Allegheny County, Pennsylvania · Pittsburgh
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With 55% of homes built before 1960 and about 28 hard-freeze nights a year, frozen and split pipes are a leading winter risk in the county.
June brings the most downpours to Allegheny County, part of 5.9 heavy-rain days a year. Check the sump first.
55% of homes here predate 1960, when clay and cast iron sewer laterals were standard. Roots and cracks in those lines are a common cause of backups.
In Allegheny County, 3.78 inches fell on the wettest day of the 2015–2024 record. Storms like that, and ice dams in snowy winters, cause most roof leaks.
2% of occupied homes in Allegheny County heat mainly with wood or propane, below the Pennsylvania county median of 10%.
Muggy summer nights, lows of 65°F or more, come about 30 times a year in Allegheny County. Mold after a leak spreads fastest from June through August.
Local risk profile
With 606,827 homes and around 1,238,177 residents, Allegheny County is 730 square miles of southwest Pennsylvania. Besides Pittsburgh, the county seat, the biggest communities are Bethel Park, Monroeville and Plum. It has some of the oldest housing in the state: the median home went up in 1957.
48/100 Water Damage Risk Index: Elevated Allegheny County ranks 37 of 67 Pennsylvania counties. See the statewide ranking and method.The three factors where Allegheny County ranks highest compared with other Pennsylvania counties.
Allegheny County is milder than most of Pennsylvania, but not mild enough to skip winterizing. It averaged 104 freezing nights a year over 2015–2024, 28 of them at 20°F or colder, cold enough for pipes in outside walls and crawl spaces to freeze. Among 67 Pennsylvania counties that's 54th.
The longest cold spell was straight 13 days without the temperature rising above freezing, ending in January 2018. The coldest night reached about -10°F on February 20, 2015. Burst pipes usually show up when a spell like that breaks and the ice thaws.
The freeze season here runs November to March, with January the coldest. If you travel then, leave the thermostat at 55°F or above and open sink cabinets on outside walls.
On average the first fall freeze arrives around Nov 1 and the last spring freeze around Apr 23.
Allegheny gets fewer downpours than most Pennsylvania counties, but they still fill basements. Of roughly 44.5 inches of yearly precipitation, the damage comes from the 5.9 days a year with an inch or more, ranked 50th of 67. April, June and September see the most. The single wettest day in the record: 3.78 inches, September 10, 2018. Multi-day storms matter most for basements; the wettest three days on record here totaled 6.06 inches (through September 11, 2018).
About 83 days a year swing from below freezing at night to above freezing by day. Those freeze-thaw cycles feed ice dams on roofs, open cracks in foundations and driveways, and stress pipes that are already marginal.
Housing
Pennsylvania's 67 counties range widely in housing age; Allegheny ranks 8th, with 77% of its homes built before 1980.
55% were built before 1960. Homes from that era often still have galvanized steel supply pipe, which rusts from the inside until it pinholes, and cast iron drains that crack with age. Slow leaks behind walls are a common start to water damage in these houses.
Renters occupy 35% 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
Allegheny County averages 30 warm, muggy nights a year (lows of 65°F or more) and gets the most rain in June. 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 Allegheny County it's 81% utility gas, 16% electric, 2% propane and under 1% wood. Most homes here heat with gas or electricity, so cooking and electrical faults are the likelier fire sources. Even a contained kitchen fire can send soot through the ductwork to every room.
Fire and smoke cleanup: first stepsCoverage
Calls connect to restoration companies that work across Allegheny County. The largest communities by population:
Population from ACS 2020-2024 5-year estimates. Townships and unincorporated areas are covered too.
Nearby
Every neighboring county gets more pipe-freeze nights than Allegheny. Beaver County has the oldest housing nearby, with 78% of homes built before 1980.
By the numbers
| Factor | Allegheny | Pennsylvania median | Rank |
|---|---|---|---|
| Homes built before 1960 | 55% | 42% | 10 of 67 |
| Homes built before 1980 | 77% | 66% | 8 of 67 |
| Homes built 2000 or later | 11% | 13% | 48 of 67 |
| Manufactured or mobile homes | 0.7% | 6.6% | 65 of 67 |
| Vacant homes | 10% | 12% | 41 of 67 |
| Wood or propane heat | 1.7% | 10% | 67 of 67 |
| Nights at 20°F or colder | 28/yr | 37/yr | 54 of 67 |
| Days with 1 inch+ of rain | 5.9/yr | 7/yr | 50 of 67 |
| Freeze-thaw days | 83/yr | 98/yr | 65 of 67 |
| Muggy nights (65°F+) | 30/yr | 16/yr | 19 of 67 |
Rank 1 is the highest value. Bars run from the lowest to the highest Pennsylvania county; the tick marks the median; orange means higher water damage risk than the median, green means lower.
Questions
Peak risk months in Allegheny County: freezing from November to March, heavy rain in April, June and September.
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