Matching underlayment to roof type

Hello, I am curious about the proper underlayment is for different kinds of roofs.


Synthetic felt
Granulated I&W
Smooth I&W
High Temp I&W

In conjunction with:

peel and stick roll roofing
architectural shingles
screw down metal
standing seam metal

Is the difference between smooth and granulated I&W that big? In what circumstances is high temp appropriate? It seems to me that the high temp is the most expensive, what is the reason and is it bad to use it with any of the above roofing types?

Any info or guidance to other resources would be very helpful. Googling the issue brings up related information but not exactly what Iā€™m trying to figure out.

Thank you!

Synthetic felt is a replacement for regular felt. It is typically used with shingles.

I&W is used at your valleys, eaves, and rakes of shingle roofs.

There is no real difference AFAIK between granulated and smooth I&W, perhaps the only use I can think of is the granules would prevent shingles or other products from sticking to the I&W as well.

High Temp I&W is designed to be used under metal roofs to withstand the higher temps from the metal in the sun.


Dtris is correct about the high temp i&w , the only difference I know of between granulated and non is on hot days walking on granulated can get a little dangerous depending on the pitch. Kind of like walking on ball bearings