How a tile roof is built
- Roof deck (sheathing)
- Underlayment: the waterproof layer
- Battens on many roofs, which hold the tile and let water drain
- Tile: shades the roof and sheds most of the water
Over years of heat, the underlayment can dry out and crack, especially where it's exposed at broken tiles, eaves and valleys. Once it fails, water that slips past the tile reaches the deck.
The re-lay process
- Tiles are removed and stacked on the roof or ground
- Old underlayment comes off and the deck is inspected; damaged sheathing is replaced
- New underlayment, and often new battens and flashings, go on
- Original tile is reinstalled, with broken pieces replaced by matches
- Ridge and hip details are reset
Related: roof replacement · leak repair
Underlayment FAQ
How do I know if my underlayment is worn out?
You often can't tell from the ground. A roofer lifts a few tiles to look. Warning signs include leaks without obvious tile damage, and underlayment that is brittle, cracked or torn at the edges where it's exposed.
Can I reuse my existing tiles?
Often, yes. Concrete tile is durable, and many re-lays reuse most of it. Some breakage during removal is normal, so ask how the roofer will source matching replacements.
Is synthetic underlayment better?
Underlayment products differ in heat tolerance and longevity. Ask the roofer which product they specify, why, and what the manufacturer's warranty says about tile applications.