Thermal Bridging Calculator

Effective R-value accounting for framing factor.

About this calculator

Effective Whole-Wall R-value is set by Framing Type and Cavity Insulation together, with Continuous Insulation layered on top -- but Thermal Bridging Penalty (%) doesn't move the way you'd expect when you improve the cavity fill. Switching Cavity Insulation to closed-cell spray foam (R-6.5/in, the highest-R option) actually RAISES the Thermal Bridging Penalty from about 21% to about 42% at the default 2x4 @ 16 in framing, even though Effective R-value itself goes UP (10.16 to 14.18) -- because a better cavity fill widens the gap between the insulated path's R-value and the framing path's R-value, which doesn't change, so bridging accounts for a bigger SHARE of what's now a higher-performing wall, not a smaller one. Framing Type has the largest swing on both figures: switching from 2x4 wood @ 16 in OC to steel stud 3.5 in drops Effective R-value from about 10.2 to 6.1 and pushes the bridging penalty to about 53%, since steel conducts heat far better than wood (R-0.5 vs.

R-4.38 for the same cavity depth). Exterior Sheathing R-value looks like a minor spec -- its whole range is only 0 to 5 -- but it moves Effective R-value more than that narrow range suggests, from about 9.5 up to about 15.0, because it's added to the framing path's already-low total R, where each extra point matters disproportionately once averaged against the cavity path in the parallel-path U-value calculation.

Inputs

Framing type

Cavity insulation

Continuous insulation R-value

Interior finish R-value

Exterior sheathing R-value

Tab to move between fields

Results

Effective whole-wall R-value

10.16

Thermal bridging penalty

20.9%

R-value (cavity path)12.85

R-value (framing path)6.24

U-factor (effective)0.1

Heat loss per 1000 sq ft4,921 BTU/hr

Extra heat loss from bridging1,030 BTU/hr

How to Use This Calculator

Select Framing Type: wood 2×4 or 2×6 at 16" or 24" on-center, or steel stud (3.5" or 5.5") if applicable.
Select Cavity Insulation type (fiberglass batts, mineral wool, cellulose, or open/closed-cell spray foam) filling the stud cavities.
Enter Continuous Insulation R-value for any exterior rigid foam or mineral wool layer outside the sheathing.
Enter Interior Finish R-value and Exterior Sheathing R-value, or leave the drywall and OSB/plywood defaults.
Review Effective Whole-Wall R-value and Thermal Bridging Penalty (%) to see how much framing cuts into the nominal insulation.
Compare R-value (Cavity Path) against R-value (Framing Path) to see the best-case and worst-case heat-flow routes side by side.

How the result changes with Exterior sheathing R-value

Exterior sheathing R-value	Effective whole-wall R-value	Thermal bridging penalty
0.28	9.84	21.7%
0.42	10	21.3%
0.84	10.48	20.2%
1.4	11.1	18.9%

What each input means

Framing type: Wall framing type and spacing. Steel studs have much worse thermal bridging.
Cavity insulation: Insulation filling the stud cavities.
Continuous insulation R-value: Exterior continuous insulation (rigid foam or mineral wool). Eliminates bridging through this layer.
Interior finish R-value: R-value of interior finish. 1/2" drywall = R-0.45.
Exterior sheathing R-value: R-value of sheathing. 7/16" OSB = R-0.56, 1/2" plywood = R-0.63.

What each result means

Effective whole-wall R-value: True R-value including thermal bridging through framing. Always lower than nominal.
R-value (cavity path): Total R-value through insulated cavity — the best-case path.
R-value (framing path): Total R-value through framing members — the worst-case path.
U-factor (effective): Overall U-factor (BTU/hr·ft²·°F). Lower is better.
Thermal bridging penalty: Percentage of total R-value lost due to thermal bridging.
Heat loss per 1000 sq ft: Heat loss at ΔT=50°F per 1000 sq ft of wall.
Extra heat loss from bridging: Additional heat loss caused by thermal bridging vs. uniform insulation.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Framing type = 0, Cavity insulation = 0, Continuous insulation R-value = 0, Interior finish R-value = 0.45 = 5 input(s) provided
Calculate Effective whole-wall R-value
Effective whole-wall R-value = 1 / uEffective
10.16 = 10.16
Calculate Thermal bridging penalty
Thermal bridging penalty = rNominal > 0 ? (rLostToBridging / (rNominal + interiorAirFilm + interiorFinis...
20.9 = 20.9
Calculate R-value
R-value = interiorAirFilm + interiorFinishR + cavityR + exteriorSheathingR + continuous...
12.85 = 12.85
Calculate R-value
R-value = interiorAirFilm + interiorFinishR + config.framingR + exteriorSheathingR + co...
6.24 = 6.24

Engine last updated August 14, 2026. Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

If I upgrade to the best cavity insulation (closed-cell spray foam), does the thermal bridging penalty go down?

No -- it actually goes UP, from about 21% to about 42% at the default 2x4 @ 16 in framing, even though Effective R-value itself improves (10.16 to 14.18). A better cavity fill widens the gap between the insulated path and the framing path, which doesn't change, so bridging ends up accounting for a bigger share of a now-higher-performing wall.

How much worse is steel stud framing than wood for thermal bridging?

Substantially. At the same cavity depth and insulation, switching from 2x4 wood @ 16 in OC to steel stud 3.5 in drops Effective R-value from about 10.2 to 6.1 and raises the bridging penalty from about 21% to 53%, because steel conducts heat far better than wood -- roughly R-0.5 for the steel stud web versus R-4.38 for the equivalent wood stud.

Does Exterior Sheathing R-value matter much given its narrow 0-5 range?

More than the narrow range suggests. Sheathing R-value gets added directly to the framing path's total R, which starts out low, so each additional point matters disproportionately once the framing and cavity paths are averaged into the composite U-value. At this calculator's other defaults, moving Exterior Sheathing R-value from 0 to 5 raises Effective R-value from about 9.5 to about 15.0.

Does adding Continuous Insulation reduce the thermal bridging penalty percentage?

Yes, and sharply -- unlike cavity insulation, continuous insulation sits outside the framing entirely, so it benefits both the cavity path and the framing path equally rather than widening the gap between them. At this calculator's other defaults, raising Continuous Insulation R-value from 0 to 40 drops the Thermal Bridging Penalty from about 21% down to about 3.5%.

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