ASHRAE Journal - October 2011 - 76

BUILDING SCIENCES
The shoemaker’s children are, in fact, barefoot. The message here is obvious: keep things dry and you will not have ants. By the way, keep things dry and you won’t have a lot of other bad things as well. The dry/wet thing with ants is pretty much proving to be the case in all the ant foam infestation cases I (and others) have looked at over the years. My barn foam was expanded polystyrene (EPS). Why did I pick EPS 15 years ago? It was cheap. I didn’t care much about R-value per inch as I was insulating from the outside and I had lots of space and I had lots of experience with installing thick layers of foam on the exterior of wall as- Photo 7 (left): Poly Air/Vapor Barrier. The sheathing tape worked well. The polyethylene semblies. I was a Canadian. We know how had trouble withstanding the construction process. The membrane wrap around the window to do these things. One of my colleagues boxes held up well, except where it was reverse lapped and fishmouthed. Easy to prevent had ants, and his foam was extruded now that we know about the problem. Yes, I know, face-sealed window. I know better polystyrene (XPS). Another buddy had now. They didn’t leak, but I should have known better. Photo 8 (right): Sheathing Tape polyisocyanurate and had ants. I have seen Works. Look at how good this looks after 15 years. That is not new tape; that is 15-year ants in low density and high density spray old tape. Awesome. Note the aluminum C-section at the bottom of the blue XPS capping foams. But only in spots that are wet. The the bottom protecting it from critters. Note how good the untreated wood furring looks. type of foam does not seem to matter. Wet matters. How wet? Really wet. Saturated wet. Or where there is a layer of water trapped between a layer of foam and something else that stays wet for a long time. Flash, drain and ventilate and you do not have ants in foam or anything else for that matter.5 What else did I learn? Some neat stuff. Obvious, but neat nevertheless. Polyethylene sheets make a lousy air barrier, even when supported on both sides. It is just too difﬁcult to get it done right with something so “ﬂimsy.” There were lots of gaps, rips and tears. Original construction defects for sure. Stuff that I missed 15 years ago that I shouldn’t have missed. But, even so, it is not a very “robust” approach. I should have known better. Dumb again. Having said that, the tape used to seal the polyethylene was Photo 9: Insect Mesh. Polypropylene mesh acting as an insect fabulous (Photo 7). In fact the same tape was used to seal sheets barrier is installed between the furring strips at the bottom of of XPS together on the main house and performed fabulously there the wall. This particular mesh typically is used in attic ridge vents as well. I opened up a bunch of spots on the main house to check to keep bugs out of roofs. adhesion and after 15 years the sheathing tape was like new (Photo 8). There was nothing wrong with the main house; I just needed strip (aka, “ﬂashing tape”) with a sheathing tape. The technical to know. I really, really needed to know. I have been ﬁnding this to term for this is “terminated”—as in “fully adhered membranes be the case pretty consistently in other projects that I have opened that are reverse lapped need to be terminated at their top edges.” up, as have others. Sheathing tapes are proving to work over the Guess what? No bees. Say what? Yup, no bees in the air gap long term in terms of sealing XPS joints, foil-faced isocyanurate behind the siding. After 15 years absolutely no bees, wasps, board joints and joints in housewraps/buildingwraps. or critters of any kind anywhere behind the siding. For years, However, membrane strips or membrane tapes are a different decades actually, I have been hearing the argument that vented story. They tend to pull away from surfaces over time; they “ﬁsh- cladding systems are prone to insect infestation. And for years, mouth” if they are not sealed at their top edge with a bead of sealant decades actually, I have not been ﬁnding that to be the case. or if they are not “taped” at their top edge with a sheathing tape. Here is the caveat: don’t leave the air gap completely open at the As strange as it seems, I like to tape the top edge of a membrane bottom or at the top. Check out Photo 9. I used a polypropylene
5 OK,

a few other minor points, don’t run your foam into the ground. If you do, you will have ants even if it is dry because they love the pathway. Even with borate treated EPS foam. The borate keeps the ants out of the EPS foam but not out of the gap between the foam and the foundation wall. You can break the pathway and make this issue go away by capping the joint at the top to the foundation wall, or not run the foam into the ground and now you don’t have the pathway. This is also effective with termites: the “don’t run the foam into the ground” part.

ASHRAE Journal

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October 2011

ASHRAE Journal - October 2011

Table of Contents for the Digital Edition of ASHRAE Journal - October 2011