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

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Right-sizing Under-slab Insulation

Structure Magazine, April 2014

Structure Magazine, April 2014

Originally published in Structure Magazine, Structural Economics section, April 2014

Structural Economics:  cost benefits, value engineering, economic analysis, life cycle costing and more…

Applying the Theory of Plates on Elastic Foundations to Save Material Costs.

Article (pdf)  |  Digital Edition

A common, simplifying assumption used for specifying polystyrene insulation under concrete slabs results in material costs that are significantly higher than necessary. Using a design equation based on a more rigorous analysis of the design conditions can help avoid over-engineering the insulation and save thousands of dollars on the project.

Rigid foam insulations, such as expanded polystyrene (EPS), have been used successfully under concrete slabs for more than 40 years. Such insulation helps reduce heat loss to the ground in residences, cold storage units, warehouses and other commercial, institutional and industrial structures.

The problem is that designers often do not adequately account for how the concrete slab and underlying subgrade interact. Many designers assume that a concentrated load applied to the slab transfers to the rigid foam subgrade through a triangular load path. This assumption, while not necessarily incorrect, can be very conservative.

Concrete slabs distribute loads in a more even fash- ion, which means that the insulation does not need as high a compressive resistance compared to the typical simplified approach. A more accurate approach to this problem is to use the Modulus of Subgrade Reaction (K) to determine the slab’s deflection and the resultant stress applied to the elastic insulation subgrade. The pressure beneath a given slab under a load can be determined using the following formula, found in the Theory of Plates on Elastic Foundations, as described by Timoshenko and Woinowsky-Krieger:

Pressure on the subgrade = (P/8)√(K/D) Where:

  • P = concentrated load on concrete slab in pounds
  • K = Subgrade reaction modulus of total EPS insulation in pounds per cubic inch (k/t)
  • k = Stiffness of one inch of EPS insulation in pounds per square inch
  • t = EPS insulation thickness in inches
  • D = Eh3 / 12(1-u2)
  • E = Modulus of elasticity of concrete in pounds per square inch (57000√ f’c)
  • f’c = specified concrete compressive strength in pounds per square inch
  • h = Thickness of concrete slab in inches
  • u = Poisson’s ratio for concrete (0.15)

An example illustrates the significant difference in the calculated results.

EPS insulation in an under-slab application

EPS insulation in an under-slab application

Take the case of a warehouse with a 6-inch-thick, 2,500-psi concrete slab on 2 inches of EPS insulation with a rated stiffness of 360 psi for one inch. Forklifts to be used in the building impart 8,000 pounds of force at the wheel, which has a 6-inch by 10-inch tire footprint on the slab. If the designer assumes that this load distributes at a 45-degree angle through the slab, the 8,000 pounds ends up distributed over approximately 396 square inches [(6 + 6 + 6)(6 + 10 + 6)] of the insulation’s surface, for an average pressure of 20.2 psi.

Taking into account the fact that concrete slabs distribute loads more evenly, using the Modulus of Subgrade Reaction method, the pressure on the insulation is actually much lower – approximately 1.85 psi. Since EPS insulation rated for 1.85 psi costs about 50% less than other rigid foam insulations rated for the much higher value of 20.2 psi, using the more precise method reduces insulation costs substantially. In fact, the 20.2 psi value is beyond the elastic range of the EPS material, and long-term creep effects must be taken into account when using that design approach. With:

P = 8000 pounds, h = 6 inches, f’c = 2,500 psi,

E = 57,000√ 2,500 = 2,850,000 psi, u = 0.15,

k = 360 psi for 1-inch EPS

K = 360 psi / 2 inches = 180 pci

D = Eh3/12(1-u2) = 2,850,000 (6)3/12(1–(0.15)2) = 52,480,818 lb-in

Pressure on EPS = (P/8)√(K/D) =

8000/8 √(180 / 52,480,818) = 1.85 psi.

The k value can be found by consulting the insulation manufacturer. One EPS insulation brand available throughout the U.S. has k values ranging from 360 to 1860 psi for one inch of insulation thickness. The specific value depends on the product type selected. Note that increasing the thickness of EPS insulation decreases the overall subgrade modulus.

Using the above method to determine the pressure that a slab transfers to the subgrade allows for proper specification of rigid foam insulation and avoids over-engineering the insulation for compressive strength. In the example application discussed in this article, the simplifying assumption of triangular load transfer through a concrete slab results in a compressive force on the insulation 11 times higher than the result from the more rigorous (but not much more complicated) analysis. Specifying higher compressive resistance insulation than necessary not only is overly conservative for the given design, it also does not improve the insulation’s thermal performance, and the cost to the project is excessive and unnecessary. It is a lose-lose scenario.

