What happens when
the tiles move
A concrete tile roof is two systems doing two different jobs, and the one that keeps water out of the house is not the one you can see from the street.
Dispatched 24 hours a day across the valley.
The tile is not
the waterproofing
Concrete tile does two things well. It sheds the bulk of the rain, and it shades everything under it from the sun. Neither makes it watertight. Tile is laid in overlapping courses with open ends and head laps, and in wind driven rain a certain amount of water gets past it. That is designed for.
What keeps the water out is the underlayment, the membrane fastened to the deck beneath the tile. Water that gets past the tile lands on it and runs down to the eave. The tile is the rain shield and the sunshade. The underlayment is the roof.
Twenty years, in the heat
Their lifespans are very different. Tile can last as long as the house. Underlayment here is often put at around twenty years, because the deck under tile does not sit at air temperature. It runs far hotter than the shade reading, and asphalt based membrane ages by heat: it hardens, gets brittle, and cracks at the fastener holes. A roof can look sound and be at the end of its waterproofing life.
What outflow wind does
to a tile field
The wind that damages roofs here is not a steady blow. When a monsoon thunderstorm collapses, the cold air inside it falls and races outward as an outflow wind of 40 to 60 mph, ahead of the rain and changing direction as the cell passes.
Wind does not lift a tile by pushing on it. It pulls. Air moving across a roof accelerates over the edges and produces suction, strongest where the field of tile ends: hips, rakes, eaves and ridge. Those tiles have the least holding them down and the most exposed edge to get under, so failures cluster at the boundaries. A tile lifts, drops back out of position and slides out of course.
From the ground that looks minor, and in terms of the tile it is. One displaced tile removes the shade from a patch of underlayment and exposes the head lap of the course below to angled rain. Cracked mortar along a ridge does the same along a line rather than at a point.
- 01
Hips and rakes
The tile field ends there, so suction is highest and there is an exposed edge to get under.
- 02
Eaves
The lowest course has the least holding it down.
- 03
Ridge
Mortar seals a long line, so damage there opens a line rather than a point.
- 04
What it costs
One tile out of course removes the shade from a patch of underlayment and exposes the head lap below to angled rain.
Roof damage here is usually two storms, not one. The wind that moved the tile is rarely the rain that comes through the hole, and that is why the ceiling stain appears weeks after the storm that caused it.
Why the stain arrives
weeks later
In late July an outflow wind slides a few tiles out of course near a hip. Nothing leaks, because the rain that follows runs onto underlayment that is still intact, and nobody looks at the roof because nothing happened inside the house.
That strip of membrane then spends a fortnight in direct sun at a temperature it was never meant to see uncovered. It hardens, it cracks, the fastener holes open. In the middle of August an ordinary storm pushes rain into that section, and this time the water goes past the membrane and into the building.
What the homeowner sees is a stain on a bedroom ceiling after a rain that did not seem like much. The wind that caused it was three weeks earlier, one storm among several.
Three weeks, in order
- 01
Late July
Outflow wind slides tiles out of course near a hip. Nothing leaks, and nobody looks.
- 02
The fortnight after
Uncovered membrane bakes, hardens and cracks, and the fastener holes open.
- 03
Mid August
An ordinary storm drives rain past the membrane and into the building.
Why that delay matters
to a claim
Wind is a covered peril on a standard homeowners policy. Deterioration and wear are not. When a roof claim is examined, the carrier is deciding which of the two produced the damage.
That is easier to answer when the damage can be tied to a dated storm. A claim that a specific wind event on a specific date displaced tile at the hips, supported by photographs and by weather records for that day, is a claim about a covered peril. A claim that the roof started leaking at some point over the summer invites the other conclusion, because a brittle twenty year old membrane and a neglected roof look identical in a photograph taken afterwards.
So the time to look at the roof is after a wind event, when nothing is leaking, rather than after the leak, when the connection has blurred. Dated photographs taken the morning after a storm cost nothing, and damage is worth reporting promptly.
- 01
A dated event
Tile displaced at the hips by a specific wind on a specific date.
- 02
Photographs
Taken the morning after the storm, while nothing is leaking.
- 03
Weather records
For that day, tying the damage to the event rather than to the summer.
- 04
Prompt reporting
Damage reported when it is found, not after the ceiling stains.
What to look for from
the ground after a storm
None of this requires going up. It is visible from the driveway with binoculars.
- 01
Tiles out of line
Sight along each course. Tile is laid in strict lines and the eye picks up a break quickly. A tile sitting low, high or twisted has moved, and no longer laps the one below it.
- 02
Anything dark showing between tiles
A black or grey patch in a uniform field is exposed underlayment. That matters most, because the waterproofing layer is now taking sun directly.
- 03
Broken pieces on the ground
Fragments of tile in the yard, on the driveway or in the pool came from somewhere on the roof. Walk the perimeter after a serious wind; the debris shows before the gap does.
- 04
Cracked or missing mortar at ridges and hips
That mortar seals a long opening. When pieces are gone, the opening runs the length of the line rather than sitting at one tile.
- 05
Rakes, eaves and edges before anything else
Start at the gable ends, the hips and the lowest course, where suction is highest.
How roof water behaves
once it is inside the ceiling
Water that gets past the underlayment does not fall straight through to the room below, and what it does instead is why ceiling damage is so consistently misread.
It meets the attic first. Insulation lying on the ceiling holds a surprising volume before releasing any of it, which is why the ceiling below can look perfect for a day after a leak starts, and why it stays wet long after the rain stops.
Water also travels sideways before it drops. Running off the deck, it lands on the top chord of a truss and follows it, because framing is an efficient channel, until something interrupts it: a brace, a splice, a run of wiring, an electrical box. So the stain is frequently several feet from the entry point, sometimes in another room, and the first sign is often water at a can light.
This is why nobody can point to the hole from inside the house, and why an inspection maps the wet area with a moisture meter and works back up the framing instead of assuming the leak is above the mark. It is also why the insulation comes out: air aimed at a ceiling with saturated insulation above it is drying the paint. The window before mold establishes is the same 24 to 48 hours as anywhere else, covered in the 48 hour window.
A ceiling that is sagging or bulging downward is holding water, and water is heavy enough to bring the whole section down at once and without warning. Keep people and pets out of the room, do not stand underneath it, and do not try to release it yourself.
- 01
Insulation holds it
A surprising volume goes in before any of it comes out, so the ceiling can look perfect for a day.
- 02
Framing carries it
Water follows the top chord of a truss until a brace, a splice or a box interrupts it.
- 03
The first sign
Often water at a can light, several feet away and sometimes in another room.
- 04
So it is mapped
A moisture meter marks the wet area and the work runs back up the framing.
What the work
looks like inside
The roof is a roofing repair, and the sooner a tarp goes on, the smaller the interior problem stays. Inside, the work follows the water rather than the stain: readings across the ceiling and down the walls, wet insulation removed, ceiling material opened where it cannot be dried, and drying equipment logged daily. The same wind also drives fine dust through every opening it finds, which is in what the dust gets into.
Read next
-
01
Why desert homes take on water in August
The monsoon mechanism, and the four openings water uses.
-
02
What the dust gets into
Haboobs, outflow wind, and where the fine material ends up.
-
03
The 48 hour window
Why drying, not cleaning, decides whether mold follows.
-
04
Monsoon season
Everything here about the storms from June 15 to September 30.
If a storm has opened the roof and water is coming through a ceiling, go straight to dispatch.
Emergency service across the valley, dispatched 24 hours a day
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