Insulated Concrete Forms Energy Performance & R-Values

Fact or Fiction: "The R-value tells me how much energy my building will use, right?" R-value measures the resistance a material has to conductive heat transfer, this much is true. R-value alone, however, does NOT fully describe the energy performance of a building. Everyone in the ICF community knows that ICF buildings far outperform framed buildings with comparable stated R-values in terms of energy efficiency and comfort level, but why is that? Let's look at the main factors affecting actual energy performance of a building: Thermal Conduction, Convection, Radiation & Mass.

Thermal Conduction is the heat transfer through a material by contact of one molecule to the next. This is the only factor an R-value measures.

• We have all heard builders claim to build "R-13" or "R-21" walls with wood frame construction. The problem is that only the highest rated component in the wall - the insulation itself - performs at these stated R-values. A wood frame wall is made up of several components, not all of which have the same R-value. For instance, a 2x4 or 2x6 stud has an R-value of about R-5 or R-7. Every 16 inches or so, one of these components breaks the insulation layer and forms a "thermal bridge", conducting heat through the walls at high rates. Adding up the area of studs, plates, and headers, 12% to 16% of the total wall area is an R-5 or R-7 thermal bridge, all detracting from the stated R-value. In addition, batt insulation tends to sag over time and leave spaces without any insulation! How can those builders claim only the highest-component R-value? From a whole-wall perspective, framed walls operate at far lower R-values - sometimes only half of the advertised value.
   
• ICF walls consist of a center cavity to contain concrete between two layers of EPS which provide two continuous layers of insulation rated at R-22 and higher. From a whole-wall perspective, ICF walls actually live up to the advertised R-values because thermal bridging is absent.

Thermal conduction is not the only mode of energy loss in a building. In fact, conduction often contributes less to energy losses in wood frame buildings than convection, which is not even measured by R-values.

Thermal Convection is heat transfer by movement of currents within fluids or gases. When considering energy performance of buildings, it's air moving between the inside and outside or "air infiltration". A common measurement is 'Air Changes per Hour' at a blower-door induced pressure differential of 50 Pascal (ACH₅₀). US Energy Star standards for new homes require less than 3 ACH₅₀. In comparison, Canadian R-2000 standards are 1.5 ACH₅₀, and Swedish standards are 0.5 ACH₅₀ or less.

• In wood frame buildings convection can be felt as drafts and is usually the biggest source of energy loss. Air infiltration accounts for up to 40% of the energy losses of a wood framed structure. Energy escapes via conditioned air leaking through thousands of cracks, openings, and joints between all the components of the building envelope. Major culprits include vented attics, framing connections, wall, floor & roof intersections, shrinkage of wood and caulking, and poor installation of components and sealants. A typical new wood frame home has between 1.5 and 3 air changes per hour (ACH₅₀) and after some years it's often between 4 and 6 ACH₅₀ as the wood shrinks and sealants deteriorate. Old wood frame homes commonly have 10 to 20 ACH₅₀.
   
• ICF walls & roofs are an effective air barrier because the concrete is solid without passages for air to leak, thus eliminating a major percentage of air infiltration. ICF buildings consistently get results of 0.5 to 1.5 ACH₅₀, largely depending on the installed roof type and sealing. Most air infiltration in an ICF home is through a conventional roof and around windows & doors, so pay attention to these areas, e.g. use Quad-Deck for the roof or attic floor of the building.

Adequate air exchange must be ensured in airtight buildings, typically with mechanical ventilation that can be combined with 'heat/energy-recovery' units or ground heat exchangers for additional savings where conditions & budgets allow it. Allergen filtering is also easy to incorporate, and in 100% ICF buildings air humidifiers can be added due to the very low risk of condensation in the building shell.

Thermal Radiation transfers heat via electromagnetic waves, which for buildings are mostly the sun's rays. Depending on factors like site & location of the building and the prevailing climate, Passive Solar Building Design helps optimize a building's absorption and reflection of solar radiation through solar orientation, placement of windows and shading elements, choice of finishes, and incorporation of thermal mass.

Thermal Mass refers to a material's capacity to store heat. Concrete and (Adobe) bricks have high thermal mass, which can act like a battery for heat. The classical use of thermal mass is in desert climates where outside temperatures swing above inside temperatures during the day and below at night. High mass building shells can store the heat from the outside during the day and release some of that heat to the inside at night - keeping the inside comfortable using almost zero energy. In temperate climates, thermal mass is best used in combination with the principles of passive solar design, e.g. let the winter-sun heat high-mass floors through windows.

• Wood frame buildings have almost no thermal mass - unless finished with brick, which is on the wrong side of the insulation to be effective.
   
• High mass construction built into ICF walls & floors can further reduce the requirements for active heating & cooling in many climates and projects. Another benefit is evident during power outages, when the interior temperature of ICF buildings takes days to change instead of hours.

The superior thermal performance of insulated concrete forms has been proven in recent side-by-side tests per ASTM standards:

• The ICF wall assembly provided 58% better effective R-Value than the tested 2" x 6" wall assembly
   
• The charts on the last two pages of the study's report illustrate that ICF walls provided an infinite instant apparent R-Value, literally "off the chart", for the first TWO DAYS. Then the ICF walls took another 3 DAYS to go from R-90 to below R-50! And another 5-6 DAYS to finally reach steady-state of about R-24. In contrast, the 2x6" wood-framed walls got close to their steady-state of around R-15 in about one day - versus 10 days for ICF walls.

All of the above translate into significant ongoing energy savings and savings from smaller sized HVAC equipment.

Getting back to the original questions, the answers are...
 
"No - the R-value of one component alone does not tell you how your building will perform". Remember, the Building Code is only a MINIMUM standard and there are many factors that influence actual energy performance.

"Yes - ICF buildings far outperform framed buildings despite similar advertised R-values". The secret lies in the combination of reduced conduction & thermal briding, less convection, and high thermal mass. The result is a building with a lower appetite for energy and vastly improved comfort inside the building due to more consistent temperatures and lack of drafts. Plus you get superior sound absorption and greatly reduced risk of condensation, rot and mold.

Every building should be considered from a 'whole system' perspective and designed using an integrated systems approach. Besides walls, roof and slab, windows also have a significant impact on performance since they usually make up 10% to 20% of the total wall area and vary widely in energy performance. Energy Raters and some engineers & architects now offer energy modeling services that will paint a much more accurate picture of how your building will actually perform. A small investment in a computer analysis helps in formulating the best-value design of a building to save tens of thousands in energy costs, even hundreds of thousands for larger buildings, over a building's lifetime.

Please contact us to get started.

Thermal Imaging reveals the hidden truth

Conventional, recently built Office:

Church with Quad-Lock R-22 ICF (see testimonial, project info):

Light = Warm / High Energy Loss (when heating)
Dark = Cool / Low Energy Loss (when heating)
The images of these two nearby buildings were taken on the same winter day. The Quad-Lock church is largely cool outside due to the efficient walls and efficient windows. The conventional building's walls are almost as warm (light) as its windows - they are heating the environment and we can almost see the dollar bills being thrown out the windows.

* Source: Portland Cement Association Technology Briefs

Further Reading:
(Research) Thermal Metrics for High Performance Enclosure Walls: The Limitations of R-Value

Sustainable Building Info:
Five Steps to Zero Energy
ICF Energy Science
Superinsulated Building Shell
Green Roof Research
Sustainability Checklist
Reuse & Recycle Tips

Links to other websites:
Passive Solar Building Design
Green Hotels with ICF
EPS and the Environment
Concrete CO₂ Fact Sheet