Building Science
Continuous Insulation
CI
Insulation installed as an uninterrupted layer outside the structural framing, so studs and joists do not penetrate it. Its purpose is addressing thermal bridging, not simply adding R-value.
In more detail
Continuous insulation is insulation installed as an uninterrupted layer outside the framing, so studs, plates, joists and rim boards do not pass through it. Rigid foam, mineral wool board and insulated sheathing are the usual materials; ASHRAE 90.1 and the energy codes describe the layer as uninterrupted except by fasteners and service openings.
The purpose is not simply more R-value. Wood framing typically occupies a fifth or more of a wall's area and conducts several times better than the insulation around it, so cavity insulation is bypassed in proportion to that framing factor. An exterior layer covers the bypass, which raises whole-assembly performance by more than the same R-value added inside the cavity would.
It also changes where the assembly is cold. Exterior insulation raises the temperature of the sheathing behind it, reducing condensation risk within the wall. That benefit is climate- and ratio-dependent: codes prescribe minimum exterior-to-cavity R-value ratios precisely because a partial exterior layer can shift the condensing surface rather than remove it.
Why it matters
Continuous insulation is a structural decision rather than an upgrade. It changes sheathing details, window bucks and flashing depth, cladding attachment and trim dimensions, so it is either designed in or absent. For a house aiming at high performance it does more for measured whole-assembly performance than deepening the cavity does, and that is the primary reason to accept the added complexity at the exterior.
The common misunderstanding
That R-value adds up regardless of where it goes. Cavity R-value is bypassed by framing; exterior R-value is not. Two walls with identical nominal totals can differ substantially in whole-assembly U-factor depending on the split, and the exterior portion also carries a moisture benefit the cavity portion does not.
Related terms
On Compound
Where this term does real work — and where the decisions get made.
Sources
Last reviewed July 2026 by Compound Editorial. Definitions are educational and not project-specific engineering or medical advice.