Tapes, tapes, tapes
I’m about to start putting up continuous exterior insulation on my walls, with seams taped as the primary water barrier (primary air barrier is a membrane behind the foam, though.) Due to supply chain issues, the polyiso foam I ended up with is Johns Manville AP Foil Faced, which is specified for this purpose per their instructions (https://www.jm.com/content/dam/jm/global/en/building-insulation/Files/BI%20Toolbox/BID-0150-Residential-AP-Foil-Above-Grade-Exterior-Walls-9.10.13.pdf)
Referencing the first page of that document, they suggest “Flashing tape such as 3M 8067, Grace Vycor Pro, or Lamatek”
Referencing BSI-067 (https://www.buildingscience.com/documents/insights/bsi-067-stuck-on-you), Joe Lstiburek says: “Most butyl tapes are typically called “flashing” tapes and the acrylic tapes are typically called “sheathing” tapes. The butyl tapes are “thicker” and are “gooey” on the back. The acrylic tapes are very thin. The butyl tapes handle movement better than the acrylic tapes. The acrylic tapes “stick” better – they stick unbelievably well. The acrylic tapes are often used to “terminate” the top edge of a butyl tape. This is necessary as butyl tapes can fishmouth – their top edge peels away or roll away over time – as such their top edge needs to be “terminated”. This type of fishmouthing with acrylic tapes does not occur. Although most flashing tapes are butyl, advances in acrylic technology have allowed a limited number of acrylic tapes to function as both flashing tapes and sheathing tapes.”
3M 8067 is acrylic-based and sold as a flashing tape — apparently one of the “limited number” that Lstiburek refers to?
Grace Vycor Pro is butyl-based and sold as a flashing tape — per Lstiburek, using this tape woudl require terminating the top edge with an acrylic-based “sheathing tape”, though the Johns Manville instructions don’t mention this.
Lamatek appears to be a manufacturer of a variety of tape-related products, not a specific type of tape.
My air barrier membrane is Adhero, and my interior vapor retarder is Intello, so I’ve also been using a lot of proclima tapes — Tescon Vana and Contega Solido Exo — which are acrylic-based and simply sold as “tape”. They’re also pretty expensive.
So, I’ve got foil-faced polyiso (which, according to some of martin’s old articles, is generally one of the easiest substrates to stick to.) The foam manufacturer is recommending an acrylic-based flashing tape, a butyl-based flashing tape, or a manufacturer of tapes. It feels like the Proclima acrylic-based tapes would probably work fine. It also feels like I should use something directly mentioned in the foam instructions so the building inspector doesn’t have any question about it. Of those choices, the 3M 8067 is acrylic-based and thus (per Lstiburek) shouldn’t need any special treatment at top edges — and is also a fair bit cheaper than Tescon Vana. Is this a reasonable conclusion to go with?
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