Quantifying the Geometric Thermal Benefit of 3D Concrete Printed Cavity Walls: Introducing the Thermal Effectiveness Index

Three-dimensional concrete printing (3DCP) enables the fabrication of wall sections with internal cavities that are impractical to form with conventional methods. Although individual studies demonstrate that cavity geometry influences thermal resistance, the magnitude of this effect has not been quantified on a common basis across the literature. This paper introduces the Thermal Effectiveness Index (TEI), defined as the ratio of the theoretical U-value of a solid concrete wall (calculated using the material’s actual thermal conductivity) to the reported U-value, in order to isolate the purely geometric contribution to thermal performance. A structured extraction from 24 Scopus-indexed articles yielded an analysis dataset of 255 variants from 23 articles (after the exclusion of one study whose composite mix made the geometric effect inseparable from material substitution), spanning 17 typology categories. Results show that standard rectangular air cavities perform worse than solid printed counterparts of the same material (median TEI =0.56 versus 1.00 for solid walls) due to internal convection and thermal bridging, whereas sinusoidal infills with post-printed insulation reach a median TEI of 8.9 (18 variants from a single study, so the magnitude requires independent replication). These patterns are descriptive; an article-level sensitivity check indicates that the number of independent studies per wall-type group is not yet sufficient for confirmatory statistical inference. A compliance analysis against five building energy codes showed that only 22% of variants meet the 0.30 W/(m2 K) threshold, in line with the component-based U-value criteria specified in the Passive House Institute’s EnerPHit Standard for building retrofits and warm-climate classifications, as opposed to the more stringent ≤0.15 W/(m2 K) requirement applicable to new construction in temperate climates.