Moisture Barrier: A Bad Place for Plastic

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.

 

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

  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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 two inches or more) of closed cell spray foam applied to the underside of the roof steel.

      Reply
  10. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
  34. I have a 28×32 typical pole barn, bubble insulation between roof panels and trusses. No wrap on outside between metal and girts. Unwilling to remove metal walls to install wrap. Only plan on A/C and heat intermittently. My plan is to use rock wool between 2×3 studs and vapor barrier under osb interior walls. I’ve read previous replies and think this is correct method……am I right?

    Reply
    1. I would suggest you use two inches of closed cell spray foam insulation on the inside of your wall steel, this will eliminate any possible condensation on inside of siding. Rock wool is a good wall insulation choice because it is unaffected by moisture. Make sure to well seal your vapor barrier and use a can of closed cell spray foam to seal around any electrical boxes.

      Reply
  35. We built a traditional metal pole barn and do not have house wrap under metal siding. There is double bubble on the underside of the roof. We will have horses in the barn, which create moisture by breathing, and create heat. I would like to put insulation on the walls to help the temperature in the barn by a few degrees. The barn will not have AC, but the horses emit heat and I may turn on a heater when trying to stay just above freezing. Can we insulate with foam board panels or will we have moisture problems without the house wrap?

    Reply
    1. The problem with foam board is it is impossible to perfectly seal it between girts and alongside posts, so warm moist air is going to get through and condense on the inside of your wall steel. I’d suggest using two inches of closed cell spray foam insulation on your walls – you will get roughly R-13, it completely seals any voids and it will be an excellent vapor barrier.

      Reply
    1. Other than in extremely cold climates the IBC (International Building Code) does not allow vapor barriers on the warm side of an unconditioned attic space. The idea is for moisture to escape into the attic and be exhausted through passive attic ventilation.

      Reply
  36. I have a 32×48 pole barn. There is a blanket between the roof steel and the trusses. There is no blanket between the sidewall steel and the purlins. I have no plans to remove the steel and do so. My plan is to finish off a 32×24 space, studding out the interior walls, install faced insulation, cut slits in the paper facing, then install a vapor barrier, before finishing off the walls. For the ceiling I had planned to place a vapor barrier before using steel for the ceiling, then blow in insulation. Any ventilation in the attic space would probably come from vents on the ends. Was wondering if the 32×24 space is finished off and closed in, does the attic space need to be closed in at the end of my 24 foot space? Or do I need to button up the truss at the end of the finished space or can I leave it open, which means cold or hot air will invade the space above the finished off space. Thanks

    Reply
    1. If you do not have a Weather Resistant Barrier between wall steel and framing, might I recommend you do two inches of closed cell spray foam, then use unfaced batts (or better yet BIBs) and then a well sealed interior vapor barrier. Unless you are in the extreme north, you should not install a ceiling vapor barrier. Code requires you to have a fire separation between living area and garage, so you will need to run drywall up to your roofline. Ventilation for above your living space could be a challenge as you need at least 369 square inches of net free ventilation in the top half of your dead attic space.

      Reply
  37. Building a 50×50 metal garage in Florida where the humidity is 90% most of the year. I want to condition half of the space and use a radiant barrier which is perforated to allow the moisture to be carried away in the 2″ air gap between the metal siding and the outward facing reflective foil. Was planning another air gap and then a visqueen vapor barrier and OSB interior siding. I believe that using a gable-mounted exhaust fan will carry away heat and moisture through the air gaps because of the perforated surface of the radiant barrier. If it doesn’t work I plan on using 1-inch foam boards between the visqueen and the OSB. A white metal roof and the radiant barrier will handle 98% of the solar heat and 10 mil visqueen below the 4″ concrete slab should restrict moisture. Was planning on a lay-in ceiling on the conditioned space with the gable fan venting attic heat. I’d use house wrap (Tyvek) if I could fit it. Do you think I should use a more aggressive layer of insulation?