Article (pdf)  |  Digital Edition

ARTICLE QUESTIONS

Joe Pasma

Joe Pasma, Insulfoam Technical Manager

Contact Joe Pasma, PE, Insulfoam Technical Manager

800.469.8870 x104

joe.pasma@insulfoam.com

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New Mexico Schools Save on Construction Costs with EPS Insulation

 

APS

APS Food & Nutrition Services Kitchen & Storage Warehouse, R-Tech Installation

Albuquerque Public Schools (APS) in New Mexico have been undertaking a massive classroom and educational rebuild and remodel.  All new construction has been designed using sustainable materials and energy-efficient principles with LEED certification as the end goal.

As part of new buildings under construction is a 108,000 sq. ft. central Food and Nutrition Services Kitchen and Storage Warehouse.

Originally specified XPS was replaced with Insulfoam R-Tech VI 40 psi over the sub slab freezer floor.  The project utilized 2 lifts of 3″ R-Tech instead of 3 lifts of 2″ XPS ultimately saving the  concrete contractor approximately $20,000 in material costs.

(More photos below)

Useful industry publications references on specifying EPS in below grade or under slab applications:

APS

APS Food & Nutrition Services Kitchen & Storage Warehouse, R-Tech Installation

APS

APS Food & Nutrition Services Kitchen & Storage Warehouse, R-Tech Installation

APS

APS Food & Nutrition Services Kitchen & Storage Warehouse, R-Tech Installation

PROJECT DETAILS

Questions on this project or application?

Travis Montgomery, Insulfoam Territory Manager

Travis Montgomery, Insulfoam Territory Manager

Contact Travis Montgomery, CSI, Insulfoam Territory Manager

Email: Travis.Montgomery@insulfoam.com

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Insulation Choices: EPS or XPS?

Originally posted in Concrete Construction

As a specifier, architect and contractor….you must make well-informed decisions when it comes to below-grade, under slab, and cavity wall insulations in your projects.  Below are two informative articles listing the similarities and differences between both EPS (expanded polystyrene) and XPS (extruded polystyrene) insulations.

Insulation Choices:  Whether to use EPS or XPS can be a matter of cost.

Originally posted in Concrete Construction, November 2013, written by Mayilvahanan, Insulfoam’s Product-Marketing Manager

EPS insulation helps reduce heat loss through concrete foundations and floor slabs.

EPS insulation helps reduce heat loss through concrete foundations and floor slabs.

What’s the difference between XPS insulation and EPS insulation, other than a single letter? For installation on concrete foundations and under floor slabs, the rigid foam insulation you choose can make a difference of tens of thousands of dollars on a project. A careful evaluation of these materials’ performance attributes against the project’s needs can dramatically shrink labor and material costs. The savings could mean the difference between a profitable job and one you just have to chalk up to experience.

When it comes to concrete and insulation, contractors tend to be most familiar with extruded polystyrene (XPS). Yet, expanded polystyrene (EPS) performs as well or better than XPS, and at a substantially lower cost. Below are three important factors to consider when comparing these two insulations for any belowgrade or under-slab applications, read FULL article to see more side by side comparisons of EPS and EXP for these insulation factors:  1.) Compressive strength  2.) Moisture retention  3.) Insulating capability.

Full Article:  Insulation Choices

EPS vs XPS:  Insulation industry advances with EPS developments

Originally posted on Concrete Construction, February 2014, written by Frank Keisecker, ACH Foam’s VP of Sales and Marketing

There is much competition among polystyrene insulation manufacturers for the below-grade, under slab, and cavity wall insulation market. Claims made by the XPS (extruded polystyrene) industry are conflicting with that of EPS (expanded polystyrene) manufacturers. The validity of some claims is debatable. Specifiers, architects, and contractors must make well-informed decisions.

Read FULL article to thoroughly understand the similarities and differences between EPS and XPS insulations.  Key differences include: 1.) Moisture resistance 2.) Environmental impact  3.) Long-term R-value  4.) Compressive strength   5.) Panel sizes  6.) Cost per R-value.

