Energy Efficiency: Understanding R-value, Mass Walls, Continuous Insulation and Air Tightness
R-VALUE ISN’T THE ONLY VARIABLE THAT AFFECTS A BUILDING’S ENERGY EFFICIENCY.
How to talk about materials, design and construction to help your clients reduce their energy footprint—and their cost of ownership.
When it comes to energy efficiency, the industry buzz of “R-Value” (thermal resistance or ability to prevent heat transfer) continues to cause confusion – and false assumptions. R-values continue to be used synonymously with building energy efficiency performance. In reality, R-value is only a partial predictor of a building’s energy efficiency, at best.
A structure’s optimal energy efficiency is achieved when important variables work in harmony: architecture and building system design, materials and construction method. Relying on just one is like removing two legs from a three-legged stool. Imperfections in the installation of insulating materials – including air gaps and improper compression of the insulation – can dramatically reduce the performance of a wall system. Other factors, such as thermal mass and air in ltration through the wall envelope can also make a signi cant impact on energy performance – positively or negatively.
While walls are very important to the energy efficiency of a building, other critical items such as windows, doors, roof assemblies, penetrations through the envelope, and the design of the heating, ventilation and air conditioning system will all contribute to the energy efficiency and performance of a structure.
The Bautex Wall System, including Bautex Block and Bautex Air and Moisture Barrier, creates an extremely energy-efficient building envelope with greater thermal mass, continuous insulation, and very low air permeability.
R-value is a starting point for comparing insulation systems, but remains only one factor. Design, materials and construction science will play a huge role in energy efficiency.
According to the American Society of Heating, Refrigeration and Air Conditioning (ASHRAE) 90.1 standard*, the “e ective” R-value of a wood-framed building with studs on 16-inch centers, using conventional R-13 cavity insulation (i.e., the actual thermal resistance provided by the insulation in a given assembly), is only R-9. For a wall assembly using light gauge metal framing and the same R-13 cavity insulation, the e ective R-value is only R-6 – more than a 57 percent reduction in insulating performance.
This happens because thermal bridging occurs through the structural framing members and un- insulated design features of the walls, which reduces the overall effectiveness of the wall insulation.
While using more insulation may appear to increase energy efficiency, there is a point of diminishing return when adding insulation to a wall system no longer improves energy performance. This was demonstrated in a National Concrete Masonry Association (NCMA) study** completed in 2013 that showed for every building, there is an optimal amount of insulation that can be installed in a wall system. Adding insulation beyond that optimal amount no longer produces any savings in energy consumption. They summarized that money for excess insulation would be put to better use by improving other components of the building envelope and mechanical systems.
By specifying continuous insulation, architects and contractors can improve energy efficiency while meeting the speci cations of recent building codes, which strongly recommend continuous insulation for most wall types.
In wall systems with framing members that span the width of the wall (such as wood framing, steel framing, CMU, tilt panel), adding a layer of continuous insulation to the outside of the wall becomes absolutely critical for energy efficiency. For example, in a commercial building located in Central or South Texas (2012 IECC climate zone 2) built with wood framing, the prescriptive R-value tables require either an R-20 cavity insulation, or a combination of R-13 cavity insulation and an additional R-3.8 of continuous insulation on the outside of stud members.
In buildings with metal-stud construction in the same region, the prescriptive code requires an R-5.0 continuous insulation in addition to the R-13 cavity insulation that is usually specified.
The Bautex Wall System provides any building with an R-14 continuously insulated wall system. Bautex enables architects and contractors to be con dent that the building will surpass the energy efficiency demands of even the most stringent building codes. And building owners will realize years of substantial, reliable savings from reduced energy costs.
When designed to work together, mass walls and continuous insulation create buildings that provide extraordinary levels of energy efficiency.
Mass walls have been used for centuries. From mud huts to stone castles, buildings constructed with thick and dense walls have always been valued for their thermal properties. In parts of the southwest United States adobe buildings have been the housing of choice for as long as people have resided in that area. Adobe buildings provide exceptional thermal bene ts, keeping residents inside cool on even the hottest summer days, and warm at night in spite of winter temperatures that can drop below freezing.
This thermal mass, or thermal inertia, e ect is well understood in the architectural world and is also featured prominently in recent building codes. While insulating materials in the building envelope help to slow down the rate of transfer of energy through a wall system, thermal mass ampli es the energy efficiency of the system by absorbing a signi cant amount of heat energy that reaches the insulation. This boost in energy performance is strongest in climates and seasons where there are large swings in temperatures throughout the day.
