Post Frame Barndominium Exterior Wall Questions
Reader IAN in RIDGWAY writes:
“I am looking for help understanding a couple of exterior wall questions.
- My county is enforcing the 2018 IECC for energy efficiency. In my region this requires R-20 cavity + R-5 exterior wall assembly. From everything I’ve read, this means a continuous layer of 1″ rigid between the framing members and the metal siding. Is this an accurate understanding in your mind? Does the 1″ of rigid between framing and siding affect the integrity of the structure at all? Are the fasteners that are shipped with your kits long enough to accommodate the 1″?
- We will be living in our pole building, which means we will need to meet minimum code standards for receptacles at the exterior walls. I am under the impression that the poles must remain whole and are not designed to have a hole drilled through each for ease of pulling wire. Am I correct here? What is the suggested solution? Conduit everywhere below my slab?”
Mike the Pole Barn Guru responds:
Nice to see jurisdictions enforcing IECC (International Energy Conservation Code) requirements, as it will result in more energy efficient structures. In Ouray County, you are in Climate Zone 6B. This requires ceiling R-49, wood frame walls of R-20 plus R-5 (or R-13 plus R-10) where second value is continuous insulation and slab edges to have R-10 four feet deep.
According to Martin Holladay (Green Building Advisor editor) your continuous insulation is just as effective when installed on the interior of your wall framing. This is very important when it comes to fully engineered post frame construction. Properly engineered, post frame construction relies upon shear strength of steel skin to transfer wind loads through building planes to ground (https://www.hansenpolebuildings.com/2011/12/lateral-wind-loads/). Having rigid insulation between framing and siding would reduce or negate your siding’s shear strength and result in a less than satisfactory outcome. My recommendation would be to use a Weather Resistant Barrier on the outside of the framing, directly inside of steel siding. Fill insulation cavity with unfaced batts (preferably stone wool such a Roxul as it is not affected by moisture https://www.hansenpolebuildings.com/2013/03/roxul-insulation/) or BIBs (https://www.hansenpolebuildings.com/2011/11/bibs/), then a well sealed rigid insulation board between framing and interior finish. Done this way, your wall will ‘dry’ to the exterior, making your home’s HVAC system less responsible for reducing interior humidity levels.
Your wire pulling is far easier than you may have initially envisioned.
Very little drilling, if any, will be needed for holes in order to run electrical wires. Wall framing (girts) extend or are placed so as to leave a 1-1/2 inch space between outside of wall columns and siding.
Think of a hole being drilled through as being an “open knot”. Lumber grading rules refer to these as being “Unsound or Loose Knots and Holes” due to any cause. Most structural framing – like wall girts and roof purlins or posts and timbers are graded as Number 2.
For practical purposes, a hole up to just less than ¼ of board face being drilled through will be within grade in #2 lumber. Example: 3-1/2” face of a 2×4 a hole up to 7/8” may be drilled through, as often as every two feet. Allowable hole sizes are reduced and spacing increased for higher grades of lumber.
Any holes drilled through pressure preservative treated lumber or columns, especially near grade, should be treated with a Copper Naphthenate solution. Copper Naphthenate is available as a brush-on (Cuprinol No. 10 Copper-Green® Wood Preserver https://www.homedepot.com/p/Copper-Green-1-gal-Wood-Preservative-176223/300502829)
or spray-on(https://www.homedepot.com/p/Copper-Green-Wood-Preservative-14-fl-oz-
uilding Designer Doug asked, “I’m sorry to keep beating the insulation horse, but I have a client who wants to put up a 60×100 building on his timberland. I asked him about heating it and he wants to put a wood stove in it. So he wants to heat it occasionally. It’s in Clackamas County, OR, so it will get cold. 
DEAR POLE BARN GURU: I am building a 24×30 pole building 15 foot wall height. I am l am planning on not putting in a ceiling and insulating directly in the purlins up to the OSB. Soffits are vented but should I put in just some small gable vents for outlet flow? MIKE in SEDRO WOOLLEY 
Use two inches of closed cell spray foam against your wall and roof steel – if not, you run a high risk of condensation troubles. If you are going to blow insulation into your walls, use a product such as BIBs.
