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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 infil­tra­tion through the wall envelope can also make a sig­nif­i­cant 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 bau​texsys​tems​.com.