GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X 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

Minimum continuous insulation thickness vs. fastening requirements

PatriciaCranberry | Posted in General Questions on

Climate Zone 3, central Oklahoma. I’m struggling with my wall assembly detail given the fastening requirements of the engineered wood siding I’m considering. Assembly: 2×6 stud, osb, housewrap, 1.0 inch rigid foam, 0.25 inch rainscreen wrap like houseslicker, 0.375 inch LP smartside panel siding, 0.625 inch smartside trim battens

My builder has very little experience with CI and my siding choice…He is concerned about my siding install over the foam. He has worked with CF siding (much heavier). But I don’t want to miss the opportunity to get it right so I’m searching for a compromise. Bottom line question: If I only went with 0.50 inch of XPS would I still get the thermal break benefits of continuous insulation? By the time the insulation is put between the 2×6 studs I will have no issues meeting R value requirements.

If I reduce rigid foam to 1/2″ the nails for attaching the engineered wood panel siding could be 3.50 inches, still meet the required 1.50 inch depth into the studs. (otherwise 4 inch?)

My only other problem left to consider is how to attach the engineered wood trim as battens. I think the manufacturer allows for the use of nails and construction adhesive if the trim is only used as battens. Any thoughts/past experiences? Thanks

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. user-2310254 | | #1

    Inger. Your proposed strategy is consistent with the LP installation instructions, so I wonder why your builder is so concerned. Are your studs 24 inches on center or 16 inches? If it were my house, I would use 1 x 4 strapping instead of the rain slicker WRB. I would also tape the sheathing and foam layers.

  2. GBA Editor
    Martin Holladay | | #2

    I would urge you to stick with the 1-inch foam rather than reducing the foam thickness to 1/2 inch. If necessary, you should call a rep at LP to confirm that your plan meets their installation instructions.

    -- Martin Holladay

  3. GBA Editor
    Martin Holladay | | #3

    One more point: in your climate zone (Zone 3), there is no minimum thickness for exterior rigid foam. Either 1/2 inch foam or 1 inch foam -- or no foam at all -- can work from a building science perspective.

    That said, thicker foam does a better job of interrupting thermal bridging through the studs. Thicker rigid foam raises the R-value of your wall assembly, lowering your energy bills.

    For more information on these issues, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

    -- Martin Holladay

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |