In late 2012 the Florida Masonry Apprenticeship and Education Foundation (FMA&EF)³, in joint cooperation with the National Concrete Masonry Association Education and Research Foundation², contracted with Pacific Northwest National Laboratory (PNNL)¹ to study the effects of various wall systems on the annual energy usage by one‐ and two‐story residential homes in all climate zones across Florida and the United States

The study’s objective was to obtain a direct comparison of the actual energy and dollars⁷ expended using different types of walls in a typical residential home while keeping all other aspects of the house EXACTLY the same.

This research was done using EnergyPlus™, a simulation software developed by the Department of Energy and acknowledged as one of the most accurate and powerful energy simulation tools available today.

Standard or “Prototype” homes were used in the computer modeling. These prototypes were developed using both Florida and National standards. Once established, all aspects of the prototype were kept identical except for the exterior wall system.

The basic output from the research is the total “whole house” annual energy usage. This usage includes only heating, cooling and ceiling fan energy (referred to as HVAC) and does not reflect all other household energy usage, such as hot water, lighting, electronic equipment, cooking, etc. As previously stated, all other HVAC variables are held equal so that differences in annual energy usage reflect exterior wall changes only.

In all, 607 different wall systems were modeled for both one‐ and two‐story prototypes in 18 different Florida and National climate zones. A total of 21,852 separate wall system analyses were made. Of these, 3,642 wall system analyses were made specifically for Florida. For those wishing a more in‐depth review of the research, please go to www.FloridaMasonry.com and click on the PNNL Research Report under the Resources tab.

The PNNL research provides valuable information for Florida. The research confirms the superior performance of thermal mass and the diminishing returns of over‐insulation. It also gives us a better understanding of where in Florida mass performs best.

This report is limited in scope to 14 different wall systems prevalent in Florida and is not meant to be exhaustive in comparing the energy usage of all 3,642 analyses. It is intended to use the PNNL research, the most complete residential energy information currently available, to address four common misconceptions regarding residential energy usage. See “4 Common Energy Myths” above.

Residential wall component manufacturers have heatedly discussed the effect of added insulation since the late 1960s. Although it may seem like the walls of a house would constitute a major component of energy efficiency ‐ in reality, they do not. The answer is clear-cut from past research. Study after study over the past 30 years has shown that the energy savings resulting from wall insulation diminishes rapidly as more is added. Unfortunately, it always seems the research doesn’t apply to the exact wall system being discussed, so there has always been “wiggle room” for inflated saving claims from unique wall insulation products.

The current PNNL study confirms what we already knew—heavy insulation in Florida’s walls is a waste of money. This research, however, has the scope and breadth to include all of the current wall types being constructed and compare them on an apples-to-apples basis.

As a pointed example, three walls were picked to compare the difference in annual energy usage. The first wall is a typical CMU with interior R-4 foil insulation. The overall R-value for the entire wall, including exterior finish and drywall, is R=5.8. This is the lowest R-value for any standard wall used in Florida. This wall was compared to a masonry wall with interior R7 foil insulation and to a highly insulated ICF wall with R20 insulation split between the interior and exterior. The overall R-value for the masonry wall with R-7 foil is R-8.3. The overall R-value for the ICF wall is R=21.7. This would be one of the highest R values for any Florida wall system4.

The results are in Table 1.

Total Energy $ Savings per Year Over Standard CMU w/R4 Added Insulation (2000 sf Single Story Home)

The annual savings achieved by going from a wall with an overall R-value of 5.8 to a wall with an overall R-value of 21.7 is $101 – that’s it. This represents the absolute maximum yearly payback that you can obtain by changing the insulation value of the exterior walls in a typical 2000 sf single-story home. In order to get that $101 you had to invest $4207.⁵. Your return on investment at 41.5 years far exceeds a reasonable 20-year payback period⁶ and is simply a poor investment.

As an alternative, you could upgrade your interior insulation on the CMU to an R-7 for approx. $463⁸ with a payback in Miami of 11.5 years.

The bottom line is that CMU, with a small amount of R-4 insulation, combined with the thermal mass of concrete, makes for an extremely cost-effective and hard-to-beat wall system anywhere in Florida. Upgrading insulation slightly from R-4 to R-7 is somewhat cost-effective in Miami, but any additional insulation becomes a waste of money.

The Chart in Figure 1 gives the $ savings per year as you increase insulation from R-1 to R-24 on a typical CMU wall in the three Florida climate zones. As you can see from the chart, putting SOME insulation on the wall is really essential. Your R-4 foil insulation at around $360 pays back $71 in Miami in the first year and gives you an approximate five‐year payback. This makes perfect sense. On the other hand, that same R-4 added to R-20 gives you a payback of only $5 per year. This money would be better invested in some other component of energy efficiency.

The bottom line is that your heavy energy costs, in Southern climate zones, do not come from heat or cold making their way through the exterior walls. Once you have added some moderate insulation to the wall system, the rest of your energy cost is from air infiltration through windows/doors/ walls, thermal and solar gain through windows, hot water, lighting, electronic equipment, cooking and particularly thermal gain through the roof and ceiling.

