Tag Archives: visqueen vapor barrier

Vapor Barrier for a Ceiling

Reader GEORGE in LOUISVILLE writes:

“I am looking to install tin on the ceiling of my 54 X 75 pole shed. I was wondering if 6 mil plastic sheeting with all seams taped would work for a vapor barrier? My concern is not to have it rain in my building after the tin is up and the heat is on.”

Mike the Pole Barn Guru:

Well George, this answer is not going to be nearly as simple as your question.

Prevention of internal rain (condensation) is going to be a function of several aspects.

#1 Controlling source – if there is not a well-sealed vapor barrier under your concrete slab on grade, you should be planning on two coats of a good sealant for it. If you do not know if there is a vapor barrier under it or not, leave a wrench on it overnight. Next day, pick the wrench up and if there is a dark place on the floor surface where the wrench was, you have no under slab vapor barrier.

#2 Source of heat – some heat sources add significant amounts of water vapor into your internal air (propane being a prime offender). Know what you are getting into before it becomes a challenge you do not want.

#3 How are you currently controlling condensation? If your building has a thermal break between purlins and steel roof – excellent. If not, your best solution is going to be two inches of closed cell spray foam applied to the underside of roof steel. This is not an inexpensive solution, but it is more practical than removing roofing, adding a thermal break, and reapplying roofing (plus roofing never goes back on as well as it was originally installed). Plan on $4000 to $4500 for closed cell spray foam.

vented-closure-strip#4 Ventilation – you are going to create a dead attic space above an insulated ceiling. If it is not adequately vented you are going to have problems. Best combination is vented eaves and ridge. Your building will require at least 1944 square inches of net free ventilation area (NFVA), distributed equally between eave and ridge. If this is not possible (building has no sidewall overhangs), then your choice is limited to gable vents and it will take many of them to provide adequate NFVA.

#5 You are in Climate Zone 5. This means a Class I or II vapor retarder is required for the interior side of framed walls. This could be 6 mil polyethylene (Visqueen) or Kraft-faced fiberglass batt insulation. For your ceiling a plastic vapor barrier should only be installed in vented attics in climates with more than 8,000 heating degree days. In Nebraska, heating degree days for a normal year is 6322.

Mixing Tyvek and Radiant Reflective Barrier

Mixing Tyvek and a Radiant Reflective Barrier
Reader JOHN in PENNSYLVANIA writes:
“Hi, My name is John and I have been reading the blogs and questions from prior customers.  However I have one of my own that has not been asked or that I can see has been answered.  I my pole barn I am putting Tyvek barrier between the outer metal siding and the horizontal 2×4 girts going from post to post.  I am insulating my building as I am making it into a butcher shop at some point.  I want to put the double bubble foil on the interior side of the girts, however I do not know if the Tyvek barrier would overheat in the summer and cause a fire or shrink.  Have you seen anyone do this and would you recommend it.  The reason I want to use the double bubble foil wrap inside is to reflect the radiant energy away from the parts of the building I want to keep at a constant 40 degree temp without having to super insulate everything.  I planned on using a r-30 insulation or blow it in like you guys suggest on your web site.  Any help would be appreciated.  Thanks.”
In my humble opinion, what you propose should not harm the Tyvek, however there are some other considerations.

Mike the Pole Barn Guru answers:

First – a reflective radiant barrier is a vapor barrier. You are creating a cavity in which moisture will be able to be trapped between two vapor barriers in your wall – not a good choice.

Second – the reflective radiant barrier is defeating the purpose of the Tyvek – which is to allow any moisture in your wall to pass through to the outside.

Reflective InsulationThird – if you insist upon using the reflective radiant barrier, single bubble will do everything double bubble will, at less cost.

My recommendation for your walls is to install another set of girts flat wise (barn style) on the inside of the columns. Use BIBs (https://www.hansenpolebuildings.com/2011/11/bibs/) to completely fill the wall cavity with insulation (the money you save from eliminating the reflective radiant barrier will pay for it). Install a clear visqueen vapor barrier on the inside, then your choice of interior finishes.