    Reply
    1. admin Post author

      Hopefully your reflective radiant barrier will work as you expect it to. Consider using a rock wool insulation for the walls, such as Roxul as it is not affected by moisture. Make sure to completely seal the visqueen vapor barrier at the inside of the walls. As you are going to insulate at the ceiling level, use vented eave overhangs and a vented ridge to provide attic insulation and remove warm moist air from inside. Consider a dehumidifier in your conditioned space.

      Reply
    2. I have a 40 x 60 metal building with sag and bag insulation (fiberglass with vinyl facing) between sheet metal and purlins on ceiling and walls. I’m wanting stud it in and Sheetrock the whole interior with additional insulation. I’m concerned the dead air space between The two layers Of insulation will create moisture problems. Any suggestions? Thank you. PS in central Arkansas.

      Reply
      1. admin Post author

        You are right to be concerned. On the walls the metal building insulation should be removed, or cut out to avoid trapping moisture in the wall. If you are insulating the attic at ceiling level, you can leave it in place to prevent condensation on the underside of the roof steel, however you need to insure your newly created dead attic space will have adequate ventilation https://www.hansenpolebuildings.com/2018/03/adequate-eave-ridge-ventilation/

        Reply
        1. Could the sag and bag on the walls be left in place with cuts or perforations to allow air exchange. Then use paper backed roll insulation between studs? This would still leave air space between outer walls and inner walls but provide for air movement.

          Reply
          1. admin Post author

            By “sag and bag” I will guess you are referring to vinyl faced fiberglass metal building insulation. If so, you will want to perforate it significantly. I would recommend either unfaced batts, or even better BIBs – filling the insulation cavity completely. Cover the inside with tightly sealed clear visqueen.

  38. I have a 36×60 pole barn that we are enclosing and turning into a shop. We will be spray insulating the walls and ceiling. I will then be finishing the inside with some 26 gauge tin. The shop will be heated with forced air heat. A wall divides the barn into two areas. One side will be finished with tin on the walls and ceiling and the other will just have the walls finished. Do I need the vapor barrier installed on the walls and ceiling before the tin is installed or just the walls since the ceiling is being spray insulated? Thank you!

    Reply
    1. admin Post author

      If you are using closed cell spray foam in the walls, then you would be best to use a Weather Resistant Barrier on the inside as it allows moisture to exit the wall into your conditioned space. You should not have a ceiling vapor barrier. You should have a dehumidifier incorporated with your HVAC system.

      Reply
  39. hi, i had a 24x40x10 metal pole bldg installed in PA. tyvek housewrap all sides on top of the framing under the metal. continuous metal ceiling in 40′ sheets with 8″ blown in insulation on top of that. roof insulated under metal with bubble insulation. full soffit and ridge vents. thick plastic under 4″ concrete slab with 3″ of gravel under that. plan is to have some heat source, either pellet stove or wood at some point. was planning on studding in between the 8′ OC wooden posts and insulating with fiberglass. i will finish the walls inside with a variety of wooden material, plywood, ship lapped paneling, etc. the question is to use either faced or unfaced in the stud bays. i was thinking faced but am not so sure reading other answers.

    Reply
  40. Built a 22×40 pole barn, bookshelf framing, 2′ OC trusses. OSB on roof and exterior walls covered with tyvek before the metal siding and roof. Ridge vent and fully vented soffits. interior area of building we put R19 faced in the walls and R38 faced in the ceiling and plan to finish the interior with metal on three walls, back wall will be OSB covered with FRP (kennel/dog area). Do we need a plastic vapor barrier. I’ve read all the comments here and I’m frankly not sure. Amish builder says No to interior plastic as water will get trapped between plastic and underside of metal? HELP, we’re at the next step.

    Reply
    1. Your AMish builder is correct, but not for the reason he believes. The kraft facing on your insulation serves as a vapor retarder, so adding visqueen is redundant.

