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

ZIP roof sheathing, plywood + Blueskin for walls?

woobagoobaa | Posted in General Questions on

Driving by a new zone 5 build today and noticed this sheathing combination.  Roof looks to be 5/8 ZIP with taped seams.  Exterior walls are plywood + Blueskin.  If I trust ZIP system for the roof sheathing, why the extra time and materials for plywood walls + Blueskin?

Shear strength?

Last year I was following a Cape Cod shoreline build that did ZIP for roof and walls.


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. Jon_R | | #1

    For a roof (unvented, vented or attic) the low vapor permeability of Zip doesn't matter. Many walls depend on the perm ratio for drying.

  2. user-5946022 | | #2

    Because if the framers don't properly apply the zip tape at the roof, it will be evident at first rain. Also, some cheap builders apply shingles directly over zip without sheathing.

    At the walls it is far more difficult to get the framers to apply the zip tape and to properly roll the tape. The zip tape is applied by the framers. Then the electrician, plumber, HVAC, gas, pest deterrent system and whatever other sub come in and poke holes all over the siding. Far better off to sheath it, have all the trades do their work, then hire a real waterproofing sub to come in and apply the Blueskin. They can run the blueskin over the top of the sheathing and to the top plate, seal around the penetrations, etc.

  3. ohioandy | | #3

    Might be because of something as mundane as market fluctuations--where I am, OSB (and prsesumably ZIP) has doubled in price in the last month. Maybe the switch to plywood was an on-the-fly cost decision. Or maybe the kickback understandings got complicated. If you try to figure out a build from the street, you've got hours of speculation. I do it all the time!

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |