Thermal Bridging Calculator

Calculate the effective R-value reduction and heat loss penalty caused by thermal bridges in your building envelope.

About this calculator

Gross Wall Area is the one input this calculator treats two completely different ways depending which output you're reading, and the difference is a straightforward algebraic cancellation, not a bug. The linear and point thermal-bridge contributions (studs, lintels, shelf angles, cladding anchors) are each divided by Gross Wall Area to get a per-area U-value contribution -- but Annual Bridge Loss then multiplies that same per-area contribution straight back by Gross Wall Area, so the wall-area terms cancel exactly, and Annual Bridge Loss and Gas Wasted end up depending only on how many bridges you have (their total psi-length and chi-count) and the climate's heating degree days, never on how big the wall itself is.

Effective R-Value and Heat Loss Penalty (%) go the opposite way: since those ARE the per-area contributions, a bigger wall spreads the same fixed set of bridges over more clear-field area, diluting their percentage impact -- doubling Gross Wall Area roughly halves the R-value hit from the same physical bridges. Assembly R-Value only sets the clear-field baseline (Clear-field U-Value = 1/R), and linear versus point transmittance (Linear Psi times Total Linear Bridge length, Point Chi times Point Bridge count) simply stack additively on top of it -- there's no interaction term between the two bridge types in this model, they just add.

Inputs

Gross Wall Area (sq ft)

sq ft

Assembly R-Value

Linear Psi (Btu/hr·ft·°F)

Total Linear Bridge (ft)

Point Chi (Btu/hr·°F)

Number of Point Bridges

Heating Degree Days (HDD65)

Tab to move between fields

Results

Effective R-Value

16.48

Clear-field U-Value0.05

Effective U-Value0.06

R-Value Reduction3.52

Heat Loss Penalty (%)21.3%

Annual Bridge Loss (kBtu)1,920

Gas Wasted (therms)24

How to Use This Calculator

Enter Gross Wall Area in sq ft and the Assembly R-Value without bridging.
Enter Linear Psi value in Btu/hr·ft·°F and Total Linear Bridge length in feet.
Enter Point Chi value and Number of Point Bridges for bracket mounts and anchors.
Enter Heating Degree Days for your climate to calculate annual energy penalty.
Review Effective R-Value, R-Value Reduction, and Annual Bridge Heat Loss to justify continuous insulation.

How the result changes with Assembly R-Value

Assembly R-Value	Effective R-Value
10	9.04
15	12.93
30	22.73
50	32.61

What each input means

Gross Wall Area (sq ft): Total opaque wall area in square feet (excluding windows/doors).
Assembly R-Value: Clear-field R-value of the wall assembly without bridging (hr·ft²·°F/Btu).
Linear Psi (Btu/hr·ft·°F): Linear thermal transmittance per foot of bridge. Steel studs ~0.03-0.08, shelf angles ~0.05-0.15.
Total Linear Bridge (ft): Total length of all linear thermal bridges (studs, lintels, floor edges, shelf angles).
Point Chi (Btu/hr·°F): Point thermal transmittance per bridge. Masonry ties ~0.01, bracket mounts ~0.2-0.5.
Number of Point Bridges: Total count of point thermal bridges (cladding brackets, anchors, penetrations).
Heating Degree Days (HDD65): Annual heating degree days for your climate zone. Miami ~200, Denver ~6000, Minneapolis ~8000.

What each result means

Effective R-Value: True R-value of the assembly including all thermal bridges.
Clear-field U-Value: U-value of the wall without any bridging.
Effective U-Value: True U-value including linear and point thermal bridge contributions.
R-Value Reduction: How much R-value is lost due to thermal bridging.
Heat Loss Penalty (%): Percentage increase in heat loss due to thermal bridges.
Annual Bridge Loss (kBtu): Estimated annual heat loss through thermal bridges alone.
Gas Wasted (therms): Equivalent natural gas wasted annually through thermal bridges (assumes 80% furnace efficiency).

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Gross Wall Area (sq ft) = 1500, Assembly R-Value = 20, Linear Psi (Btu/hr·ft·°F) = 0.05, Total Linear Bridge (ft) = 200 = 7 input(s) provided
Calculate Effective R-Value
Effective R-Value = 1 / uEffective
16.48 = 16.48
Calculate Clear-field U-Value
Clear-field U-Value = 1 / assemblyRValue
0.05 = 0.05
Calculate Effective U-Value
Effective U-Value = uClear + uLinear + uPoint
0.0607 = 0.0607

Engine last updated August 28, 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

Does a bigger wall mean more annual heat loss through the thermal bridges?

No -- Annual Bridge Loss (and the Gas Wasted it implies) is completely unaffected by Gross Wall Area across its full 1-500,000 sq ft declared range. The per-area bridge contribution is divided by wall area to compute it, but then multiplied by that same wall area to get the total loss, so the wall-area terms cancel exactly. Annual Bridge Loss depends only on the bridges themselves (their psi-length and chi-count) and the climate's heating degree days.

If wall area doesn't affect annual heat loss, what DOES it affect?

Effective R-Value and Heat Loss Penalty (%) -- both of those ARE per-area quantities, so a bigger Gross Wall Area spreads the same fixed set of thermal bridges thinner, diluting their percentage impact on the wall's overall R-value. A larger wall with identical bridging gets a smaller effective-R hit than a smaller wall with the same bridges, even though the total energy lost through those bridges stays the same either way.

Do linear bridges (studs, shelf angles) and point bridges (anchors, brackets) interact, or just add?

They simply add -- there is no interaction term between Linear Psi times Total Linear Bridge length and Point Chi times Point Bridge count in this calculator's model. Effective U-Value is Clear-field U-Value plus the linear contribution plus the point contribution, each computed independently before being summed.

Does raising the assembly R-value always lower the clear-field U-value?

Yes, monotonically across Assembly R-Value's full 1-80 declared range -- Clear-field U-Value is exactly 1 divided by Assembly R-Value, a strictly decreasing relationship with no plateaus or reversals, so a higher-R clear-field assembly always produces a lower Clear-field U-Value, independent of how much thermal bridging is present.

What happens to the effective R-value if there are zero thermal bridges?

Effective R-Value equals Assembly R-Value exactly, R-Value Reduction and Heat Loss Penalty (%) both read 0, and Annual Bridge Loss reads 0 -- with Total Linear Bridge length and Point Bridge count both at 0, the linear and point U-value contributions vanish and the wall performs at its clear-field rating with no bridging penalty at all.

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