What the January 2023 Storms Showed About Roofs in San Jose

What did the storms bring, and how is it recorded?

The storms brought a run of rain and flood watches over several days, and the county's emergency declaration marked the seriousness of the wet period. The record is kept by the National Weather Service and by Valley Water.

The flood watch for the Bay Area on 4 and 5 January 2023 is a forecast of possible flooding, and the countywide flood emergency on 4 January 2023 is the county's own declaration. Both are reported by Valley Water, citing the National Weather Service.

An owner who wants the detail of a particular day should check the National Weather Service's Bay Area office, which keeps the local summaries and the daily records.

Why does a long wet spell test a roof differently?

A long wet spell saturates the sheathing and the framing, and the joints that were dry in a light rain take water once the wood beneath is full. Valleys, vent flashings and outlets are the parts that fail first.

Light rain runs off the covering and drains away. A sustained wet period soaks the layer under the covering, and the water then has to find a route. It finds the nail hole, the lapped joint or the sealant line that has aged.

The technician therefore reads the attic for days after the storm, since wet wood that remains wet days later shows that a sustained wetting reached it, and the route of that wetting is traced.

A longer account of why the roof and the drainage fail together is in the attic and outlet notes of each visit. The technician writes what the attic showed and what the outlet was doing on the day, so the link between the two is recorded for any later question.

What did the creek flooding mean for the drainage?

Valley Water's report of localised flooding along four creeks shows that the ground around some properties was full. Water from the roof then had nowhere to soak away, and it ran toward the foundation.

The creeks named by Valley Water were San Francisquito, Upper Penitencia, West Little Llagas and Uvas creeks. A house near one of them can have its outlets and its foot-of-wall drainage tested by the same storm that fills the creek.

The outlet is carried clear of the wall, and the ground is graded so it falls away from the building. A splash block or a short buried pipe is the usual fix, and the scope names the route.

What is known about damage, and what is not?

The storms' public record covers the watches, the emergency and the creek flooding. The record does not give a count of damaged roofs in the valley, and this guide does not invent one.

The city's own damage estimates for the storms concerned public assets, not private roofs, and they are not used here as a roof figure. The absence of a roof count is stated plainly, so the owner is not given a false sense of the scale.

An owner who wants to know how the storms affected a particular roof should rely on that roof's own record: the photographs, the dates and the findings of the technician who looked at it.

What should a valley owner do before the next long storm?

Before the next long storm, the owner clears the outlets, checks the discharge at the wall, looks at the valleys and walks the attic beneath the worst stains. A list kept with the file makes the check repeatable.

The outlets are the first thing to clear, since a blocked outlet is the most common cause of water spilling over the edge. The valleys are next, then the flashings at the vents and the chimney.

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

What does a flood watch ask of a homeowner?

A flood watch asks for action before the rain, not after it. The owner clears the outlets, looks at the valleys and the flashings that are visible from the ground, and checks the ground at the foot of each downspout.

The time between the watch and the rain is short. A blocked outlet can be cleared in minutes, and a loose piece in a valley can be re-set in a dry hour. A roof checked on the day of a watch is in a better state than one checked after the water has come.

The owner records the check with the date and the weather of the day, and photographs the outlets and the ground. That record is useful if the storm leaves a leak to trace, since it shows the condition before the rain.

How do the creek floods and the roof leaks differ?

Creek floods and roof leaks are separate faults that can arrive in the same storm. The creek water is outside the building and the roof water is inside it, and each is checked by a different route.

A house near a creek can have its ground saturated while its roof sheds water normally. The water then has nowhere to soak away, and it can reach the foundation through the soil. A technician checks the outlets, the discharge and the ground at the wall before deciding the route.

A leak in the ceiling after a flood watch is traced from the attic in the usual way. The creek is a reason to check the drainage, not an answer to where a roof leak came from.

What should a homeowner keep from the storm?

A homeowner keeps the dated photographs, the notes of what was seen and the records of any repair. The file is the simplest evidence of the storm's effect on the roof, and it is useful for any later repair or claim.

The photographs should be taken from the same spots when the roof is checked again. A set of photographs before and after a repair shows whether the fault has been fixed and whether a 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 back bedroom on the morning after the storm is more useful than a general statement that the house was damaged.

Why does the duration of a storm matter more than its peak?

A long storm soaks the building and the ground, and the damage it causes builds over days. A short heavy burst may do little, while a steady rain for a week reaches the joints and the wood that a burst cannot.

A roof's drainage is designed to carry peak flows, and a peak is often brief. A steady rain delivers a smaller flow for much longer, and the wet wood beneath the covering holds water against the joints for days after the rain has stopped.

The technician therefore tests a roof differently after a long wet spell. The attic is read on the day after the rain as well as on the day of the storm, since the wet that appears later is the sign of water still moving through the building.

How should the outlets and the ground be treated after the storm?

After the storm, the outlets are checked for blockage and debris, the discharge is checked against the wall, and the ground at the foot of each downspout is checked for washing and sinking.

A downspout that was carrying a large flow may have pushed debris into its elbow, and a blockage there can cause the water to overflow at the top. The outlet is cleared and the run is tested with water.

The ground is checked for a trench, a sinking patch or a wet area that does not dry. A splash block or an extension carries the water further, and the grade is restored where the soil has moved.

How should a valley owner plan for the next long storm?

A valley owner plans for the next long storm with a short written plan: the outlets to be cleared, the valleys to be checked, the attic to be read after rain and a roofer's number ready to call. The plan is kept with the file and repeated each autumn.

The plan names the first action in the order it should be done. The outlets come first, the valleys second, the flashings third and the attic last. Each action has a date by which it should be finished, and the owner keeps the plan where it can be found in a hurry.

The plan also names who to call and what to say. A short note with the address, the storm's date, the rooms affected and the first sign of the leak lets a technician start the trace before arriving.