Tile roof underlayment in Arizona: what it is and when to replace it

Concrete and clay tiles are very durable. The underlayment beneath them is made of asphalt-saturated felt or synthetic material, and it lives in an oven. On a summer afternoon in the Valley, the space under the tile gets far hotter than the air temperature, and the roof goes through that heating and cooling cycle day after day for months.

Over years, that heat drives oils out of traditional felt, and it becomes dry, brittle and cracked. Wherever tiles are cracked, slipped or missing, the underlayment is also exposed to direct UV light, which speeds up the damage. Foot traffic from solar installers, pest control, holiday lighting or satellite work can crack brittle tiles and tear aged felt beneath them.

The result is a pattern many Arizona homeowners discover the hard way: the tiles still have decades of life left, but the waterproofing under them is worn out. How long underlayment lasts depends on the material, the installation, the roof pitch and how much sun the roof gets, which is why an inspection is more reliable than a calendar.

A lift-and-relay replaces the underlayment and reuses your existing tile. Because the tile stays, the finished roof looks much the same as before, and the existing tile does not have to be hauled off. Here is how the job usually goes:

1. Inspection and scope. We look at the tile, the underlayment, flashing and the deck, and write up what will be replaced, including how broken tiles and damaged decking will be handled.
2. Permit. Where the city requires it, the permit is pulled before work starts.
3. Remove and stack the tile. The crew lifts the tiles in sections and stacks them on the roof or staged nearby, sorting out any that are broken.
4. Tear off the old underlayment. Old felt, battens and worn fasteners come off down to the deck.
5. Inspect and repair the deck. Soft, rotted or delaminated sheathing is replaced so the new system has a sound base.
6. Install new underlayment. The new membrane is laid with proper overlaps, starting at the eaves and working up.
7. Flashing and details. Valleys, wall and pan flashings, vent pipe flashings and drip edge are replaced or reset as the scope calls for.
8. Battens and tile. Battens go back where the system uses them, and the tiles are relaid and fastened, with replacement tiles where needed.
9. Ridges, hips and cleanup. Ridge and hip tiles are set, debris is hauled away, and the yard is checked for nails before final inspection.

Some tiles break during removal and reinstallation no matter how careful the crew is, and some are already cracked from foot traffic or age. A good estimate explains how replacements are handled, for example whether a set number of replacement tiles is included and how additional tiles are priced.

Replacement tiles come from a few sources: matching new tile if the profile and color are still made, salvaged tile from other jobs, or borrowing tiles from a less visible area such as a back slope and using the closest available match there. Moving original tiles to the street side keeps the front of the house uniform.