Several years ago we transitioned from tar paper to synthetic felt. Tar paper is typically used under shingles or siding as a “last defense” to prevent the elements from getting inside of your home.
This was standard and all that was available in my dad and grandfather’s day and my own early career. Tar paper is still the number one seller for roofing underlayment mostly due to the fact that it costs less. One quality of traditional asphalt-based paper is that it tends to shrink after exposed to the sun. Or, on the other hand, if applied in the winter it expands. Either way, this is a problem for us when we lay it all down nicely one day and come back the next day and it looks horrible. When it is applied in the summertime the nails or staples tear from shrinkage and it tends to want to blow off; alternately, in the wintertime, it expands and causes bubbles that telegraph to the finished roofing. We have tried at least 5 different brands of synthetic paper and found titanium to be the best product. Not only does it not expand or shrink, this product makes the roof safer by providing good traction. We can use this for up to 6 months to hold water out of the building until our finished roofing is installed. I wish Grandpa could see this – he might say what he always said in exclamation, “By gum!”