Tag Archives: blown in insulation

Plastic Vapor Barrier, PermaColumn, and a Fire Resistant Barrier

This Wednesday the Pole Barn Guru answers reader questions about use of 6 mil plastic vapor barrier in Michigan, if Hansen provides the option of a precast concrete pier to keep columns out of the ground, build heights, and “if anything needed between interior PVC panels, closed cell spray foam and the exterior metal siding.”

DEAR POLE BARN GURU: I have a pole barn that I am planning on insulating. The trusses are 2 foot on center and it has a shingled roof, the outside of the pole barn is steel. I live in Michigan and I was wondering if it is a good idea to put 6 mil plastic on the bottom of trusses before I hang steel on the ceiling. I will be blowing in insulation up there later. KAL in HUDSONVILLE

DEAR KAL: You are in Climate Zone 5A, so a ceiling vapor barrier is not required by Code. Building scientist and founding principal of Building Science Corporation Joe Lstiburek states, “Plastic vapor barriers should only be installed in vented attics in climates with more than 8,000 heating degree days.” (More on degree days here: https://www.hansenpolebuildings.com/2022/11/what-is-degree-day/).

I would only recommend you installing a vapor barrier above your steel ceiling if you were to be considering blowing in cellulose insulation. Why cellulose? https://www.hansenpolebuildings.com/2022/10/cellulose-post-frame-attic-insulation/


DEAR POLE BARN GURU: Do you deal with post frame designs that: 1) use the precast column to keep wood out of the ground? 2) Deal with designs that are 20′ eave height to accommodate 2 story interiors. JONATHAN in ZANESVILLE

DEAR JONATHAN: We have had several clients provide their own pre-cast Permacolumns and they can be incorporated into our engineered designs. There is, however, a less costly option to explore: https://www.hansenpolebuildings.com/2018/04/perma-column-price-advantage/

We can engineer and provide up to 40 foot tall walls and three stories without needing fire suppression sprinklers, so 20 feet eave heights are not a problem.


DEAR POLE BARN GURU: Hello, my question, which I can’t seem to find a straight answer anywhere online. Is anything needed between interior PVC panels, closed cell spray foam and the exterior metal siding? The pole barn is located in southern Indiana. It’s used as a shop and being heated occasionally with a wood stove. BENJAMIN in INDIANA

DEAR BENJAMIN: As your PVC and closed cell spray foam are both flammable, I would use an intumescent fire proof paint on interior face of closed cell spray foam, then fill balance of wall cavity (if any) with rockwool batts. As an alternative to intumescent paint, you could place sheetrock between wall framing and PVC panels (panels will lay much smoother).

A Barndominium Challenge

A Barndominium HVAC Challenge

My now dear friend (thanks to his barndominium) LONNIE in COLORADO SPRINGS writes:

“Hi Mike, I’m still around and still working on the house and making some slow but constant progress so I thank you all for your help and support. I have run into an issue (it’s not related to my Hansen building but I’m hoping you can offer advice anyway).. I ran into a problem getting a HVAC contractor to install my HVAC system. Not too many companies are willing to work with a owner/builder and HVAC install is way out of my wheelhouse. I was able to find a contractor that was willing to do the install but they were pretty much unwilling to do anything different than their “normal” installation (i.e. supply and return ducts in the attic). I was really wanting to do at least return air in my conditioned crawl space but they wouldn’t even consider doing that. So, in order to make progress on the project, I okayed the installation. All the building guru’s say that HVAC duct should not be placed in an unconditioned attic due to leakage and inefficiency so I’m trying to figure out how to mitigate duct losses. There are a couple of ways that I’ve thought of but I’d like your thoughts.


1: As described in some articles I’ve read and encapsulate all the ductwork with spray foam then bury all the ducts in my blown in insulation

2: Just leave the ducts as is and just bury the ducts as deep as I can afford with insulation3: I’ve thought of covering all the ducts with 6 mil plastic down to the ceiling drywall.. i.e. kind of enclose the ducts in a bubble that is attached to the ceiling, then bury it all in insulation. Covering the ducts in plastic seems like it would basically move the ducts to the conditioned space. Anyway, thank you for all your input and all the help you guys have been to me.

Thanks Lonnie”

Lonnie ~

Mike the Pole Barn Guru responds:

You are most certainly among my favorite all time clients, it has been such a pleasure working with you. While I am excited for you to be moving in, I have to admit it will be sad to not hear from you once all is completed. Since you started, one of our sons has moved to Colorado Springs, so if we get down to visit, I will drop you a message and maybe come by to see your beautiful home for real.

Your HVAC experience is why our Construction Industry in general is so far behind the curve of efficient building design – very frustrating. I would look to make those ducts as efficient as possible – I’d start with two inches of closed cell spray foam on sides and top, then bury it with enough blown in insulation to achieve an R value equal to the balance of your attic space. Closed cell spray foam will seal up any leaks in your duct work (trust me, there will be some). Return air through your crawl space would have been a no-brainer, in my humble opinion. I worked with stick frame builders nearly four decades ago who insulated their crawl space perimeters and then used those crawl spaces as one huge air return. Then, it was less expensive than running ducts.

