Secrets of Slate Roofing
It's hot, heavy, and hard work installing it, but few roofs look as good or last as long.
Synopsis: Remodeler and roofer Andrew Grace describes the process of working with slate on one slate-roofing project. He begins by determining the layout of the slate courses, with the appropriate amount of side lap, head lap, and exposure. Using tools specific to working with slate, he makes his way up the roof, punching holes for nailing and showing the method of cutting slates for rakes, valleys, and other transitions before capping the ridge.
Although I have repaired many slate roofs, opportunities to install an entire new slate roof are few and far between. When these customers first contacted me about their rapidly deteriorating 80-year-old slate roof, the conversation began with talk of replacing the slate with standing-seam metal. When they later asked me about pricing the job with new slate, I gave them a quote, but I’ll admit I was a little surprised when they chose slate over steel at nearly twice the price.
My crew and I are all experienced roofers, but I felt a project of this scale required some additional training. The Slate Roofing Contractors Association (SRCA) offers slate roofing training courses at sites across the country. Luckily for us, Joe Jenkins, the man who literally wrote the book on slate roofing— The Slate Roof Bible is a tome I’ve owned for many years— lives two hours from me and offers classes at his shop.
I learned that installing slate is as much about feel as it is about technical knowledge. The hands-on training proved invaluable, and after an intensive and informative class, we were ready for our first whole-house slate project.
Getting slate to your job
The color and durability of slate depends on where it’s quarried. My customers wanted to approximate the color of their old roof, so they chose a non-weathering black slate from Glendyne, a quarry in Quebec, Canada. It is high-quality slate with a consistent color that cuts easily and predictably. Slate roofs can have complex geometric patterns, a mix of different slate sizes, and even a completely random layout. We went with a 12-in. by 20-in. size and a simple running-bond layout. I ordered the slate directly from the manufacturer and it was shipped by LTL Freight. It took a little over three weeks to arrive once I placed the order.
In addition to our 12×20 common slate, I ordered a few hundred 15×20 slates. These wider slates can substitute for a common slate plus a small piece, eliminating skinny pieces of slate, which are prone to breakage. I also ordered 100 starter slates and 100 lb. of copper nails for this 40-square roof (one square is equal to 100 sq. ft.). When the materials arrived at the site, I was responsible for unloading the 11 crates, which weighed north of 5000 lb. each. I had a friend with a large all-terrain forklift unload the truck and place the pallets on three sides of the house, so we wouldn’t have to move them any farther than necessary when getting the slates to the roof.
From Fine Homebuilding #296
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Also read the bonus article, Make a Copper Flashing Boot.