Moisture Barrier: A Bad Place for Plastic

Pole Barn Guru Blog

Eric, one of the owners of Hansen Buildings, was chattering with me today about the number of interesting telephone calls he fields. Many of these are probably due to this blog, as well as “Ask the Pole Barn Guru” – the weekly advice column for those with pole building questions, concerns, or who just are looking for free therapy.

A gentleman had recently erected a pole building, and placed six ml (0.15 millimeter thick) clear plastic visqueen as a vapor barrier between his sidewall girts and wall steel.

clear-plastic-wrapVisqueen is a brand of polyethylene plastic sheeting produced by British Polythene Industries Limited, and has become a generic description for any plastic sheeting (think Kleenex). Because I know lots of near worthless trivial information, it is important to know Visqueen was first produced about 1950 by the Visking Corporation, a company founded in the 1920s by Erwin O. Freund for the purpose of making casings for meat products. Visking investigated the post-World War II emerging technology of polyethylene, and developed manufacturing techniques to make pure virgin polyethylene film. Originally spelled VisQueen, the film is an excellent moisture barrier and was marketed to many industrial, architectural, and consumer applications, such as moisture barriers, plant seedbed protection films, building fumigation barriers, drop cloths, case liners, and tarpaulins.

Anyhow, in the application above, there isn’t any problem….until the building owner wants to insulate the building walls, then place another vapor barrier on the inside of the walls.

Every Fall, when I was a youngster, my grandmother would make massive quantities of apple sauce, at their lake cabin. All of the wonderful smelling boiling concoction put lots of water vapor into the air of the kitchen. When this warm moist air met the nice cool window glass, it became condensation. The same happens with any surface or material which stops vapor. For example, the painted surface of the drywall will also prevent most moisture from passing through …. which is why higher gloss paint is used in kitchens and bathrooms. If the drywall were not painted, the moisture / vapor would simply absorb into the drywall material. So think of the paint as a type of moisture barrier to protect the drywall.

But vapor can occur even without obvious introduction of moisture into the air. Wherever warm air meets cold air there will be a high concentration of vapor in the area. So wherever the vapor barrier is placed in a wall is where the condensation will occur.
Think of it as a cold and warm weather front meeting inside a wall …. and the forecast is rain.

The condensation held by the vapor barrier will eventually go back into the air once the volume of vapor decreases. This is allowed to happen only if there is good ventilation on both sides of the barrier.

Vapor will penetrate any material in its way until it hits a barrier, this is why it is important to position vapor barriers on the warm (inside) side of walls. When warmer air meets colder air condensation will develop. Imagine the damage to insulation if the barrier was on the outer side of the insulation? Warm air (and/or moisture) would create condensation on the vapor barrier which would eventually absorb into the insulation causing all kinds of water damage and possible mold growth.

Our friend would have been so much further ahead by having used a house wrap between the wall girts and the steel siding, as house wrap is permeable (it allows excess moisture to pass through).

My expert advice would be to slice holes in the visqueen to allow any accumulated moisture to pass through.

 

72 thoughts on “Moisture Barrier: A Bad Place for Plastic

  1. Mike Aimone

    I added a 24 foot extension to my 30x40x10 pole barn, and want to heat the extension for use as a shop. I have begun piecing 1-1/2″ styrofoam between purlins against outer steel walls, and wish to add more fiberglass insulation, using 2×6 studs on 2′ centers between poles, and paneling with OSB. Should I use craft-backed fiberglass, or should I staple a plastic vapor barrier over the glass prior to installing the panels? I also will install some used pole barn steel roofing for a ceiling — how do I install a vapor barrier here? Staple to the truss chords prior to installing the ceiling panels? I will probably blow in insulation above the ceiling, or use used fiberglass batts there, and will do my best to keep the attic area ventilated (although this barn has no eaves, making ventilation more difficult). Any caveats, insights, or direction would be greatly appreciated! Thanks.

    Reply
    1. polebarnguru Post author

      Mike ~ Thank you very much for your questions.

      I would remove the wall steel and install building wrap between the wall girts and steel. After residing, then insulate with your product of choice. If you want to use kraft faced insulation, make sure to overlap the tabs at each framing member, and seal any seams. Many professional installers prefer to use unfaced batt insulation in the walls, then a clear plastic vapor barrier over the inside face, as it is easier to seal.

      Hopefully you have installed a vapor barrier between the roof purlins and the roof steel. If not, then you could use a reflective insulation (see http://www.buyreflectiveinsulation.com) on the udnerside of the purlins. It is again essential to make sure the vapor barrier is sealed tightly. Before using any materials for a ceiling, verify the roof trusses are designed to support the weight of the material being added, as well as any insulation.

      If the trusses have the load carrying capacity, I would recommend using drywall for a ceiling, rather than steel. I prefer blown in insulation for attics, and there should not be a vapor barrier between the ceiling insulation and the conditioned space. If you did not install vented closure strips under the ridge cap, now is a good time to remove the ridge cap and install them. Although they no longer meet the ventilation requirements of the Code (in conjunction with ridge vents), adding gable vents is probably your best solution.

      Best of luck with your project.

      Reply
    2. Kevin Bryan

      We have a 32×36 x12 foot pole barn concrete slab roof has perlins and foil one side white other with metal roof 1 foot all around overhang with soft a and facia we put 7/16osb and used butyl window and door flashing also taped all seams and corners have Kraft faced insulation for walls and ceiling should we use good house wrap on outside as we have a very large quantity of foil faced bubble barrier can I use this as outside wrap or can it be used on inside this is a home it will not have stud walls all walls interior and structure use 6×6 post as the interior doors are all pocket doors

      Reply
  2. Brian

    I have a 30×40 pole building as a garage. I have a double bubble reflective insulation between the metal roof and the purlins with a ridge vent and vented soffits. I want to insulate the walls now that the building has been built and I do plan on heating the building in the winter with a propane heater. I live in Maryland so nice hot humid Summers and cold winters with what can be lots of snow. I want to use Stone wool rigid boards placed inside the building up against the girts. I do not plan on finishing the walls or ceiling of the building and I know the Stonewool will not attract carpenter ants or termites like foam will and will not mold and when it dries out it retains its r-value. My main question is should I use a foil faced version of it and place that foil face facing outwards to reflect the heat radiating from the metal back out? or should I not using any facing so that it breaths? Or put a vapor barrier on the inside after it is insulated? Thanks!

    Reply
    1. admin Post author

      Brian ~ In your walls, the aluminum facing out should help to reflect radiant heat in the summer. If you do not have a house wrap under the wall steel, it would behoove you to remove the siding a wall at a time, add the house wrap, then replace the steel. You will need a vapor barrier on the inside face. If you are intending to use the rigid wool boards against the roof purlins, it will be all but impossible to seal it tight against the roof purlins, and will pose some ventilation challenges. Your best bet (provided the trusses have been properly designed to support the weight) is to install it on the underside of the roof trusses. Do not use a vapor barrier on the underside of ceiling insulation.

      Reply
  3. Matt

    Built a 50 ×80 pole barn.have condesation blanket installed under roof metal.going to put pex tubing in half of barn with a loft overhead and a dividing wall separating unheated half. There is no vapor barrier under metal walls.what is my best option to insulate walls and ceiling under loft on heated side.do not wish to remove steal panels for outside vapor barrier.thanks

    Reply
    1. admin Post author

      Matt ~ As long as your condensation blanket has no punctures and the seams are tightly sealed, you should not have condensation issues from under the roof steel. On the walls, if you are unwilling or unable to remove and reinstall the wall steel, to place a building wrap between the girts and the steel, then you are probably best to use an inch of closed cell spray foam against the wall steel. You can then finish the wall insulation with either batts or better yet BIBs, with a vapor barrier on the inside face. For the ceiling, use unfaced batt insulation if there is a dead air space above (which must be properly ventilated).

      Reply
  4. Mark

    I am finishing my pole building.
    Have 1/2” rigid insulation on the sides between the steel siding and the framing, alum. Facing inward.
    Put 1 1/2 solid on top of that in between the 2×4.
    Not planning to add anything else to the side walls . Then nailing tongue and groove carsiding/shiplap for the walls.
    I have 10 inches of unfaced insulation in the ceiling.
    2×4 running horizontal 24 on Ctr to the engineered trusses.
    Should I use plastic sheeting before drywalling the ceiling or just seal with 2 coats of primer then paint.

    Thanks
    Mark

    Reply
    1. admin Post author

      You should not have a vapor barrier between your climate controlled space and the insulated dead attic space. Make sure to adequately ventilate the attic area above the insulation. If you do not have a vapor barrier on the underside of your roof steel – you should have an one inch layer of closed cell spray foam insulation applied to it, otherwise it will probably rain in your attic.

      Reply
  5. Tami

    We have a 30×40 metal pole barn. We need to keep supplies in the building and must keep the temperature above freezing, so we’ll just have minimal heating. On the inside, we were going to glue 8′ x 4′ polystyrene (foam) sheets (2″ thick). We were told to glue to studs, so it would look like this, starting from outside in. Metal siding, 1″ air gap, 2″ foam board and finish the inside with plastic for vapor barrier. And possibly, a year or 2 later, finish the inside wall with drywall. Does that sound like the correct order to avoid issues down the road?

