Bidding a project and Wondering why XPS 250 (R-10)
is specified for foundation insulation?
XPS (Extruded Polystyrene) and EPS (Expanded Polystyrene) are both closed cell rigid insulation that have the same compressive strength abilities. Many Specifiers and Contractors do not really understand the difference. You should! There is a BIG cost difference.
Many Specifiers and Contractors believe that XPS insulation provides a consistent R-value of R-5/inch in foundation insulation. Not even close. Two reasons: One, XPS uses a blowing agent that provides additional R-value that escapes and over time lowers the R-value. In fact, the federal government has now stepped in and mandated XPS rate their product using the R-value method of LTTR (Long-Term Thermal Resistance) as of October 2019 (see Full Disclosure Article). According to new research by the EPS-IA, XPS insulation’s 50 year age adjusted (LTTR-50) R-value is estimated to be 4.3 R-/inch. Two, research has shown that XPS placed below grade loses 48% of its R-value. This is due to the cell structure and manufacturing process of XPS. The study concluded that once XPS takes on water it has a hard time breathing it out.
Insist on Plymouth Foam Engineered EPS
The technological advancement for Engineered EPS is truly amazing and the new research is showing why you should insist on using Engineered EPS Foundation Insulation on your project. EPS’s R-value stays consistent over the life of the product and we guarantee it! EPS Type IX (250) has a R-Value of 4.35/inch. EPS is a greener product as it does not off-gas a harmful blowing agent and it is 100% recyclable. Want to save money on a project? Ask your specifier to value engineer and use Plymouth Foam Engineered EPS. The saving will surprise you.
Need more help convincing the specifier that Plymouth Foam's Engineered EPS is the best product? Ask us for our substitution package.
Ever since I saw my first bullt-up roof blister caused by off-gassing of Polyisocyanurate Insulation (1988), I have been analyzing and studying R-values in insulation. My major concern and conclusion was that R-value was not being stated correctly. This made predictive energy modeling and utility cost estimating not very reliable, not to mention over paying for overstated R-values. I believed that full disclosure through a method like LTTR (Long-Term Thermal Performance) would help with give a more accurate accounting. (LTTR - Read Article)
This October 2019, the US Federal Trade Commission will finally close a loophole in regard to Extruded Polystyrene (XPS) and their avoidance to “fully reflect the effect of aging” on their product. “The final rule, though not mandating a prescriptive LTTR method, requires that manufacturers publish R-values” that are more accurate.
The EPS Industry Alliance in a recently published paper, (Polystyrene Foam Insulation in Long-Term Building Applications, Effective R-Values) provided a method to estimate effective R-value for polystyrene insulation. This has started to address my two biggest issues with Effective R-values - 1) “Long-Term” and 2) testing temperature of 75ºF.
Long-term testing statements in insulation should not be 5-15 years (we don’t build building to last 5 years) but rather 50 years. So what is the average R-value over 50 years in a building? Fifty year testing is more reflective of homes and buildings insulation life cycles. Even though the Federal Trade Commission is mandating LTTR for XPS, they are still leaving a loophole by allowing “open” LTTR test methods and not requiring a 50 year prescriptive method. It will be interesting to see what the XPS industry comes up with for R-value. Will it be 4.3r/inch like the testing showed from the EPS Industry Alliance?
The issue of “Testing Temperature” has bothered me for years. Why test at 75ºF? Who needs R-value at 75º? In the Northern States, where heating is a concern, it is more realistic to look at R-value testing temperature at 40º, if not 25º in some states. The opposite is true in the South during summer where 90º may be a more reflective testing temperatures. Knowing the R-value performances of insulation, at various temperatures, is critical for designers to make important R-value decisions. They would have the ability, based on their climate, to select the most appropriate insulation. However, the current testing temperature approach of 75º is really a “one shoe fits all” approach and is not very helpful and leads to poor energy conservation decisions.
It has taken over 30 years to see a more accurate accounting of what the R-values of rigid insulation really is and I applaud the FTC for one more step forward. Just 2 more to go - 50 year LTTR and Variable Temperature Testing Disclosure. Accomplish that and we can finally focus on a really important issue — moisture in insulation and its effects.
John Calkins - JC Edison and Associates
Early this year, the National Roofers Contractors Association, made a recommendation to it's members that Polyisocyanurate Insulation revise "its design in-service R-value recommendation to 5.0 per inch thickness." This declaration was the second time Polyisocyanurate's R-value was downgraded in the last 2 years. For some of us "Energy Aficionados," who understand the principles of insulation off-gassing, determined it was time to re-examine LTTR testing (View Technical LTTR Bulletin).
LTTR really looks at Long-Term Thermal Performance of insulation as 5 years. Do we expect a building to last only five years? How is 5 years a true quantitative analysis of R-value performance?
We do not replace insulation in a building every 5 years, why would we think that is long-term? Most building in the U.S. are built to last 50 years, some 100 years. Long-term R-value should be figured at 50 years… right? We know off-gassing continues to happen after 5 years. Let's re-evaluate what we are doing as an industry and modify Long-Term Thermal Resistance to at least 50 years.