By: Bill Downs, Sales Representative - Architectural Products
The site has been excavated, the foundation poured, now it’s time for the below-grade insulation. If you are the building owner you want the best below-grade insulation for your money, RIGHT? What is most important in choosing below-grade insulation? Performance, environmental impact or maybe cost & constructability? How about all of these?
If you visit our website and drag your mouse on the construction tab and then click on below-grade & underslab, you will find that ACH Foam has EPS for below-grade applications in both unfaced and faced material. These products meet ASTM C578 physical properties, the standard specification for rigid foam insulation. 25 psi EPS has a published R-value of 4.80 per 1.0 in. thickness at 40°F. 25 psi XPS has a published R-value of 5.4 per 1.0 thickness at 40°F.
The XPS R-value is the published R-Value and not its long-term R-Value. When considering long-term R-Value you have to take into consideration the warranty of the insulation. The EPS warranty covers 100% of the R-Value for 20 years. The XPS warranty covers 90% of the R-Value for 15 years. If you break that down 90% of 5.4 = an R-Value of 4.8 per inch. That is the same as EPS.
A key concern with below-grade insulation is and should be moisture resistance; after all, moisture affects R-Value. Studies done by Stork Laboratories in Minnesota have shown that over a 15 year period EPS insulation maintained 94% of its stated R-Value and had a moisture content of 4.8%. It seems to be a common thought that EPS absorbs more moisture than extruded polystyrene insulation but in the study by Stork Laboratories, the extruded insulation retained only 52% of its stated R-Value over the 15 year study. Why? The answer is because of moisture content. The extruded after 15 years below-grade had a moisture content of 18.9% upon excavation from the site. This is a REAL WORLD STUDY COMPLETED BY A 3rd PARTY TESTING LABORATORY.
We encourage you to learn more about the moisture resistance study. When the below-grade samples for this study were placed in a controlled environment for 28 days at 72°F and 50% relative humidity the moisture content and R-Values changed. The XPS moisture content upon removal was 18.9% and after 28 days in the controlled environment that dropped to 15.7% and the R-value rose from 2.6 to 2.8. The EPS upon removal had moisture content of 4.8%, R-Value of 3.4 and after 28 days had a moisture content of 0.7% and an R-Value of 3.7. This study is very important when selecting below-grade insulation.
Environmental impact is another factor in choosing below-grade insulation. EPS can contain recycle content up to 15% and still meet ASTM C578. 100% of all scrap related to the manufacturing process of EPS is recycled. Currently XPS sheet insulation has limited recycled content, which varies by product and manufacturer. In 2011 ACH recycled 4.3 million lbs. of EPS.
Cost is also major factor in choosing below-grade insulation. EPS Type IX, in sheet size of 4’ x 8’ x 2” thickness at 25 psi, with an in-service R-Value of 4.8 per inch costs under $21.00 compared to a sheet of XPS the same size with an IN-SERVICE R-Value of 4.8 per inch which is about $25.00. This is a huge savings for building owners! Keep in mind that cost does vary slightly depending on location.
So, when selecting below-grade insulation please consider all factors and chose the right insulation for your project!
