Slate to asphalt · fix or replace

Should You Fix or Replace a Leaking Slate Roof?

Many leaking slate roofs have years left in the stone. The test is how much of the slate itself has failed, not whether the roof leaks.

Ask which one your roof needs How estimates work

Based on National Park Service guidance
Honest about when we are the wrong call
No-cost referral if you need a slate specialist

Should you fix or replace a slate roof?

Fix it if fewer than about 20% of the slates are broken, cracked, missing or sliding; replace it if 20% or more are. That threshold comes from the National Park Service, which says that past it, replacing the roof is usually less expensive than individual repairs. Flashing failures alone rarely justify replacement.

RoofVista's Pennsylvania guide (March 2026) uses a similar 20% to 25% threshold. Whichever number you use, it applies per roof or per slope, so one bad slope on an otherwise sound roof is not a reason to strip the whole house.

Black-and-white detail of a worn slate roof where two roof sections meet — Illustrative stock photo.

How long does a slate roof last?

Slate lasts roughly 60 to 125 years or more, depending on the stone. The National Park Service gives Pennsylvania soft-vein slate a life of over 60 years, Pennsylvania hard-vein about 100, Vermont and New York slate about 125, and Peach Bottom slate at least 200 years.

So the age of the house is not the test. A 1925 roof of soft-vein slate can be near the end, while a hard-vein roof the same age may have decades left. A slate specialist can usually identify the type.

Signs that point one way or the other

What you see	Points toward	Why
A few cracked or missing slates on one slope	Fixing	Below the roughly 20% guideline in the NPS brief
Leaks at the chimney, valleys or walls only	Fixing (flashing)	The NPS notes flashings often wear out before the slate
Slates that flake, delaminate or crumble when tapped	Replacing	The stone itself is failing, not just its fasteners
Slates sliding everywhere from rusted nails	Replacing	Widespread nail failure means re-laying the whole roof
Water stains with no visible damage, in cold weather	Neither yet	The NPS describes false leaks from attic condensation
Tar or mastic smeared over many slates	Get it inspected	The NPS says mastic is not a viable repair

Summarized from National Park Service Preservation Brief 29. A rule of thumb, not a diagnosis.

Who should look at a slate roof that might be fixable?

A slate specialist should, because the job is replacing individual slates, flashing and nails with the same craft the roof was built with. We replace slate roofs with asphalt and don't do that work. If our inspection says the slate has life left, we'll tell you and point you to a specialist.

The National Park Service also warns that significant slate roofs should not be stripped off and replaced with asphalt, which is why we start from the condition of the stone rather than from a sale.

Close-up of rough, weathered stone slate roofing — Illustrative stock photo.

Before you decide

Count the damaged slates on each slope from the ground with binoculars, or from photos.
Note where the stains are inside: under a chimney or valley points to flashing.
Ask what kind of slate it is; soft-vein Pennsylvania slate wears out first.
Ask whether the deck under the slate is sound if you are leaning toward asphalt.
Check whether the house is designated before anything is stripped.

Fix-or-replace questions

Can you replace part of a slate roof with asphalt?

On a single slope or a rear section it is possible, and sometimes allowed where the main roof is protected. The two materials need careful flashing where they meet, and on a designated house the review board decides. We look at it case by case at the inspection.

Will you send me to a slate specialist if you can't help?

Yes. If your roof needs slate work rather than a replacement, say so on the form and we'll point you to someone who does that work. There is no charge for that.

Sources and checked date

National Park Service, Preservation Brief 29: The Repair, Replacement, and Maintenance of Historic Slate Roofs (Levine, 1993) 20% guideline, lifespans, flashing, false leaks, mastic
RoofVista, Historic slate roofing in Pennsylvania (Mar 26, 2026) accessed Oct 29, 2026

Last checked 2026-10-29.

Fix or replace? Tell us about the roof

Tell us where the house is, how old the roof is and what it is doing. If you have photos, say so and we will ask for them by email. Outside our core area? Send the form and ask.

We answer form requests Monday to Friday, 9am to 5pm. There is no phone line, so the whole conversation stays in writing.