Making a Good Thing Better
Foam plastics such as expanded polystyrene can greatly enhance the energyefficiency of traditional masonry
Long known for its structural, acoustical, and fire-resistant benefits, masonry-based construction has endured the test of time and is recognized today for its role in reducing energy costs. Because of its exceptional thermal mass, a masonry wall can quickly absorb excess solar heat and stabilize indoor temperatures, making masonry an energy-smart choice for both structural load-bearing and nonstructural applications.
Originally, concrete and brick building blocks were used as the sole material to build thick, heavy walls in factories and homes, taking advantage of their aptitude for direct thermal storage. That is, as heat flows from hot to cold, the heat can be stored within the exterior wall on a hot day, delaying the heat flow into the building’s interior. Once the outside temperature decreases below the temperature inside the building, the stored heat flows back out.
Today, masonry construction is often partnered with foam plastics insulation such as expanded polystyrene (EPS) to further enhance both thermal capacity and heat-flow retardation. Because an insulated masonry wall system is compatible with other construction methods, it allows for design configurations that can meet the environmental demands of diverse climates, from moderate to extreme. Furthermore, one can select materials and the type of wall assembly to meet specified performance criteria to an exact degree, simplifying compliance with minimum energy code requirements.
Measuring energy efficiency
A building’s energy consumption under steady-state conditions is calculated using the overall steady-state resistance of its building materials to heat transfer, or their R-value. It is important to note, however, that measurement systems used to determine the thermal performance of these independent building materials are not geared to evaluate their performance within a building system and cannot deliver an accurate representation of the interdependent energy savings that can be achieved. For example, whereas a material’s R-value might be 14.5 using only steady-state data points, accounting for the benefits of thermal mass, added insulation, and a 2-in. air space in a cavity wall system could increase the theoretical R-value to 22. Other factors that determine thermal performance include thermal lag and thermal dampening.
Keeping in mind the other factors that affect a building’s energy efficiency (such as thermal conductivity, or U-factor), one may use the materials’ R-value for baseline comparison.
Types of insulated masonry
Foam plastics insulations such as EPS complement well the energy profile of masonry wall assemblies and are available as board insulation, custom-molded core inserts, and as aggregates for lightweight concrete.
Interior insulated masonry is a good choice for those familiar with the more traditional block construction. Lightweight metal brackets and rigid foam insulation replace more costly wood studs and fiberglass insulation while allowing ample space for plumbing and electrical wiring and improved moisture protection.
In an exterior insulated system the insulation is mounted onto the outside of the block wall and then finished with a simulated stucco or stone facing. These siding systems effectively stop moisture penetration since the insulation and finish are uninterrupted. Wiring or plumbing can be run through the block cavities, or traditional furring for drywall can be used on the inside surface. Furthermore, by increasing the thickness and/or density of the insulating foam board, a builder can easily improve the structure’s energy performance. This method is ideal in climates that experience temperature swings, since the concrete mass on the inside is optimal for storing heat or coolness.
Custom-molded core inserts
Several methods are available for in-block insulation, most commonly used to insulate single-wythe construction. Although a number of substances can be mixed and forced under pressure into the concrete core, a newer approach fits molded EPS inserts into the block cavity. This approach eliminates the need to insulate the interior of the wall—further cutting costs—and is ideal for occupied warehousing that doesn’t require finishing on either side of the wall.
With in-block insulation, the masonry units are either shipped to the jobsite with the insulation already inserted between the interior and exterior surfaces of the block or is added at the point of installation. Built-in insulation eliminates the need for a separate shipment to the jobsite, minimizing transportation costs.
Masonry walls are often grouted and/or steel-reinforced, with the masonry blocks placed in designated block cavities. If a wall assembly has vertical and horizontal grouted steel every 48 in. on center to meet structural requirements, conceivably up to 31 percent of the wall could remain uninsulated. However, EPS offers a significant advantage in its ability to be used within the block cores where grouting and reinforcement are placed without interfering with the structural function of these supports.
Another type of in-block insulation that offers even higher Rvalue is referred to as a preinsulated block. By using partially expanded EPS or recycled-content regrind EPS, bead-sized particles are used as an aggregate in the concrete to increase the block R-value. When adding the EPS foam inserts described previously, the block can deliver an R-value as high as 20. Other benefits of these lightweight blocks include their ability to be cut, nailed, and screwed like wood, facilitating inside mechanical installations without furring strips. Furthermore, lightweight aggregates can reduce the weight of the concrete block by up to 25 percent and effectively reduce installation time by substantially increasing the number of units per hour that a mason can lay.
Impact of energy codes on concrete block design
To meet the more stringent requirements in today’s energy codes, single-wythe masonry blocks have been reengineered to further enhance performance. The majority of these efforts have focused on reducing the web area of the block and, in some cases, eliminating it altogether. EPS has become the material of choice for the insulation used in the redesigned blocks. One example of redesigned units is the Hi-R Masonry Wall System. This system reduces the web area by nearly 50 percent and provides an EPS insert nearly 3 in. thick that overlaps to insulate the mortar joints as well. The Hi-R Wall System has been used extensively in correctional facilities and schools because of its ability to provide higher thermal values and at the same time allow walls to be grouted and reinforced both vertically and horizontally at 8 in. on center, offering a more cost-effective means of employing masonry construction within stricter budget requirements.
