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Has anybody out there used fanfold insulation as a rain screen gap material?

alumniu | Posted in Green Building Techniques on

I’m wondering if anyone has used 1/4″ XPS fanfold insulation for a rain screen gap and if there are any downsides I should be aware of. This was one of several materials to use in this application suggested in Martin Holladay’s 2013 “All About Rainscreens” article.

Buildup Details:
Plywood sheathing
Tyvek Housewrap
<<– rain screen gap material–>> (wrapped with insect screen)
Fiber Cement Siding

Climate zone 5

I’m leaning towards using fanfold here instead of 1/4″ wood lath for the following reasons:
1. High levels of termite activity in the area (less likely to chew through XPS than wood)
2. Brittleness of fiber cement siding. (The thinner more flexible fanfold material should help prevent breakage if the event of any impact to the siding, such as children running into it.)
3. Price. (corrugated plastic products like Cor-a-vent are much more expensive). I’ve already purchased the Tyvek house wrap so using a different dimpled drainage/housewrap is not an option.


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  1. GBA Editor
    Martin Holladay | | #1

    I know that builders have done it, which is why I included it as an option in my article. I imagine that it works fine.

    The only downside -- a minor one -- is that any rainscreen gap that measures only 1/4 inch deep will remove moisture more slowly from the back side of the siding than a gap that is 3/4-inch thick -- because the ventilation drying mechanism is somewhat less effective. In most areas of the country, however, this difference doesn't matter.

  2. Chaubenee | | #2

    Why don't you get some coraplast "plastic cardboard" which you see the political lawnsigns that litter the landscape are made with? They make 8x4 sheets. Go to the sign shop and see what they will charge you. Cut it into two inch by eight foot long strips and staple it up to the sheathing and nail your Hardin over that.

  3. alumniu | | #3

    Thanks Martin. I think Ill use that technique.

    Thank you for the suggestion. I like the product very much but it's not worth the added cost in my opinion, unless I can shred a bunch of political signs on the cheap.

    1/4" thick 4'x8' sheet sells for about $30/each
    360' perimeter house = 4,320"
    4,320"/16" on center= 270 two inch strips
    4' wide sheet = 24 eight foot long strips
    270/24 = 11.25 (12 full) 4'x8' sheets needed
    12 x $30=
    total $360

    -as opposed to-

    1/4" thick 4'x50' folded sheet = $30/each
    360' perimeter house = 4,320"
    4,320"/16" on center= 270 two inch strips
    50' long sheet = 300 four foot long strips (double stacked for 8' tall) = 150 eight foot strips
    270/150 = 1.8 (2 full) 4'x50' sheets needed
    2 x $30=
    total $60

    Also, since I'm using a fragile siding material, i will probably go every 8" on center which will double those prices.

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