    Reply
    1. admin Post author

      While what you propose may very well perform as you anticipate, it sounds like a lot of work. I’d probably look into using closed cell spray foam.

      Reply
  6. Tim

    Similar situation as some of the others. Not able to remove siding to add house wrap. Don’t like the idea of using spray foam due to cost and issues if I need to replace a section of metal siding. Was thinking of applying a radiant barrier type of material to posts and gifts (inside) then a 2″ airspace then 3 1/2″ fiberglass insulation. Interior walls would be either OSB or drywall. Garage is 30 X 60 with 30 X 16 area where I’m insulating. 4″ concrete floor. Any ideas besides spray foam?

    Reply
    1. admin Post author

      The radiant barrier (reflective insulation) is a vapor barrier, so you would be sealing insulation between two vapor barriers – not a good choice. If your post frame building has barn style (flat on the exterior of the columns) girts, how about install a thin layer of OSB to the inside of the girts, then spray foam against the OSB. This would not eliminate the investment, however it would give a superior ability to insulate. 3-1/2″ of fiberglass only gives an R-11 about the same an 1-1/2″ of closed cell foam. In the event you do decide to go with fiberglass batts, make sure to place a well sealed vapor barrier on the inside of the system, before application of your interior finish.

      Reply
  7. Ralph Johnson

    Hello, I had a 30′ X 36′ X 12′ pole barn garage built this past summer. I had House Wrap installed on the Walls and Double Bubble with the White Facing installed over the roof purlins and directly under the roof sheeting. What would be the best way to insulated the roof and walls? I was planning to install 6″ fiberglass Insulation with the White Vapor Barrier to the underside of the Trusses using banding and for the walls I was planning on framing in between the post and install regular Kraft Face Insulation and cover with Plywood, But after reading some of these post I am not sure which way would be best. I want to do it right and not have any moisture problems, but at the best cost possible. Can you advise on best method? Thank You

    Reply
    1. admin Post author

      For the ceiling – you do not want to have a vapor barrier between your conditioned area and the dead attic space. The attic must be vented either with a combination of soffit vents (intake) and ridge vent (exhaust) OR (not AND) gable vents. Six inches of fiberglass is something, but probably not nearly adequate. Provided your trusses are designed to support a ceiling, you would be better served to blow 12 or more inches of insulation above a ceiling. On the walls – use enough thickness of unfaced insulation to entirely fill the cavity, then place a clear visqueen vapor barrier on the inside, making certain to seal all of the seams, any tears, etc.

      Reply
  8. Lisa Hutto

    We have a metal building that has double bubble between the metal and frame. It is on the walls and ceiling. The building is heated and cooled. We are wanting to install pine boards to the interior and want to insulate without creating condensation. Any suggestions?

    Reply
    1. admin Post author

      Double bubble is a reflective radiant barrier (assuming it has an aluminum face towards the exterior), it is not insulation. In order to properly complete your building – remove the wall steel a wall at a time, remove the reflective barrier and replace it with a quality building wrap, then reapply the steel. If this is not possible, then the reflective barrier should be cut out of the walls as much as possible. Either BIBs insulation or unfaced fiberglass batts can then be placed in the walls – provided the entire wall cavity is being filled. Place a clear visqueen vapor barrier on the inside of the insulation, making certain to seal all seals and any incidental holes.

      With the guess your “metal” building is a steel covered post frame (pole) building – rather than a true red iron all steel frame building, if your pine boards are across the bottom chords of the trusses, then a dead attic space is being created and it must be adequately ventilated (either by eave and ridge or via gable vents, but not both). Insulation can then be blown in on top of the boards. Do not place a vapor barrier in the ceiling.

      Reply
  9. John

    Hi we built a shop with wood trusses 4 ft on center then finished out the interior with liner steel and blew in 18″ of fiberglass on top of that. Now we’re having bad problems with condensation raining down off the roof steel. Do you have any suggestions on what we could do?

    Reply
    1. admin Post author

      This is a challenge we so all too often when condensation control is not addressed at time of construction. Your solution is to have a layer (typically an inch of so) of closed cell spray foam applied to the underside of the roof steel.

