Ask ten people in Delco what it means to own a house in a historic district and you'll get ten different answers, and most of them will be wrong in one direction or the other. Some think it means a government board approves their paint color. Others think a plaque on the porch means nothing has really changed. Neither is quite right, and which one applies to you has almost nothing to do with the county itself. It comes down to which of the 49 municipalities your address sits in, because that's where the actual authority lives.
National Register listing isn't a local historic district
Start with the distinction that trips up the most people: being in a historic district and being on the National Register of Historic Places are not the same thing. Rose Valley's historic district, for example, was added to the National Register back in 2010. That's a real designation with real meaning, mostly around eligibility for preservation grants and tax incentives on income-producing buildings. But National Register status by itself doesn't put anyone in front of a review board before they replace a window. It's an honor and a paper trail, not a permitting layer.
How a local historic district actually works
The kind of historic district that changes what you're allowed to do to your house is a local one, created by the township or borough under Pennsylvania's Historic District Act, the 1961 law that lets a municipality set up its own historic district and get it certified by the state. Once that happens, the municipality typically stands up a board, usually called a Board of Historical and Architectural Review or HARB, and from that point on, exterior work visible from the street needs a Certificate of Appropriateness before it can move forward. Sometimes that's a step before the building permit. Sometimes it's required even for work that wouldn't otherwise need a permit at all.
Radnor Township is a good working example, because it runs three of these districts under one HARB: North Wayne, Louella Court, and South Wayne. Media Borough runs its own separate process, where the review board looks at an application, meets with the applicant, and sends a recommendation to Borough Council, who actually issues or denies the certificate. Media's ordinance even builds in a hardship provision, so a certificate can't be denied if it would create an unreasonable burden on the owner. The point isn't to memorize either town's specific rules. It's that these are two different, independently run programs, a few miles apart, and neither one tells you anything about what a third township requires. There is no county-wide historic district permitting office. Delco doesn't work that way.
What gets reviewed, and what doesn't
What actually gets reviewed tends to follow a pattern even though the details vary. Anything visible from a public street or right-of-way is fair game: new construction, additions, demolition, replacement windows and doors, roofing, siding, sometimes exterior paint. Interior renovations are almost always exempt, since the whole point of these ordinances is protecting what the street sees, not what happens behind the front door. Plenty of local ordinances also carve out straightforward in-kind repairs, meaning if you're replacing rotted trim with matching trim rather than changing the design, the process is lighter than a full board review. But "plenty" isn't "all," and this is exactly the kind of detail worth confirming rather than assuming.
Before you hire anyone
If there's one practical takeaway here, it's this: before you plan anything on the exterior of an older Delco home, call your specific municipality's building or zoning office and ask one direct question, is this property inside a locally designated historic district, not just an old house, not just a National Register area, but the kind of district with an actual board and an actual certificate requirement. If the answer is yes, build the board's meeting schedule into your timeline. Most of these boards meet monthly, and a COA that has to go on next month's agenda can add real time to a project before a shovel ever goes in the ground.
It's also where working with a contractor who's already sat through one of these reviews starts to pay for itself. Someone who's done it before knows what the board wants to see on the drawings and won't leave you scrambling over a rejected material sample three weeks into a permit clock you didn't know was ticking. That kind of experience is worth screening for specifically when you're hiring, not just assumed because someone's been doing renovation work in the area for years.