Insulated Cavity Masonry Wall Design: Maximizing Energy Performance BY PETER DAMORE AND KENNETH NEIGH, AIA The continually rising cost of energy along with concerns about tionally known for durability, maintainability, strength, fire a dwindling amount of natural resources remain critical con- resistance, noise control, minimal embodied energy, economic cerns of most building owners, architects, engineers and costs, aesthetic and design flexibility, but also provides great builders. The current energy code in Michigan for nonresiden- thermal benefit. The additional properties of insulation, whether tial buildings includes the language that buildings meet batt-type, foam bead, loose fill, foam panel or spray applied, ASHRAE 90.1-1999, Energy Standard for Buildings Except Low- resist heat flow, helping to improve comfort, indoor air quality, Rise Residential Buildings. Energy codes typically provide mini- envelope tightness and energy performance. A successful insu- mum levels of energy performance for each component of the lated cavity masonry wall combines the properties of masonry building envelope. Programs like LEED (Leadership in Energy and insulation in a system that makes it possible to surpass min- and Environmental Design), developed by the US Green imum energy requirements and achieve additional “Optimized Building Council, provide certification to buildings that surpass Energy Performance” credits from LEED. It is critical to give these minimum levels of energy performance outlined in state attention to masonry and insulation selection early in the design energy codes. Design professionals and owners are often left process and to understand their thermal properties to achieve with the question: How can we increase building envelope per- the desired envelope perform- formance and decrease energy costs in our buildings? The use ance and energy savings. The use of an insulated cavity of an insulated cavity masonry wall can provide methods to Material thermal proper- masonry wall can provide maximize energy performance beyond the minimum code ties are often in values requirements for the life of the structure. expressed numerically and are methods to maximize energy fundamental to communicat- performance beyond the Understanding Material Thermal Properties ing and understanding any minimum code requirements By utilizing masonry and insulation in cavity wall construction, dialogue of heat flow within a for the life of the structure. designers may reap benefits from the inherent properties of each building envelope. Materials material, providing energy and cost savings. Masonry is tradi- like masonry and insulation are widely available in standard thicknesses. Each material has a known rate of heat flow for each standard material thickness. This rate is known as Conductance (designated as C). The abil- ity of that material to resist heat flow and act as an insulator is Learning Objectives known as Resistance, or “R-value.” R-values are useful when After reading this article, you will have learned: comparing insulation and are typically listed as “per inch of 1. How the thermal properties of materials in a wall system are calculated thickness.” The higher the R-value of a material, the greater its and expressed resistance to heat flow. The reciprocal of the R-value (1÷R) is 2. How an insulated masonry cavity wall will surpass minimum energy known as the “U-value,” or the rate of heat loss. U-value is the requirements for a building overall coefficient of heat transmission of a system of materials 3. How computer-based programs can perform whole building energy and is equal to the total reciprocals of all material R-values. U analysis to determine energy savings of insulated cavity wall systems and R-values are used in building envelope calculations when See page 98 for test and answer form. meeting energy code requirements. 52 the story pole MASONRY RESOURCE GUIDE 2008 Thermal properties of masonry can vary greatly according to affect HVAC systems helping to additionally shift peak demand wall design and density of the CMU selected. Material density, to off-peak hours. expressed in pounds per cubic foot (lb/ft3) of CMU, is directly Internal loads generated from occupancy, equipment, light- related to the R-value. ASTM C90 Standard Specifications for ing and building operational times have effects on cooling and Loadbearing Concrete Masonry allows for three weight classifica- heating energy consumption, which can minimize thermal tions of CMU: mass benefits due to the time lag of masonry. Time lag is the amount of time for heat to transfer through a material. A Normal Weight ≥ 125 lb/ft3 masonry cavity wall has a time lag of six hours (per ASHRAE Medium Weight ≥ 105 < 125 lb/ft3 Fundamentals Handbook) helping to