      Reply
  10. Janet Cox

    Have built a home on concrete slab, wood frame with metal siding. Vinyl faced fiberglass insulation was installed between the metal siding and the wood frame with the vinyl facing toward the inside of the house. Now I want to add insulation in the walls and on the ceiling before I sheet rock. Should I use paper faced insulation and face the vapor barrier towards the inside of the house next to the sheet rock in the walls and on the ceiling? The roof also had the same vinyl faced fiberglass insulation installed between the metal siding and the wood trusses. Have soffits and open end vents in the attic. Any advice would be great.

    Reply
    1. admin Post author

      On the walls, the vinyl faced insulation should be removed and replaced with housewrap. Otherwise you will be creating the potential for water vapor to be trapped in the wall between two vapor barriers. For the walls you should use unfaced insulation batts (or even better BIBs) with a clear visqueen vapor barrier on the inside, carefully sealing any tears and seams.

      For the ceiling, since you mention “attic” I will have to guess you are looking at a finished ceiling at the level of the truss bottom chords. If this is the case, hang the drywall then blow fiberglass insulation in on top of the drywall. Do not install a vapor barrier between the ceiling framing and the ceiling sheetrock.

      Make sure to adequately vent the dead attic space (either vented soffits and vented ridge or gable vents – but not both).

      Reply
  11. Bruce Batten

    I am building a 64 x 52 x 16 pole building wanted to install metal liner inside on walls & ceiling. was was going to install single bubble between roof metal & purlins. on the walls put house wrap between metal & girts I was going to use fiberglass R-19 faced on the walls. i was going to use cellulose
    R-38 insulation in ceiling. The building is in Indianapolis. I am going to heat when working in building estimate heating 30 hrs per week and air condition the same in summer. Please help me should I use faced insulation on walls or unfaced should i use plastic sheeting over insulation behind liner metal. On ceiling should I put plastic sheeting between ceiling liner & bottom trusses then put the cellulose insulation. note building will have ridge vent & vented soffit. PLEASE HELP THANK YOU Bruce

    Reply
    1. admin Post author

      Use unfaced in the walls, with well sealed 6 ml clear visqueen on the interior. On the ceiling do not place plastic between the trusses and the liner panels. Make sure to allow at least an inch of airflow over the insulation above the walls, so as to not block the function of the soffit vents. A cautionary note – you may very well end up with condensation on the underside of the ceiling liner panels (it is just a function of using metal liner panels on the ceiling).

      Reply
  12. Mike Mitchell

    Building a 48X30 building attached to a48X48 building. Will put house wrap over purlins prior to the steel.
    Then if I understand correctly, insulate the wall girts and cover with 6 mil plastic before I rock it?
    I was going to insulate with R30 fiberglass?

    Reply
    1. admin Post author

      I will interpret “purlins” to be “wall girts”, if so then placing housewrap between the wall framing and the steel siding would be the correct application. You want to use unfaced fiberglass (no paper kraft or foil facing) and completely fill the insulation cavity without compressing the insulation. Clear 6mil or thicker visqueen on the inside (tape all of the seams as well as any holes), then gypsum wallboard (sheetrock) the interior.

      Reply
  13. IRIS GRUPSKI

    My builder is wrapping the inside walls with plastic and then intents to nail the ship-lap right on top. I am not a builder but I think this will cause condensation that can cause mildew and mold. Am I correct ?

    Reply
    1. admin Post author

      By “inside walls” I will take as being the inside of the exterior walls. If so, then unfaced insulation should be used in the walls, then the vapor barrier (6 mil or thicker clear visqueen typically), then whatever finish material you intend to utilize. If the ship-lap is on the exterior of the wall, it should have housewrap between it and any underlying framing.

      Reply
  14. Trent Rees

    We built a 20×36 pole barn that will be used for a hunting cabin (only heat ac when we are there). Exterior is metal then house wrap, then plywood on studs. We are looking to use old metal sheeting for the ceiling (attached to the trusses) What would you recommend for insulation above the the metal ceiling. (ridge vent & soffit) Thanks for you help.

    Reply
    1. admin Post author

      Provided you have adequate depth at the eave walls – blown in is going to be least expensive and give you the most bang for your investment. If the area close to the walls is too shallow, you could use closed cell spray foam in the first several feet closest to the wall as it will give you about R-7 per inch of thickness.

      Reply
  15. Mark

    We have an existing “pole barn” which is not metal sided. The interior has an office, a full bath and a well room. An interior wall has been covered with knotty pine and the barn itself is permitted as a workshop. The remaining interior wall to be finished is 10′ x 16′, the exterior wall is covered with wood siding and we plan to insulate the interior between the studs and cover it also with knotty pine. The comments I see are focused on metal exterior walls. Ours is wood siding. Should we be installing regular fiberglass insulation with a craft cover (paper) or leaving it unfaced?