Insulation Options, Building Plans, and a Swing Table

This week Mike the Pole Barn Guru discusses about insulation options, building plans for a back yard pavilion, and steel gauge for a “swing table.”

DEAR POLE BARN GURU: We are well on our way toward breaking ground. Our biggest concerns that we seem to keep going back to are these. We want a tight, dry efficient house. Although we get a little winter we are way more concerned with cooling. I love the dark metal for the roof but my husband thinks it will make the house hotter. Any advice you can offer to achieve our goals would be appreciated. We can afford to do it right but don’t want to overdo. JENNY in ARTEMUS

DEAR JENNY: If you are going to build a fully engineered post frame building, then you should be able to meet with all of your goals. By using flash and batt (https://www.hansenpolebuildings.com/2020/01/flash-and-batt-insulating-barndominium-walls/)  for your wall insulation system, you will have tight walls. Kentucky is in Climate Zone 4 where ceiling R-value must be at least R-49 by Code. For the small difference in investment, I would suggest blowing in R-60 and using 22″ energy heel trusses to get full insulation thickness from wall-to-wall. Here in NE South Dakota we have a black steel roof and R-60 attic insulation. Our typical late summer is 90 degree plus days and with our attic insulated as it is, any heat gain from our black roof is negligible. For more information on energy efficiency please read: https://www.hansenpolebuildings.com/2019/11/post-frame-building-insulation/.


DEAR POLE BARN GURU: First, thanks for this website. I have found it very useful in my research. I work in tech and am not a carpenter, but I have worked construction before and I am taking on building an out door pavilion in our back yard. The dimensions are 20’x14′ hipped roof with posts at 18′ and 12′. I have found a couple of plans online and have purchased them and studied them inside and out to see whether or not I could take this on. I believe that I can. The plans that I have both have a 6 post layout. I would like to modify them a bit to eliminate the center posts and only have 4 posts. I have solved that by using an LVL microlam beam for the roof stringers. My real question though is around knee braces. the plans have knee braces in them, but I would like to not have them if at all possible. I have seen similar construction images that don’t have them. I am planning on using 6×6 posts and notching out the top for the stringers. Would not having braces influence the joinery choice of the stringers? Including a couple files for reference. Thanks for any and all help!! BJ in WASHINGTON

DEAR BJ: Thank you for your kind words. In all reality, when it comes to post frame construction, if you are physically capable and will read assembly instructions then you can successfully erect your own beautiful building. Your structure should be able to be done without a need for knee braces, however it would behoove you to have it designed by a Registered Professional Engineer. In most instances they will save you more money in eliminating inefficiencies than you will pay them for their services. Depending upon your building’s eave height and overall height of your roof, 6×6 columns may or may not be adequate for your purpose, again – your engineer can specify this as well as all needed connections.


DEAR POLE BARN GURU: I was going to make this for a client, probably 2 or 2.5 inch square tubing. Just curious to what thickness I should use? I was thinking 11ga- 1/8 inch thick steel. I just don’t know if that will be strong to enough to support a human. The part they will be hanging from will be about 4 foot wide. BLAKE

DEAR BLAKE: Sizing steel members is most certainly out of my wheelhouse, although I appreciate your inquiry. Given pricing of this unit, I would recommend you consult with a Registered Professional Engineer to size members as well as design connections – since people will be potentially injured (or worse) in event of a failure, you do not want to be in a liability position. My one recommendation would be to have it powder coated to minimize rusting potentialities.


How Tall Should My Eave Height Be for Two Stories?

How Tall Should My Eave Height Be for Two Stories?

I have learned a couple of things in 40 years of post frame building construction. One amongst these is – most people are dimensionally challenged (no offense intended).

As much as some folks would like to believe, you cannot legitimately put two full height finished floors in a 16 foot eave height post frame building.

Now fear is a strong motivating force. Perhaps it is fear of a building “appearing” too tall or of OMG it will be too expensive keeping people from considering what it actually takes to create a Building Code conforming two story building.

Back in my early roof truss selling days, I had two clients who had relocated from New York state to North Idaho and were building new homes on adjacent properties. Both of them (and their spouses) were relatively short of stature and had decided to build their homes to Code minimum ceiling heights of seven feet. Their reasoning was it would be less space to heat and cool and they could chop two studs out of 14 foot long materials.

Missed in all of this was how much sheetrock waste would be created!

Sidebar – modern Building Codes allow seven foot ceilings under International Residential Code (IRC), however IBC (International Building Code) requires six more inches.

Now I am vertically challenged at 6’5” and would feel very uncomfortable with seven foot ceilings. In my own personal shouse, most ceilings on both floors are 16 feet high!

In today’s exciting episode we will learn together how tall eave heights should actually be to give reasonable ceilings in post frame buildings.

Setting a “zero point” at exterior grade (and assuming slab on grade for lower floor), top of slab will be at +3.5 inches.

