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The R-value of the insulation filling the stud cavity.
R-13 batts are common for 2x4 walls; R-19-21 for 2x6 walls.
The R-value of solid wood at the stud's thickness.
Wood has roughly R-1.25 per inch — a 2x4 (3.5 in actual) is about R-4.4, a 2x6 (5.5 in actual) is about R-6.9.
The percentage of the wall's area taken up by studs, headers, plates, and other framing rather than insulated cavity.
0.25 (25%) is a commonly cited average for standard 16 in O.C. wood framing with typical corners, openings, and headers; advanced framing techniques can reduce this to 0.15-0.20.
Effective assembly R-value
8.73 R (effective)
This parallel-path method is a widely used simplification — it doesn't account for more complex heat flow effects like point thermal bridges at intersections, which a full 2D/3D heat transfer model would capture more precisely.
- Nominal cavity-only R-value
- 13 R
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Thermal Bridging Effective R-Value Calculator: 8.73 R (effective) — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Parallel path method: effective R-value = 1 / ((framing fraction / framing R-value) + ((1 - framing fraction) / cavity R-value)) — the standard simplified method for estimating whole-wall R-value impact from framing
Inputs used
- Cavity Insulation R-Value
- 13
- Framing Member R-Value
- 4.4
- Framing Fraction
- 0.25
Intermediate steps
- Nominal cavity-only R-value
- 13 R
Confidence note: This parallel-path method is a widely used simplification — it doesn't account for more complex heat flow effects like point thermal bridges at intersections, which a full 2D/3D heat transfer model would capture more precisely.
What this calculation does not cover
- This is the framed insulation layer only. Drywall, sheathing, cladding, air gaps, interior and exterior air films, and any exterior continuous insulation are not in the arithmetic, so the figure is not the wall's total R-value and should not be read against a target stated for a whole assembly.
- The parallel-path split describes timber. Steel studs, Z-furring, spacer bars and brackets, and masonry ties spread heat sideways into the surrounding material, so the bridged area behaves larger than its geometric fraction and this method will not give you the right penalty. For metal, use a steel-specific method or the system supplier's tested U-value.
- One framing fraction is applied evenly over the whole wall. Corners, headers over openings, rim joists, the wall-to-floor and wall-to-roof junctions, and anything penetrating the envelope lose more heat than a plain stud bay, and none of them are resolved here.
- The cavity is assumed filled to its rated R-value everywhere. Gaps at the edges, batts compressed behind wiring and pipework, settled blown insulation, and air moving through the framed layer all put real performance below this number, and none of them are inputs.
- Not a compliance calculation. An energy code submission or a declared U-value needs a whole-assembly figure produced by the method your code names, with junction losses handled separately. Use this to see how much of the batt's label the framing takes back, not as the document you submit.
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This result is a specification — 8.73 R (effective) — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Parallel path method: effective R-value = 1 / ((framing fraction / framing R-value) + ((1 - framing fraction) / cavity R-value)) — the standard simplified method for estimating whole-wall R-value impact from framing
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