    Reply
    1. admin Post author

      Hopefully you have a housewrap between the framing and the wood siding. In answer to your question, you need to have a vapor barrier between the insulation and the interior. If you are going to use fiberglass, I’d recommend unfaced with 6 mil (or thicker) clear plastic as a minimum. The kraft facing is a vapor barrier as well, but only when properly installed, which it rarely is.

      Reply
      1. Mark

        If there is any housewrap, I don’t see it. The exterior walls have wood siding. On the wall I want to finish, I can see the back side of the siding (between the studs) and appears to be simply the back siding of the exterior wood siding. If I proceed with kraft facing insulation, is this going to create more moisure problems, or does the lack of housewrap (if I’m seeing this properly) impact what we plan to do with that wall?

        Reply
        1. admin Post author

          Housewrap allows moisture to pass through out of the insulation cavity to the outside world, while preventing moisture from entering from the exterior (it is a directional product). Lack of housewrap will not change what you do to the inside wall finish.

          Reply
  16. Mark

    I don’t see housewrap under the exterior siding, it’s simply exposed wood (from the back side of the wood siding). On the wall I want to finish, I will do so as you suggested with unfaced fiberglass and 6 mil clear plastic for the vapor barrier. Can I place the black tar paper against the backside of the wood siding before placing the unfaced fiberglass? I’m assuming that will help since there is no housewrap?

    Reply
    1. admin Post author

      Black tar paper is a vapor barrier and you do not want to potentially trap moisture between two vapor barriers.

      Reply
  17. Jim Zahn

    Hello, I have a 24×40 pole building with 8ft oc poles and 2ft oc purlins. I did not wrap the outside prior to putting uo the netal. I have decided to finish the inside and sometimes heat it, I live in northern minnesota. My plan is to use 5.5 in unfaced insulation then 6mil plastic covered with osb sheeting. Will this work or am I going to have moisture problems? Thank you for your help.

    Reply
    1. admin Post author

      Chances are good you are going to have a plethora of challenges.

      Challenge #1 is chances are more than good your roof trusses are not designed to support the extra weight of the OSB you intend to add.

      As you propose to do, you will probably have condensation on the underside of the roof steel.

      Provided your trusses are adequate to support the loads, you need to have adequate ventilation of the dead attic space you are creating – this means having either eave and ridge vents, or gable vents. I’d look at spraying two inches of closed cell foam insulation on the underside of the roof steel, support the OSB with framing between the bottom chords of the trusses, then blow 15-20 inches of fiberglass insulation in on top of the OSB.

      Reply
  18. Chuck Christensen

    I have a 36 x 30 pole barn. Metal sides, no wrap. Will fiberglass insulation with vapor barrier and osb for interior wall cause any problems. I really don’t want to take tin off to wrap, pros / cons.
    Used for storage, boat, tools etc.

    Reply
    1. admin Post author

      Building wrap should be placed between the framing and the siding, in an ideal world – this allows for any moisture which would become trapped in the wall cavity to pass through, rather than condensing on the inside of the siding and wetting the insulation. You might consider rock wool insulation, rather than fiberglass, as its performance is not impacted by moisture.

      Reply
      1. Elijah Bouwens

        I also built a pole barn without a vapor barrier . Plan on putting osb up on the inside. Will rockwool insulation be my best option, without removing outside steel? I am going to frame it out with open studs on top to vent to the soffit.

        Reply
        1. admin Post author

          Mineral (rock) wool insulation is not affected by moisture, so could be a good choice for insulating value. Leaving the studs open on top will create a possible access point for moisture to enter the assembly and create condensation on the inside of your wall steel. Your vented soffit should be used as an intake for the dead attic space, rather than trying for it to be an exhaust from the walls.

          Reply
  19. Trent alm

    Try to be short. 30×50 pole barn. 5′ o.c rafters. No wrap on walls. White bubble between roof and rafters. I thinking walls 1″ closed cell then blow in followed by vapor barrier and steel panel. Plan is to after foam put barrier and steel panel up and then fill the cavity with blown cellulose.
    Sound Correct? For the ceiling I will be using the steel panels with 13″ Cellulose blow in on top. Vapor barrier between panels and insulation? Attic side walls are getting 1″ closed cell and calling them good.

    Reply
    1. admin Post author

      I am not a cellulose fan due it it settling about 20% after installation. Discuss thickness of closed cell spray foam with your installer – normally most like to see a two inch thick minimum. I’d probably look at doing BIBs rather than cellulose on the walls. You do not want to have a vapor barrier between the ceiling panels and the attic insulation.

