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Community and Q&A

Carpenter ants and foam insulation

Jayne_Torres | Posted in General Questions on

I am preparing to put siding on my tiny house on wheels.  

Exterior wall assembly is:

Hydrogap rainscreen house wrap
1″ R-max rigid foam-sealed seams
1/2″ densglass-sealed seams
2×4 steel framing
R-15 Batt insulation
5/8″ drywall

Question:  I had not planned to seal the bottom edges of the foam/dens glass outer materials in order to let any moisture drain out.  Now, I’m worried about Carpenter Ants having easy access to the foam board for nesting purposes.
Does anyone know of a product that will seal the raw edges of foam board?  
I have spoken with R-max tech department and was told to deal with potential issue by using appropriate insecticides.  Any input, readers?

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  1. Expert Member


    At the least you should wrap the bottom of the foam and cavity with stainless-steel insect screen. A better solution is a perforated J flash like this:

    If you have time I'd call back the tech support at R-Max and tell them they are idiots.

  2. Jayne_Torres | | #2

    In all fairness, the tech guy said since R-Max is foil on both face and back it could be wrapped with foil tape.

    Thanks for the tip. The widest available in that product is 3/4". I need to cover 1". On further inspection, I should be able to tape the bottom edge. Just enough room and pliability to get my fingers up under it.

    1. Expert Member
      MALCOLM TAYLOR | | #3


      I just posted that as an example. You should be able to get any profile you want bent out of perforated stock by a metal shop.

  3. Expert Member
    BILL WICHERS | | #4

    If you have a metal fabricator form perforated sheet for you, I recommend you use stainless sheet. You don’t need very thick material, even 0.020” is ok if you can find it. Stainless costs more but lasts forever. You can use alloys 304 or 316, 316 being most corrosion resistant, or save some money and use 303 which is magnetic, less corrosion resistant, and is commonly used for outdoor electrical boxes.

    Try not to use perforated galvanized sheet. The sheet is galvanized first, then the perforations are punched out. The result is the inside edges of all the holes is bare steel. The galvanizing helps as a cathodic protection system for a while, but eventually the perforated area will rot away and then you lose your insect protection. How long “eventually” is depends on your local weather and soil conditions, but commercially in cooling towers I usually see around 5-10 years — not all that long.


  4. Jayne_Torres | | #5

    Thanks to you both. The perforation diameter at is 1/8". Is this small enough??

    1. Expert Member
      MALCOLM TAYLOR | | #6

      That's what we use. It's big enough to allow good ventilation and drainage, but the only thing I've seen get through it are tiny sugar ants. And nothing stops them.

  5. JC72 | | #7

    I'd still apply foil tape to the bottom edge regardless. Seems like a good idea.

  6. Jayne_Torres | | #8

    Thanks to all. So happy I joined up with GBA. Always get answers.

  7. Jayne_Torres | | #9

    Further, How would I attach the perforated metal??

    1. Expert Member
      MALCOLM TAYLOR | | #10


      If you get it bent to J profile you nail the long leg to the sheathing and lay the rigid insulation and battens into the bottom. The siding then is installed against the short leg.
      Here is a picture of similar flashing without the foam:

  8. Jayne_Torres | | #11

    Thanks, Malcolm. The big hindrance is that the foam is already adhered to the sheathing. I can only get between the two to a small degree...a couple of inches with my fingers. Definitely no way to nail anything to the sheathing. I WISH I had known about the carpenter ant issue prior. I'm going to call the tech guy at R-Max and enlighten him about the insect screen. Definitely a must for exterior application.

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