A Guide to Below-Grade Insulation and Moisture

Originally posted online at Buildings.com in Buildings Buzz!

OLYMPUS DIGITAL CAMERAWet insulation is ineffective insulation – rigid foams that retain high volumes of moisture lose about half of their insulating R-value. Because insulation installed on below-grade building foundations and under concrete slabs is often exposed to moist soil, it is crucial to choose an insulation that has minimal long-term moisture retention and the ability to dry quickly.

For facility professionals that are evaluating insulation for building retrofits or for new construction, paying attention to moisture performance helps ensure effective long-term thermal resistance. Because the insulation will be hidden from view, any problems with degraded materials will not be obvious, although the effect on higher energy bills will be very real.

One challenge in selecting insulation is cutting through the competing claims of insulation manufacturers. Producers of extruded polystyrene (XPS) and expanded polystyrene (EPS) – common below grade insulations – both claim that their products are superior at resisting moisture. In their own ways, each one is right, but it depends on whether one is looking at abstract, standardized tests or performance in actual installed conditions.

Claims that XPS insulation absorbs less moisture than EPS are based on ASTM 272Standard Test Method for Water Absorption of Core Materials for Sandwich Constructions. This test calls for fully submerging an insulation sample in water for 24 hours, then weighing it for moisture absorption immediately upon removal from the water.

How does this test represent reality? The truth is it doesn’t reflect real-world conditions for two reasons:

1) Unless your building is in a lake or river or subjected to severe flooding, the insulation will not be fully submerged.

2) It doesn’t account for how much an insulation dries out or does not dry out between periods of moisture exposure.

Entire marketing campaigns have been built around this test, but when it comes to what really happens on your building, it’s necessary to look at actual exposure during in-situ tests. Studies of insulation exposure to moisture in actual field conditions show that EPS outperforms XPS by a wide margin, largely because EPS dries much faster than XPS.

For example, the independent lab Stork Twin City Testing evaluated the moisture content of EPS and XPS buried side-by-side for 15 years on a building foundation in St. Paul, MN. At the time the insulations were removed, the EPS was four times drier than the XPS – the EPS had only 4.8% moisture by volume compared to 18.9% moisture content for the XPS. After 30 days of drying time, the EPS had dried to only 0.7% moisture by volume, while the XPS still contained 15.7% moisture.

The high moisture absorption of XPS is further seen in a 2012 report from the U.S. Department of Energy’s Oak Ridge National Laboratory. Researchers found that XPS insulation installed below grade for 15 years had absorbed 67% or more moisture. The resulting loss of energy savings performance for the XPS was 10% for a full basement (“deep basement”) and 44% for a slab-on-grade installation.

Insulation manufacturers are well aware of how their products will perform over the years. Evidence of this is seen in the limitations stated in warranties they offer. This is why XPS manufacturers typically warrant only 90% of the insulating R-value of their products during time in service, whereas most EPS manufacturers warrant 100% of the R-value. Some XPS manufacturers will also void warranties in case of ponding or water immersion, which runs contrary to their highlighting of 24-hour, full-immersion testing.

There are many claims in the market about whether EPS or XPS offers the best moisture resistance. When evaluating such statements, it is important to consider the basis upon which the statements are made. Does the testing involve guys in lab coats dunking insulation into a fish tank for one day, or does it replicate how insulation performs on actual buildings over many years? If facility managers are making the investment in insulation, this is an important distinction to pay attention to, otherwise the product might not perform as desired.

EPS QUESTIONS?

 

Ram Mayilvahanan

Ram Mayilvahanan

Contact Ram Mayilvahanan, Insulfoam’s Product-Marketing Manager

Ram.Mayilvahanan@insulfoam.com

Connect with Ram on LinkedIn  |  Follow Insulfoam on LinkedIn

Read more on Insulfoam.com

Below Grade and Under-Slab Building Insulation

Originally posted in Modern Contractor Solutions Magazine, June 2014 issue

Modern Contractor Solutions Magazine, June 2014 Digital Issue

MC_june 2014

Modern Contractor Solutions, June 2014

Three tips for choosing the right material for your project

Which insulation is best for use on buried building foundations and under concrete slabs? Sales reps, naturally, will tell you that their company’s product is best. But, what does independent testing and research say?

These three tips will help your firm select a cost-effective and high-performance rigid foam insulation type for your next below-grade insulation job.

1.  CONFIRM LONG-TERM THERMAL PERFORMANCE

Two of the rigid foam insulations most commonly used below grade and under slabs are expanded polystyrene (EPS) and extruded polystyrene (XPS). Although both are closed cell insulations, they perform very differently over the long term.

XPS has a higher initial insulating R-value than does a similar thickness and density of EPS, but the R-value of XPS degrades over time. EPS does not experience such “thermal drift,” and the reported R-value remains the same throughout years of installed service.

This is a crucial point when selecting insulation, as a decreasing R-value means lower thermal performance over time, and thus increased heating and cooling energy and costs for the building owner.

Below Grade

Rigid foam insulation is increasingly common in below-grade and under-slab applications.

A simple way to confirm an insulation’s long-term thermal performance is to review the warranty. Established EPS manufacturers typically warrant 100 percent of the published R-value for 20 years. By comparison, most XPS warranties typically cover only up to 90 percent of the published R-value, to account for the R-value degradation that occurs in the field.

2.  ENSURE MINIMAL LONG-TERM MOISTURE ABSORPTION

In addition to R-value stability, rigid foam insulations differ in their rates of moisture absorption and their ability to dry. Wetted insulation provides lower thermal resistance and can degrade over time. Since insulation installed below grade frequently contacts wetted soil, rates of moisture absorption and the ability to dry is key in these applications.

