R-Value / U-Value Wall Assembly Calculator

Inspectable records

Ledger state

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

Area

Mechanical, Civil & Structural Engineering — Statics/Dynamics, Strength of Materials, Machine Design, Civil, HVAC, Vibration

Tranche

tranche-7

Evidence ID

t7-132

Ledger rows

1

No ledger note is attached.

Review findings

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.

Formula and scope findings

• 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.

Unit assumptions

• 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.

Boundary hardening

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.

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_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."
}

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