After the feature, “Out of Sight, Not Out of Mind: Specifying Thermal Insulation Below-grade and Under-slab” ran in our December 2013 issue, we received a letter from retired architect, Joseph S. Bond. Mr. Bond wrote that the article in question “seems to reverse the findings” from both his personal and professional experience with expanded and extruded polystyrene (EPS and XPS):
I am a retired architect, and may not have the best current information on EPS and XPS, but when these two products were mistakenly used as ‘flotation’ for lake docks and later removed, the XPS bales were like new and had no water soakage beyond the first (1/8 in.). However, I remember the EPS bales were waterlogged to the extent it took two people to even carry the bales. On top of this, the EPS bales showed a lot of disintegration due to freeze-thaw.
My observations may have been on EPS that had much less density (1-1/2 -2 #) than implied by The Construction Specifier article, but many reading will probably have the same concerns and begin to question the piece’s validity.
We asked the article’s author, Ram Mayilvahanan, to respond.
Mr. Bond raises a frequently discussed point about the long-term problems that arise when using rigid foam insulations that do not conform to ASTM standards.
Since insulation, especially below-grade, is out of sight, it can also be out of mind when it comes to ensuring the product being used at the jobsite matches the product that was specified. As with other building products, there are numerous companies making rigid foam insulations, often with varying degrees of quality. We building professionals share the responsibility in making sure the selected rigid-foam manufacturer can consistently deliver product that meets the specified performance.
To ensure performance on key factors, including moisture resistance, it is crucial to not only specify foam insulation that has been manufactured and tested to meet ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, but also to ensure the manufacturer supplying the foam insulation can consistently deliver quality product. A manufacturer’s longevity and track record with past projects should help in assessing this.
As an example, the floating green on the 14th hole in the world-famous Coeur d’Alene Golf resort in Idaho—considered one of the coolest shots in golf—was built with EPS. It continues to be a testimony to well-engineered flotation insulation. Projects like this help establish the ability of manufacturers to deliver quality product.
Mr. Bond’s observation is a timely reminder for us building professionals that it pays to make sure the right product gets to the jobsite.
For technical background expanding on the moisture resistance comparison between EPS and XPS in the article, two useful references are: