Tag Archives: rigid foam insulation

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.

Foam Boards, Foundations, and Rat Walls

Today the Pole Barn Guru answers reader questions about adding kraft-backed insulation to rigid foam boards, if posts go in the ground or a foundation system, and if a pole building needs a “rat wall” poured.

DEAR POLE BARN GURU: I have an existing pole barn, the front portion being 30×30 with 11′ walls. The walls have R tech faced rigid foam board between the girts with the reflective side facing the shop interior. The shop is only heated when I work out there by a vented propane unit heater. The walls will be finished off with steel liner panels. My question is can kraft faced fiberglass insulation be placed over top of the rigid foam board that is “foil faced” with the kraft paper backing facing the interior of the shed (back of liner panels)? JACKSON in COLEMAN

DEAR JACKSON: You should use unfaced batt insulation to avoid creating a situation where insulation is being trapped between two vapor barriers. It may prove necessary to dehumidify your shop space due to wall drying to interior, especially if your concrete slab on grade does not have a vapor barrier beneath it.


DEAR POLE BARN GURU: Do all your post go directly into the ground?  Do you have any type of foundation system? Thanks TONY

DEAR TONY: Our most common design solution utilizes properly pressure preservative treated columns (UC-4B rated) embedded in ground, with bottom of column hole below frost line (or 40″ below grade, whichever is greater). If potential decay of columns is a concern (https://www.hansenpolebuildings.com/2020/09/pressure-treated-post-frame-building-poles-rot/) we can provide plastic sleeves to isolate columns from surrounding earth. We can also design using columns mounted to wet set brackets to either be set in piers or atop of a foundation wall or thickened edge slab. We have also had clients utilize concrete Permacolumns, however this is rarely a cost effective choice https://www.hansenpolebuildings.com/2018/04/perma-column-price-advantage/.


DEAR POLE BARN GURU: Building a barndominimum what or how do you get a foundation or rat wall with pole construction do you dig out between the poles and pour it? LLOYD in ONSTED

DEAR LLOYD: There is no structural reason to pour a “rat wall” between columns (https://www.hansenpolebuildings.com/2012/06/rat-wall/).

My recommendation (and we can show this on your engineer sealed plans provided with your building) would be to use 19 gauge, 1/2″ x 1/2″ galvanized wire mesh around your building’s perimeter to a depth of three feet. This can be done be means of a trench and will be far less expensive than pouring a wall between columns.





Insulated Bookshelf Wall Girts

While we United States residents like to think of ourselves as perhaps the center of our universe, post frame construction appears world wide.

Reader JONATHAN in HALIFAX picked Alabama as his state when he filled out his online request for information when he wrote:

“What insulation do you suggest between bookshelves of wall?”

With so many post frame buildings being used for residences, commercial buildings, shop/houses and barndominiums, properly addressing how to insulate has become of utmost importance.

I am going to take a stab and guess your Halifax is in Nova Scotia, rather than Alabama. My lovely bride and I made a stop there on a cruise from New York City a few years ago – beautiful area (and I got a Harley-Davidson T shirt).

If so, you are in what would be an equivalent to our IECC (International Energy Conservation Code) Climate Zone 7. For wood frame walls, this would require an R-20+5 or R-15+10, where your plus value is for continuous insulation.While continuous insulation is most often usually on exterior of framing, Martin Holladay – editor of Green Building Advisor feels confident in it working as well on inside of framing. Given this, I would put a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) between wall framing (bookshelf wall girts) and siding, then fill your cavity with rock wool (as it is not negatively affected by moisture), then use rigid foam insulation inside of your framing. You can glue these sheets to your framing (bookshelf girts) to eliminate any thermal bridging from fasteners and then glue your interior finish to it. Make sure to tightly seal your rigid foam boards and to caulk along the bottom of exterior walls to get a good seal. Built in this fashion, your walls will ‘dry’ to the outside, reducing the need for dehumidifying inside.

Of course you will want to get approval from your local permit issuing jurisdiction before moving forward.

For extended reading on rock wool insulation please see https://www.hansenpolebuildings.com/2013/03/roxul-insulation/

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.

Harnessing Radiant Heat

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday segment.  If you want a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: I work for the US Army Corps of Engineers in Toledo Ohio. We need to get a layout and price for a building that is around 35′ X 45′ with 15 foot tall doors at each end to be able to run a boat on a trailer thru it and to be able to use it to work on it and have storage for the survey equipment we use on it. Please send whatever you have that is close to those dimensions that I can send up to the main office for their consideration. Thank You, MITCHELL IN TOLEDO               

DEAR MITCHELL: As a starting point, it would be quickest for you to request a quote by going to: https://www.hansenpolebuildings.com/freequote/. One of our Building Designers will be in contact with you to work out fine details and guide you towards a solution which will best meet with needs and budget.

If this is a project which will have to be put out for bids, our team works with any governmental agency and will product structural plans for bidding, with no upfront investment. Oftentimes, it is most cost effective to split the project up into two portions for bid – the building design and materials delivered to the site in one, the construction labor and any concrete in another. This eliminates the contractor marking up the materials and gives agencies more building for their investment. Mike the Pole Barn Guru

DEAR POLE BARN GURU: Instead of using your free building quote which is different than what I want. Can you quote sketches for me? I can get by with a 30X60, but I wanted to see what the price difference would be to go to a 36X60. Put the total cost down including delivery. What I want is two open bays for equipment storage with a 24′ shop. The inner shop wall will have a man door that enters the shop. I will build the pole barn myself. Can you separate the costs of the inner shop wall and overhead door? I figure if the cost is more than I can do this year I can at least have the shell completed and install the rest at a later date. I hope this isn’t too confusing. I have included my contact information below if you need to contact me. Roof would be 4-12 pitch. All steel with two colors (Black and white). DAN IN OHIO

DEAR DAN: Most certainly we can begin with your sketches. You are after a building which in the bygone days (at least in the Pacific Northwest) was known as a machine shed/shop. They were very popular in the 50’s through 80’s because wind analysis technology had not yet figured out the forces on a three sided building (which the non-shop portion is).

To read more about what happens with three sided buildings: https://www.hansenpolebuildings.com/blog/2014/03/three-sided-building/

Ultimately it would be less expensive to do a fully enclosed pole building.

Mike the Pole Barn Guru

DEAR POLE BARN GURU: I’m planning a 32×64 pole building, metal sides, shingle roof. The building will not be heated. However, I am intrigued by the thought of harnessing the radiant heat in the ground under the slab and allowing this to radiate through the floor into the building during the winter. Is this even a realistic idea? If the slab were insulated vertically around the perimeter to isolate it from the frost and also a perimeter horizontal insulation under the slab (say two to four feet of rigid foam), will this theory work? How would this be done and have you done it successfully in the past? ANDY IN CLARKLAKE

DEAR ANDY: Before I answer your question, a couple of suggestions which will help you get some more bang for your buck.

 #1 Going with either 30’ or 36’ in width and 60’ or 72’ in length will lower your per square foot investment.

#2 Unless you have an HOA which requires a shingled roof, steel is going to be by far more durable and economical. Read more here: https://www.hansenpolebuildings.com/blog/2015/03/shingle-warranties/

 Your idea might work. Basically what you propose to create is in effect a frost-protected shallow foundation (although the columns would extend through the bottom of the slab around the perimeter). Here is a guide which can help you towards this design: https://www.cs.arizona.edu/people/jcropper/desguide.pdf

 It is not something I have tried, so I can’t speak towards the results. I can imagine you would have to do a thorough job of insulating the building itself, in hopes you would be able to retain enough heat to prevent the ground below your slab from also freezing.

Mike the Pole Barn Guru

Frost Heave: Some Methods That Don’t Work

In yesterday’s posting, I quoted Harris Hyman, an engineer from Portland, Oregon, who appears to know his stuff when it comes to preventing frost heave.

In a July 1994 article, in the Journal of Light Construction he listed some methods which don’t work to prevent frost heave:

frost-heave“Another method for dealing with frost involves wrapping posts with plastic, so that the ice slips when it heaves. I suspect that this will work for a year or two – maybe – but eventually the deterioration of the plastic will bring the whole dream to an end. It seems that filling postholes with uniformly graded 1-1/2-inch crushed stone might work a little better. However, I do admit never having worked with plastic wrap and look forward to hearing about your experience.”

Personally, I’ve always wondered about the effectiveness of plastic sleeves in the resistance of frost uplift. The most commonly seen commercially available sleeves will certainly outlast any thin layer of plastic however.

“Another technique is using rigid foam insulation to protect walls. This is useful for heat retention, not for frost protection. It should be supplemented with a drain rock backfill.

The two worst methods for dealing with frost heaving are the heated foundation and the locking bar. I call the heated foundation “structural use of energy” – burning irreplaceable fuel, warming the soil around the building, to prevent frost damage and hold a building together. This is both extremely expensive over a long period of time and socially undesirable. Even though it cuts down on initial construction costs, it should not be encouraged.”

When we put up our building in South Dakota I asked our builder about frost heave, his answer lead me to understand him as a firm believer in heating a building up far enough to chase the frost out of the ground!

“The locking bar is a bit of foolishness that seems to keep appearing on construction sites. This is a cross-bar nailed or lag-screwed to a post, usually about 2 feet below grade. Apparently the builders think this helps hold the post down, but it is usually above the ice lens and actually helps lift the post.”

I’ve seen this and other similar methods – like rebar driven through the columns or a series of large diameter nails or lags driven into the posts. All of these are going to afford the same ability to frost heave the columns.

In the words of Harris Hyman, “So the best way to beat frost is just to let it freeze – but get rid of the water first.”

I’ve written extensively on frost heave in the past. For more information, hop in the “Wayback” machine and check out: https://news.yahoo.com/first-person-snapshot-black-hills-blizzard-201300744.html