The basics
What does tile roof underlayment do, and why does it get replaced?
Underlayment is the waterproof layer under your tile. Tile sheds most water, and the underlayment stops the rest. It is often the first layer of a tile roof to wear out.
A tile roof is not waterproof on its own. Tiles overlap and shed water, but rain pushed by wind can slip under them. Ludowici, a clay tile maker, says most problems on tile roofs come from water that moves through the joints between tiles by capillary action (water creeping into tight gaps), by wind driven rain and by runoff. It calls the underlayment critical for that reason.
The Florida Roofing and Sheet Metal Contractors Association (FRSA) also says the underlayment is usually the secondary water barrier on a tile roof. Think of it as the roof under the roof. If it cracks, dries out or tears at a nail, water that gets past a tile has a way into the deck and the attic.
Here is the mismatch. Ludowici expects its tile to last over 75 years and says the underlayment should have a comparable lifespan and quality. In practice, a lot of older Florida tile roofs were built with felt (paper soaked in asphalt) that was never expected to last that long. We could not find a published number of years from a standards body, and contractor numbers vary, so we will not give you one. Your attic and your roof tell you more than a calendar does.
Who this affects: owners of tile roofs that are old, that have leaked, or that have had many tiles repaired. When it matters: after a hard storm, when tiles slide or crack, and before you buy a home with an older tile roof. Where: anywhere in Florida. A Florida roofing company notes that our heat and humidity shorten the working life of these layers. For a wider view, see our guide to how a tile roof replacement works.
