Best Insulation for Walls: Cavity Fit and Continuous Layers

Record framing size, clear cavity dimensions, spacing, sheathing, interior lining and any continuous insulation. Existing-wall retrofits and open-stud work have different access. Note openings, corners and services because they interrupt the insulated field.

Batt coverage is an area or piece-count problem. Loose-fill cavity work needs the product’s cavity application specification rather than an attic chart. Continuous rigid insulation needs sheets, layers and compatible fastening and control-layer details. Each method must fit the actual assembly.

A cavity labeled US R-20 does not make a whole wall R-20. In an illustrative parallel model with 25% framing at R-5 and 75% cavity area at R-20, U = 0.25 / 5 + 0.75 / 20 = 0.0875. Effective R is 1 / 0.0875 = 11.429 before additional common layers. These are example path values, not material properties.

The model is a simplified comparison. Complete paths, films and two-dimensional bridges can require more detailed assessment. NRCan’s wall guidance provides context for continuous insulation and retrofit strategy.

Compare declared thermal resistance at the supplied thickness, cavity fit, facing, installation conditions and compatibility with the moisture-control plan. Specify any continuous layer separately from cavity packs. Subtract windows and doors from net area, but retain a cutting allowance and a framing-detail plan. A higher nominal R per inch is not sufficient evidence that the product is the best wall solution.