      Reply
  41. Have a 36 X64 X 16 sidewall. Common trusses 4ft OC on 32ft and scissor truss 2ft OC on the remaining 32 ft. Will be building a loft studio under the scissor truss section (36×21) using 24ft ijoists cantilevered over steel I beam. I have fully vented soffit and full ridge venting. There is no wrap on building. Will be drywalling ceilings. Would like to drywall walls between posts on 2 walls leaving posts exposed, is this a bad idea? What is best way to insulate the floor, wall, ceilings? Located in Michigan’s Thumb.

    Reply
    1. If you have to WRB (Weather Resistant Barrier or WRB) under your siding, you would be best to spray 2″ of closed cell insulation on the inside of your siding, then use BIBs or unfaced batts to fill the balance of the wall cavity. Do not use a vapor barrier on the inside so wall can dry to inside. Blow in attic insulation (I would go R-60). Insulate between your I joists with batt insulation.

      Reply
  42. I have a 50’x75’ metal building that we are making into a house. 3” fiber insulation with vinyl backing and radiant barrier was installed under metal panels on roof and walls. I plan to add 5.5” of rockwool insulation to roof between 8” z purlins and strip with wood directly to roof purlins, no air gap or attic space. Walls have been studded and plan to add rockwool as well. Do I need another moisture barrier on bottom side of roof and on interior side of walls?

    Reply
    1. You do not want another vapor barrier in your system as it will potentially trap moisture between the two. As long as your vinyl backing is well sealed without perforations it should take care of potential condensation issues on the interior face of the steel cladding.

      Reply
  43. Built a new pole barn that I plan on finishing the interior. I have tyvek on the walls between metal and girts. On the roof I put double bubble between metal and purilings. Question is when I hang my interior metal on ceiling should I install a 6mil plastic?

    Reply
    1. Plastic vapor barriers should only be installed in vented attics with more than 8,000 heating degree days – so unless you are in the ‘Great White North’ the answer is probably no.

      Reply
  44. I have a 30×40 Pole barn gambrel roof with OSB roof sheeting. There is no wrap between the metal siding and the girts. I am planning on insulating the sides and roof and heating for winter. I am looking at utilizing fiberglass insulation with an attached plastic vapor barrier. Should I place a house wrap between the insulation and the metal siding? I live in Michigan, and with the major fluctuations in temperature, I’m concerned about condensation between the siding and insulation. Also, What would be the best way to insulate the roof? Would I have to add baffles for air flow between the roof deck and insulation?

    Reply
    1. Pretty tough to add a Weather Resistant Barrier to your walls without removing and reinstalling the siding. I’d recommend two inches of closed cell spray foam to the inside of your wall steel, then unfaced fiberglass batts without an interior vapor barrier – this will allow your wall to dry to the inside. For your roof system, if you are insulating with dead air between the insulation and the roof deck, you need to have adequate ventilation above the insulation.

      Reply
  45. New post frame building in central Minnesota. No WRB between the steel panels and girts. You have indicated spray foam as an option followed by non-faced fiberglass and no vapor barrier. If the spray foam is not an option, can non-faced fiberglass batts be installed into constructed walls between columns then a poly vapor barrier before sheet rocking the interior? Can house wrap be installed between columns before constructing the wall before placing batts in to prevent the fiberglass from touching the steel that is likely to condensate with no WRB? I understand it will be a lot of work…looking for options without tearing down sheeting to install wrap or hiring someone to spray foam.

    Reply
    1. Minnesota is split into Climate zones 6 (south half) and 7 (north half). IECC Code R value requirements for wall insulation are 20+5 or 13+10, where the 1st value is cavity insulation, second is continuous. In order to meet Code, your only option is closed cell spray foam with unfaced batts and no interior vapor barrier.

