Tag Archives: foam insulation board

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.

Insulating a Semi-Trailer Truck

Insulating a Semi Trailer

The beauty of being available to answer questions on the ‘net is one hears just about everything – even challenges which do not involve buildings!

Here is a recent one asked by reader BOB in NORTH CAROLINA:

Purchased a 53foot x 8.5ft dry van all metal trailer (like tractor trailer) want to frame inside ceiling w 2 x 3’s. Have 2″ Rigid foam insulation, 4 x 8 sheets. Haven’t installed anything yet bc we want to do it right. Do have condensation in mornings. Live in nc very hot in summer, and this winter very cold. Plan on putting Windows in maybe two turbines on roof if necessary. What is correct way to install rigid foam insulation? On walls and ceilings. Some tell me to glue plastic sheeting on inside metal walls and ceiling and leave a 1 inch space between that and rigid foam.

Thanks in advance”

No idea what the end goal is of your project, however it sounds like a lot of work to try to climate control a very long narrow space.

Hopefully the insulation boards you have are closed cell foam, which will give you an R-5 or so per inch of thickness. I would do away with the 2x3s and glue three thicknesses of insulation to the ceiling and two thicknesses to the walls. If your insulation has a facing, tape seal all of the joints, if not, cover with six mill clear visqueen sealing any tears or seams. Foam insulation board is highly flammable, so then glue 5/8″ Type X gypsum wallboard to the inside and at the least fire tape all of the joints.

This should at least provide an R-30 ceiling and R-20 walls and eliminates the transfer of heat and cold through the studs (wood is R-1 per inch). You do not have a dead attic space to ventilate, however you may need to provide a powered exhaust fan in order to keep it cooler in the summer.