Source: https://guthlabs.ai/docs/instruments/r-value-u-value-wall-assembly-calculator/mechanism/

instrument mechanism / verified-clean

# R-Value / U-Value Wall Assembly Calculator mechanism

The inspectable method record for R-Value / U-Value Wall Assembly Calculator, kept separate from implementation and qualification.

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

## Model scope

The stated series-resistance and reciprocal-U method is standard only for a fully specified one-dimensional assembly. Verdict is NEEDS_REVIEW because the specification does not define the film convention, unit system, layer calculation from k, table conditions, or treatment of parallel thermal bridges. The empty honest_label is a concern: the instrument should explicitly state that it is a nominal steady-state one-dimensional calculation and not a code-compliance, condensation-risk, or whole-wall performance assessment.

- R_total=ΣR_layer+R_film is conditionally correct, but R_film is ambiguous: a standard assembly normally specifies separate interior and exterior surface resistances, R_si and R_se, rather than one unspecified film resistance.

- For layers specified by thickness and thermal conductivity, the required relationship R_layer=thickness/k is missing from the stated formulas.

- The formula assumes one-dimensional series heat flow. It does not account for thermal bridges, framing fractions, parallel heat-flow paths, air cavities, contact resistances, or repeating thermal bridges.

- A material k or R-value is temperature-, moisture-, density-, and installation-dependent; the applicable table condition must be specified.

- The calculator does not state whether reported R-values use SI units or U.S. customary units, creating a major conversion ambiguity.

- The formula does not constrain thickness and k/R inputs to positive values, and does not define behavior for zero or negative values.

## Units and conventions

- All worked vectors report R_total in m^2*K/W and U in W/(m^2*K).

- For k inputs, thickness is in meters and R_layer=thickness/k, with k in W/(m*K).

- For R-per-inch inputs, the tabulated value is in h*ft^2*degF/Btu and is converted using 1 h*ft^2*degF/Btu = 0.176110 m^2*K/W.

- The examples assume series heat flow and explicitly supplied interior and exterior film resistances of R_si=0.12 and R_se=0.03 m^2*K/W.

- The examples assume the tabulated material properties are applicable at the stated generic design condition; no temperature or moisture correction is applied.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "layers": [
      {
        "material": "fiberglass batt",
        "thickness_m": 0.0127,
        "k_W_per_mK": 0.04
      }
    ],
    "R_si_m2K_per_W": 0.12,
    "R_se_m2K_per_W": 0.03
  },
  "expected_outputs": {
    "layer_resistances_m2K_per_W": [
      0.3175
    ],
    "R_total_m2K_per_W": 0.4675,
    "U_W_per_m2K": 2.1390374332
  },
  "reference_data": {
    "fiberglass_batt_k_W_per_mK": {
      "value": 0.04,
      "source_convention": "ASHRAE Fundamentals SI material-property table; widely tabulated standard value"
    },
    "R_si_m2K_per_W": {
      "value": 0.12,
      "source_convention": "ASHRAE Fundamentals standard interior surface-resistance convention"
    },
    "R_se_m2K_per_W": {
      "value": 0.03,
      "source_convention": "ASHRAE Fundamentals standard exterior surface-resistance convention"
    }
  },
  "working": "R_layer = thickness/k = 0.0127/0.04 = 0.3175 m^2*K/W. R_total = R_si + R_layer + R_se = 0.12 + 0.3175 + 0.03 = 0.4675 m^2*K/W. U = 1/R_total = 1/0.4675 = 2.1390374332 W/(m^2*K). The 0.04 W/(m*K) fiberglass conductivity is used exactly as the tabulated value."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The empty assembly with zero film resistance produces R_total = 0 and therefore an undefined U-value. The calculator must reject this input or explicitly report an undefined result. A separate unit-convention ambiguity can also produce materially different outputs if k is not dimensionally labeled.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/r-value-u-value-wall-assembly-calculator/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/r-value-u-value-wall-assembly-calculator/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/r-value-u-value-wall-assembly-calculator/qualification/>)

## Sources and evidence

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

- `VERIFIED_LEDGER.json`

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

- `BOUNDARY_HAZARD_CATALOG.json`