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Old 07-23-2021, 06:58 PM   #6
John Mercier
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Synthetic underlay is meant to ''breathe'', while the Ice & Water Shield is meant to protect areas with a high risk to building ice dams or wind-driven rain.

GAF, IKO, Certainteed, etc will have learning centers on the web to determine what is best in your situation. But with the low slope of a porch roof, I would surmise that wind-driven rain would be a serious consideration even above an unheated space with good air circulation.

It especially gets tricky were unheated space abuts heated space.
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