It’s 2020. . .Do You Know Where Your R-Values R?

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Did you hear the news? It has been reported that polyisocyanurate (Polyiso or ISO) once again reduced their R-Value claims. This “R-Value debate” has been going on for over 20 years. Tests and studies have been done and redone, proving that Polyiso R-Values diminish with time, temperature and moisture. This was recognized early on by the roofing industry. In 1987, the Midwest Roofing Contractors Association developed a position to address this followed by the National Roofing Contractors Association, (NRCA) cautioning designers and users specifying this product. Combined, they issued a joint bulletin with the recommendation to factor 5.6 per inch of thickness, at the time Polyiso was 7.2 per inch. Polyiso has now published their R-Value at 5.6 per inch. However, keep in mind that according to an article in Professional Roofing and the NRCA, “it may be prudent for designers to use an even lower R-value when designing for cold conditions, such as in northern climates or cold-storage applications.” The expanded polystyrene (EPS) industry has been trying to blaze a trail to educate the public of the independent testing of ISO and its findings. The proper insulation on your roof is critical for the integrity of the building’s thermal envelope. EPS—the older of the two products—R-Values have never wavered. In fact, in colder climates, EPS R-Values actually improve.

So how did this all begin and what does it mean to you?

Let’s take a brief look at how it all started. Expanded polystyrene was developed in the early 1960s. It is a lightweight, inexpensive solution for many applications including insulation. EPS experienced a huge success in the roofing insulation industry in the late 70s and early 80s. With that success, along came the competition. Polyiso came into market with claims of having a higher R-Value than its white counterpart. Due to inaccurate marketing and the perceived value of Polyiso, the EPS roofing insulation business virtually disappeared.

But time tells all and according to several studies, time is not Polyiso’s friend. According to these studies, Polyiso R-Value diminishes not only with time but also with temperature and moisture. Polyiso begins to lose its R-Value immediately after it is manufactured. After the manufacturing process, the gases in the pores diffuse out and are replaced with air. Multiple tests done by Building Science Corporation concluded the following: Polyiso samples showed a decrease in R-Value as outside temperatures go below freezing. It appears that the “peak” R-Value for all samples occurs only when outdoor temperatures are closer to the indoor temperature.¹ EPS, on the other hand, has been proven to retain its R-Value over time and different temperatures.² Thermal performance is the core for sustainable energy.

R-Values - EPS for construction and roofing

The perfect insulation material, EPS foam maintains its R-Values over time and temperatures.

Another important factor to consider is moisture. Although roofs are constructed to prevent water issues, moisture will occur. Whether it is from mechanical damages, workmanship issues or just long-term deterioration of the seams, moisture will encroach and deteriorate the Polyiso, degrading the R-Value. If you have a roof insulated with ISO, chances are it is wet and certainly not maintaining claimed R-Values creating a drain energy.  Tests have proven moisture resistant EPS maintains its R-Value even after long-term exposure in northern climates. For construction—especially large scale industrial projects, schools, hospitals, etc.—this equates to huge news with long term energy savings and cost savings using EPS over any Polyiso product. EPS is also more user friendly, available in various sizes and densities and is able to be customized for roofing projects. As an additional bonus, EPS is also recyclable!

Now we do applaud the Polyiso industry for correcting their previous R-value claims. However, the R-Values that are currently applied will still decline as the product ages and/or gets wet. So what can you count on? The answer is EPS. We are what we say we are. Our R-value is a constant and will not diminish. Isn’t it great to be able to count on something and not have to worry?

It’s 2020 – do you know where your R-values are?

To help with your roof design and estimate please contact: or call 610-791-4200.

Building Science Corporation –  Info 502: Temperature Dependence of R-Values in Polyisocyanurate Roof Insulation 4/11/2013

EPS Below Grade Series 103 11/08

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This article was posted on February 7, 2014, by Insulation Corporation of America (ICA) – a Women-Owned manufacturer of Geofoam and Expanded Polystyrene (EPS), which is commonly but mistakenly referred to as Styrofoam™. ICA is located in Allentown, PA and services the entire Mid-Atlantic Region from Virginia to Maine to Ohio.