and a fixed DOE recommendation convention before its outputs can be treated as unambiguous. Vectors 1 and 2 land exactly on the commonly tabulated DOE target entries R-30 and R-60. The honest-label warning is appropriate and should explicitly state that local code, assembly design, installation quality, and air sealing may change the result.

### Formula and scope findings

- R_total = ΣR_layer is correct when every layer R-value uses the same units and represents a series layer in the heat-flow path.

- The material-thickness calculation must use a material-specific R-per-unit-thickness table; a single generic conversion is invalid.

- The recommendation comparison is underspecified because DOE guidance commonly gives ranges and differs by attic/ceiling versus roof assembly, climate-zone version, and whether existing insulation is included.

- The calculator should define gap as total R-value minus recommended R-value; a negative result indicates a shortfall.

- The formula excludes framing thermal bridges, air films, air leakage, moisture effects, compression, and parallel heat-flow paths, so it computes insulation-layer R-value rather than necessarily the whole roof assembly effective R-value.

### Unit assumptions

- All reported R-values are in h·ft²·°F/Btu, conventionally written as R-value.

- Thickness is explicitly supplied in inches or millimetres; millimetres are converted using 25.4 mm = 1 in.

- Material table values are assumed to be nominal R-value per inch at the stated material condition; loose-fill density, compression, temperature, and installation quality are not modeled.

- The test vectors use a selected DOE/ENERGY STAR attic-target convention: climate zone 1 → R-30, zone 2 → R-49, and zone 4 → R-60.

- The recommended target is treated as a single target, not as the midpoint or lower/upper endpoint of a published range.

## Boundary hardening

**BREAK_CLAIMED** · SELF_FLAGGED

An extreme but numerically representable thickness causes the layer multiplication to overflow ordinary floating-point arithmetic. An implementation that accepts it without range validation can return Infinity or a non-finite gap instead of rejecting the input.

## Errata and corrections

No applied erratum is attached to this unique-name record.

## Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

````
{
  "inputs": {
    "layers": [
      {
        "material": "fiberglass batt",
        "thickness": 9.375,
        "thickness_unit": "in"
      }
    ],
    "climate_zone": 1
  },
  "expected_outputs": {
    "total_R_value_h_ft2_F_per_Btu": 30,
    "recommended_R_value_h_ft2_F_per_Btu": 30,
    "gap_h_ft2_F_per_Btu": 0
  },
  "reference_data": {
    "material_rows": [
      {
        "material": "fiberglass batt",
        "R_per_in": 3.2,
        "source_convention": "widely tabulated standard value"
      }
    ],
    "climate_zone_row": {
      "climate_zone": 1,
      "recommended_attic_R": 30,
      "source_convention": "DOE/ENERGY STAR attic insulation target convention, 2023 guidance"
    }
  },
  "working": "Fiberglass contribution = 9.375 in × 3.2 R/in = 30.0 R. Total R = 30.0 R. Gap = total − target = 30.0 − 30.0 = 0.0 R."
}
````

## Related workflows

No source-defined multi-instrument workflow membership is recorded.

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json · VERIFIED_CLEAN`

- `evidence-tranche7/tranche7-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`