Tag Archives: XPS

Under Slab Insulation XPS or EPS?

Under Slab Insulation XPS or EPS?

Way back (okay, 2021 it just seems like it was long ago), I had extolled virtues of expanded polystyrene (EPS) for barndominium concrete slab insulation boards/

Full article can be read here: https://www.hansenpolebuildings.com/2021/11/barndominium-concrete-slab-insulation-boards/.

If there is one thing I have learned in my construction industry career, it is insulation manufacturers, suppliers, installers, etc., will seemingly come up with or say anything in order to promote their product over those of others.

As an example – consider ridiculous claims made by Reflective Radiant Barrier providers. Martin Holladay of Green Building Advisor ripped them apart here: https://www.hansenpolebuildings.com/2014/04/reflective-insulation-wars/

Or what about those insulated overhead doors? https://www.hansenpolebuildings.com/2020/07/barndominium-high-r-value-overhead-doors-part-i/ and https://www.hansenpolebuildings.com/2020/07/barndominium-high-r-value-overhead-doors-part-ii/.

When I penned my article on EPS for concrete slab insulation, and published it, one of my social media friends had done some of his own research and found this article: https://www.constructionspecifier.com/xps-delivers-high-r-values-in-below-grade-applications/3/.

Now this referenced study by Connor, seemingly refutes data I was able to glean from my previous searches. Connor’s work would lead one to favor XPS over EPS.

Of course EPS Industry Alliance has published their own Technical Bulletin, “Use Fully Aged R-values for Insulation & Building Envelope Design”: https://www.airfoam.com/EPS-vs-XPS-Aged-R-Values.pdf. In this article a claim is made XPS loses R-value as blowing agent retained in cells dissipates over time by as much as 20%, while EPS has a stable R-value, not decreasing with time.

As I was not personally involved in any of these studies, I am unable to draw any personal conclusions or make recommendations past do your own homework, and pick a product you believe will be affordable and do what you need it to do.

Fill to Grade, XPS Between Steel and Framing, and a Post Frame Home

This Wednesday the Pole Barn Guru advises readers on adding 6″ fill to the site and the affect it would have on columns, the use of XPS insulation between the steel and framing of the building, and some thoughts on building a 3 bedroom, two bath house.

DEAR POLE BARN GURU: Hello, The site I am looking to build a pole barn had to be filled to bring the area up to a level grade. The depth of the fill is about 6′ at the deepest point. How does this impact the setting of the post? CRAIG in EAST WATERBORO

DEAR CRAIG: Provided fill was mechanically compacted to no less than 90% of a Modified Proctor Density in lifts no greater than six inches, it can be treated as native soil. If proper compaction was not achieved, then columns should be lengthened in order to provide full embedment into undisturbed soil beneath fill.

 

DEAR POLE BARN GURU: So I was going to place 2 layers of 1″ xps foam under my metal on the walls and roof of my pole barn. So it would be, purlins 2 1inch of xps and then my metal, is this a good or bad idea? Thanks BJ in JACKSON

Pole Barn Guru BlogDEAR BJ: Absolutely a bad idea. Pole barns “work” (e.g. stay standing) due to shear strength of steel sheeting (or OSB, plywood, etc., if used). When you place insulation boards between steel and framing, you are severely impacting ability of steel to carry those loads, as steel can shift slightly under wind loads. Eventually this will cause screw shank deformation (would take some very long screws), as well as slotting under screw gaskets, creating leaking (provided building doesn’t just fail first). If you really want to use XPS sheets, cut them to fit snugly between purlins and girts, taping all edges to achieve a tight seal.

 

DEAR POLE BARN GURU: I would like to think of something for my 2 boys and I. One story 3 bed 2 bath. Living room dining room kitchen, laundry room with walk in closets. About what size would you recommend? SHANNON in KIPTON

DEAR SHANNON: In order to determine best size for any particular client, I encourage them (and you) to utilize links found at #3 in this article https://www.hansenpolebuildings.com/2021/02/a-shortlist-for-smooth-barndominium-sailing/ This will assist you to work towards your ideal dream home, within budget.

Meeting IRC Slab Edge Thermal Breaks With Post Frame

Meeting IRC Slab Edge Thermal Breaks With Post Frame

Reader CHUCK in MUNCIE writes:

“Morning sir, I read your link in your post about post frame buildings for barn houses… one thing I am wondering, is how does the building pass energy code for residential construction, plus the IRC talks about a building being used for residential occupancy needs a thermal break at the foundation wall…. in a conventional post frame building the posts are on footings, and a slab on grade is poured, so how do you provide the thermal break to meet the building code?”

Mike the Pole Barn Guru says:

 

Post frame construction for residences has no appearance of going away at any time according to my crystal ball. And why should it? Post frame is more economical than stick frame, very DIY user friendly and can be readily super insulated. Here, I previously expounded upon post frame’s residential virtues: https://www.hansenpolebuildings.com/2022/01/why-your-new-barndominium-should-be-post-frame/

Slab edge thermal breaks (slab perimeter insulation) is only required in Climate Zones 3 and greater. You can look up your Climate Zone at codes.iccsafe.org/content/IECC2021P2/chapter-3-re-general-requirements When required, it must be a minimum of R-10 and down two feet (Climate Zones 4 & higher adds a horizontal R-10 component or becomes down four feet).