      Reply
  20. Brent

    I am purchasing a prefab metal garage, 24×36 – the kind with 14ga steel tubular framing and metal siding attached to that. They offer 1/4″ double bubble radiant barrier that was going to cost me a little over $2K and I think I can do much better for less money (or at least equivalent $$). I am concerned about vapor and want to ensure I understand the proper materials and order in which they should be applied. I have been thinking about 1.5″ rigid foam insulation that has foil on one side for a radiant barrier and installing this directly against the steel frame on the inside, the foil side facing out. That would leave a 1.5″ air space between the foil side and the metal siding. Later on I will add OSB sheathing on top of the rigid foam. I was going to do this for walls and the ceiling. Is this adequate or will I be creating a corrosion nightmare?

    Reply
    1. admin Post author

      I am not a fan of the steel tube buildings – I have seen too many of them blown away or collapsed due to snow. Am curious as to why this choice as a design solution.

      If you were constructing a permanent structure, such as a post frame building, I would recommend a Weather Resistant Barrier (like Tyvek) between the wall framework and the steel siding. For the roof, I’d go with Dripstop/Condenstop.

      Double bubble Reflective Radiant Barrier really offers very little over single bubble – except for being much more expensive. You could install either between the framework and the siding or roofing. It only works well if all of the seams are properly sealed.

      Rigid foam sounds expensive and a lot of work. It also would need to be well sealed in order to prevent warm moist air from inside of your building contacting the steel.

      Reply
  21. Dave Callan

    We have a pole barn. There is a 12’x20′ work area that is walled off in one corner, which was never finished. It consists of two exterior walls and two interior walls. I’d like to finish the interior walls by insulating them, covering both sides with OSB. Then om the interior walls of this room, an additional sheeting of fire rated sheet rock. I work with with both wood and metal, so there is a fume extraction arm and a dust collector, both rated at 2,800 cfm’s. And there is a large fresh air return vent with a blast gate, on the opposite side of the room.

    I’m insulating the interior walls of this room to heat it when I only wish to heat the one room, instead of the entire shop. And also to help absorb sound. My concern is the when I turn on either ventilation system in the winter, a rush of cold humid air will fill the room quickly and condensate when it hits the interior walls. I live in Oregon where it’s very humid in winter time, and rains a lot. Some have told me to place a vapor barrier on the inside of the room while other’s say the outside of the room’s walls. And most say not to use any at all. what do you think? Some say it should go under the OSB and sheet rock, and others say between. Everyone says not to use any moisture barrier on these interior walls at all.

    What do you think would be the best bet?

    Reply
    1. admin Post author

      In the decade I lived in the Willamette Valley it seemed as if it rained every day, so I feel your pain. Vapor barrier should go on the inside of the framing, between framing and gypsum wallboard. The purpose is to keep warm, moist air from inside your conditioned room from entering the wall cavity where the moisture could reduce the effectiveness of the insulation and potentially become a cause for mold and mildew growth in the wall. You want to reduce the sources of moisture as much as possible. If there isn’t a vapor barrier under your concrete floor – seal the concrete. It may be necessary to run a dehumidifier inside this room.

      Reply
  22. Neil

    Barn 4×6 posts, wall girts and wood siding. Was thinking of laying in building wrap then installing 1.5″ foam in between girts. Plastic sheet then 1/2″ osb?

    Reply
    1. admin Post author

      With the assumption your building is under construction – Weather Resistant Barrier should be placed on outside of framing, directly under siding. In most cases, girts installed flat on the outside of the columns will have excessive deflection when used with wood siding. You should consult with the engineer who designed your plans to verify girts will be within Code limits. If your idea is for the 1.5″ foam to actually be an effective insulation, you should use bookshelf girts then place a continuous layer of closed cell foam insulation board on the inside of all girts and columns to create a thermal break. Foam should be glued to framing, then interior finish glued to the foam. If the insulation sheets are well sealed, they will act as your vapor barrier.

      Reply
  23. Mark

    We had a building erected. 4’ center. Laminated 2X8 posts. Steel walls inside and out. They put plastic on the ceiling before tinning but the walls they put none. Blown in insulation in the ceiling. Bats in the walls.
    Should we be concerned about the walls. Everything seems to be ok. We heat it to 10 degrees No issues to speak off. Just concerned since there was no plastic or paper installed on the walls.

    Reply
    1. admin Post author

      If the bats are kraft paper faced, then you have a vapor barrier. Chances are little moisture will pass through the steel liner into the walls anyhow.

