Winter rain-on-snow damage and why it is not only frozen pipes

What is rain-on-snow, and why is it different from snowmelt?

Rain-on-snow is rain that falls on a snowpack, adding its own water to the melt and sending the total toward the ground, the street and the building. Snowmelt alone warms gradually, while rain on snow can raise the runoff quickly.

A deep snowpack holds a great deal of water in its layers. Rain soaks into the snow and melts the bottom, and the combined water runs toward the lowest point it can find. Drains and ditches that are clogged with snow and debris push that water toward the building.

The Spokane County Flood Insurance Study lists winter rain-on-snow events as one of the two main flood types, separate from spring snowmelt. The distinction matters because the speed of the rise determines how little time a homeowner has to move things and stop the water.

The distinction also shapes the record. A rain-on-snow event that reaches the entry, the garage and the lower level in one storm leaves a single water line on the walls, and that line is worth photographing before any cleanup begins, because it shows how far the water rose in that one event.

Why do frozen pipes get mixed up with winter flooding?

Both happen in cold weather and both put water in a house, but they come from different causes. A frozen pipe is an inside problem, where water in a supply line freezes and splits the line. Rain-on-snow is an outside water event that enters through doors, windows and foundations.

A split supply line usually shows at one point, such as a sink, a wall or a fixture, often on a cold night. The water is clean and comes from inside the house. Rain-on-snow water comes through the threshold, the garage, the window wells or the foundation, and it brings silt and leaves with it.

Because they can happen in the same winter, the crew checks for both. A house with a split line and a rain flood needs the line repaired by a plumber, and the outside water removed and dried by the cleanup crew.

What does the City of Spokane advise about frozen pipes?

The City of Spokane advises insulating exposed pipes, keeping the home at 55 degrees Fahrenheit or above when away, shutting the water off before thawing a frozen pipe, and thawing slowly with a hair dryer or a low-setting heating pad. Those steps reduce the chance of a split line in a cold snap.

Insulating pipes in unheated spaces such as a crawl space, a garage or an outside wall is the first step. A pipe that is wrapped and kept above freezing does not split as easily as one that is exposed.

If a pipe is frozen, the City advice is to shut the water off before thawing it, so that water does not flow into the break when the ice melts. Thaw the pipe slowly with a hair dryer or a low-setting heating pad, and never use an open flame. These are the steps a homeowner can take safely, and a plumber handles any repair.

How does the water usually reach the house?

Runoff follows the lowest route it can find, and a door, garage or window well below the grade of the street or driveway becomes that route. The water can pass under a door, through a gap at the sill or down a window well and along the foundation.

A threshold a few centimeters lower than the outside grade can take a flood of runoff. Garage doors and their floor joints are rarely sealed to hold back standing water, and the water often reaches the garage first and then travels along the wall into the living space.

Window wells fill with melt and rain and drain slowly. The water sits against the window and finds a seal or a crack. A well that drains into the foundation area is a common route for water into a basement.

What should I do when rain is coming into the house?

Keep away from moving water and standing water near electrical equipment, switch off the power to the affected area if it can be done safely, and move valuables up off the floor. Photograph the water and the entry point, then call for water removal.

Do not drive or walk through runoff in the street or the driveway. The depth and the speed can be hard to judge, and the road under the water may be damaged. Keep children and pets away from the water at the door.

If it is safe to do so, place towels or sandbags against the bottom of the door to slow the flow. Do not put yourself in moving water to place them, and tell the crew what you did when it arrives.

How do I stop the next storm from finding the same route?

Find the water path first, then address it. Clear the drains, the gutters and the window wells, keep snow away from the doors and the garage, and check the grading with a contractor if water keeps arriving at the same point.

Clearing snow and debris from the entry and the window wells before a warm rain is the simplest protection, and a homeowner can do it with a shovel and a broom. Keep the gutters and downspouts discharging well away from the house.

A regrading, a higher threshold or a door change is work for a qualified contractor. The crew's record of the water path gives that contractor a starting point, and the design of the change depends on the house and the lot.

What should I keep after a winter flood?

Keep the photographs, the crew's record of the water path and the readings, and a list of the damaged items with their age and approximate value. Do not discard the damaged items until the insurer has seen them, unless they are a health hazard.

The insurer will want to know when the water first appeared, where it came in and how far it reached. A dated photograph of the water line and the entry point answers much of that question.

The Washington Office of the Insurance Commissioner handles consumer complaints about how a claim is handled. The insurer and your policy decide what applies to outside water and to sudden water from inside the house.

What does the crew do on the first visit after a winter storm?

The first visit finds the entry, removes the standing water and checks the rest of the house for the route. The crew reads the lower structure, sets the drying plan and gives you a written record of what it found.

The crew starts at the entry and works inward, because water that came through a door or garage usually followed a path that the crew can trace. Standing water is removed and the debris is cleaned from the floor and the threshold.

Readings are taken on the wall, the floor and the framing at the entry and beyond it. The drying plan and the record are given to you before the crew leaves the first visit, so the next steps are clear.

How do I check the garage and the crawl space after a storm?

Check the garage floor, the wall to the house and any crawl-space access after the storm, because water can travel along those routes out of sight. A wet mark, a musty smell or a soft floor are the signs to note.

Look at the garage floor for water at its edges and along the joint with the house wall. A stain that climbs the wall between the garage and the living space is a sign that water has moved along the framing.

If the crawl space has water or a musty smell, do not enter it until the crew has checked the access. Note the signs and tell the crew, so the readings include the joists and the subfloor above the crawl space.