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.

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