Westlake has some of the best-built homes in North Texas, and a growing number of owners want a roof that’s actual stone. Not a slate-look shingle or a composite. Real slate. Once you decide on natural slate, the next question is the one most websites skip: where does the slate come from, and does it matter?
It matters a lot. The quarry decides the color, how that color changes over decades, how thick the slate can be split, what it weighs, and what warranty comes with it. I’m Blake Snow. I’ve been roofing for 30 years. Here’s how the main natural slate sources compare, using what each company publishes about its own slate.
The short version
| Source | Where the slate comes from | Color range | What stands out |
|---|---|---|---|
| Greenstone Slate | Vermont’s Slate Valley; manufactured in Poultney, VT (two colors are the exception) | Grays, gray-greens, purples, mottled green/purple, red, gray-black, plus Unfading Spanish Black | Five thickness grades with published weights and hail ratings; 100-year warranty; Miami-Dade approved |
| Evergreen Slate | Vermont slate; yard in Middle Granville, NY, near the Vermont line | Unfading green, gray, red and mottled green-purple; Vermont black; royal and variegated purple; semi-weathering gray and gray-green; Canadian black | Supplying slate since 1916; sources from about two dozen quarries; Florida Product Approval FL8802 |
| New England Slate | Vermont slate from Poultney, VT, plus a Spanish black | 14 colors including North Country Unfading Black, Penrhyn Unfading Purple and Spanish Black | Family business; detailed guidance on sizes, headlap and weathering |
| Buckingham Slate | Arvonia, Virginia, quarried at the same site since 1867 | Unfading blue-black | Long proven track record; roofing slate now sold as clearance inventory |
| CUPA PIZARRAS | 24 quarries and 29 processing plants in Spain | Black and dark gray tones, smooth or rough | World’s largest slate producer; 100-year manufacturer’s guarantee; READYSLATE lightweight system |
Sources: Greenstone Slate, Greenstone Vermont slate colors, Evergreen Slate, Evergreen slate colors, New England Slate: Our Slate, Buckingham Slate: About, CUPA PIZARRAS roofing slate.
Start with the grade: ASTM C406 S1
Every serious slate conversation starts with ASTM C406, the standard for roofing slate. Grade S1 is the top grade. Greenstone says S1 slate is rated to last at least 75 years and that all its colors have been tested to S1. Its Vermont slate absorbs less than 0.0025% of its weight after 72 hours underwater. Buckingham notes that most companies now say they have S1 slate, and points to its 150-year track record on real buildings.
What I tell Westlake owners: ask for the S1 test documentation on the specific color and quarry, not just the brand. Slate is stone, and stone varies by vein.
Thickness and weight: the numbers that decide your framing
This is where natural slate differs most from every synthetic. Greenstone publishes five grades:
| Greenstone grade | Thickness | Weight per square (100 sq. ft.) | Hail rating (per Greenstone) |
|---|---|---|---|
| Standard Grade Selects | about 1/4” | 680 to 780 lbs | Not listed |
| Standard Grade Rough Texture | 1/4” to 3/8” | 900 to 1,000 lbs | Class 3 |
| Architectural Grade | 3/8” to 1/2” | 1,200 to 1,600 lbs | Class 4 |
| Heavy Grade | 1/2” to 3/4” | 1,800 to 2,200 lbs | Class 4 |
| Estate Grade | 3/4” and up | 2,500 to 3,000 lbs | Not listed; Greenstone expects 150+ years |
Source: Greenstone Grades of Slate.
For comparison, CertainTeed lists its slate-look Belmont shingle at about 275 lbs per square and Grand Manor at about 418. On a big Westlake roof, going from Standard to Architectural Grade slate can add many tons. We check rafters, decking and ridge support before we price slate. If the house wasn’t framed for it, there are options:
- Greenstone SlateTec and Nu-lok are lightweight installation methods. Greenstone says they can cut installed slate weight by up to 40%, to under 6 lbs per sq. ft.
- CUPA READYSLATE is a pre-assembled natural slate roofing system CUPA describes as lightweight.
Hail in North Texas: what the slate makers actually claim
Greenstone says its Architectural Grade Vermont slate (3/8” and thicker) received a Class 4 hail rating in independent lab testing. Its Standard Grade Rough Texture (1/4” to 5/16”) received Class 3. Greenstone’s HailFire product was lab tested against 2-inch hail at 120 mph and earned a Class 4, FM 4473 rating. New England Slate says natural slate is rated Class 3 and Class 4 for hail impact (3/4” to 2” ice balls).
The pattern is simple: thicker slate takes hail better. If your goal is fewer hail claims on a Westlake estate, put the thickness on the quote in writing. And ask your insurance agent how they rate slate. Greenstone itself says to check with your agent about slate coverage.
