Thermal Protection—Energy Codes

By their very nature, CMUs have good thermal properties. Yet technology is ever expanding, and insulated units may well be the next generation of masonry. This type of unit contains an insulated thermal barrier, which effectively creates high-insulated thermal mass, high heat capacity, and a long thermal lag time—attributes that combine to create walls that require just a fraction of the energy normally needed to keep the interior cool in the summer and warm in the winter. Because they consume less energy, a smaller HVAC can be utilized, which promotes cost savings and reduction of building energy use. The block design creates an energy barrier between the exterior wall veneer and the interior core, with the installation creating a thermal mass design and reducing air temperature fluctuations. Some insulated units have attained an equivalent performance value of an R-22 wall and an STC rating of 53. In addition to delivering these benefits, insulated CMUs may contribute to LEED points in several categories including recycled materials.

In any event, the thermal performance of building materials is governed by building codes which benefit public safety and support the industry's need for one set of standards without regional limitations. Prime among them is the International Energy Conservation Code (IECC), which is published by the International Code Council (ICC). The ICC develops model codes and standards used in the design, building, and compliance process to construct safe, sustainable, affordable, and resilient structures, and its I-Codes are a complete set of comprehensive, coordinated building safety and fire prevention codes.

The IECC then is a model for states and other jurisdictions to establish codes for energy-efficient buildings. The IECC references the energy efficiency standard of ASHRAE (the American Society of Heating, Refrigerating, and Air-Conditioning Engineers), the building technology society that focuses on building systems, energy efficiency, indoor air quality, refrigeration, and sustainability within the industry—writing standards that shape tomorrow's built environment. ASHRAE 90-1975 was the first energy standard in the U.S.; it was published in reaction to the oil embargoes of 1973. The original standard had multiple editions and in 1999 the standard was placed on continuous maintenance, which allowed it to be updated many times a year consistent with rapid change in technology and energy prices. Now the standard is ASHRAE 90.1, which took effect in 2001, with updates in 2004, 2007, 2010, and 2013 due to newer and more efficient technologies.

As states and local jurisdictions adopt the IECC model as their energy code, they often make changes to reflect regional building practices, or state-specific energy-efficiency goals. The Advanced Codes Initiative has called for the development of stronger residential codes, with the first being the 2012 IECC, which is 30 percent stricter than the 2006 version and requires more insulation, a tighter envelope, tighter ducts, better windows, and more efficient lighting than the 2009 code. The goal is that all states will adopt the 2012 IECC codes by no later than 2017. Note that code stipulations may vary by county within a given state based on climate differentials, and that several large cities, including Chicago and New York, have their own codes.

The 2012 IECC offers three options for compliance: prescriptive tables, compliance software, and the performance method.

Prescriptive Tables

These tables list minimum energy performance criteria for roofs, above and below grade walls, slab-on-grade floors, and fenestration by climate zone. Straightforward and relatively simple to apply, the prescriptive method is the easiest of the three options to tackle, though it offers little in the way of design flexibility. There are two prescriptive compliance paths.

• In Option A, tables set forth the minimum R-requirement of only the continuous insulation (ci) that is used in a wall assembly. There is a widespread misconception that all walls must have continuous insulation in order to meet the IECC. But continuous insulation is required only to comply with this particular table; other compliance options are available, including compliance via U-factor which is detailed below.

• In Option B, tables set forth the maximum U-factor of the entire wall assembly. Using the U-factor criteria, rather than the insulation R-values, allows walls without continuous insulation (such as concrete masonry with insulated cores) to comply prescriptively. The U-factor compliance table may also be preferable in other instances, such as concrete masonry walls with proprietary inserts, or other walls that exceed code performance. Again, this option does not require continuous insulation.

Consider this example. Table 2, the Prescriptive Wall Insulation R-Value Minimum Requirements Table stipulates that in Zone 5 this layer of ci must have an R-value of 11.4 or greater. Using this option, a layer of continuous insulation would be added to the wall system that has a minimum R-value of 11.4 for the insulation only. This translates to 1½ inches of poly-iso. Now consider the real-world example below showing the use of rigid insulation to arrive at a 19 or even a 22.35 R-value—a scenario that far exceeds both prescriptive requirements.