What underlayment membranes are used under tile roofs?
Short answer. Tile roofs use three main underlayment types: heavy asphalt felt, often in two layers, high-temperature self-adhered membranes that bond to the deck and seal around fasteners, and synthetic underlayments rated for tile. Because water regularly gets under clay and concrete tile, the membrane is the real waterproofing layer, so long-life, high-temperature products are the usual recommendation on a new tile roof or a re-underlayment.
The options
- Asphalt felt: No. 30 or heavier, sometimes with a mineral-surfaced cap sheet. Traditional and lower cost, but it dries out under hot tile and often fails long before the tile does.
- High-temperature self-adhered membrane: rubberized asphalt or butyl sheets that stick to the deck, seal around batten and tile fasteners, and resist high heat. Often the premium choice.
- Tile-rated synthetic: strong, light and walkable. Check that it is rated for tile loads, foot traffic and the heat under tile.
- Two-ply systems: a base sheet plus a cap sheet, common in hot climates and on lower tile slopes.
Battens and counter-battens
Many tile roofs hang tiles on wood battens fastened over the underlayment. Counter-battens running up the slope lift the battens so water and debris can drain beneath them. Every batten fastener punctures the membrane, which is one reason self-adhered products are favored.
Flashing still matters
Valleys, walls, chimneys and penetrations need metal flashings and pans designed for tile. The membrane is the backup, not a substitute.
Georgia notes
Clay and concrete tile are uncommon in North Georgia, so experienced tile crews are limited. Summer heat under dark tile is intense, so high-temperature ratings matter. Concrete tile is heavy, so a structural check is wise if you are converting from shingles.
Questions to ask
- Which membrane, and is it rated for tile and high temperature?
- Battens or direct-to-deck, and how is drainage handled?
- Which flashings will be replaced?
- What does the tile maker's installation guide require?
See synthetic underlayment vs felt and ice and water shield in Georgia.