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Community and Q&A

Should I tape the bottom edge of the VaproShield with this wall buildout?

benjamin_wooten | Posted in General Questions on


Where we live (Atlantic Canada) it is not uncommon for drifting snow to pile against the sides of our home in winter.

Our foundation is skinned in rigid foam insulation, and the walls are wrapped down to the foundation in VaproShield (orange frogskin). The interior wall cavities are sprayfoam insulated, so our concern here is not really with air seals.

The exterior wall buildout is as follows:

1. A flange of metal skirt flashing slips behind the frogskin around the perimeter of the foundation (the flashing steps out and down the rigid foam to form a metal cap). The skirt metal flange is nailed to the plywood sheathing, and the seam between the top edge of the flange and the plywood is taped with 3M all-weather flashing tape.

2. 1.5″ thick Roxul Comfortboard IS mineral wool planks cover the frogskin;

3. 1″ thick strapping goes over the Roxul;

4. 3/4″ wood siding goes on the strapping.

The windows are all “innies,” with their flanges in the same plane as the frogskin. The roughly 3 1/4″ deep window cavities will be flashed with metal.

My builder friend and I are debating about whether or not it is a good idea to spring for a couple more rolls of the 3M flashing tape, and tape the bottom perimeter of the house, joining the bottom edge of the frogskin to the metal skirt flashing.

I have read that concerns associated with taping the bottom edge of housewrap (in the event water were to run down the wall and pool behind it) are perhaps overstated, and that the enormity of construction errors, flashing failures etc. would have to be fairly significant for that to be an issue.

The idea for us is reversed: that it might possibly help mitigate any issues arising from the snow backing up under the wall buildout. Seems like it might be overkill, though. Is any extra protection afforded the lower edge of plywood in this instance, were we to tape the edge off? Any extra red flags or concerns from doing this (Roxul wicking up moisture, metal flashing condensing moisture, etc.?)

Any general thoughts/opinions/experience to share?

Thanks everybody!

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  1. GBA Editor
    Martin Holladay | | #1

    I'm not able to visualize what you are describing. I think it's time to make a quick sketch, take a photo of the sketch, and post your photo.

  2. benjamin_wooten | | #2

    Absolutely, and thanks very much for the reply. Attached are three images to illustrate what we've been doing as we lay the skirt metal on.

    My basic general question is whether or not we should trim the VaproShield up 1" or so off the metal skirting (see picture number three) and tape it to the metal?

    After the metal skirt is on, we'll be putting up Roxul batts/strapping/siding on the walls. At the end of the day, the final vertical buildout plane will be proud of the vertical plane of the foundation foam/metal skirting by about 2 1/4".

    When we peeled the VaproShield up to take those photos (North side of the house), we noticed a little moisture beading on the underside of the 3M tape, where it joins the skirt flashing flange to the sheathing. We just had a snowstorm, and there was snow piled against that side of the house for a few days, until about one day ago (it has since melted). That side of the house gets the least sun, and we checked the rest of the tape around the south wall and gable ends... no moisture under the tape there.

    Maybe the moisture we noticed is just from the metal sweating? One side is pressed against the warm wall of the house, and the outside face of the metal is exposed to the cold? Maybe we should just leave the vertical flange of the skirting nailed - and not taped - to the sheathing?

    And, if so, would that impact whether or not we should tape the VaproShield to the metal skirt?

    I hope this helps illustrate things better.

  3. GBA Editor
    Martin Holladay | | #3

    If none of these membranes are part of the air barrier -- and you've said they aren't -- then I would just leave the lap as you have it. I don't see any advantage to adding tape.

    If you're not happy with my advice, and you go ahead and use more tape, I don't think any harm will be done.

  4. benjamin_wooten | | #4

    Advice is exactly what I'm here to get! I thank you for yours, and will happily take it.

    As a followup, should I be concerned at all about the little droplets currently under the tape that joins the skirt to the sheathing? Should we take that tape off?

    We've also been taping the tops and sides of the windows, to keep the VaproShield from ripping away when the wind gets under it (see newly attached image). The wind gets very high up here, coming right off the ocean and up the hill. We found our Dow Corning wasn't holding the VaproShield well enough on its own around the perimeters of the windows. The 3M tape seals it all up wonderfully, and the wind doesn't get under it anymore, however there is a little condensation on the back of the tape in some spots where it stretches from the window flange to the VaproShield, just like the aforementioned places where the metal skirt flange is sealed with 3M tape to the sheathing.

    I wonder if all/most of this wont be eliminated with the addition of the rest of the wall buildout and flashings...

    Thanks very much!

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