Should a slate roof be repaired or replaced?
Most slate roofs should be repaired, not replaced. Good slate can last 75 to 100 years or more, and most leaks come from the flashing, the valleys, or a few broken, slipped, or wrong slates. Replacement starts to make sense only when a large share of the slates themselves are soft, flaking, or breaking apart.
If you want me to take a look, text a picture to 443-900-4815 or call the same number. I'm James. I've worked on roofs around Baltimore City and Baltimore County for 24+ years, including slate and copper on older homes, and I'm licensed and insured, MHIC #154344.
Why is slate usually worth saving?
Slate is stone. The slates on many older Baltimore homes still have decades left in them, even when the roof is leaking. What wears out first is usually everything around the slate: the flashing at chimneys and walls, the metal in the valleys, and the nails that hold each slate. Those can be repaired while the good slate stays on the roof. The National Park Service's guide to slate roofs makes the same point: Preservation Brief 29.
How can I tell if the slate itself is done?
- Flaking or peeling layers on the face of the slates.
- Soft slates that crumble at the edges or break easily when handled.
- White powder or crusty spots on many slates, not just a few.
- Lots of broken or slipped slates all over the roof, not just in one spot where someone walked or a branch hit.
A handful of broken slates isn't a worn-out roof. A roof where most of the slates are soft and flaking is.
What usually goes wrong on slate roofs?
- Flashing and valleys. Old metal rusts through or pulls loose long before the slate wears out.
- Nails. When the nails holding a slate rust off, the slate slides down and leaves a gap.
- Foot traffic. Walking on slate cracks it. A lot of damage comes from people getting on the roof for other work.
- Wrong materials and patches. Tar smeared over slates, mismatched replacements, or slates put in the wrong way.
A slate repair from our work
The real slate on this roof was fine. The leak came from how the patch had been put in, so the fix was redoing that section the right way, not a new roof.
How we work on slate
- Look at the roof first, from a roof ladder or with the drone, so nobody walks on the slate. I'm an FAA-licensed drone pilot.
- Find what's really leaking: flashing, valleys, or particular slates.
- Send you pictures of what we found, with a price before any work starts.
- Replace broken and slipped slates to match, and fasten them so they stay put.
- Repair the flashing and valleys, including copper. We re-solder copper seams when they open up.
See roof repair for the other roofs we work on, roof materials for how slate compares, and roof lifespan for how long each kind of roof lasts.
You can text me at 443-900-4815 with pictures of the roof and where it's leaking, or call the same number.
Slate roof questions
How long does a slate roof last?
Good slate can last 75 to 100 years or more. The flashing, valley metal, and nails usually need work well before the slate itself wears out.
Can you walk on a slate roof?
You shouldn't. Walking on slate cracks it. We work off a roof ladder so we don't crack the slate, and I can look at a steep slate roof with the drone first.
Can one broken slate be replaced?
Yes. A single broken or slipped slate can be taken out and a matching one put in its place without disturbing the rest of the roof.
Should slate be patched with tar or caulk?
No. Tar and caulk crack and trap water, and they make the slates around them harder to repair later. A broken slate should be replaced, and leaking flashing should be repaired.
Are synthetic slates OK as a patch on a real slate roof?
They can work if they're the right size, but they're not the optimal choice, and we only use them if the homeowner asks. In the job above, someone else had put them in and the roof leaked. We took them out, reinstalled them, and put in new copper transition metal.