To create eight foot finished ceilings requires 8’ 1-1/8” (allows for 5/8” sheetrock on ceilings).

In order to be able to run utilities (e.g. plumbing and ductwork) through second floor supports, I highly recommend prefabricated wood floor trusses (https://www.hansenpolebuildings.com/2020/01/floor-trusses-for-barndominiums/). Generally truss height will be about an inch for every foot of clearspan with a 12 inch minimum. 

In my own shouse, we have a 48 foot clearspan floor over our basketball court. And yes, those trusses are four feet deep!

Allow ¾ inch for OSB floor sheeting.

6-1/16″ for heel height of trusses with 2×6 top chord at 4/12 slope (provided you are using closed cell spray foam insulation between purlins)

If using blown-in insulation truss heel height should be R value of insulation divided by 3 plus 2″ to allow plenty of eave to ridge air flow above insulation.

At a bare minimum an eave height of 18’ 0-9/16” will be needed to create those eight foot ceilings.

Faced or Unfaced, Correct Screw Pattern, and Connecting Two Units

This Monday the Pole Barn Guru answers questions about use of faced or unfaced insulation, the correct screw pattern, and viability of connecting two buildings together.

DEAR POLE BARN GURU: Should I use faced or unfaced insulation in my pole barn attic w/ ridge vent? DAINE in PALMER

DEAR DAINE: In order for your ridge vent to be effective, it does need to have an intake – ideally from vented soffits. Make sure there is at least an inch of clear space above any attic insulation, to allow unobstructed airflow from eave to ridge. You should be using blown in attic insulation. Your need for a vapor barrier below your blown in attic insulation depends upon your number of heating degree days (please see link in this article: https://www.hansenpolebuildings.com/2018/10/ceiling-vapor-barriers-in-post-frame-construction/).

DEAR POLE BARN GURU: I am building a house on 24″ truss centers and want to know if this is the correct way to install the medal rood? 7/16 OSB synthetic felt and 1X4 purlins to mail the medal to will this sweat or have problems and is this the correct way to go? KENNY in OSAGE CITY

DEAR KENNY: I would recommend you use 2×4 purlins placed wide face towards your OSB sheathing. You want to make certain you have securely fastened purlins with nails long enough to penetrate through OSB and 1-1/2 inches into each truss top chord.

Reasoning for 2×4 is you should be using 1-1/2 inch long screws, placed in flats of roofing and you want entirety of your screw shanks to be firmly into solid wood (OSB will not hold your screws). Here is your correct pattern for screw placement:


DEAR POLE BARN GURU: If I buy two units, can I connect them in anyway or turn two units into 1 long unit? NATHAN in SAN LUIS

DEAR NATHAN: Yes to both – however please let us and our third-party engineer design all of your project together. When buildings become lengthy in relationship to width structural design challenges can occur in relationship to an ability to adequately transfer wind loads from roofs to endwalls. By doing an entire structural design, we can insure your finished product will remain standing and useful for a lifetime.



Slab on Grade or Crawl Space?

Slab on Grade or Crawlspace?

Long-time readers of this column recall seeing a profuse number of articles written in regards to crawl spaces. These articles have been on a gradual increase since this first one six years ago: https://www.hansenpolebuildings.com/2013/03/crawl-space/.

With residential post frame construction becoming rapidly more popular as more people discover this system’s benefits, this debate of slab on grade versus crawl space will continue.

Hansen Pole Buildings’ Senior Designer Wayde recently had a client order a new post frame building kit package with an elevated wood floor (to create a crawl space). After client has placed their building order, Wayde came back to me with this, “Can you tell me the Pros and cons of building this as we designed and sold it vs. lowering it three feet and adding a radiant concrete floor?”

I happen to be a big fan of hydronic radiant floor heat in concrete slabs, we have it in our own building: https://www.hansenpolebuildings.com/2012/08/radiant-floor-heating/.

Biggest pro of “as is” – living upon a wood floor will be so much more comfortable than upon concrete. Wayde’s client could still do radiant floor heat, should they opt to not go with a forced air HVAC system.

Slab on grade the client will have to (or should) do a post frame shallow frost protected foundation: https://www.hansenpolebuildings.com/2019/02/minimizing-excavation-in-post-frame-buildings/. This perimeter rigid board insulation must be covered with rodent proof material.

If I went to slab on grade, I would recommend a minimum R-60 for ceiling, taking a 22 inch deep raised heel truss to allow for adequate depths of blown in insulation. (Read more about raised heel trusses here: https://www.hansenpolebuildings.com/2012/07/raised-heel-trusses/).

For an 8′ finished ceiling, they would then need an eave height of 10′ 2-5/8″. I like taller rooms, so you might want to experiment with eave heights of 11′ 2-5/8″ and 12’2-5/8″ (latter of these will be easier to drywall and will result in least waste).

Making a choice between living on concrete or wood will be one only able to be made prior to time of construction and should not be taken lightly. All factors should be taken into consideration most importantly being what creates a most comfortable living space.