Overall Benefits "Green Build"

Today's consumer is looking for total value in their home and a big part of the value package is an energy-efficient home. More information than ever is sought by consumers to understand how to build a more energy-efficient home, and to understand how to evaluate the efficiency of various building material options. Until recently, R-Value seems to be the only way materials are rated for energy efficiency. (For instance, the IECC Climatic Zone Maps and Prescriptive Packages Tables now give High Mass Wall Equivalent R-values.) Unfortunately, the system does have its short-comings, due to the fact that R value testing does not utilize "real world" conditions. Currently the test requires the application of +/- 24 degrees Centigrade. The two most common tests for materials are Clear-wall and Whole-wall rating. Most R-Value is spoken in terms of Clear-wall ratings. However, the whole-wall rating system is more realistic and should be the choice of consumers when trying to evaluate materials.



Most Clear-wall R-Value calculations are based on procedures developed for the wood frame construction. Unfortunately, such testing is not representative of the way homes are built. It does not take into consideration the effects of additional construction like windows, doors, exterior wall corners and how the roof joins the walls. When factored in,
R-Values typically drop from those stated as Clear-wall R-Values. Clear-wall R-Values and their thermal performance are determined by testing a solid wall (complete with its insulation system), usually a section 8 ft. x 8 ft., with no openings for doors and windows.


Not used often, but clearly more accurate is the Whole-wall R-Value rating system. In this system, not only is the thermal performance of the wall tested, so is the typical envelope interface details. These include wall-to-wall corners, wall-to-roof, wall-to-floor, wall-to-doors and wall-to-window connections. Why include these details? Because energy efficiency is lost at these points of construction and including these elements provides a more accurate R-Value rating system.


To add to the confusion of rating walls and building materials for R-Value is the concept of thermal mass, perhaps the most confusing energy issue facing designer, builders and homebuyers today. Thermal mass ratings are determined by measuring the building materials/wall unit energy efficiency in conjunction with other layers of materials attached to the wall, i.e.; particle boards, drywall, stucco. The measurement of the energy performance of a "stated R-value" material, combined with the layering of other materials to enhance the energy value, is often referred to as "mass-enhanced R-value." Today's energy codes recognize the energy value coming from both the thermal mass of masonry and it's R-value. Depending on a professionally engineered design and application a typical wall R-value requirement of R-18 may be met by a masonry wall with a R-value of R-7.

Energy efficiency of building materials is determined by how it handles heat, how heat transfers through materials and how well materials hold or store heat. Remember, heat always moves from warm to cold, so during the summer, if the outside temperature is warmer than the inside temperature of a home, heat transfers through the walls from the outside in. Conversely during winter, if the inside air temperature is warmer than the outside, heat transfers from inside the home out.

There are a number of combinations of materials used in construction and their thermal mass and R-value efficiencies vary depending on how they are used in the region of the country (climate considerations). How efficient a system is and how much energy consumption is reduced depends on how fast heat transfers through materials, how well materials hold the heat and the fluctuation of outside temperature. High-heat capacity materials significantly reduce the time for the heat to pass or transfer through into the home. Often until late in the night, typically when systems are running more efficiently or consumers are being charged a lower rate for kilowatt usage from their utility company.

Mass effect is real. High-mass walls really can significantly outperform low-mass walls of comparable steady-stated R-value. However, the mass-enhanced R-Value is only significant when the outdoor temperatures cycle above and below indoor temperatures within a 24-hour period. High mass walls are most beneficial in moderate climates that have high daily temperature swings and nearly all areas with significant cooling loads can benefit from thermal mass in EXTERIOR walls. This is especially true for the sunny Southwest areas of Arizona, New Mexico and Colorado.

According to an article written by Jeffrey E. Christian and Jan Kosny titled "Wall R-Values that Tell It Like It Is," wall systems with significant thermal mass have the potential, depending on climate, to reduce annual heating and cooling energy requirements below those required by standard wood frame construction with similar steady-state R-value.

Masonry products, with mass-enhanced R-value or thermal mass, provide some of the best energy values for homeowners today. They consistently rank higher than steady-stated R-value of wood framed walls. Remember, the overall R-value is not as important as how the home is constructed. Attention to details like the windows you select, like low e-thermal, dual pane windows that are tinted, is just as important as the R-value in the walls. In fact, much heat loss or gain, up to 48%, is through windows, not walls! The most energy efficient building materials for the desert or Southwest climate is 24" thick adobe, which only has an R-value of less than 7. It is energy efficient because of it other attributes including thermal mass, air tightness, thermal lag and thermal dampening. This proves that R-value is just one piece of the energy puzzle, and often, does not paint a realistic picture of energy efficiency.