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Community and Q&A

Flashing tape for roof decking

Steve Young | Posted in Energy Efficiency and Durability on

We build houses for a Habitat for Humanity affiliate in a hurricane prone area along the Texas Gulf coast.
At a program on the FORTIFIED building certification, we saw something that intrigued us. They suggested taping the seams of the roof decking. This would prevent water damage in the event that the shingles were blown off in a wind storm. We started using such materials on the last few houses.
We finished decking and taping our latest house on Tuesday evening, but still can’t get our roofers here to “paper” the roof. On Wednesday, we had a small shower and the roof leaked rather badly. That evening, we received more rain and we had significant puddles in the house. We were not impressed.
So, we were using MFM flashing tape (Window Wrap PSX-20) – 6″ wide everywhere, except 9″ on the hips and valleys. We rolled it into place. The decking is foil-backed OSB, with the rough side up. I am thinking that is our problem. The tape does not stick well to the rough side (Same with the Dow Weathermate that we use around the windows. We get around that issue by making sure that we put the smooth side of the OSB sheathing outward).

Any suggestions on a different tape, technique, or material? At first, I thought about liquid applied flashing, but the horizontal joints on the decking between rafters are too squishy for that, I believe.

Steve Young, Lake Jackson, TX

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    Steve. Check out these results for Martin Holladay's backyard tape test.

    https://www.greenbuildingadvisor.com/sites/default/files/Backyard%20Tape%20Test%20-%20final.pdf

  2. John Clark | | #2

    Some tapes on OSB require a primer. One that may not is the acrylic tape used by Huber with their ZIP System.

  3. Steve Young | | #3

    First of all, thank you Steve and John for your response.
    I have an update. Our roofers still haven't put the roofing underlayment down so I went up and had a look at the tape. It appeared as though it had not been rolled. Perhaps the wide roller that we used did not provide enough PSI to properly adhere the tape. I rolled it again with a 4" roller and it made a dramatic difference in appearance. Half of the roof was re-rolled. I will look at it again on Monday to see if it looks like the adhesion failed again. If we get rain, I will compare the amount of leakage in the re-rolled area with that which was left alone.
    I will let you know what I find.

    Steve Y

  4. GBA Editor
    Martin Holladay | | #4

    Steve,
    OSB is hard to tape. Zip System sheathing with Zip System tape is the best way to go in a hurricane area like yours.

  5. Steve Young | | #5

    Thank you Martin. We looked into the Zip System. It is quite a bit more pricey than the radiant barrier OSB that we are currently using (That radiant barrier seems to work rather well down here). But, otherwise, I believe that it is a very good product and may use it for my own project (but that is for another posting).

    I should give an update on what I saw for the tape this Monday morning. It looked exactly like it did before I rolled it last Friday evening - puffy, with little detail of the texture showing of the OSB beneath. Bummer.

  6. Charlie Sullivan | | #6

    You could consider putting the radiant barrier surface up. It won't work as a radiant barrier there, but it would give you a good surface to tape. Then you can use an extra couple of inches of insulation to gain back what you lost by not having the radiant barrier.

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