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Community and Q&A

Ice & Water Shield Over Roof Underlayment

Shakeyray2000 | Posted in General Questions on

I’m in North Florida.  Just got a lot of my roof done (3/4 plywood to replace rotted planks).  Now I’m deciding on weather to do felt or synthetic (with ice and water on the eaves and valley) , or ice and water everywhere (which is the code here).  I would like something durable for hurricanes.  I’m doing shingles(metal isnt in the budget).  In Miami they fasten synthetic with metal cap nails and then put ice and water over that.  I thought since Miami had the strictest codes for wind I would follow suit but now I’m just not sure if that’s smart.  They do this also so they can remove the ice and water on repairs so it doesnt stick to the entire deck.  I have a gable style roof and am adding ridge venting with continuous eave venting.  Solid brick home.  Which method would be best yall suppose?….I’m just so undecided.  I dont want something inferior since all the trouble of putting 3/4 plywood (I just dont have the money for the metal).

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  1. Expert Member
    Michael Maines | | #1

    I've never heard of fully covering the roof with ice and water shield on top of roofing underlayment. I can see some logic in it but I would rather have the self-sealing, bituminous membrane (I+WS) sealed directly to the roof sheathing, as manufacturers intend.

  2. walta100 | | #2

    The first question that comes to mind is why did the old planks rot? Seems unlikely anyone would live with a leaky roof for the years it would take to rot away solid wood.

    Seems to me the only repairs to be made under the ice and water shield would be rotten wood that gets cut out either way.

    I can’t imagine the wind that would strip fully adhered ice shield from a roof shingles and tar paper often go away at the same time.

  3. GBA Editor
    Kiley Jacques | | #3

    This question has been asked before on GBA. Read through this thread, which begins:

    This is a perfect example of a "new" miracle product or technique becoming so widely used without understanding the repercussions that we will keep the renovators and building forensic inspectors busy for a long time to come.

    While this practice is less problematic with a vented roof, which can dry into the vent cavity, it still suffocates the wooden roof deck and relies on the principle of the "perfect" seal, which works only as long as it remains perfect. If it fails for any reason, then it becomes a moisture trap.

    With an unvented roof, particularly one which cannot dry to the interior such as a spray-foamed cathedral ceiling, it becomes an insidious moisture trap that has a high probability of contributing to roof failure.

    Any structure made of wood is most durable when it can breathe in all directions. Wood can tolerate moisture as long as it can dry.

    1. Expert Member
      MALCOLM TAYLOR | | #6

      Grace I&W does not seem to approve its installation over underlayment. It has to go down directly on the roof deck.

    2. Expert Member
      MALCOLM TAYLOR | | #7


      With all due respect to Robert Riversong, his advice on this hasn't held up over the intervening years. Impermeable underlayments have been the standard for decades. With most roofing there isn't en0ugh upward drying to offset the risk of bulk water intrusion.

  4. user-6184358 | | #4

    I thought in hurricane areas they wanted the roof sheathing joints sealed with tape so if the shingles blow off- the roof is some what water resistant and water damage will be limited. The insurance companies do research - They have a Fortified Building document to show an upgraded construction method.

    1. Shakeyray2000 | | #9

      Yes, I've seen a similar document through FEMA. I'm changing my eaves to 8 to 12 inch too as the FEMA guide outlines. My house has like 24 inch....just too much in high wind.

  5. Expert Member
    Deleted | | #5


  6. Shakeyray2000 | | #8

    Yes, it is code to tape all the seams of the plywood as well. I know I&W does not warranty the roof unless you put it directly over the plywood which is why I question Miami's method. Looks like I'm taping the seams. I&W for the eaves and valleys....and synthetic or felt for the rest with cap nails. It just seems safer. The previous owner lived in the house and it was infected with termites. That's how the planks got destroyed.

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