There is a global concern to reduce reliance on fossil fuel energy in all sectors, including the built environment. For that reason, global and regional bio-climatic codes and references tend to promote different thickness levels of insulation or low U-value construction, regardless of the climatic zone. Previous studies have already shown that outer wall insulation is the best location for cooler internal summer temperatures, and/or less cooling energy load. However, in face of this global obsession with insulation addition, no research has factually completed any comparative studies with uninsulated structures. This research is about the summer internal temperature performance of different wall and insulation configurations observed simultaneously in three purpose-built test cells under various internal conditions. The monitoring occurred in the coastal climate of Lebanon and spanned an entire summer season. The climate is defined as warm temperate with long hot summers and warm short winters. Each test cell had an internal area of 10 sqm with plastered double masonry walls and a 25 mm insulation placed on the outside, middle, and inside. By mid-summer, the middle insulation was removed to have an uninsulated double masonry wall. Results were consistent with previous studies that outer insulation is better than inner insulation for cooler internal summer temperature. Interestingly, however, once insulation was removed, test cell recorded cooler internal temperatures than the outer insulation counterpart. (C) 2018 Elsevier B.V. All rights reserved.