Independent laboratories have conducted extensive tests of moisture absorption rates for both EPS and XPS. Although XPS often rates better in laboratory short term, fully submerged tests, real-world long term tests show that EPS performs much better. The reason is that EPS has the ability to dry much faster than XPS. This ability to dry at a fast rate helps EPS remain drier during conditions of repeated exposure to moisture.

A 15-year in-situ test of EPS and XPS dramatically demonstrated this point. Stork Twin City Testing evaluated the moisture content of EPS and XPS buried side-by-side for 15 years on a building foundation in St. Paul, Minnesota. At the time the insulations were removed, the EPS was much drier than the XPS—the EPS had only 4.8 percent moisture by volume, compared to 18.9 percent moisture content for the XPS. After 30 days of drying time, the EPS had only 0.7 percent moisture by volume, while the XPS still contained 15.7 percent moisture.

The high moisture absorption rate of XPS in real-world settings is further seen in a 2012 report from the U.S. Dept. of Energy’s Oak Ridge National Laboratory (ORNL). Their researchers found that XPS insulation installed below grade for 15 years had absorbed 67 percent or more moisture.

3.  TARGET AN APPROPRIATE COMPRESSIVE STRENGTH

EPS insulation resists moisture better than XPS, including on buried foundations where it is in regular contact with wetted soil.

EPS insulation resists moisture better than XPS, including on buried foundations where it is in regular contact with wetted soil.

One of the best ways to save money on rigid foam insulation installed under concrete slabs is to ensure the material is not over-engineered. A common design assumption leads to specification of rigid foam strengths that are many orders of magnitude higher than necessary, which can double the insulation material cost.

Without getting into extensive technical details and mathematical formulas, the problem is engineers often use an overly conservative approach for insulation under concrete slabs. Many designers assume that point loads applied to a slab, such as those from the wheels of a forklift, transfer to the insulation in a triangular load path. Yet, concrete slabs distribute loads more uniformly than this, which means the insulation does not need as high of a compressive resistance as when one assumes a concentrated triangular load path.

An overly conservative design approach often results in specification of a high compressive resistance XPS product, when a more cost-effective EPS would offer sufficient strength. Since XPS typically costs more per inch than EPS, this is wasted money that comes off the contractor’s bottom line.

A simple solution for contractors is to ask the designers if they are using a formula from the Theory of Plates on Elastic Foundations, which take into account how slabs and insulation behave together. A resource to point them to for example calculations is the article “Right-sizing Under-slab Insulation,” in the April 2014 issue of Structure magazine.

CONCLUSION

With building owners’ growing desire to save money on heating and cooling costs, and increasingly stringent energy codes, contractors will be installing below-grade and under-slab insulation on more of their projects. EPS insulation out-performs XPS for both long-term thermal resistance and long-term moisture absorption, and EPS comes in a variety of compressive strengths suitable for nearly all building projects. With the highest R-value per dollar, EPS is the cost effective insulation choice.

Modern Contractor Solutions Magazine, June 2014 Digital Issue

EPS QUESTIONS?

 

Ram Mayilvahanan

Ram Mayilvahanan

Contact Ram Mayilvahanan, Insulfoam’s Product-Marketing Manager

Ram.Mayilvahanan@insulfoam.com

Connect with Ram on LinkedIn  |  Follow Insulfoam on LinkedIn

Read more on Insulfoam.com

 

Question & Response: XPS, EPS, and Dock Flotation

Useful references to support this article:  NEW moisture absorption data regarding XPS, moisture absorption and the effects on R-Value was released in March 2014.  Read more in the updated summary and in subsequent 2008 test program documents:

Originally posted on Construction Specifier online, Author Response to Reader Question, February 18, 2014

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 job site 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 right-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 fro 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 on the 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 job site.

EPS QUESTIONS?

Ram Mayilvahanan

Ram Mayilvahanan

Contact Ram Mayilvahanan, Insulfoam’s Product-Marketing Manager

Ram.Mayilvahanan@insulfoam.com

Connect with Ram on LinkedIn  |  Follow Insulfoam on LinkedIn

Read more on Insulfoam.com

Specifying Thermal Insulation Below-Grade & Under-Slab

Originally posted in The Construction Specifier Magazine (pg 34), December 2013

The Construction Specifier, December 2013

The Construction Specifier, December 2013

Read full article (pdf)

In the push to forge more energy-prudent builders, design professionals are leaving no part of the envelope unexamined.  Walls and roofs have always presented a clear target for better thermal performance.  Somewhat less obvious are surfaces that are out of sight – below-grade foundation walls and floor slabs.  Well-engineered insulation in these locations can provide significant energy savings.

What separates below-grade insulation types from one another?  Moisture retention, R-value stability, and compressive strength are the key performance attributes to consider when evaluating and comparing different below-grade insulations.

Installing thermal insulation on below-grade foundation or perimeter walls and under slabs is important because un-insulated concrete provides a thermal and moisture bridge between the heated building interior and the relatively cooler earth surrounding the building, or through exposed slab edges to the outside air.

“While insulation strength is important consideration, erroneous design assumptions can lead to over-engineering for compressive resistance, adding unnecessary material costs.” – Ram Mayilvahanan, Insulfoam Product-Marketing Manager

Continue reading the full article, Out of Sight, NOT Out of Mind (pdf), in The Construction Specifier Magazine and learn about:

  • How installing thermal insulation on foundations help much more than just saving energy
  • How XPS and EPS compare with regard to moisture retention
  • What are the degrading effects of moisture on R-value
  • What specialty insulations for enhanced moisture protection are available

Read full article (pdf)

EPS Questions?

Ram Mayilvahanan

Ram Mayilvahanan

Contact Ram Mayilvahanan, Insulfoam’s Product-Marketing Manager