The PNNL Report proves that if someone states you will save substantially more than $100 per year on your energy bill in Florida by heavily insulating the walls of a 2000 sf single-story home – they are mistaken or simply trying to sell you something using misleading information.

CMU with R-4 foil insulation added to the interior wall between the furring strips and 4″ nominal wood frame construction with R-13 batt insulation between the studs are by far and away the two main wall systems used in Florida residential construction. In a discussion strictly focused on energy, it would seem that a wood frame wall with an R-value of 10.9 is twice the energy efficiency of a CMU wall with an R-value of 5.8. This is not accurate. The PNNL research shows the difference in energy efficiency is very minor and furthermore relies on the premise that the insulation in the wood frame structure stays dry and in good condition.

However, the “dry and in good condition” is not the reality for millions of square feet of Florida wood frame walls. Wood wall leakage and condensation can dampen the batt insulation and drastically reduce the insulation value. Additionally, CMU has the advantage of thermal mass, where energy is “absorbed” by the wall rather than letting it pass through.

What the PNNL Research gives us is the exact $/year energy difference, across the State, between these two wall systems. The EnergyPlus™ software is powerful enough to accurately model the benefits of thermal mass, which has been difficult to exactly quantify in previous research done with less powerful modeling tools. No reduction in the energy efficiency of wood walls for problems due to damp and moldy batt insulation was factored into the PNNL research. The energy comparison is between the two wall systems, properly constructed and maintained. The comparison results are shown in Table 2.

Total Energy $ Savings per Year Over Standard CMU w/R-4 Added Insulation

The effectiveness of thermal mass can be clearly seen in the above table, and it is reversed from what we, in the construction industry, have always thought. Past research, using less powerful tools, indicated that thermal mass had the best advantage in Miami, then Orlando and finally Jacksonville. As it turns out, the thermal mass has the best advantage in Orlando and Jacksonville, virtually eliminating any energy cost difference between the wood frame and CMU walls in the Central and Northern portions of the State.

The construction cost difference between CMU and Wood homes is generally around $1.00 to $1.50 per sf of wall area or roughly $2530 for a typical 2000 sf home with 1530 sf of wall⁹. Since approximately 60% of all residential exterior walls are CMU in Florida, there must be some advantages that outweigh the added construction costs.

Indeed, CMU has tremendous advantages. Unlike wood walls, CMU is unaffected by water and is not a food source for mold – no rot, no mold and no deterioration over time. Because it does not burn, your home insurance rates for CMU are 10-20% lower than for wood homes. Generally, this results in a savings of $150-$575 per year¹¹ for insurance alone. Structurally, CMU has proven far superior to wood in hurricanes and wind storms. CMU is unaffected by the catastrophic termite damage to wood structures in Florida. And, getting back to energy, the minor differences in Table 2 are quickly reversed with moisture deterioration of batt insulation over time (the average rainfall in South Florida is 60 inches per year).

The real eye‐opener from the PNNL Research is not the slight energy use difference between Wood and R4 CMU in Miami. The eye-opener is that the thermal mass in R-4 insulated CMU performs extremely well in all of Central and North Florida, virtually identical to R-13 wood frame construction in energy efficiency.

An age-old discussion on proper insulation of CMU pitted the standard interior insulation against exterior insulation. From past research, it was felt that insulation on the outside of the block was much more effective than insulation on the interior. The PNNL research has given us the answer but also the $$ difference made by the interior vs. exterior insulation placement.

Table 3 shows that for two CMU walls insulated to R-10, placement of insulation on the exterior saves a small amount of money but not enough to pay back the difference in construction costs.

Clearly, the standard interior insulation on CMU walls that we have always used is by far and away the most cost-effective placement.

Total Energy Savings per Year of Exterior Insulation over Interior Insulation

This Florida‐specific report only scratches the surface of the vast number of comparisons that can be done using the output of the PNNL Research. For those wishing a more in‐depth review of the Research, please go to www.FloridaMasonry.com and click on the PNNL Research Report under the Resources tab.

The comparisons presented in this report were chosen to highlight the amount of bad information and confusion associated with them. When it comes to energy, it seems like everyone has a product to sell or a personal “green” perspective to promote. The real value of this research is being able to quickly and easily get to the cost vs value relationship between virtually all wall systems. Not having the actual yearly dollar differences between walls leaves too much room for exaggeration and the imagination.

“If no one knows ‐ then anything goes,” and myths on energy efficiency abound:

• Putting heavy insulation in your walls can save you hundreds of dollars PER MONTH – FALSE!
• More insulation is always better — FALSE!
• R-13 wood walls are much more energy efficient than R-4 CMU – FALSE!
• Insulation is only effective on the outside of CMU – FALSE!

The energy data from the PNNL research will certainly be dissected by those depending on exaggerated claims of energy savings.

The force of this research is that there is no better information currently available – anywhere

Please note: In Attachments 1 and 2, I have provided additional technical information on the wall systems reviewed in this report. Since the “whole house” energy usage is given on a square footage(sf) basis, homes slightly larger or smaller than 2000 sf for a single-story and 2200 sf for a two-story can be analyzed with reasonable accuracy by applying the per-SF cost to the actual conditioned floor area.