When do you need high temp ice and water shield instead of the standard kind?
Short answer. Use high temp ice and water shield under metal roofing, under copper or other metal that covers large roof areas, and wherever the roof covering's manufacturer requires it. Under ordinary asphalt shingles, a standard ASTM D1970 membrane is normally enough, so high temp is optional there and mostly adds cost.
Required or strongly recommended
- Standing seam and exposed-fastener metal roofs. Metal transfers sun heat directly into the layer beneath.
- Copper and other metal accents. Bay window roofs, porch roofs and dormer roofs clad in metal.
- Metal valleys and large flashings in full sun, if the manufacturer specifies it.
- Any product line that requires it. Some metal panel makers name a specific membrane or demand a high temperature rating.
Usually not needed
- Under standard asphalt shingles, including dark colors.
- In valleys and around penetrations on a shingle roof.
Shingles shield the membrane from direct heat, and shingle manufacturers often require their own standard leak barrier for system warranties.
Roofs that mix materials
Many Georgia homes pair a shingle main roof with a metal porch or bay roof. The practical approach is high temp membrane under the metal sections and standard membrane under the shingles, lapped correctly where they meet. Using high temp everywhere is harmless and simplifies ordering, but adds cost.
A note on panels and membranes
Some metal panel makers specify a slip sheet over the membrane so panels do not stick as they expand and contract. Follow the panel instructions.
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