A common question with rigid foam insulations is how well it resists water. A number of studies show EPS retains less moisture than XPS. A case in point is a side-by-side analysis of these two rigid foam types installed on a commercial building foundation in St. Paul, MN. When extracted and tested after 15 years in service, EPS had 4.8% moisture content by volume, compared to 18.9% for XPS (a four-fold difference). A testing lab also found  XPS holds water longer than EPS. After 30 days of drying time, XPS still had elevated moisture of 15.7%, while EPS had dried to 0.7%.

For installations where insulation will be exposed to large amounts of water or frequent wetting, rigid foam insulation is available with water-resistant facers or pre-cut drainage grooves. Insulation with polymeric laminate facers keep water from entering insulation and also provide an added barrier to water wicking or diffusing through.

Moisture resistance is also important for below grade and under-slab insulation, since wet products provide much lower thermal resistance. Side-by-side insulation comparison found EPS retained 94% of its specified R-value, while XPS lost nearly half of its insulating capability over 15 years.

In addition to higher moisture resistance, EPS also is not subject to thermal drift. This means its R-value stays same over time. By comparison, XPS’s manufacturing process uses blowing agents diffusing from foam’s cellular structure over product life, thereby reducing its thermal performance. EPS manufacturers typically warrant 100% of published R-value for 20 years or more, while common XPS warranties cover just 90% of published R-value.

Whether selecting EPS or XPS insulation, to ensure performance, confirm product was manufactured to meet requirements of ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation. This standard provides a key quality check on rigid insulation.

As insulation becomes increasingly common at slab edges, understanding performance and cost factors of these different materials is important. EPS offers a number of advantages over more commonly installed XPS, including having highest R-value per dollar among rigid insulations, making it a cost effective choice for many jobs.

Barndominium Concrete Slab Insulation Boards

Barndominium Concrete Slab Insulation Boards – XPS or EPS?

Other than in Climate Zone’s 1 and 2 (think deep South), International Energy Conservation Code (IECC) requires perimeter and under slab continuous insulation for barndominiums.

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. Three important factors to consider when comparing these two insulations for any below grade or under-slab application are compressive strength, moisture retention, and insulating capability.

Weight of concrete slabs and foundation backfill may imply highest strength insulation is most sensible. For many jobs, though, products with less compressive strength are more than sufficient and can reduce insulation costs. For example, installing a below-grade insulation rated for 100 psi, when only 40 psi is needed, will nearly double material costs.

Many designers mistakenly assume loads placed on slabs transfer through to underlying insulation and soil at a 45-degree angle instead of a more uniform distribution. This can result in greatly over-designing insulation’s strength. For example, with a forklift load on a typical 4-inch-thick slab, one calculation would indicate 32 psi is applied to insulation compared to only 2.5 psi under a more accurate calculation. As such, it is not uncommon for under slab insulation to be over-designed by a factor of 10 or more.

Using unnecessarily high-strength insulation, you end up paying for something you don’t really need. Since EPS is lower cost per inch than XPS, and is available in a range of compressive strengths (from 10 to 60 psi), using it below grade and under slabs can save on insulation costs.

A common question with rigid foam insulations is how well it resists water. A number of studies show EPS retains less moisture than XPS. A case in point is a side-by-side analysis of these two rigid foam types installed on a commercial building foundation in St. Paul, MN. When extracted and tested after 15 years in service, EPS had 4.8% moisture content by volume, compared to 18.9% for XPS (a four-fold difference). A testing lab also found  XPS holds water longer than EPS. After 30 days of drying time, XPS still had elevated moisture of 15.7%, while EPS had dried to 0.7%.

For installations where insulation will be exposed to large amounts of water or frequent wetting, rigid foam insulation is available with water-resistant facers or pre-cut drainage grooves. Insulation with polymeric laminate facers keep water from entering insulation and also provide an added barrier to water wicking or diffusing through foundations and slabs.

Moisture resistance is also important for below grade and under-slab insulation, since wet products provide much lower thermal resistance. Side-by-side insulation comparison found EPS retained 94% of its specified R-value, while XPS lost nearly half of its insulating capability over 15 years.

In addition to higher moisture resistance, EPS also is not subject to thermal drift. This means its R-value stays the same over time. By comparison, XPS’s manufacturing process uses blowing agents diffusing from foam’s cellular structure over product life, thereby reducing its thermal performance. EPS manufacturers typically warrant 100% of published R-value for 20 years or more, while common XPS warranties cover just 90% of published R-value.

Whether selecting EPS or XPS insulation, to ensure performance, confirm the product was manufactured to meet requirements of ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation. This standard provides a key quality check on rigid insulation.

As insulation becomes increasingly common under slabs, understanding performance and cost factors of these different materials is important. EPS offers a number of advantages over more commonly installed XPS, including having highest R-value per dollar among rigid insulations, making it a cost effective choice for many jobs.