What One Wet August Day Showed About Roofs in San Diego

What did the storm bring, and where is it recorded?

The storm brought 1.82 inches of rain to San Diego in one day, which the National Weather Service recorded as the wettest August day on record there.

The record is the National Weather Service's own summary of the storm, reported by local news on 20 August 2023. The figure is a daily total at the San Diego station, so it does not describe every roof in the city equally, since rain can fall unevenly across a city.

A roof owner who wants the record should check the National Weather Service's San Diego office website, which keeps the local summaries and the climate tables for the area.

What does a single heavy day do to a roof?

A heavy day sends a large volume of water through the gutters, the outlets and the valleys in a few hours. The faults a dry year hides, such as a blocked outlet, a lifted flashing or a split at a seam, are the ones that show.

Outlets and gutters are often overwhelmed first, because they were sized for a normal rain and not a peak flow. Water that overflows the front edge runs onto the fascia and into the soil beside the wall, and that can soften the trim and wet the foundation.

Flashing and valleys carry concentrated flow. A flashing that was lapped correctly on a dry day may lift under the pressure of a heavy flow, and a valley with a nail hole will send water into the attic. The leaks that follow often appear in a room far from the entry point, which is why the trace starts from the attic side.

• Gutters and outlets that overflow at a low spot or a blocked downspout
• Flashing at a valley or a vent that has lifted or was never fully lapped
• A seam on a flat section that had opened and now lets water under the membrane
• A tile that was loose and moved in the wind-driven rain

What is known about the wider impact, and what is not?

The storm's wider impact is partly documented. The power outage and the one direct fatality are recorded in the agencies' reports. The roof damage in San Diego is not, so this guide does not state a number.

UC San Diego's Center for Western Weather and Water Extremes summary reported that more than 50,000 people in Central and Southern California lost power during the storm. The National Weather Service's post-tropical report recorded one direct fatality.

No count of roofs damaged in San Diego was found, and this guide does not invent one. An owner who wants to know how the storm affected a particular roof should rely on the roof's own record: the photographs, the dates and the findings of the technician who looked at it.

How should a homeowner trace a leak that came with the storm?

Start from the stain and work toward the roof. The trace follows the wet wood in the attic and then the flashing and the covering above it, rather than starting at the most obvious spot on the outside.

The stain shows where the water landed, not where it entered. Water follows rafters and boards before it drops, so the entry point can be several feet away and higher up the slope. A photograph of the stain, with the room and the date, is the first record.

In the attic, follow the wettest framing from the stain upslope. Look for staining on the sheathing, rust on nails and the dark line of a valley. The first place the wood is dry on one side and wet on the other is often near the source.

On the roof, check the flashing at vents and chimneys and the seams of any valley or flat section first. A sealant joint that has cracked, a flashing lapped the wrong way or a seam that has lifted are the faults that a heavy flow finds.

Why does the date matter for a repair or a claim?

The date of a leak shows whether it began with the storm or was already present. The record of that day is therefore part of the evidence for the repair and for any claim, and it should be kept with the photographs.

A leak that appeared on the day of a storm and was not there the week before points to the storm. A leak that has been growing for months may have been present before, even if the storm made it worse. The technician records the owner's account of when the stain first appeared, since that account is part of the picture.

The record is written while the facts are fresh. A short note with the date, the rooms affected, the photographs and the first thing the owner did is more useful than a memory of the storm weeks later.

What about a tarp after the storm?

A tarp is a temporary cover that keeps water out while the permanent repair is scoped. It is fixed to the structure, not only to the covering, and it is checked after each rain.

A tarp left on for weeks can trap moisture beneath it and rot the deck. The cover is therefore a stopgap, and the permanent repair follows as soon as the scope is agreed.

The owner should not climb to fix a tarp. A crew with fall protection does that work, and the tarp is adjusted as the wind changes direction.

What did the storm add to the list of things to check?

The storm reinforced a short list: the gutter outlets, the valleys, the flashing at each vent and chimney, and the attic above any stain. Each one can be checked from the ground and the attic without climbing.

Gutter outlets are the first check after any heavy rain. A blocked outlet is the most common cause of water spilling over the edge, and clearing it costs little.

The attic check after a storm is the most informative. A new stain, a wet board or a dark line along a rafter is a sign that water has reached the structure, and that sign is worth recording before the ceiling is painted over.

What did the storm show about gutters and outlets?

Gutters and outlets were the first part of many roofs to overflow in a storm of that size, because they were sized for a normal rain. The overflow then soaks the fascia and the soil beside the wall.

A gutter that overflows at a low spot is usually sagging, and a gutter that overflows along its full length is usually undersized or has too few outlets. The technician tests the run with water and watches the outlet to show which one applies.

Once the outlet is clear and the run is pitched, the discharge is placed so the water leaves the foundation. A splash block, an extension or a short buried pipe carries the flow to a clean outlet, and each is recorded on the scope.

How should a homeowner record the storm for the future?

A homeowner keeps the photographs, the dates, the list of rooms affected and the notes of any repair. That record is the simplest way to show what was seen and when.

The photographs should be taken from the same spots at the same time of day when the roof is checked again later. A set of photographs taken before and after the repair shows whether the fault was fixed and whether any new one has appeared.

The notes should be plain: what was seen, where, when and what was done. A note that says the ceiling was wet in the bedroom on the morning after the storm is more useful than a general statement that the house was damaged.

What is the lesson for a city roof after a heavy day?

The lesson is to check the parts of the roof that a dry year never tests, and to keep a record of what the first heavy rain shows. A city roof that is checked before the next storm is in a better position than one that is checked only after it.

The checks that matter most are the outlets, the valleys, the flashing at each vent and chimney, and the attic above any stain. Each can be done from the ground and the access hatch, and each takes little time. A list kept on the wall of the garage or the hall makes the check easy to repeat.

The record of the storm also gives the owner a baseline. The next heavy day can then be compared with it, so the owner can tell whether a fault has been fixed, has returned or has never been seen before. That comparison is the most valuable thing a homeowner can keep after a storm of this kind.