      Reply
  46. I have a 30×42 pole shed with no WRB on the walls or roof, the back portion of the shop (12×30) is walled off and insulated -walls are 1.5″ unfaced foam boards in between the girts and the ceiling, from what I can tell, appears to be rock wool type insulation placed between the purlins with a vapor barrier on the bottom of the purlins running across the roof stapled to the bottom of each purlin. the vapor barrier also appears to have crosses cut into it every so often as a vent? This room is heated with a propane heater and everything appears to be very dry and it stays wwaaarrrmmm. it has also been this way for 26 years for the previous owner and no signs of condensation, mold, or other issues) The front portion (30×30) has the walls insulated between the girts with RTech 1.5″ foam that is faced on both sides (reflective side facing inward) and nothing on the ceiling. This room will be heated with a vented 75kBTU LP gas unit heater. My question is what would be the best way to insulate the ceiling? do the same thing as the other room and stuff rockwool between the purlins and staple a vapor barrier to the bottom across the shop? I know closed cell spray foam is probably the best option but what are some other options? without removing the roof steel etc. Thank you!

    Reply
    1. I would do two inches of closed cell spray foam (roughly $2600-2700) and call it a day. Trying to place insulation board between purlins would be hugely labor intensive (plus the material is not free) and such a chore attempting to get any sort of an air tight seal.

      Reply
  47. I just had a 30x32x12 pole barn built and unfortunately no body sed any thing about vapor barrier! I guess thats on me! Do you think I can add the vapor barrier [ tyvek ] directly to the inside of the metal over top of the girts, rather then between the metal siding and girts? Also I will be putting a celling in, so would it be ok to use some kind of reflective insolation next to the bottom of the roof so moisture doesn’t rain down on the celling insolation? If so what is the best reflective insolation or other solution for under side of roof? I don’t think spray foam insolation would be something I could afford! Thank you for your comments.

    Reply
    1. No – it isn’t on you, as you cannot know, what you do not know. IMHO there are too many providers and builders who are selling on a low price, rather than trying to actually provide the best building possible for their clients. For your roof, the only true solution is to do two inches of closed cell spray foam on the underside of your roof deck. Make sure they do not seal off your vented eaves and vented ridge. Anything else will be virtually impossible to achieve an adequate seal and to do nothing (or try a vapor barrier at ceiling level) will result in wet attic insulation. Plan on investing roughly $2000 for this. On your walls, about your only cost effective choice will be to use unfaced batts – totally filling the insulation cavity, then a vapor barrier on the inside.

      Reply
  48. I have a 24×30 carport type metal building. On the roof trusses it has half inch foil faced foam board, foil side to the inside of the building screwed to the trusses but not sealed where the sheets meet. There is a couple of inches air pocket between the foam board and metal roof. There is no ridge vent, soffit vents only a power vent fan mounted in the gable below the foam board. Should I seal the seams of the foam board and do I need to add soffit vents or ridge vents to vent the air pocket or is it not enough space to worry about? Just trying to prevent condensation in the building. The walls have osb board on the inside and roughly half the walls have 1 inch foil foam board sealed with about a 1 inch air pocket between the foam board and metal siding. Planning to foam board al walls. Nothing in between the foam board and Osb board. The floor is cement and isn’t cooled but has a ceiling mounted electric heater. Just need advice on what to do.

    Reply
    1. Without the roof foam boards sealed, there is a potential for condensation to occur. I’d suggest sealing the seams, then watch to see if you are getting condensation above it (it should drip out the bottom edge at the eaves if it is). If you are getting drips, then vent eave and ridge. If you do not have a well sealed vapor barrier under your slab on grade, seal the top of it.

      Reply
      1. I also mentioned to ask if I did seal the foil foam bod would I b better off to just remove it from where it is and install i directly to the roof metal eliminating the air pocket all together? Would that be better to to control the condensation or just seal it as you said and if it does sweat just vent the race and ridge? Thanks for the answers.

        Reply
  49. We have a small metal storage metal building converted to a cabin. It has a bubble wrap insulation against the metal, then we applied r13. We are noticing condensation. We have a ventless propane heater and 2 vents in the rafters. Can you suggest anything to rid of the condensation?

    Reply
    1. Seal your concrete slab, use a heat source other than propane and mechanically remove moisture from the air.