Other examples include blocks that have been designed with a series of staggered cores to retard heat flow through the wall. It is important to consider that blocks redesigned for energy conservation should be sufficiently evaluated for structural performance as they are not considered equivalent to standard blocks until properly tested.
Masonry and insulating plastics, either individually or working in tandem, meet numerous green building criteria and can contribute toward green building recognition in a variety of point or credit categories. EPS insulation provides long-term R-value and does not need to be adjusted for thermal drift. It also tests favorably for mold resistance in accordance with ASTM C1338 and does not adversely affect indoor environmental quality. Beyond the environmental benefits of the installed product, manufacturing EPS can require less energy than can some alternative materials.
According to the National Concrete Masonry Association (NCMA), concrete masonry units contribute significantly to meeting sustainability goals for building construction. Beyond its high thermal mass, it offers unquestionable durability and supports indoor environmental quality with high sound transmission ratings. No longer limited to gray ash, colorants are now incorporated to produce concrete blocks in a wide array of colors that eliminate the need for other finishing materials or even VOC-emitting paints. Other additives can reduce moisture absorption as well.
Together, foam plastics insulation and concrete masonry are perfect candidates to take advantage of the Energy Policy Act (EPAct) 2005. Commercial buildings demonstrating a 50 percent reduction in energy use, based on the ASHRAE minimum standard (see sidebar on page 21), are eligible for a tax deduction of up to $1.80 per square foot. Recently the IRS issued rules on how commercial building owners can qualify for the tax benefit, including a requirement that the energy savings be calculated using software that has been tested according to ANSI/ASHRAE Standard 140-2004, Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs.
With the variety of materials and building system options available, there are numerous ways to improve energy efficiencies. As the U.S. Environmental Protection Agency states, “In most climates, it is both easy and cost effective to increase insulation levels beyond the minimum code requirement.” In addition to the improved energy efficiencies, increased insulation also improves comfort and indoor air quality, increases construction quality, reduces obsolescence, improves resale value, and, most obviously, reduces utility bills.
ASHRAE energy standards
The ASHRAE Standard 90.1-2004 Energy Standard for Buildings Except Low-Rise Residential Buildings is the most commonly referenced standard used to establish minimum requirements for energy efficiency in the design and maintenance of indoor environments, and serves as the basis for energy code requirements at the federal level and within most states. It is also acknowledged as the benchmark reference for commercial buildings looking to qualify for tax deductions under the new Energy Policy Act.
ASHRAE 90.1-2004 addresses the building envelope’s vital role in optimizing energy efficiency and covers both prescriptive and performance-based criteria. The prescriptive method assigns minimum requirements for eight designated climate zones. Performance methods can be used to assess or project actual energy use and allows for trade-offs in meeting the minimum requirements rather than dictating specifics.
Section 5, covering the building envelope, outlines space conditioning categories, compliance paths and detailed product information and installment requirements for insulation and other materials making up opaque building elements of any wall, roof, or floor assembly. Citing eight climate zones, minimum insulation R-values are stipulated for the various construction methods with the reciprocal U-factors for the assembly maximum. In addition, normative appendix B provides information to determine both U.S. and international climate zones.
In the prescriptive method, most energy codes will make adjustments for walls with thermal mass, such as concrete and masonry, recognizing that R-values are not a true indicator of energy performance. In most climates, buildings with insulated mass walls will save energy compared to buildings without mass having the same R-value. And, since the mass reduces peaks in the mechanical system loads, first costs for HVAC equipment may also be reduced in some climates. For example, for Tulsa, Oklahoma the ASHRAE standard requires a R 8.3 frame wall or a R 4.3 mass wall in some buildings. These requirements are based on the fact that an R 4.3 mass wall is as energy efficient on an annual basis as an R 8.3 frame wall in this particular climate. Thermal storage benefits in mass wall construction will vary by climate and is influenced by frequent temperature variations, solar radiation, wind, and how the building is designed, operated, and maintained.
First published in 1975, it has undergone numerous revisions designed to simplify and, thereby, broaden its use. Largely tied to the green building movement and with foresight to increased energy costs, many of the 2004 revisions are intended to facilitate improved energy conservation. This includes a new appendix to rate the energy efficiency of building designs that exceed its minimum requirements and provides guidance on how to design for green building certification, such as LEED.
About the Author
Betsy Steiner is executive director of the EPS Molders Association (EPSMA) in Crofton, Md. She can be reached at 800-607-3772 or firstname.lastname@example.org.
- Energy Codes and Standards, Martha G. VanGeem, Construction Technology Laboratories, Inc. for Whole Building Design Guide, December 2005
- Standard 90.1-2004 Energy Standard for Buildings Except Low-Rise Residential Buildings SI Edition, American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2004
- Concrete Masonry Units, Portland Cement Association, 2006 http://www.cement.org/homes/ch_bs_concretemasonry.asp
- Concrete Masonry Use & Applications, National Concrete Masonry Association, 2006
- Increased Insulation Building Envelope Improvement, US EPA, 430-F-97-028, December 2000
- Thermal Storage, Energy Efficiency and Renewable Energy, Building Technologies Program, http://www.eere.energy.gov/buildings/info/design/integratedbuilding/passivethermal.html
- Masonry Technical Manual, Masonry Institute of British Columbia, http://www.masonrybc.org/index.php?p=ManualIndex