In the 2015 International Energy Conservation Code (IECC), for example, the amount of added insulation required for a commercial building in Dallas, Texas (IECC Zone 3, Prescriptive R-value Method) constructed of light gauge framing is R-13 in the wall cavities – plus an additional R-7.5 continuous insulation on the outside of the wall. For the same building constructed of a mass wall system, the code only requires the addition of R-7.6 of continuous insulation to achieve the same level of performance.
While wood and light-gauge steel framing are still very popular, they have become more complex and costly to construct. New building codes with stricter energy-efficiency requirements are forcing builders to add more and more layers of expensive insulation, as well as pay for the additional labor and costs of adding these materials. In the end, the new building might pass code, but it will fail to provide nearly as much energy efficiency as a mass wall system. Just as important, cavity wall buildings fail to provide the level of re and storm safety that has been demonstrated by many mass wall systems.
In contrast to light-frame cavity-wall systems, Bautex Block is a lightweight, insulated concrete block that, when used to construct a building, provides structure, envelope, re and storm resistance, an air and moisture barrier, and continuous insulation – all in a single integrated assembly. It’s a modular, mortarless wall system where blocks are stacked and then lled with reinforced concrete to create an insulated structural wall. The wall system is constructed using the same labor, tools and techniques as those used in traditional concrete masonry construction. Plumbing and electrical systems are typically added a er the walls are constructed.
The result is a simple, single, integrated wall assembly that creates an airtight, R-14 continuously insulated mass wall for the building envelope with higher energy efficiency performance than most cavity-wall or traditional mass wall systems – all without any additional insulation – while providing substantially improved levels of performance and safety.
Air and moisture barriers improve more than just energy-efficiency. They create a healthier indoor environment.
“Air Tightness” refers to the ability of a building envelope system to resist the infiltration of air – and the moisture it brings – into the conditioned spaces of a building. Air tightness is important because, according to the DOE, air leakage accounts for between 25 - 40 % of the energy used for heating and cooling a building.
Air infiltration can be caused by the natural air permeance of the materials used to construct the building envelope, as well as by gaps, cracks or other interruptions in the air barrier system. Even small improvements in air-tightness can lead to signi cant reduction of air in ltration, minimizing the amount of energy consumed in order to maintain the proper indoor climate and decreasing the amount of moisture – warm, dense, humid air -- that can come into the building. The consequences of air leakage go far beyond the loss of energy efficiency. Air in ltration can be harmful to building occupants, with molds, allergens and pollutants penetrating indoor environments.
An air-tight building envelope signi cantly reduces the amount of work that the HVAC system has to do in order to maintain the desired interior temperature and humidity.
Walls built with Bautex Block also provide a rm and stable substrate on which to apply the air and moisture barriers. As a result, there is no movement, vibration or decay, like that which occurs in light framing systems over time. It’s also much easier to get a good installation of the air and moisture barrier on the Bautex Block wall than many other systems.
Bringing together the right design with the right building materials has enabled architects and builders to make great strides in improving the level of air tightness in structures of every size and purpose. Today, it’s possible to construct a new building with levels of air tightness that would have been inconceivable even a decade ago.
ENERGY CONSERVATION BEGINS WITH THE BUILDING ENVELOPE
Bautex Block is ideal for any architect or contractor interested in constructing air-tight building envelopes that provide unprecedented levels of energy efficiency.
A prime example of a building with unprecedented levels of energy efficiency would be the Bautex headquarters, a 3,900 square-foot, light-o ce building constructed with Bautex Block in San Marcos, Texas. It’s one of the most energy-efficient office buildings in the state.
A building of this size usually has energy bills of more than $385 per month. On average, monthly energy bills for heating and cooling of the Bautex headquarters are $120. Reduction of air in ltration contributed signi cantly to achieving this high level of energy efficiency. In fact, our building received a tested air in ltration score of two air changes per hour at 50 Pascals (ACH50). That is 300 percent better than conventionally constructed buildings of this type.
While the Bautex headquarters building uses significantly less energy than others in our region, just as important is the fact that the indoor air quality and comfort is outstanding. Employees benefit from even temperatures and an extremely quiet working environment, even though we’re located near an interstate highway. What is perhaps most impressive is that our building was constructed at competitive market costs by standard trades and laborers using traditional building practices.
We invite you to learn more about the unprecedented level of energy efficiency that can be achieved with Bautex Block at bautexsystems.com.