You may surprised to learn that you can install slate shingles. When you think of slate roofs, images of churches and historic Victorian homes come to mind. You can’t run down to Home Depot and grab slate tiles at 20% off. Still, when you drive around neighborhoods of slate-topped homes, you can’t help but admire the subtle beauty of natural stone roofs.
If you live in a slate-shingled house, you might need to make repairs or want to add-on a room with a matching roof. Perhaps you’d like to build an authentic shed or gazebo, and want to use slate for the crowning touch. While it’s best to employ professionals for large or steep roofs, you can tackle smaller projects yourself with great results.
Slate Roofs Are Different
Asphalt shingles are of uniform size and are easy to install. Not so for slate! Each slate tile is unique in size, thickness, and hue. This variation is what makes a natural slate roof so beautiful. Consider the installation of slate an artistic challenge, rather than a chore.
You probably don’t own the right tools. Rent or borrow what you need; don’t take shortcuts. In addition, slate roofs aren’t walkable. One industry expert asserts: “Roof slate is not to be walked on – period. It is not a floor…” (source: Joseph Jenkins of traditionalroofing.com – Grove City, PA) Techniques for staging on asphalt are useless for slate. Consult your supplier for cutting tools, ladder hooks and roof scaffold brackets.
Find The Right Slate First:
To get started, use the Internet to locate a supplier in your region. If slate roofing is common in your area, chances are there’s a quarry less than 500 miles away. Slateroofers.org, for instance, lists 27 suppliers in 13 states. In addition, “salvage slate” may be an option.
Slate is described by color and origin: Vermont green or Spanish black, for example. To match an existing roof, you’ll need samples and/or good close-up pictures. Slate tiles come in various standard sizes, too. You may want to pay a consultant for a site visit. Your slate source can also help you find the right flashing and cap materials.
Before you begin, sort your delivered slate by thickness. Typically, you’ll install the thickest pieces first and graduate to thinner tiles closer to the ridge. Cull out damaged slates and set them aside for cuts. If your job involves more than one pallet, thoroughly mix the tiles. Be sure all of your slate is from the same lot source!
What Goes Under A Slate Roof?
If you’ve done any roofing, you know about plywood sheathing and felt paper. The ideal deck for slate, however, is solid wood at least 3/4″ thick. In addition, the rafters beneath MUST be strong enough to carry the extreme weight of slate roof tiles (from 8 to 15 lbs/sq ft). As for underlayment, one expert notes:
“Properly installed slate roofs need no underlayment. The main purpose of underlayment is to keep water out … until the slate and flashings are installed.” (Jenkins)
* A correctly installed slate roof will not leak. *
That a bold statement places the right emphasis on your efforts.
Note these critical steps:
- Starter rows at the eaves
- Correct headlap (the overlap layer to layer)
- Correct sidelap (the overlap of successive shingles)
- Proper nailing
- Flashing design and materials
- Cap and other trim details
Slate Shingle Installation Starter Course:
Your first row sets the stage for success. A slate roof’s starter course uses full tiles installed face-down, with a “cant strip” (or raised drip edge) to induce the right angle from the beginning. Even this first, hidden row of shingles will have headlap: the bottom edge of the second row above it will overlap the top of the starter shingles by at least 3″ (depending on roof pitch).
Headlap and sidelap:
As noted, all tiles should overlap those two rows below by about 3″ (varies by roof slope) – that’s the key for preventing leaks. Sidelap is the shift of joints from one row to the next, ideally about 1/2 the width of a tile. If you get either of these wrong, be prepared for failure.
Nailing Slate Roof Shingles:
Each slate has 2 drilled, recessed holes for nailing. Add 2 shingles’ thickness plus the roof deck to find the correct nail length. Neither over-drive nor under-drive the nails; broken tiles will result from either error.
Flashings, caps, and trims:
Most slate installations use soldered or folded copper trim. Your roofing supplier should provide complete documentation for these crucial transition materials.
Once you understand the important differences between slate and asphalt shingles, covering your roof with stone tiles isn’t quite so scary anymore. Work carefully from the bottom-up, using the proper tools and techniques, and you’ll be proud of the gorgeous roof you build.