Tag Archives: condensation barrier

Moisture Reduction, Window Sizes on a Building, and Frost Heave

Today the Pole Barn Guru addresses reader questions about moisture reduction in pole barn with dirt floor, what size windows can be added to a structure, and how to eliminate frost heave.

DEAR POLE BARN GURU: I have a 60 x 120′ pole barn with dirt floors and an insulated ceiling 18′ high. I believe the walls are also insulated but I haven’t checked. It stays very humid in there with the service door closed, which I like to do in the winter. There are 6 modestly sized windows but they’re 10′ high, hard to close in the rain and don’t ventilate much. I assume all this moisture is from the soil, is there a cost effective way to add a floor moisture barrier? ROSS in NORTHFIELD

DEAR ROSS: You are correct about where moisture is coming from – and it is made even worse in Winter, when ground outside of your building is frozen and inside your building is where all ground moisture is trying to escape (basically think of your building as being a cork pulled out of a genie’s bottle). While pouring a concrete slab on grade of a vapor barrier would be your best (and permanent) solution, concrete is costly. With this said, my best recommendation would be to remove top two inches of dirt inside of your building, making sure there are no sharp rocks projecting up above surface. Place a 15mil black vapor barrier across entire floor, overlapping seams by 12 inches and taping them tightly shut. Run vapor barrier up onto splash planks on walls (if possible) as well as sealing to each column. Cover vapor barrier with two inches of clean sand. You may need to mechanically dehumidify, in order to fully resolve your challenges.


DEAR POLE BARN GURU: Hello I am curious about window sizing in post frame buildings. Can I add any size window I want in any wall without affecting the structural integrity of the building? My largest windows are roughly 42″ wide by 64″ tall. WESLEY in DULUTH

steel pole building metal interiorDEAR WESLEY: Post frame buildings “work” due to their skin. Placing openings, without approval from your building’s engineer, could result in catastrophic structural failure.

For extended reading, please visit: https://www.hansenpolebuildings.com/2011/12/lateral-wind-loads/


DEAR POLE BARN GURU: The frost heave issue: how does a guy insulate his foundation? TONY in MARION

DEAR TONY: Most important for avoiding frost heave is having a properly prepared building site: https://www.hansenpolebuildings.com/2011/10/preventing_frost_heaves_in_pole_building_construction/
Here is information on insulating: https://www.hansenpolebuildings.com/2022/09/272982/

Spray Foam, Second Floor, and Bending Posts

This week the Pole Barn Guru discusses a reader’s concern about “condensation leaks” when using spray foam, advice on costs of attic trusses vs traditional second floor, and how to stop posts from bending when the wind blows.

DEAR POLE BARN GURU: I am building a 40×50 post frame building as my garage. It will have concrete floors and HVAC. I intend on insulating the entire building (walls & ceiling) with closed cell spray foam. I’ve read a lot about people having condensation leaks, so my question is: Should I wrap the walls (and/or ceiling) with Tyvek or spray foam directly to the metal? Second question is should I use plywood on the roof for better structure and to have something to spray foam to? Any advice is appreciated. Thanks. CHRIS in BLOOMFIELD

DEAR CHRIS: Closed cell spray foam is a great product, however it would not be my first choice for your climate zone. For best results, closed cell spray foam should be two inches or thicker to prevent condensation, and applied directly to the roof and wall steel. Hopefully you have a well-sealed vapor barrier beneath your building’s slab. With closed cell spray foam, you may experience condensation on your building’s interior, so do not be surprised should you have to mechanically dehumidify. Unless specified as necessary on your engineer sealed building plans, you should not add plywood or OSB to your roof system, as it will add unexpected dead loads to your building system.


DEAR POLE BARN GURU: Hello. We are wanting to build a 2 story pole barn winery. First floor winery and second would be air-bnb type rental. We aren’t sure if we should use attic truss or complete the build with a traditional second floor. Cost is probably biggest concern. Space second as we know attic truss would be less room. Would you do an attic truss or traditional 2nd floor type build and roughly cost difference between the 2? Building size will be roughly 40×60. Thank you for your time. CRAIG in ROCK CREEK

DEAR CRAIG: If cost is your biggest concern, then having rental on ground floor will be least expensive, easiest to climate control, more accessible for your guests and easiest to fire separate from your winery.

