BUILDING ASSEMBLY TOOL

Effective R-Value Calculator

Compare framing and insulated-cavity heat-flow paths without directly averaging their R-values. Build an interior-to-exterior assembly from documented materials, then review imperial and metric results.

ASSEMBLY INPUTS

Build the layers from inside to outside

Search the source-backed library, then assign each layer to both paths or to the cavity or framing path.

Assembly setup

Assembly preset

Examples use documented material values but remain simplified starting points, not compliance assemblies.

Assembly name

Framing fraction

Calculated cavity fraction: 77%

Load saved preset

Presets stay in this browser only; no project or address data is sent.

Assembly layers

Order layers from the conditioned interior to the exterior. Continuous layers contribute to both parallel paths.

Layer 1

Interior air film — Wall heat flow horizontal

R-0.68

Layer 1 category

Layer 1 material search

Layer 1 heat-flow path

Source details

Source: BC Building Code 2024 Table A-9.36.2.4.(1)-D
Last verified: 2026-07-18
Value type: Fixed R-0.68
Scope: Generic code table value converted from RSI 0.12. Direction-specific fixed film value.

Open source document

Layer 2

Gypsum board — Generic

R-0.44

Layer 2 category

Layer 2 material search

Layer 2 thickness

Layer 2 heat-flow path

Source details

Source: BC Building Code 2024 Table A-9.36.2.4.(1)-D
Last verified: 2026-07-18
Value type: R-0.88 per inch
Scope: Generic value converted from RSI 0.0061 per mm; not a proprietary product value.

Open source document

Layer 3

ROCKWOOL Comfortbatt — Wood stud R14; 3.5 in

R-14

Layer 3 category

Layer 3 material search

Layer 3 thickness

Fixed product value at its documented reference thickness; it is never scaled.

Layer 3 heat-flow path

Source details

Source: ROCKWOOL Comfortbatt Technical Data Sheet CA
Last verified: 2026-07-18
Value type: Fixed R-14
Scope: Product-specific fixed batt value tested to ASTM C518; do not scale to a different thickness.

Open source document

Layer 4

Wood structural framing — Spruce-pine-fir

R-4.31

Layer 4 category

Layer 4 material search

Layer 4 thickness

Layer 4 heat-flow path

Source details

Source: BC Building Code 2024 Table A-9.36.2.4.(1)-D
Last verified: 2026-07-18
Value type: R-1.23 per inch
Scope: Generic value converted from RSI 0.0085 per mm. Use actual species data when known.

Open source document

Layer 5

Oriented strand board — Generic

R-0.71

Layer 5 category

Layer 5 material search

Layer 5 thickness

Layer 5 heat-flow path

Source details

Source: BC Building Code 2024 Table A-9.36.2.4.(1)-D
Last verified: 2026-07-18
Value type: R-1.41 per inch
Scope: Generic value converted from RSI 0.0098 per mm; density and product can affect performance.

Open source document

Layer 6

Exterior air film — Ceilings, floors and walls; winter wind 6.7 m/s

R-0.17

Layer 6 category

Layer 6 material search

Layer 6 heat-flow path

Source details

Source: BC Building Code 2024 Table A-9.36.2.4.(1)-D
Last verified: 2026-07-18
Value type: Fixed R-0.17
Scope: Generic code table value converted from RSI 0.03. Fixed film value; do not scale by thickness.

Open source document

ESTIMATED RESULT

Example 2×4 wood-framed wall

Effective whole-assembly R-valueR-11.81

Framing path R-value: R-6.3
Cavity path R-value: R-16
Continuous R-value: R-2
Reduction caused by framing: 26.14%
Effective RSI: 2.08
Effective U-value: 0.0846 Btu/(h·ft²·°F)0.4806 W/(m²·K)

Path comparison

Cavity pathR-16

Framing pathR-6.3

Effective assemblyR-11.81

Wall assembly — interior to exterior

Interior air film — Wall heat flow horizontalcontinuous · R-0.68
Gypsum board — Genericcontinuous · R-0.44 · 0.5 in
ROCKWOOL Comfortbatt — Wood stud R14; 3.5 incavity · R-14 · 3.5 in
Wood structural framing — Spruce-pine-firframing · R-4.31 · 3.5 in
Oriented strand board — Genericcontinuous · R-0.71 · 0.5 in
Exterior air film — Ceilings, floors and walls; winter wind 6.7 m/scontinuous · R-0.17

This calculator provides a simplified estimate of effective thermal resistance using parallel heat-flow paths. Actual performance may also be affected by corners, headers, rim joists, windows, doors, fasteners, balconies, shelf angles, installation quality, and other thermal bridges. Confirm project requirements through appropriate energy modelling, code review, or professional analysis.