What is high heat ice and water shield, and when do you need it?
Short answer. High heat ice and water shield is a self-adhered roofing membrane made to stay stable at high temperatures, with many products rated to roughly 250 to 260 degrees Fahrenheit, compared with about 200 degrees for some standard versions. It is the right choice under metal roofing and other hot-running coverings, where a standard membrane can soften, ooze or stick to the panels.
Why heat matters under some roofs
Asphalt shingles insulate the membrane beneath them somewhat. Metal panels do not. In a Georgia summer, sun on metal heats it far above the air temperature, and that heat passes straight into the layer below. A standard rubberized asphalt membrane can soften and flow downslope, bleed out at laps, or bond to the underside of the panels.
What can go wrong with a standard membrane under metal
- Flowing. Softened asphalt migrates, leaving thin spots and drips at the eaves.
- Sticking. Panels glued to the membrane cannot expand and contract freely, which stresses clips and seams.
- Odor and staining. Overheated asphalt can outgas and stain.
Where high heat membrane belongs
- Under standing seam and exposed-fastener metal roofs.
- Under metal valleys, wall panels or large flashings that sit in full sun.
- Wherever the roof covering manufacturer requires it.
What to look for
Check the data sheet for a stated high-temperature or in-service rating, compliance with ASTM D1970, and the allowed sun exposure time before covering. Some metal panel makers also specify a slip sheet between membrane and panels. Under ordinary asphalt shingles, a standard membrane is normally enough. More in ice and water shield in Georgia and metal roofing in Georgia.