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Community and Q&A

Roof membrane

Dave B | Posted in Green Building Techniques on

Getting set to install aluminium shingle on my new build. The house has a 8/12 gable roof with a complete wraparound porch that is 4/12. The eaves on the porch to the exterior wall is 7′, where would ice and water membrane be installed normally?
The wrap around porch has one valley and 3 hips, would the valley need any membrane?
The detached unheated garage I assume should not need any ice and water?
I have had numerous conflicting answers, so I figure I can solve it here with the expert roofers!!

Thanks for any input
Dave

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Dave,
    The answer to your question depends on your climate zone. The code requirements in the 2018 IRC are shown in the image below.

    1. Dave B | | #2

      Thanks Martin Climate zone 6. Ontario
      Interpreting its says from lowest point of the roof, back to 24" inside exterior wall but in my case I have 8/12 so 36" .
      So all my porch and 36" up from the exterior wall?
      That seems overkill on the 7' of porch then 3' up the main roof? 10' wide of peel and stick?

      thanks

  2. Expert Member
    Peter Engle | | #3

    If the porch is open, it does not require ice dam protection. Ice dams don't really happen on open porches because you don't get the heating from inside the house that melts the water. Also, if the porch roof leaks, it doesn't destroy your ceilings.

    In general, ice dam protection is only required for heated buildings. There is an explicit exemption for detached buildings in the code reference provided by Martin.

    There is some leeway in my interpretation, and your local code people may see it differently. Also, your local codes may differ in their specifics. Always check with local code enforcement when there is an issue of interpretation.

    Also, if the porch roof is continuous with the main roof, you might want ice dam protection for the porch, because of the risk of water backing up and into the house. You might want ice dam protection anyhow, just in case. Water falling from the main roof could refreeze on the porch roof and make a mess of things. It's not a very expensive upgrade.

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