      Reply
  50. I’m building a 60×112 shop with insulated, radiant heat floor (though I’ll probably only heat to 55 or 60 degrees). I plan to install house wrap under the steel on the walls and plastic vapor barrier on the interior with batt insulation (bookshelf construction).
    For the roof, I’d like to put a paper under the roof steel on top of the purlins to catch condensation and/or incidental water infiltration. What do you recommend, or do you recommend something else?
    I will use blow in insulation in the attic. I’ve read you recommending no vapor barrier above the ceiling/below the attic insulation. Why? Also, why the recommendation for drywall vs. steel on the ceiling?

    Reply
    1. Condensation is caused from warm moist air in your building rising and coming into contact with the cooler roof steel (or any non-insulated barriers in contact with the steel), so it is impossible to ‘catch’ it. I would recommend using roof steel with a factory applied ICC https://www.hansenpolebuildings.com/2020/09/integral-condensation-control-2/.

      You will want to order raised heel trusses in order to get full advantage of your blown in insulation.

      See jlconline.com/how-to/insulation/q-a-ceiling-vapor-barrier-yes-or-no_o for an explanation from the expert on building envelopes for the ceiling vapor barrier.

      IMHO steel ceilings are relatively expensive, the reflect noise and can have condensation on the underside. 5/8″ Type X drywall provides fire resistance, it absorbs sound and is cost effective.

      Reply
  51. I have a 36×64 shop/ apartment with 14″ sidewalls, scissor trusses in the back 24′ area. The walls and roof were sheeted with 7/16 O.S.B. prior to the steel siding and roofing with no Tyvek. Radiant heat. I had the walls sprayed with 2″ of closed cell foam. I have a ridge vents and plan to cut in soffit vents.
    I plan on additional fiberglass bats for the walls. Should i use a faced insulation? My other question is; what is the best way to insulate and combat condensation in the ceiling/roof area? There will be a living quarters in the area with the scissor trusses.
    This is located in northeast Wyoming.

    Reply
    1. admin Post author

      You want to use unfaced batts in the walls – otherwise you are trapping insulation between two vapor barriers. I would recommend using rock wool as it is not affected by moisture. With proper attic ventilation and OSB under the roof steel, attic condensation should not be an issue. Hopefully you used trusses with raised heels so you can blow in full insulation depth from wall-to-wall in your attic.

      Reply
      1. Thank you for the information. Unfortunately i do not have raised heel trusses. I think i have about 10-12″ of height in the trusses. Would i want to use a vapor barrier on the ceiling? would it be best to place it below the insulation prior to installing the drywall?

        Thank you again for your time and expertise.

        Jim

        Reply
  52. I am having a 32x40x12 post frame garage built. There will eventually be a concrete slab with radiant heat tube through it. I live in Pennsylvania, cold winters and hot humid summers. I plan on finishing the interior walls and ceiling with metal. There will be 40′ of Ridge vent, and vented soffit on all four sides of the 1′ eaves. I’m not getting good feedback from the builders, aside from saying they can use Tyvek on the girts before the wall steel. Can you suggest how I should insulate/seal walls, ceiling, and roof? I’m open to any form of insulation, vapor barrier, foil, whatever. Thanks for your time.

    Reply
    1. admin Post author

      THis will meet IECC requirements: Insulate perimeter of your slab down four feet with R-10 rigid insulation. Use same under your slab on top of a well sealed vapor barrier (I prefer 15mil, however 6mil meets code). Walls – Tyvek (or similar WRB) between girts and wall steel, then faced batts or unfaced batts (minimum R-20) with a well sealed R-5 rigid insulation board on inside on inside. Ceiling – 22″ raised heel trusses with R-60 blown in fiberglass. Order roof steel with a factory applied Integral Condensation Control (Dripstop or Condenstop).

      Reply
  53. I am considering buying a metal building to use as a cabin 24×40 it will be used on snd off throughout the year heated in winter cooled in summer. What kind of moisture barriers should I have installed, and what type of insulation should I use. Any direction would be appreciated.
    Thanks

    Reply

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