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Community and Q&A

Sill flashing with exterior mineral wool

Jon_Lawrence | Posted in Energy Efficiency and Durability on

I am getting ready to install 3” of exterior mineral wool and I have attached the installation detail from ROXUL.  They show a typical z-girt flashing, which I plan to create using copper. They don’t show an insect screen between the furring strips, but I will have those too.  Based on things that I have read, I am concerned about carpenter ants getting around the girt and into the ROXUL.  Is this really an issue and if so any suggestions on how to deal with this?

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  1. Expert Member


    Rather than use a drip-flashing and insect screen, we typically use a J-shaped flashing made of perforated material. It should be deep enough to cover both the mineral wool and the furring. Something similar to this:

    That said, carpenter ants are very difficult to keep out. They may bypass the flashing and find a gap between lapped siding, or trim - or even climb up to the roof and enter at the soffits or fascia. The best advice I can give is to keep all planting a foot or so away from your foundation wall, regularly inspect that gap for signs of an infestation, and treat the soil if necessary.

  2. GBA Editor
    Martin Holladay | | #2

    Malcolm gave good advice. Carpenter ants and many species of insects prefer damp environments. The greater the distance between grade and the lowest wooden components of your house, the dryer the wood components will be. So keep the grade low and the plants away from the foundation, and your risk of infestation will be lower.

  3. arnoldk | | #3

    What's the typical recommended distance/height between the grade the lowest wooden component?

  4. GBA Editor
    Martin Holladay | | #4

    Lots of experts say 8 inches (and I think 8 inches may be a code minimum), but I like to see 12 inches or more. Of course, if the house is handicapped-accessible, a high first floor requires a long ramp, so sometimes a compromise is necessary.

  5. Jon_Lawrence | | #5

    Malcolm and Martin,

    Thanks for your responses. I will make sure to keep grade low enough and avoid placing shrubs too close to the house. I am also using Boral for the skirt board and siding, which won’t take on water or provide food for insects. I do want to keep the drip cap as shown in the ROXUL detail which should keep out larger vermin given the small gap between that and the skirt board, but I also like the idea of adding a perforated rain screen cover as Malcolm suggested. I have 4 1/2” of depth between the ROXUL and 2x4 furring, so I would need at least 6” wide material. I was able to find some copper insect screen rolls including the one attached. It may not keep out sugar and or even carpenter ants, but should keep most everything else out. Ironically I am on vacation in Denver now and the store in the link is 15 minutes away, so I headed down there and got a sample which is attached. I figure I can tape this to the sheathing when I tape the drip cap and then once the Roxul and furring strips are attached, I could pull it tight around the ROXUL and staple it to the furring strips. This will allow me to avoid the added expense of Cor-A-Vent at that location, which only comes in 3/4” thickness anyways, so I would have had to double it up or add a 3/4” horizontal nailer to fill the 2x cavity. I am thinking I can do the same thing at the top of the cavity, but just wrapped around the top of the 2x.

  6. Expert Member

    Sounds like a good plan.

  7. Jon_Lawrence | | #7

    Thanks Malcolm.

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