We hear all too often that “my other contractor told me my roof leaked because the tar paper failed”. While this statement is sort of true it is incredibly misleading. Tar paper also known as underlayment, felt or moisture barrier, is exactly that….. a moisture barrier, not a water barrier. It is designed to extend the life of the plywood (sheathing) of the roof by acting as a barrier to keep off the moisture that will accumulate in the air gap under the tiles. Tar paper is made with oils in it and so will repel water to an extent and will “help” to keep a leak from happening when it is new, but it is not designed to get wet on a regular basis aside from the normal moisture that collects under the tiles in the air gap. Tar paper that gets wet on a regular basis will fail prematurely and water that is running on these areas will once the tar paper fails leak into the home through seams in the roof sheathing (plywood). On a properly maintained roof where the tar paper is not getting wet the tar paper will last 35 + years before it really starts to age out. Heat from the sun over time evaporates and bakes the oils out of the tar paper as it ages out.

Tar paper is fine for most areas of the roof, but some areas of the roof and some roof designs require an actual water barrier under the tiles. This is called ice and water shield and there are many brands available. Many ice and water products are not properly rated for high heat tile roof applications so make sure that the quote you are getting from the other guys includes the right ice and water shield!