GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Wall Envelope for Post Frame Building?

Allan Crouse | Posted in Energy Efficiency and Durability on

I am getting ready to insulate the walls/ceiling in my post frame (pole) garage and wish to get the input of more experienced builders. I think I have the floor installed correctly for our western PA climate; 6″ of 3/4″ limestone on a clay base, covered with a 20 mil vapor barrier, topped with 2″ thick Foamular 250 rigid insulation and pex tubing embedded in a 5 1/2″ slab. I also have 4″ of rigid insulation around the perimeter of the slab (placed between the posts and resting on the base soil and extending 12″ above the floor level to prevent having to place fiberglass against the concrete ).

I didn’t become a student of wall envelopes until after the building was erected so I have metal siding installed directly against the 2×4 wall girts without any building wrap in place. If the wrap is needed I can place it inside the girts and seal it against the posts with a lot of effort. Since the post are on varying centers up to 8 ft I will have to cut fiberglass to the correct lengths for each space.

I have access to 6″ thick fiberglass insulation that is commonly used in pre-engineered metal building walls that can be ordered with varying vapor retarders with perm ratings from 0.02 -1.0, depending upon the facing material. I plan to blow 15″ of cellulose into the space above the ceiling that is vented through the soffit / ridge. Again, what type of vapor barrier is needed for the ceiling. To complicate the envelope even more it is common practice in our area to install metal liner panels on the walls and ceiling to protect the insulation facing from sparks from grinding metal during fabricating operations.

Since the building will not be kept heated continuously I am aware of potential dew point issues as the wall /building heats up from our ambient winter temperatures. I haven’t found any information from insulation manufacturers that directly address these issues.

Thank you all for your patience with my first posting!

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Riversong | | #1

    No vapor barrier required in the ceiling (cellulose manufacturers frown on VBs), but I would install the WRB on the inside of the girts to isolate the fiberglass from the condensing surface of the metal cladding.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |