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Community and Q&A

Grace Ice and Water Plus on roof parimeter – but what in the middle?

lookloan | Posted in General Questions on

Hi – I was planning on doing my whole roof with Grace Ice and Water underlayment. One of my lumber yard contacts said he doesn’t understand why builders put more than 3 to 6 feet from the outside parimeter and recommends just leave uncovered wood sheathing in the middle. 

What do others think?  Or what would you put in the middle of your roof if the outside parimeter was just ice and water?  Thanks!

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  1. Expert Member


    Either roofing felt or a synthetic sheet underlayment. Check the installation guide of whatever roofing manufacturer you are using to make sure you meet the warranty requirements.

    Your lumberyard contact should stop giving advice like that. No one has put roofing down directly on the sheathing for decades. Here it is a code violation.

  2. lookloan | | #2

    Thanks Malcom - my original plan was to do the roof with all Grace Ice and Water - I'm thinking t The deck under the roof will be closed cell spray foam. Zone 5 - on one hand I think I will have a tight roof and on the other hand the roof won't breath - not sure if my over doing it will be a problem.

    1. Expert Member
      MALCOLM TAYLOR | | #3


      You won't get any appreciable drying through most ro0fing materials. I don't think it makes any difference whether you use felt, synthetic underlayment, or a waterproof membrane on the sheathing.

    2. Expert Member
      BILL WICHERS | | #4

      Ice and water shield is a “fully adhered membrane” and can be a good thing in some situations, yours being one of them. Less chance of moisture getting in with the membrane there, and the membrane has some limited self-healing ability for small punctures like nails.


  3. Jon_R | | #5

    A fully adhered membrane over the entire roof provides additional waterproofing over non-fully-adhered. A permeable fully adhered membrane is better with wood or tile shingles. There is some evidence that a permeable membrane under asphalt shingles results in slightly dryer sheathing than non-permeable. Enough to make it better than Grace I&W over the whole roof? - not clear.

  4. Expert Member
    Akos | | #6

    Ice and water is used for specific reasons.

    -you installed it where you might get ice dams
    -install it around potential trouble areas (valleys, dormers, goofy roof intersections)
    -low slope areas
    -air sealing roof deck (ie for exposed t&g ceiling with foam over roof)

    If your the rest of your roof doesn't fall into this any of the above, save the money and install a standard underlayment.

    P.S. The presence of closed cell foam underneath doesn't have much to with this. You can completely cover foam with I&W.

  5. Colin63 | | #7

    It will void your shingle warranty go on GAF website and read the warranty card

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