Duncannon was laid out in 1792 under the name Petersburg, on ground that falls toward the Susquehanna, and our crew repairs and replaces the roofs on its houses, most of them built in 1939 or earlier.
Duncannon has about 0.4 square miles of land and roughly 1,391 people. It sits about 12 miles northwest of downtown Harrisburg-Carlisle. We cover ZIP code 17020.
No completed roof in Duncannon is logged in our job records yet.
Of Duncannon's 715 homes, 505 were built in 1939 or earlier, and only 2% went up in 2000 or later. Houses that old typically have roof boards laid as planks rather than plywood sheets, rafters that may be lighter than a new house would get, and attics with little headroom or insulation. Just 51% of the homes are single detached houses, and most of the rest are attached houses and buildings divided into apartments. On an attached house one roof often runs into the next, so a re-roof has to tie into the neighbor's roof at the line.
The borough drops from about 506 feet at its western edge to about 340 feet at the Susquehanna River, so its houses sit between mountain slope and river. Snow piles on these roofs in winter, and meltwater that refreezes at the eaves builds ice dams, most readily over old attics where house heat warms the underside of the roof. The Appalachian Trail comes off the mountain onto Inn Road and runs through town mainly along North High Street, so tear-off on that street goes on above a route hikers walk, and debris has to stay off it.
Electricity heats 53% of Duncannon households, while fuel oil heats 239, wood 17 and coal 12. Oil burners and wood and coal heaters usually vent through a chimney, and on a house this old the brick, its mortar and the metal flashing where the chimney meets the shingles are often where water first gets in.
On houses this old in Duncannon the deck is usually solid boards, not plywood, and boards shift: gaps open, nails work loose, and a shingle nailed over a gap holds on to nothing. Chimneys and wall joints often still carry their original step and counter-flashing, which is where many leaks really start while the shingles look fine. Two or three roofs piled on one another are common on streets like these; every extra layer hides the deck, adds weight and voids most manufacturer warranties. Any original slate or tile on the house calls for a different plan from an asphalt tear-off.
By the Census Bureau's estimate there are 715 homes in Duncannon, with a median year built of 1939 or earlier, the oldest band the survey reports. 505 of them (71%) went up before 1940 — the 3rd-highest pre-1940 share of the 37 places on this site — and 11 (2%) in 2000 or later. More of today's homes date from before 1940 than from any decade since. On the pre-1940 share, Duncannon sits above Perry County's 21%.
A roof's first layer has a service life of about 20 years, according to HUD's Residential Rehabilitation Inspection Guide. By that measure, 98% of Duncannon's homes — the 704 built before 2000 — are past their first roof, and 89% (637 homes) go back before 1970, two roof lives and more. Homes from the 2000s (6 in Duncannon) are reaching their first replacement, while the 5 built since 2010 are mostly still on the roof they were built with. At that age it pays to know whether the last roof was torn off or laid over the one before it, because a second layer hides the deck.
Detached single-family houses make up 51% (366); attached houses and townhouses 11% (82). 195 homes (27%) sit in two- to nine-unit buildings and 64 (9%) in buildings of ten units or more, where the roof is usually a landlord's or an association's decision. Owners live in 51% of the 639 occupied homes. When we look at houses like these, our work can include full tear-offs on houses past two roof lives, deck and flashing checks on pre-war board sheathing and flat and low-slope sections, which turn up more on attached and multi-unit buildings.
| Built | Homes | Share | |
|---|---|---|---|
| Before 1940 | 505 | 71% | |
| 1940s | 48 | 7% | |
| 1950s | 57 | 8% | |
| 1960s | 27 | 4% | |
| 1970s | 53 | 7% | |
| 1980s | 6 | 1% | |
| 1990s | 8 | 1% | |
| 2000s | 6 | 1% | |
| 2010s | 5 | 1% | |
| 2020 or later | 0 | 0% |
Census ACS 2020–2024, tables B25034, B25035, B25024 and B25003: 715 homes, 639 occupied. Survey estimates.
NOAA’s Storm Prediction Center logged 2 reports of hail 1 inch or larger within 5 miles of Duncannon’s center from 2016 through 2025, on 2 different days. None was 1.75 inches or larger. The largest, 1.25 inches, came on July 17, 2021, about 3.3 miles southeast of the center. The most recent was 1 inch on September 7, 2023. These are reports, not a full record: they come from spotters and the public, so busier areas log more.
A bruised shingle can look fine for a season or two, which is why a storm inspection after a date like these is worth having.
Duncannon publishes no rule either way on a like-for-like re-roof, so we ask the building department before we start and pull whatever it wants.
Duncannon does not publish the code edition it currently enforces. We confirm the edition with the building department before we write the scope.
What goes into a new roof, layer by layerDesign wind here is set by location, not one figure for the whole area: across the Harrisburg-Carlisle, Pennsylvania metro, we build to the design wind speed set for the address; Township of Upper Allen’s published table gives 90 mph. The building department for Duncannon can tell you which figure applies. What it does to a roof is in the roofing code guide.
| City | Re-roof permit | Code | Median built |
|---|---|---|---|
| Duncannon | Not published | Not published | 1939 or earlier |
| Bloomfield | Not published | Not published | 1943 |
| Marysville | Not published | Not published | 1955 |
| Newport | Not published | Not published | 1939 or earlier |
| Unincorporated Perry County | Not published | UCC (2021 IRC) | — |
Every Perry County city we cover, side by side →
Humid summers keep shingles damp here, and a roof face that gets little sun, whether shaded by the mountain slope, trees or the house next door, can stay wet long enough for moss and algae to take hold. The dark streaks are mostly algae and stain more than they harm. Moss holds water against the shingles and can lift their edges, letting water reach the boards underneath. Scraping or pressure washing can strip granules, so gentle cleaning is safer.
National Weather Service storm reports put 1-inch hail 0.4 mile north of town on September 7, 2023, and 1.25-inch hail 3.3 miles southeast on July 17, 2021. Stones that size can knock granules off worn asphalt shingles and crack brittle old slate, and the marks are hard to see from the yard. A roof that looks fine from the street may still carry bruises that show up only up close.
Duncannon publishes no rule on it. We ask the building department first and pull whatever it requires.
Median year built 1939 or earlier, by the Census Bureau's 2020–2024 estimates. Of 715 homes, 704 were built before 2000 and 505 before 1940, so most roofs in Duncannon are not the first one the house has had.
2 reports of 1-inch-plus hail fell within 5 miles of Duncannon between 2016 and 2025, the biggest 1.25 inches on July 17, 2021 (NOAA Storm Prediction Center).
Not yet: no completed roof in Duncannon is in our job records, so this page shows no job count.
Researched 2026-11-09; housing, Census ACS 2020–2024; hail, NOAA SPC. Sources: data.census.gov · data.census.gov · data.census.gov · www2.census.gov · www2.census.gov · data.census.gov · data.census.gov · en.wikipedia.org · www.spc.noaa.gov. Rules and staff change; check with the jurisdiction.