      Reply
  24. Chris Livingston

    32’X40′ METAL BUILDING WITH WOOD FRAMING. NO WRAP WAS INSTALLED PRIOR TO BUILDING. I WOULD LIKE TO INSULATE WITH ROLL INSULATION. WHATS THE BEST WAY? I WAS PLANNING RUNNING PLASTIC ON THE WALLS THEN INSTALLING FACED INSULATION ROLLS OVER THAT THEN FINISHING WITH OSB? WILL THIS BE OK? SO IT WOULD BE METAL EXTERIOR, WOOD FRAMING, PLASTIC, ROLL INSULATION, THEN THE FACED PORTION OF THE INSULATION, THEN OSB.

    Reply
    1. admin Post author

      Rather than placing plastic inside your wall framing, how about two inches of closed cell spray foam insulation, then use unfaced fiberglass batts. Cover inside of batts with either 6mil clear visqueen or (better yet) two inches thick closed cell insulation boards (glued to inside of framing).

      Reply
  25. Chuck

    Question about the 6 mil plastic vapor barrier recommended to place on inside wall between drywall and interior insulation:
    Wouldn’t that just trap any moisture trying to exit the walls behind the drywall,? Wouldn’t it be better for the vapor to move on through the wall and out?

    Thanks for all your useful information!

    Reply
    1. admin Post author

      The idea of the inside vapor barrier is to keep moist air from inside your building from entering the wall cavity. In combination with properly sealing any openings in the vapor barrier (electrical boxes, around windows and doors), you should have a dry wall cavity.

      Reply
  26. Mark

    Hay Mike,
    I’m converting a metal grain bin into a small home. What is the best way to insulate the walls, floor and ceiling.
    Your help would be much appreciated.
    Mark

    Reply
  27. Tim

    I have a 40x60x10 polebarn in SD that is uninsulated and has a dirt floor. Steel over girts and purlins. I have condensation as you might of guessed. It is used purely for unheated storage of stuff I really should sell. Thinking of installing reflective foam ‘insulation’, similar to the bubble stuff but with 5mm of foam in the middle. Could I just run the foam under the purlins in one flat plain or do I need to individually tuck it up tight to the steel between the purlins in separate pieces? Also is there any performance advantage between the bubble style over the foam?

    Thanks for all of the info you have here!!

    Tim

    Reply
    1. admin Post author

      Thank you for your kind words.

      Whether foam cored, or a layer of air cells, radiant reflective barriers will perform equally well as long as they can be installed so they are totally sealed – no air gaps. I’d venture this will be impossible to achieve without removing the roof steel, placing the barrier and then reattaching the steel. None of which is fun, quick or easy.

      The only real practical solution is going to be spraying two inches of closed cell foam insulation across the underside of your roof assembly. It will not be an inexpensive solution, but it will work.

      Reply
  28. Ken

    Wow.. Awesome info! Don’t see MY scenario however.. HA
    Having a 14×36 prefab ‘shed’ delivered this week.
    We had manufactor apply tydek(?) over osb before attaching t111 siding. This has a roof/Ridgeline vent.
    Plant to run wiring the WAS going to spray foam walls fully.. Was told I am better off spraying only a couple inches of foam to make air tight then add R11.. Also heard about the wool with backing. That backing is vapor barrier, yes? And any insulation I apply over spray foam, backing goes toward foam or drywall? I.. Assumed.. Drywall side.
    It’s barn style, so no attic.. Plan to drill holes with mesh covering, add sheets of plastic or foam vent tubes between a few studs from eve up to ridgeline (SHOULD all have them (between each stud))
    My only quandary, I believe, is how I will enclose the ridgeline vent system before drywall it.
    Thank you in advance!

    Reply
    1. admin Post author

      Your best bet is probably to flash spray two inches of closed cell foam on roof and walls – this will seal off the ridge vent. There is then no need to ventilate, unless you find you are trapping excess moisture inside your shed. Provided you have an adequate depth of remaining framing, you can then fill the balance of the insulation cavities with unfaced insulation, placing a vapor barrier on the inside. Make sure to fill any wall or roof cavities completely with whatever insulation you choose. If you use a faced insulation, “backing” is a vapor barrier which goes towards the sheetrock.