Full Article:  EPS vs XPS

EPS QUESTIONS

Ram Mayilvahanan

Ram Mayilvahanan

Contact Ram Mayilvahanan, Insulfoam’s Product-Marketing Manager

Energy Efficient Construction at World of Concrete

EVENT:  World of Concrete, Las Vegas   |   DATE:  February 5-8th   |   BOOTH:  N2915

ABOUT INSULFOAM

The future of architecture and construction is not only going to expand and grow at a rapid pace this New Year, but it is also becoming one of the r-tech_blog copybest industries in regards to saving the environment. When it comes to ultimate respectability in the industry, two names have come together to form one truly amazing ‘gift’ for all the building-owners and contractors out there. The name, Insulfoam, is synonymous with the creation of quality polystyrene-based engineered insulation products that have become even better than before. In addition,Carlisle Construction Materials has been known in all areas of architecture and construction for single-ply roof systems and waterproofing products that are unmatched in quality, durability, and savings. With Insulfoam, the largest manufacturer of expanded polystyrene in all of North America, being a part of Carlisle Construction Materials for several years now, these two powerhouses have shown the rest of the industry that they are not only still among the most respected names in construction, but are also constantly looking out for everyone from architects to building owners to contractors. With this ‘team,’ everyone has the ability to purchase and utilize energy-efficient construction products that are a ‘must-have’ in this ‘greener’ world. Insulfoam’s products insulate buildings, from the foundation to the roof and everything in-between. Versatility is a key word when it comes to these products. Not to mention the product line is 100% recyclable. Being leaders and visionaries when it comes to new product development, the latest in technology, and code approvals, the brands of InsulFoam® and R-Tech® also contribute immensely toward LEED® credit requirements, which is one of the biggest and most important issues to address nowadays. Insulfoam products, which have warranted long-term stable R-values with no thermal loss, are built upon sustainable manufacturing practices. Dye-free, free of formaldehyde and HCFCs, no toxic chemicals or heavy metals are leeched, and prevention of mold or mildew growth, are just a few of the benefits that come with these products. Offered under the InsulFoam® and R-Tech® brands, Insulfoam’sexpanded polystyrene (EPS) products for under-slab and below-grade applications insulate foundation walls, protect water and/or damp proofing, and can be used during backfilling in both commercial and residential projects.

roofing copyStudies have shown that R-Tech® below-grade insulations have some of the lowest levels of long-term water retention among below-grade insulation products. Combined with high compressive strength and long-term stable R-values, these properties make Insulfoam’s products among the most efficient in below-grade insulation. When speaking about wall installations, Insulfoam offers a variety of insulations that cover applications ranging from exterior, interior and cavity wall applications to tongue-and-groove sheathing, whole wall, and gable end applications. Not to mention, these products are extremely lightweight and have physical properties that are well ahead of their time. But below-grade and wall installations are not all that Insulfoam is renowned for. It also makes GeoFoam, a geo-synthetic structural fill that literally exceeds the requirements of ASTM D6817 Standard Specification for Rigid Cellular Polystyrene Geofoam. This is a fantastic alternative to other fill-materials, providing excellent lateral-load support and dimensional stability as a soil and slope stabilizer in various engineered applications.  And, yes, before one asks - roofing applications are also completely covered by offering roof insulation panels that help reduce overall energy consumption, and end up creating a fantastic and comforting environment for the occupants of the building. The company has a wide-range of code-approved composite roof insulations that work with fully adhered, mechanically attached and ballasted roof systems without the need for coverboards or slip sheets. Insulfoam’s high-density composite has code approval for direct-to-combustible decks without a thermal barrier, an excellent illustration that Insulfoam products work for virtually every type of roofing system. And what’s one of the most important words to hear when it comes to building and construction products? Cost-effective! Insulfoam’s products provide some of the best R-values per dollar. These products resist almost everything, which makes these products necessary for a long list of projects ranging from highway retaining walls to parking structures to foundations, loading docks, levees, underground utility protection, railways, runways, and so much more. Are you working on an entertainment construction project that will involve theater or stadium seating? This is what you need. Working on creating that pool with deck outside? …Need I say more? Even the website that is available discussing each and every one of these products proves how efficient and up-to-date this company is. Data, research, analysis, facts, figures – even instructional and technical information is offered on each one of these products, leaving absolutely nothing to doubt. And this includes questions and data regarding global warming, RA standards and the true goal that Insulfoam and Carlisle have to decrease our ‘carbon footprint and make this a healthy place where the next generation can thrive! For more information, head to this amazing website now and get to work making that next project the absolute best and ’greenest’ it can possibly be. http://www.insulfoam.com