If your only option is to have rental above winery, going with a second floor type build is going to give you far less costly investment per square footage of rentable space.


DEAR POLE BARN GURU: I built a pole barn for my r/v a couple of years ago. I used 4×4 for my posts with a metal roof and purlins with no siding. The posts are set 3′ into the soil with no concrete. Posts are 10′ out of the ground. When we get a strong wind the posts bend slightly at ground level allowing the structure to flex. Is there a way to add strength to the posts or do I need to replace with a larger size post and should I embed the post in concrete or will it rot? MARK in BRADENTON

DEAR MARK: I am frankly amazed your building is standing! This response is not to be taken as a replacement for an actual engineered structural design and should be verified by an engineer prior to moving forward. You should replace 4×4’s with at least 6×6 (it may require 8×8’s depending upon design wind speed and exposure at your site) #2 Southern Pine columns pressure preservative treated to UC-4B (there will be a treating tag on one end of each). Columns should be at least 40″ in ground and backfilled with pre-mix concrete.

Seal Walls, Fill for Compaction, and Condensation Control

Let’s close out the week with another installment of Ask the Pole Barn Guru! First up is a resolution to seal up a building, followed by assistance with compacted fill, and finally an alternative to spray foam to control condensation.

DEAR POLE BARN GURU: I purchased a pole building from you last year and there was an error that I wanted an insulated building. So I will be insulating this myself. What keeps all the drafts and bugs out at the roof eve and lower edge of side panels? I am doing house wrap on the exterior walls. MARK in MOUNT VERNON

DEAR MARK: Communication – we as humans do so much of it and all too often do not fully convey our intentions. I am just as guilty as any other person, so do not feel like you are alone in this. This is one reason we strive to do everything in writing, so both parties are clear on each other’s expectations.


Also, successful construction is not measured by how perfect things went initially, but rather by how challenges are solved to arrive at a great end result.

Your roof eaves should be sealed with inside closures, provided with your building package, to install between fascia board and roof steel, so should not be an issue there. If you have not yet installed siding, same inside closures can be placed at bottom of walls, on top of your Weather Resistant Barrier to keep any little critters from entering steel high ribs in your 1/4 inch space between base trim flat and bottom edge of wall panels.


DEAR POLE BARN GURU: I’ve worked with a Hansen Building Designer, ordered my building, and materials will start arriving in two weeks. Looking forward to it, but also a little bit ‘trepidated,’ as it’s my first post-frame build (I completely remuddled a 100 year old farm house at our last place, so that’s what I have for previous experience).

My question has to do with the compacted fill that goes onto my cleared site after the poles are concreted in. Is crusher run gravel appropriate, or is a different type of gravel recommended for better drainage (I’m not familiar with the options, so please be specific if so)?

Also, please see the attached photo of the cleared site along with a drawing I created based on what I *think* are the correct dimensions based on reading the Construction Manual and a number of your blog posts. Note that I’m planning on a 5″ thick concrete floor, and have indicated same in the drawing at exactly 5″. ED in SUMMERTOWN

DEAR ED: Awesome drawing! You should have no difficulties in assembling your own beautiful building, as I can tell you are already reading directions!

Crusher run should be adequate for your sub-base. Most important is to get any clay removed from within upper levels of your grade and to have good compaction. Top two to six inches of your fill should be clean and drained sand or sandy gravel, again well compacted.

Photos: https://hansenpolebuildings.com/uploads/polebarnquestions/7bea6f6c3d75e192515b8bd12303c72c.jpg


DEAR POLE BARN GURU: If not spray foam on the underside of metal roof then I saw you recommend reflective siding insulation. Would that suffice in lieu of spray foam?


DEAR DYLAN: My first alternate choice would be to use an I.C.C. (Integral Condensation Control) https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/ easy to install and no seams to worry about. Next choice would be a Reflective Radiant Barrier – we have it in six foot wide rolls with an adhesive pull strip to seal joints. Contact Materials@HansenPoleBuildings.com for delivered pricing (rolls are 128′ long).