Washtenaw County, Michigan · Ann Arbor
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Pipes freeze in Washtenaw County on about 46 nights a year, mostly November to March. Older homes, 25% of the stock here, are most at risk.
Basements flood here mostly in May. Washtenaw County averages 4.9 days a year with an inch of rain or more.
Sewage backups in Washtenaw County spike on heavy-rain days, about 4.9 a year, when sewer mains fill up and water finds the lowest drain.
Roof leaks here come from summer downpours and, with about 96 freeze-thaw days a year, from winter ice dams. Most show up as ceiling stains in the room below.
4% of occupied homes in Washtenaw County heat mainly with wood or propane, below the Michigan county median of 29%.
About 19 nights a year here stay at 65°F or warmer, so basements and crawl spaces can grow mold even without a leak.
Local risk profile
About 369,822 people live in Washtenaw County, 706 square miles in southeast Michigan, in roughly 159,782 homes. The county seat is Ann Arbor, and Ypsilanti, Saline and Whitmore Lake round out the largest towns. Half the homes here were built before 1978, half after.
48/100 Water Damage Risk Index: Elevated Washtenaw County ranks 47 of 83 Michigan counties. See the statewide ranking and method.The three factors where Washtenaw County ranks highest compared with other Michigan counties.
Pipe-freeze risk in Washtenaw County sits near the middle of the state. In the 2015–2024 record the county logged about 46 nights a year at or below 20°F (50th of 83) and 132 below freezing. Twenty degrees is roughly where uninsulated pipes start to freeze.
The longest cold spell was straight 21 days without the temperature rising above freezing, ending in March 2015. The coldest night reached about -18°F on January 31, 2019. Burst pipes usually show up when a spell like that breaks and the ice thaws.
Expect the hardest freezes in January, inside a season that runs November to March. That's when an outdoor spigot left connected to a hose, or a pipe in a crawl space, is most likely to split.
Freezing nights typically start around Oct 19 and end around Apr 28.
Heavy rain is a bigger factor here than in most of Michigan. About 4.9 days a year bring an inch or more (19th of 83), most often in May, out of 34.5 inches of total precipitation. On August 12, 2021, 2.34 inches fell in a single day. The worst three-day stretch dropped 3.96 inches, ending September 24, 2021, the kind of soaking that overwhelms sump pumps and storm sewers.
Freeze-thaw days, below freezing overnight and above it by afternoon, come about 96 times a year here. They're the main driver of ice dams and of water working its way through foundation cracks in late winter.
Housing
Michigan's 83 counties range widely in housing age; Washtenaw ranks 64th, with 53% of its homes built before 1980.
22% of homes were built in 2000 or later, more than in most of Michigan. Newer plumbing rarely corrodes, so damage here tends to come from appliance supply lines, water heaters, sump pumps and storms.
About 26% of homes went up between 1980 and 1999. Some houses from the late 1970s to the mid-1990s were plumbed with polybutylene, a gray plastic pipe known for failing at fittings. A plumber can tell you in a few minutes whether you have it.
Renters occupy 38% of homes. If you rent, the building is usually the landlord's to repair, but your belongings are only covered by renters insurance.
Beyond water
Summer nights that don't drop below 65°F, a good marker of humid air, come about 19 times a year here, above the Michigan county median of 10. Mold grows when indoor humidity stays above about 60%, the EPA's ceiling. A basement dehumidifier set to 50% and drying anything wet within 24 to 48 hours prevents most problems.
Mold remediation: what to expectHeating fuel matters for fire risk. In Washtenaw County it's 75% utility gas, 19% electric, 4% propane and under 1% wood. Fires here are likelier to start in the kitchen or the wiring than in the furnace. After any fire, keep the HVAC off until ducts are checked, or soot will travel through the house.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Washtenaw County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Livingston gets more pipe-freeze nights than Washtenaw. Wayne County has the oldest housing nearby, with 80% of homes built before 1980.
By the numbers
| Factor | Washtenaw | Michigan median | Rank |
|---|---|---|---|
| Homes built before 1960 | 25% | 32% | 63 of 83 |
| Homes built before 1980 | 53% | 58% | 64 of 83 |
| Homes built 2000 or later | 22% | 16% | 10 of 83 |
| Manufactured or mobile homes | 3.7% | 7.3% | 75 of 83 |
| Vacant homes | 5.8% | 20% | 74 of 83 |
| Wood or propane heat | 4.1% | 29% | 80 of 83 |
| Nights at 20°F or colder | 46/yr | 54/yr | 50 of 83 |
| Days with 1 inch+ of rain | 4.9/yr | 3.9/yr | 19 of 83 |
| Freeze-thaw days | 96/yr | 95/yr | 37 of 83 |
| Muggy nights (65°F+) | 19/yr | 10/yr | 26 of 83 |
Rank 1 is the highest value. Bars run from the lowest to the highest Michigan county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Washtenaw County: freezing from November to March, heavy rain in May, June and August.
Sources: U.S. Census Bureau, ACS 2024 5-year estimates (2020-2024); weather from NOAA nClimGrid-Daily county averages (EpiNOAA), 2015–2024, averaged across the county; county boundaries from Census TIGER. Reviewed 2026-10-21. Methodology