Slate roofs in Pennsylvania: repair, replace or switch to synthetic?
Updated · KeystoneProGuide editorial team
Why do so many older Pennsylvania homes have slate roofs?
Because the American slate industry grew up here. The National Park Service says the first commercial slate quarry in the United States opened in 1785 in Peach Bottom Township, Pennsylvania, that quarries later opened in Lehigh and Northampton Counties, and that Pennsylvania was historically the largest producer of all. Slate roofs were in use in Philadelphia as early as 1699.
The industry peaked between 1897 and 1914 and began to decline in 1915, the Park Service says, as skilled labor became scarcer and cheaper asphalt shingles took over. The National Roofing Contractors Association (NRCA), the trade's association, says slate is still quarried in Pennsylvania, New York and Vermont, and that many older homes, especially in the Northeast, are still protected by it.
How long does a slate roof last?
Much longer than most roofs. The Park Service says a properly installed slate roof needs relatively little maintenance and lasts 60 to 125 years or longer, depending on the type of slate, the roof's configuration and the location, and that some slates have lasted over 200 years. It credits slate's very low water absorption, under 0.4%, with making it resistant to frost damage. NRCA, for comparison, says most new roofs are designed for about 20 years of service.
Should a leaking slate roof be replaced?
Not if it can be repaired. The Park Service says historic slate roofs should be repaired rather than replaced whenever possible, and that all too often they are mistakenly replaced when they could have been effectively repaired.
Repairs often center on the metalwork. The Park Service says that, given how long slate lasts, it is poor economy to use anything but the most durable metals and the best workmanship for flashing, and it names copper as one of the best flashing materials, with lead-coated copper often used in restoration. The building code points the same way: in a reroof, existing flashings, edgings and vents that are rusted, damaged or deteriorated must be replaced.
HomeAdvisor's survey gives an average slate roof repair of $1,800, and HomeGuide gives a range of $500 to $2,100.
What if the slate has to be replaced?
Then the choices are new natural slate, reused slate, or a substitute. The code allows existing slate to be reinstalled, but not damaged, cracked or broken pieces. It does not allow a new covering to be laid over existing slate: a slate roof must come off before anything else goes on.
New slate is expensive. HomeGuide puts a natural slate roof at $10 to $30 a square foot installed, or $22,000 to $70,000 on average, and Fixr gives $20,000 to $60,000 for a roof of about 2,000 square feet. The Park Service's view is that replacement, though costly, can be very reasonable when spread over the life of the roof.
Is synthetic slate a good substitute?
It depends on what you want from the roof. HomeGuide prices synthetic slate at $9 to $12 a square foot installed, or $12,500 to $26,000, well below natural slate.
The Park Service is unenthusiastic, at least for restoration work. It says artificial mineral fiber slate is not recommended there because it looks man-made, and that artificial slates may fade over time. It also argues the saving is smaller than it looks: the total initial cost of an artificial slate roof is only marginally less than a natural one, because labor, flashing and tearing off the old roof cost the same either way. Over the long term, it says, several artificial slate roofs would be needed during the life of one natural slate roof.
NRCA's general caution applies too. It says synthetic roofing materials simulate traditional coverings such as slate but do not necessarily have the same properties, and that it is important to research any synthetic product before choosing it.
Is slate too heavy for some houses?
The sources read do not give a slate-specific answer. The building code requires any roof structure to be able to carry its roof covering and the loads of materials and equipment during installation. NRCA makes the point for tile, which it calls heavy enough that you must verify a house can support it before it replaces a lighter covering. If you are thinking of putting slate on a house that does not have it now, ask the roofer how the structure will be checked.
What if the house is historic?
In Philadelphia, a property on the city's Register of Historic Places needs a review by the Historical Commission for the installation, repair, removal, replacement or covering of roofing and flashing. The review is free, and the city suggests contacting the commission's staff while the project is being planned. Outside the city, ask your municipality whether the house is in a local historic district.
How do you find the right roofer for slate?
Ask about experience first. NRCA says slate's application requires special skill and experience, and the Insurance Institute for Business and Home Safety (IBHS) says to make sure any roofer has worked on your roof type before, because different materials need different skills and not every contractor handles them all. Ask how many slate roofs the company has repaired, how it will match replacement slates, and what flashing metal it proposes.
Should you repair or replace covers the general decision, how to choose a roofer the wider checks, and the Philadelphia guide the city's rules. Roofers serving the area are on the roofers directory page.
Sources
- Should I Replace My Slate Roof with a Synthetic?, National Park Service
- Roofing Materials, National Roofing Contractors Association (NRCA)
- Chapter 9 Roof Assemblies, 2021 International Residential Code, International Code Council
- How Much Does Roof Repair Cost in 2026?, HomeAdvisor
- How much does a roof replacement cost?, HomeGuide
- How Much Does a Roof Replacement Cost? [2026 Data], Fixr
- Tips for Hiring a Roofing Contractor, Insurance Institute for Business & Home Safety (IBHS)
- Get approval for work to a historic property, City of Philadelphia