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What barrier should I use under wall shingles to increase insulation in a single wall cabin?

Callendar | Posted in GBA Pro Help on

I have a 100 year old redwood cabin in Northern California in the coastal area.

It is single wall construction consisting of 1×12 redwood boards and framing visible on the inside, and with cedar plank covered by redwood shingle on the outside.

I am replacing the shingle and will be repairing damaged cedar plank as necessary.

I do not want to turn the cabin into double wall construction with interior insulation as it will wreck the character.

In addition to building paper, what can I use between the ceder plank and shingles to increase the energy efficiency of the cabin?

Please take into account that this old redwood should not be wrapped in a plastic bag as it needs to breath in this foggy climate.

Thank you,

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  1. GBA Editor
    Martin Holladay | | #1

    I advise you to install a layer of rigid foam; polyisocyanurate is the most environmentally friendly foam. The thicker the foam, the higher the R-value of the resulting wall.

    On the exterior side of the polyiso, you'll probably want to install a layer of plywood or OSB. Then you install your asphalt felt, and then you install your shingles.

    Such a wall will be able to dry out in both directions. The shingles and plywood will dry to the exterior; the redwood sheathing and the studs will dry to the interior.

  2. Expert Member
    Dana Dorsett | | #2

    Good recommendation! Adding 1.5" of iso with taped-seams with an OSB nailer for the shingles through-screwed 24" o.c. to the framing with pancake-head timber screws would yield a wall only 2" thicker than where you started, but it would outperform most 2x4 batt-insulated construction due to the air-tightness and low thermal bridging (no framing penetrates through the ~R10 insulation, only screws every 24".)

    Take care to not ruin that with extra-long nails for the shingles- keep them so that they don't penetrate the iso by more than 1/4".

  3. albertrooks | | #3


    If you want to maintain the natural material list, I think Expanded Cork Insulation Board could be a good option for this project. It's apply's like the Polyiso that Martin and Dana suggest, insulates at around R-4 per inch, remains permeable, but is nothing but real tree bark expanded into an insulation board.

    You can read an independent review by Alex Wilson here:

    Our (rather long winded) info page on Cork is here:

    Take care of that old redwood. Your lucky to have it!

  4. Callendar | | #4


    I am intrigued by the cork option. I remember fondly discovering rooms in Portuguese home lined in cork for sound insulation. Many monastries used cork.

    Do you have any idea how it holds up to beetles? Beetle damage is common in the area where I have the cabin in almost any wood except redwood (which fortunately accounts for 80 of the timber in my cabin).

    Is there a really thin material that is efficient, say 1/2 inch thick or thinner?

    If I take all the shingles and then the sheathing off the exterior of the cabin, and start with new insulation and then build up with new sheathing and shingles, I will have to re-trim all the windows or they will all be inset below the level of the shingles. Not an impossible task, but just another added cost.....

  5. Callendar | | #5

    The cabin in question images files attached (may not be reproduced without permission).

  6. albertrooks | | #6


    Yet another incidence of a "small world". I just checked back on this post this morning and found your question. Since I wasn't sure, I checked with Portugal (Amorim) and found that you had made an inquiry yesterday. Francisco (at Amorim) just answered both of us. His reply to the beetle question is:

    "Regarding beetles, historically we have no claims which is a good indicator. The reason might be because when cork when is processed into expanded insulation cork board due only to the action of steam and pressure (we say when cork is cooked) the Expanded Insulation Cork Board will be a carbonized material so there is no cellulose or food available for any bugs."

    The food being "cooked out" is an interesting situation. I like it.

  7. albertrooks | | #7


    I did not answer your thickness question. The thinest panel that we can buy is 1" thick. I've got plenty of 2" & 4" thick on the way and will order some 1.5" thick also.

    For your project, I think I'd go for the extra long term value and put 1.5" to 2" on the walls and re-trim all of it. A thin layer seems like too much work for too little insulation.

    Btw... We can get a higher density cork that is made to be the facade. Perhaps you only re-shingle part of the cabin, and certain "accent area's" are sided with natural cork as the final facade. That could look dynamite!

    Your own monastery in the woods.

  8. Callendar | | #8

    Indeed a small world. And this is the site that helped me find you.
    I was considering using cedar lapstrake below the floor level, and shingle above both for looks and speed of application. It is a traditional look in the neighborhood. Maybe that should be shingle above and cork below (or the other way around for greater insulation value) for an interesting look.

  9. Callendar | | #9

    Or the 1927 bumped out sleeping porch (see right side of exterior photo) could be sided entirely in cork with the rest of the building shingled....

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