Masonry Connectors for Concrete Block Back-up Walls

THERMAL ANALYSIS OF RAP TIES

evaluatION OF effective R-values of FERO Rap ties

FERO RAP TIE AND FAST SYSTEM THERMAL ANALYSIS
Initial report by - Michael Wilson MEng PEng and James Higgins Dipl.T, - RDH Building Engineering Ltd. Vancouver, BC, Canada

Engineered FERO Products Ensure Meeting Energy Efficiency Requirements

Synopsis by Yasser Korany - Associate Professor of Structural Engineering
Department of Civil and Envoronmental Engineering, University of Alberta

National, Provincial and Municipal building codes in Canada have for some time referenced either ASHRAE Standard 90.1 or the National Energy Code for Buildings (NECB, previously MNECB) for the energy efficiency requirements for buildings. Both of these energy standards have been recently updated (2011 NECB and 2010 ASHRAE 90.1) and more stringent thermal requirements for walls (i.e. minimum R-values) have been adopted. As part of the new energy code requirements, there has been a shift away from nominal insulation R-values towards required effective insulation R-values. Nominal insulation R-values are the rated R-value of the insulation product being installed and do not account for losses due to thermal bridging. Thermal bridging is the energy loss that occurs through framing, gaps, fasteners, structural elements, and any other penetrations through the installed insulation.

Historically, most building codes have specified nominal insulation R-values in order to simplify the requirements for builders and designers of small buildings (i.e. Part 9). The effective assembly R-values that could be constructed using the nominal insulation value vary depending on the type of framing and degree of thermal bridging, thereby resulting in a significant range of actual thermal performance. Therefore, the use of effective R-values is a more rational measure of the true thermal performance. Figure 1 summarizes the thermal insulation requirements within the 2011 NECB, ASHRAE 90.1-2010, and 2010 NBC for walls of all types in climate zones across Canada.

Gigure 1:

Fero commissioned RDH Building Engineering Ltd. to evaluate the effective R-values of Fero RAP Ties compared to generic ties of similar size fastened to different backup wall construction (concrete, steel stud/gypsum, and wood-frame). The results of a three-dimensional finite element analysis using HEAT3 showed that Fero RAP ties can significantly reduce the impact of thermal bridging and maximize the effective R-value of masonry walls with exterior continuous insulation. The analysis also included the effective R-values for Fero FAST System for shelf angle support compared to conventional types of shelf angle support.

As shown in Figures 2 to 4, the use of stainless steel Fero RAP Ties or galvanized Fero RAP Ties with punched holes resulted in the lowest insulation reductions (4% - 16%) compared to generic ties of similar size without holes (5% to 24%) over concrete/steel stud backup and lower for wood frame.

Figure 2   Figure 3

Figure 2:

 

Figure 3:

     
Figure 4    

Figure 4:

   

The analysis also revealed that directly attached masonry shelf angles perform quite poorly thermally with exterior insulation R-value reductions of over 40% for 4” of exterior insulation with stainless ties over a 6” concrete backup wall. Shelf angles supported outside of the exterior insulation with the Fero FAST System have more tolerable insulation reductions in the order of 15% for the same wall as shown in Figure 5. With Fero FAST System for shelf angle support, the exterior insulation reduction factor is only 16% with 4” of exterior insulation over an uninsulated 3-5/8” steel stud backup wall. This is significantly better than the reductions of about 50% to over 70% which can be seen with other cladding materials supported on continuous Z-girts and Z-girt clips.

  Large Angle Fero FAST System
  Large Angle Wall Fero FASt Wall
  Large Angle Fero FAST Angle
Effective
Assembly
R-Value
R-10.6 (RSI1.87) R-16.3 (RSI 2.87)
Effective
Reduction
43% 14.6%
Figure 5    

Read the full report from RDH Building Engineering Ltd.