      Reply
  29. Jeff

    I live in Spokane, WA, where we get cold weather and snow all winter and temps into the 90s-100s in the summer. I built a 36’ X 40’ X 14’ shop this past Fall and installed a wood burning stove to keep it warm while I’m out there in the winter. It’s standard pole building construction with horizontal gifts. I used metal siding and roof. I used the standard 3” insulation blanket/ vapor barrier on the walls. The building supply co. I bought my kit from recommended 15lb tar paper on top of OSB under the roof metal. I added R30 exposed batt insulation between the 8” purlins directly under the OSB with 6 mil plastic on the under side/ interior side. I only have a ridge vent with NO soffit or vents down low.
    As the temps are warming up so far this spring, I’m noticing a small amount of condensation inside the plastic vapor barrier (insulation side) in some areas of the open attic area. I find it impossible to completely seal all seams in the attic due to the double trusses and their construction.
    Should I remove the plastic barrier, or perhaps add an attic vent fan or something else? Please don’t tell me to use a closed cell foam or blown in insulation. I will not be using this for living space or adding drywall. Do I need better venting or less vapor barrier, or better seal?
    Thank you in advance for your time and recommendation.
    Jeff

    Reply
    1. admin Post author

      I spent most of my life living in the Spokane area, so am all to familiar with it! Right now you have fiberglass insulation trapped between two vapor barriers – the tar paper on top of the OSB and the visqueen below. The nearly sealed plastic is allowing moisture from inside your building to enter the insulation area and it is then condensing. You should remove the plastic (you could hold the fiberglass in place by using something like galvanized chicken wire).

      If you do not have a well sealed vapor barrier under your concrete slab, you should also seal the floor – as moisture is going to enter your building through the slab. Your ridge vent is an air exhaust – it will let warm moist air escape only when there is a corresponding air intake. You may need to add an equal area of venting lower in your building to act as an intake.

      Your building supply steered you incorrectly on the 15# tar paper, as steel roll formers recommend the use of 30# felt between roof sheathing and steel roofing.

      Reply
  30. Michael Kurtz

    Built a 40 x 80 – 12 foot pole shed in central Minnesota and plan to heat it. i installed 1-1/2 stryofoam board insulation and spray foamed all the cracks so its air tight right next to the exterior steel. Then installed r19 fiberglass insulation next and will be on the warm sid. Should i install a vapor barrier or will I issues with mold? Why to late in the game to install tyvek on the exterior at this point

    Reply
    1. admin Post author

      Do not add an interior vapor barrier, but do make sure your interior finish drywall is well sealed – this means having to spray foam any electrical outlet boxes.

      Reply
  31. Brian bonenberger

    Hello. I’m currently erecting a pole barn in Maryland. I chose not to do the vapor barrier under the steel roof. I’m not planning on heating but cooling half of it for a wood shop. Will I get condensation from not installing the vapor barrier ???? Thanks for all the help

    Reply
  32. Michael Morrison

    Am erecting a wood frame 24’x36′ building with metal siding and roofing. I was planning on using reflective bubble under the wall and roof metal and then using fiberglass insulation between the wall studs and roof trusses. I would then sheetrock the walls and ceilings. Will this work and if so should the fiberglass insulation be faced or unfaced:

    Reply
    1. admin Post author

      You want to use a Weather Resistant Barrier between girts and wall steel, then unfaced fiberglass with a well sealed visqueen vapor barrier on the inside. For the roof, use unfaced insulation at ceiling level above a flat sheetrocked ceiling (or better yet, have it blown in). Attic space must be adequately ventilated.

      Reply
  33. Clark

    First of all thanks for taking the time to share your wisdom – Very helpful! I am in the panhandle of NE. I have built a 20′ x 16′ leanto addition onto the back of my older (1940’s garage). It currently has dirt floors, I have skinned it, roof and siding, with re-purposed steel. The steel goes to the ground, then back filled on exterior. I plan to put 2×6’s around the parameter interior floor and either throw cement or gravel back in this cavity prior to insulating. Eventually (as funds allow) I will pour a cement floor, however not anytime soon. I would like to insulate it to keep some warmth in during the Winter. What would you recommend? Thanks again for the help and take care.

    Reply

Leave a Reply

Your email address will not be published. Required fields are marked *

What will you use your

building for?


Select a building use to get started on your Free Building Quote

Approximate

Building Dimension


A building can be a tough decision. Call 866.200.9657 for a free consultation now!

Your Building. Your Way.

A building can be a tough decision. Call 866.200.9657 for a free consultation now!

Your Building. Your Way.


A building can be a tough decision. Call 866.200.9657 for a free consultation now!

1.866.200.9657
Building KitPrice

Know more about our pricing..

Pole Barn Guru Blog

The industry’s most comprehensive post frame blog.

Ask The Guru

This guru will grant you the answer to one pole barn question!

Pole Building Learning Center

to help guide you in the design of your new pole building

Photo Gallery

Look at our collection of building photos for creative ideas!

Paint Your Building

Lets pick out some colors!