Unfading vs. weathering: choose the color you’ll have in 20 years
New England Slate’s FAQ explains it well. Unfading slate changes very little from its freshly quarried look. Weathering and semi-weathering slates turn partly brown, buff or tan as minerals oxidize. Some quarries go almost 100% brown, others as little as 10%. You often can’t tell which pieces will change until they’ve seen a few months of sun and rain.
Greenstone draws a useful line between two words people mix up:
- Fading (in the old trade sense) is a chalky residue from calcium leaving the stone. That does weaken slate, and Greenstone ties the term mostly to some Pennsylvania and Virginia blacks.
- Weathering is color change from oxidation. It doesn’t hurt the slate’s strength or life.
Practical advice: if you want a uniform gray-black roof on a modern Westlake stone home, look at unfading blacks and grays: Vermont gray-black, Unfading Spanish Black, CUPA’s dark grays, or Buckingham’s blue-black if supply allows. If you want an old-world blended roof, semi-weathering Vermont gray-green or a mixed purple can be beautiful. Just choose it on purpose.
Each source, in a little more detail
Greenstone Slate (Poultney, Vermont)
Greenstone has quarried Vermont slate since 1955 and draws from 58 quarries in the Slate Valley. All its colors are tested to S1. It offers a 100-year warranty on its slate and is Miami-Dade County approved for hurricane zones (tested at sustained 110 mph wind with rain). It also publishes the most detail of any source on grades, weights and hail ratings, which makes it easy to spec.
Evergreen Slate (Middle Granville, New York)
Evergreen has supplied Vermont natural slate since 1916 and says it sources from approximately two dozen quarries. It sells blends as well as single colors, and supports graduated-length, graduated-thickness and random-width roofs. Evergreen cautions that availability varies by quarry, size, thickness and texture, so plan large or custom jobs early. It holds Florida Product Approval FL8802.
New England Slate (Poultney, Vermont)
New England Slate began in 1974 salvaging Vermont slate and grew into a full supplier. Its current color list includes Vermont blacks, grays, greens, purples and red, plus Penrhyn Unfading Purple and a Spanish Black it describes as coming from northwestern Spain. Its FAQ covers the details that make or break a slate roof: about 36 standard sizes, lengths from 12” to 24”, standard 3” headlap (4” on slopes under 6/12), and the warning never to “stretch” slate by cheating headlap.
Buckingham Slate (Arvonia, Virginia)
Buckingham’s unfading blue-black slate has been quarried at the same 500-acre site since 1867, and the company says many Buckingham roofs are older than that. Today, though, Buckingham’s site lists roofing slate under Product Clearance (“our remaining inventory of roofing slate”) and describes its current production as hardscape products. If you have a Buckingham roof that needs repair, or you love the look, call us first. We’ll check what’s still available before anything gets designed around it. Source: Buckingham Product Clearance.
CUPA PIZARRAS (Spain)
CUPA has produced natural slate since 1892 and says one in two slates in the world carries its name. It runs 24 quarries and 29 processing plants in Spain. Its slate is black and gray, in smooth or rough textures, sorted into four selections by flatness and thickness. CUPA offers a 100-year manufacturer’s guarantee on all its natural slates, but read the steps: your roofing contractor must request it within one year of the distributor’s invoice date, with the pallet identification and the invoice. We keep those records for you. Source: CUPA 100-year guarantee.
What a slate warranty does and doesn’t do
A 100-year slate warranty covers the stone. It doesn’t cover nails, flashings, underlayment or workmanship, and those are what usually fail first. That’s why we use copper or stainless steel fasteners and copper flashings on natural slate, and why our workmanship warranty is in writing: from 10 years up to lifetime, depending on the job.
What goes on our natural slate quotes
- Source, color, and whether it’s unfading or weathering
- Grade and thickness range, and the weight per square
- Size, exposure and headlap for your roof pitch
- Fasteners (copper or stainless), flashing metal and weight, and underlayment
- Framing check results, and a lightweight-system option if needed
- Who registers the manufacturer’s warranty, and when
- A free digital photo report
Related reading
- Natural slate repair vs. replacement in Southlake and Westlake
- Copper flashing, valleys and gutters on slate and tile roofs
- Slate and copper on turrets, mansards and complex rooflines
- Prefer a lighter slate look? See Enviroslate on Tudor homes and DaVinci Multi-Width Slate.
Talk to us about natural slate in Westlake
We install and repair natural slate in Westlake, Southlake, Trophy Club, Keller and across DFW, installed to manufacturer specs by certified installers. We’re certified with GAF, CertainTeed, Owens Corning, Atlas, Johns Manville, Carlisle, Tropical Roofing Products, Mule-Hide and Enviroshake, and many other roof manufacturers. We’re BBB A+ rated, with 5.0 stars on Google at all three offices: Bridgeport, Decatur and Rhome. Request a free inspection or call (817) 733-9228.
