"I am tired of spending money on my slate roof! I don't know who to believe; one contractor tells me I need a new roof, the other wants to flash my chimney with tar!"
During the twenty years I worked as a slate-roofing contractor I heard many variations of this complaint. I met homeowners who wanted only to hear good news and knew contractors who operated solely out of self-interest. Ideally a customer/contractor relationship would be based on fair compensation, trust and good service. The best are, but they require an acceptance of vulnerability for both parties at the outset, and time to develop.
Slate Lifespan by Type
Understanding your slate type is the first step in making the repair-or-replace decision. Different slates have dramatically different life expectancies:
| Slate Type | Expected Lifespan |
|---|---|
| Bangor Slate (Pennsylvania Black) | 50–80 years |
| Chapman Slate | 80–100 years |
| Vermont Slate (Green, Black — soft grades) | 90–110 years |
| LaBaña Slate (Spanish) | 100+ years |
| Grayson / Buckingham Slate (Virginia) | 150+ years |
| Peach Bottom Slate | 150+ years |
There will be variations depending on the roof's exposure and pitch. Steep roofs last longer since they shed water and snow more quickly. A south-facing roof in a harsh climate will age faster than a north-facing roof in a milder one.
Note on Vermont hard slate: Vermont hard slate (ASTM S-1, such as Newmont Vermont Black) is classified as hard slate with a documented lifespan of 150–200 years. The 90–110 year figure above applies to softer Vermont grades. When specifying Vermont slate for a long-term installation, always confirm the ASTM grade with your supplier.
When to Replace
If your slate roof is requiring increasing upkeep and is past its life expectancy, a new roof should be considered. In terms of good, better, best categories: Vermont slate (black or green), LaBaña (Spanish slate), and Grayson (Arvonia, Virginia). All metal flashings should be replaced at the same time — there is no point in installing a new slate roof over deteriorated copper or lead flashings.
Warning signs that replacement is warranted include: widespread delamination (slates splitting into layers), excessive breakage across the entire roof surface, soft or crumbling slates, and pervasive flashing failure. If more than 20% of slates need replacement, a full re-roofing is typically more economical than ongoing repairs.
When to Repair
If your slate roof has not reached its life expectancy, repair is the better way to go. There is a further choice: repair with new or reclaimed slate. Reclaimed slate is good slate taken from other roofs for reuse. New slate is typically cut thicker than older slate and when inserted into a roof will cause surrounding slate to stick up — these will eventually break due to stress. Reclaimed slate will match the thickness and have the same or similar weathering.
Localized damage — from a fallen branch, storm impact, or isolated flashing failure — is always a candidate for repair rather than replacement. A qualified slate roofer can replace individual slates using a slater's ripper and bib (or "bib" nail) without disturbing the surrounding roof.
Choosing a Contractor
First and foremost your contractor should be licensed and insured. If they have employees, they should be covered for workers' compensation. Contractors should provide before and after photos. More importantly, before they are hired, photos of previous work they have completed. If they are proud of their work, they take photos — and deserve the bragging rights!
Ask for references from slate roofing projects specifically — not just general roofing work. Slate requires specialized skills and tools. A contractor experienced only with asphalt shingles may do more harm than good on a historic slate roof. The Slate Roofing Contractors Association (SRCA) is a good resource for finding qualified professionals.
Newmont Slate can recommend qualified slate roofing contractors in your area. Contact us with your location and project details.
Frequently Asked Questions
Ready to assess your slate roof? Contact Newmont Slate for expert guidance. Browse our slate roof maintenance guide or inspection checklists for more information.
