Wall Effective
R-Value Estimator
The R-value on an insulation package is not the R-value of the wall. Studs carry heat around the insulation, so the whole wall performs below the nominal number. Enter your assembly to see the effective R-value by the parallel-path method, and what continuous exterior insulation changes. Wall assemblies are part of the BC Step Code conversation; your energy advisor decides what your project needs.
Actual depth: 3.5 in for a 2x4, 5.5 in for a 2x6.
The R-value printed on the product or in your spec.
Studs, plates and headers as a share of the wall. Lower at wider spacing.
Assumed typical softwood figure.
Rigid or mineral wool outside the sheathing. Zero if none.
Air films, drywall, sheathing, cladding.
Estimate only. This is a simplified parallel-path calculation of one clear wall area. It ignores corners, window and door openings, rim joists, fasteners and other thermal bridges, and it is not an energy model or code compliance check. Your energy advisor and building department decide what your project must achieve. OG Prefab is a prefab wall panel, framing and foundation company serving builders, developers and homeowners directly. This tool does not produce a quote, and no pricing is implied.
Assumptions
- Two heat paths: through the insulated cavity and through the framing. Each path adds the continuous insulation and the other layers in series, and the paths are area-weighted by the framing share you enter.
- Framing share defaults to 25%, in line with figures published for 2x6 walls at 16 in on centre (about 25%). Published figures for 24 in spacing are lower (about 18%), and BC Housing's manual uses 23% for a wood wall at 16 in. Change the field to match your drawings.
- Wood defaults to R-1.25 per inch of depth, a commonly published figure for softwood framing. It is an assumption you can change.
- Other layers defaults to R-1.9, a placeholder for typical inside and outside air films, 1/2 in drywall and 7/16 in OSB sheathing (about 0.68 + 0.17 + 0.45 + 0.62). Cladding and any air space are not included, so adjust it for your assembly.
- Cavity R-value is the nominal figure you enter for the insulation you plan to install. Batt and blown-in products differ, and installation quality affects real performance.
- R-values here are imperial (hr-sq ft-F per BTU). The RSI value shown is the metric equivalent.
Sources
Related Guides
- BC Step Code, wall assemblies and framing tolerances
- Questions to ask before building with prefab panels
- How prefab framing works: wall systems explained
Ready to move from estimate to scope? Send plans for a written panel quote or request a quote for framing or foundations.
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