This myth is created and propagated by post frame kit suppliers and post frame builders who do not understand there is a solution – and a very cost effective one (in both labor and materials).
With only 1200 square feet of living space, you should be able to easily exceed the state mandated required number of energy efficiency credits. We are currently changing our standard windows to U-29, meeting Washington’s standards. Lesser U values are available, however added expense may well not ever be recouped by energy savings. I would recommend two inches of closed cell spray foam on your walls, then BIBs or similar to fill the balance of wall cavity. R-49 attic insulation is mandated by Code, however your added investment to go to R-60 would be minimal. With either we would recommend raised heel trusses.
Wall girts flat on column exteriors are inadequate to carry imposed loads and will not meet deflection limitations. I would suggest you reinforce each of them to create either an “L” or a “T”. Assuming you have 6×6 wall columns, you could place a 2×8 bookshelf style girt on top or bottom of each girt, nailing through 2×8 into existing girts with a 10d common nail at say 12 inches on center. This will create an insulation cavity and allow for easy interior finish.
As only incidental heat will be provided into crawl space areas, using rigid foam insulation boards beneath a thin concrete slab might very well prove to be an undue expense. 
I plan to condition the space, so I would put down between 6 and 10 mil plastic, then 2 inches of foam board insulation followed by pouring a concrete floor, just enough to keep critters out. I plan to use BIBS insulation in the walls, so I would extend that down the exterior crawlspace walls to the concrete.
The most common yardstick for measuring insulation performance will be R value, but there’s a problem. Insulation packaging shows lab analysis of R values, but it’s based upon used testing completely eliminating air movement from results. This matters a lot with fluffy insulation materials because air movement greatly lowers real-world insulation performance. Drafts and air currents often happen within wall cavities and attics and this will be why real-world insulation performance can be significantly lower than advertised values.
Why would I do this? Comparing “apples to apples”, I know our price will beat theirs, every single time. I am doing this for your peace of mind. I guarantee other prices will be higher. And I will provide you with documentation to prove it!
Reader DAVE in ROBERTS apologizes for buying from a competitor and writes:
“STEVE would like some advice on insulating. He has a Cleary Building which has blanket insulation in the walls and roof and he would like to insulate over the top of this insulation and wondered if there would be issues.
Thank you for your kind words. Sadly, most post frame home clients are just not savvy enough to be willing to make an extra upfront investment to super insulate their buildings. I have designed several post frame residential buildings for my own use, so I have learned from mistakes. Also, technologies have improved greatly in recent years, making energy efficient designs more practical.
Thanks again for the input. I read those articles you mentioned on the BIBs and the white liner panels. The liner panels are very common and popular around here but the article had very good points and gave me more to think about. As for the insulation, I was not familiar with the BIBs system and was impressed. I have done some more reading and reached out to a few contractors for quotes on the BIBs system. I do prefer to do things myself whenever possible however, so the option of installing fiberglass myself is still on the table. This is where I still have a question. You mentioned to fill the entire wall cavity with unfaced fiberglass and then cover with Visqueen. Is there an issue if the cavity is not completely filled and an air space is created between the fiberglass and the Tyvek® behind the metal sheeting? I ask because my walls are roughly 5 1/2” deep and obviously R13 is only 3 1/2” thick and R19 is 6 1/2” thick. If I go with R13 (cheaper) I end up with an air space. If I go with R19, I end up compressing it and losing r value anyway. Also, I have diagonal bracing in the corners which will also make it near impossible to tightly fill with fiberglass batts. I would love to go with the BIBs system but am waiting to see if it is within budget. If I can save considerable money insulating myself with batts I would most likely do so but need to be sure I am not causing problems down the road. Sorry for being so long winded and thank you very much for all your help and information.”








between the wall girts. If steel siding is used, it could be beneficial to use a quality housewrap between the wall girts and the siding. With commercial girts, to properly size the insulation cavity, create a space equal to the depth of the pole, plus the 1-1/2″ outside of the posts where girts extend. This allows for drywall to be attached to the inside face of the wall girts, creating a smooth wall surface.