A Practical Method to Estimate the Effective Thermal Resistance of Exterior Masonry Walls
Creators: Ismaiel, Maysoun 
Publisher: name: University of Alberta Library
Year: 2022

<p>Evaluation of the thermal resistance of building envelope elements is essential for a reliable assessment of the thermal behaviour and energy efficiency of buildings. Energy codes continue to drive the building construction industry toward more stringent thermal performance standards. To reduce energy consumption in buildings and comply with newer, more stringent energy code requirements, evaluation of the thermal resistance of above-grade wall assemblies is becoming essential. Masonry veneer cladding is typically supported by the building structure using intermittent anchors and shelf angle bearing supports. However, elements with high thermal conductivity, such as floor intersections and cladding attachment systems, often penetrate the insulation and cause thermal bridging. Thermal bridges have a significant reduction effect on the elements’ thermal resistance. Moreover, condensation on thermal bridging elements is expected. As a result, damage to building elements occurs. In terms of calculating the effective thermal resistance (R-value), the lateral heat flows caused by these highly conductive elements allow heat to be transferred in multiple directions, which is considered a challenge in the R-value estimations and causes the inability of a quick estimate of the effective thermal resistance of masonry components with sufficient precision due to the complexity of masonry construction. Currently, an accurate estimation of the R-value of masonry walls is a time-consuming task, which lengthens the design process, especially in the early design stage. Therefore, this study aims to provide efficient approaches for estimating the R-values of common concrete masonry cavity walls. Two estimation approaches are presented. First, the estimation of the R-value of common concrete masonry veneer wall configurations is presented in the form of simple design charts and R-value multipliers. Parameters such as the concrete block density, thermal insulation value, as well as the types of ties and shelf angles are addressed. The approach provides simultaneously the mechanical (the masonry compressive strength, fm′) and thermal (R-value) properties of different veneer wall configurations, allowing designers to obtain appropriate structural and thermal properties during the preliminary design phase. In addition, the design charts and R-value multipliers help designers evaluate and compare the impacts of changes in different parameters on R-values, thereby facilitating their design development. A comparison of the impacts of different parameters on the thermal resistance of masonry walls was presented. The results showed that the thermal resistance of masonry cavity walls was improved by using different tie types and materials. In the case of using galvanized, stainless-steel and Glass Fiber Reinforced Polymers (GFRP) perforated fastened on block’s surface ties, the thermal resistance improved by 25%, 43% and 60%, respectively, compared to the traditional galvanized solid block ties. Using knife plate galvanized and stainless-steel shelf angles in the intermediate floor intersection assemblies improved the overall average R-values by 30% and 63%, respectively, compared to the traditional galvanized steel directly attached shelf angle. Moreover, the results showed that the shape and material of the ties and shelf angles are more effective in the masonry wall assemblies with higher insulation R-values. Also, the effect of the concrete block density was addressed, and the results showed that, on average, the reduction of the concrete block density by 10% showed an improvement in the effective R-value of 3.5%. In addition, configurations with an expected lower effective thermal resistance are more sensitive to the concrete block density. Also, cases using solid ties are more sensitive to block density reduction than cases using perforated ties.<br>
The second approach provides adjustments to current analytical methods of thermal resistance estimation (i.e., isothermal plane and parallel path methods) to include the effect of the thermal bridge resulting from veneer ties and slab intersections. The R‐values obtained from the suggested adjustments were compared with numerical simulations using a 3D steady-state finite element method (FEM) in addition to experimental validation obtained from the literature. The clear wall adjustment factors result showed an average accuracy of 2% in the case of using the suggested adjustments, compared to 19% and 25% for isothermal plane and parallel path methods, respectively. With the presented approaches, designers can choose the optimum wall components’ material properties in the early design phase to meet structural and thermal requirements without using computer simulations or experimental investigations.</p>