Why Tile Underlayment Fails Before the Tile — A Practical Guide
What goes wrong first on a tile roof in Hollywood Hills, and the signs that show up years ahead.
Understanding why something fails is more useful than a list of symptoms, because the same symptom has several causes and they need different work. What follows is what actually goes wrong on tile roofing in Los Angeles, and what it looks like from the ground before it becomes a ceiling stain.
What actually goes wrong
Clay and concrete tile will outlast the person who buys it. What fails is the felt underneath. That is the single most useful thing to understand about a tile roof, because it explains why a roof that looks perfect from the street can be leaking, and why the quote is for labour and underlayment rather than for new tile.
Why it happens when it does
Thirty-pound felt baking under clay for twenty years becomes brittle enough to crumble between finger and thumb. Once it has gone, the tile is decoration: it sheds the bulk of the water, the underlayment handles what gets past, and with nothing underneath the next storm finds the deck. A re-felt lifts and stacks the existing tile, strips the old underlayment, repairs whatever the deck needs, lays new membrane and relays the same tile. Modern synthetic underlayments last considerably longer than the felt they replace, which is why the second re-felt tends to be further away than the first.
How Los Angeles makes it worse
On hillside properties, seismic movement works tiles loose along hips and ridges, where the mortar bed cracks and lets water track sideways under the courses rather than down over them. In the older neighbourhoods the harder problem is matching a discontinued profile — an original barrel tile from the nineteen-twenties has no modern equivalent, and sourcing salvage is the single most common cause of delay on a tile job in this city.
What we look at on an inspection
- Underlayment condition at eave, valley and every penetration
- Cracked, slipped or previously walked-on field tiles
- Mortar along hips and ridges, and whether it has parted from the tile
- Sherman Oaks metal for corrosion and for debris packed under the courses
- Batten condition where the tiles are batten-hung
- Framing deflection, because tile is heavy and older framing was not always sized for it
Common questions
Can this be repaired or does it need replacing?
It depends whether the cause is localised or systemic. A failed penetration is a repair; a covering that has gone brittle across the whole roof is not.
How urgent is it?
Anything open before the rains is urgent. Anything cosmetic can wait for a dry-season schedule, which is also when it is cheaper.
The honest summary
In most cases the tile is fine and only the underlayment has failed. Anyone quoting a full tear-off and new tile on a roof with sound tile is quoting the wrong job. Ask specifically whether your existing tile can be relaid, and how much of it is expected to break in handling — ten per cent is normal, and it should be priced up front.
Free inspection, drone photography where access is difficult, and a written estimate with deck repair priced per sheet. No obligation.