reduce heat loss or gain 3 Light Weight < 105 lb/ft through the wall. By incorporating thermal mass properties of masonry into a building’s design and understanding the inter- The lower the density of the CMU — the higher the R-value, relationship between these factors on heating and cooling however, grout spacing and reinforcing must additionally be demands, HVAC systems can be sized to maximize energy effi- considered. The amount of grout and reinforcing within a wall ciency and reduce equipment costs. system as determined by building height, load and structural framing requirements will increase the conductance (thus low- Insulated Cavity Masonry Wall Systems ering the R-value), and is critical when considering insulated Insulated cavity masonry wall systems combine the natural cavity masonry wall design. material and thermal efficiency properties of masonry and insu- lation to provide a method to maximize energy performance. The A successful insulated cavity Thermal Mass construction of an insulated cavity masonry wall system prima- masonry wall combines the Efficiency rily consists of brick veneer or concrete masonry units separat- The density of masonry used ed by a varying dimensional air gap, insulation, mortar, grout, properties of masonry and within an insulated cavity wall anchorage systems, movement control and moisture barriers. insulation in a system that system will naturally provide Each component of the wall system, whether backed up with makes it possible to surpass varying thermal mass proper- CMU or metal studs, requires detailing, quality materials, instal- minimum energy requirements ties. Thermal mass refers to the lation accuracy and scheduling coordination of multiple trades to capacity to absorb and retain avoid performance failure. Any single failure can result in water and achieve additional heat. The absorption and reten- damage, expensive repairs, maintenance costs, health concerns “Optimized Energy Performance” tion of heat by masonry pro- due to mold and excessive air infiltration. credits from LEED. vides several benefits contribut- Masonry units and insulation in elementary form are not ing to increased energy per- expensive materials. Cost is accumulated due to manufacturing formance. By slowing the trans- infrastructure, energy used in production, transportation and fer of heat or cold through the building envelope, temperature jobsite installation. Costs may vary among types of masonry fluctuations can be minimized. Indoor temperatures are addition- cavity walls as a result of specification and design details. ally moderated when masonry remains warm or cool after HVAC Masonry material costs and R-values are displayed in Table 1 equipment is shut off reducing peak heating and cooling loads. reflecting these additional costs. This reduction in peak heating and cooling loads shifts demand to off-peak hours often resulting in reduced energy costs by avoiding peak utility rate periods. In Michigan, energy suppliers MASONRY MATERIAL R-VALUE COST/SF INSTALLED have discounted rates for commercial and industrial applications Normal Weight 2.0 $9.35 of power use during these off-peak times. Medium Weight 2.1 $8.90 Dependent upon the actual amount of heating and cooling Light Weight 2.2 $8.45 load reduction due to thermal mass, HVAC system sizing could Brick Veneer 0.4 $13.30 be affected. Before reducing HVAC system sizing, some factors Table 1. R-Values and Costs for Masonry should be considered such as climate, internal loads and time [References: NCMA TEK 6-2A (2005), RSMeans Building Construction Cost Guide (2007)] lag. In climates where there are large daily temperature fluctu- ations above and below the building balance point tempera- INSULATION MATERIAL R-VALUE PER INCH COST/SF INSTALLED ture, thermal mass provides the greatest benefit. In Michigan, OF THICKNESS seasonal change demands that a mechanical system provide Perlite 2.7 $0.82 both heating and cooling. In Michigan, however, being a heat- Rigid (Extruded Polystyrene) 5.0 $1.09 ing dominated climate, the greatest benefits of thermal mass Foam Fill 3.34 $2.97 are used to absorb and retain heat. Absorbed thermal energy, Foam Spray 3.8 $2.16 which is often underutilized, is provided by solar gain from the Table 2. R-Values and Costs for Insulation sun. Maximized by proper building orientation, solar gain can [Reference: NCMA TEK 6-2A (2005) MASONRY RESOURCE GUIDE 2008 the story pole 53 INSULATED CAVITY MASONRY WALL DESIGN ASSEMBLY NO COMPONENT ASSEMBLY ASSEMBLY COST/SF software have been developed to help determine code compli- U-FACTOR R-VALUE INSTALLED ance, one of which is COMcheck. Assembly 1 8˝ CMU — Medium Weight U = 0.19 R = 5.3 $21.69 COMcheck, provided by the US Department of Energy, 2˝ Airspace + Air Film (available