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

instrument implementation / implementation-contract

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

A source-bound implementation contract for R-Value / U-Value Wall Assembly Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t7-132

**Effect**: Computation or source lookup only

## Input and validation requirements

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.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "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."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/r-value-u-value-wall-assembly-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/r-value-u-value-wall-assembly-calculator/mechanism/>)[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`