Repairing Slate Roofs, contined
Slate comes in various sizes and thicknesses. Typical roofing
slate is about 3/16 inch thick and ranges from 6 to 14 inches
in width and 12 to 24 inches in length. To match what's on the
roof, try to measure an existing slate on a gable end (or on
the ground if one has slid loose). If you have to guess,
measure the exposed course height, double it and add 3 inches
for headlap (Figure 5). If the pitch is less than 4 in 12, use
a 4-inch headlap; very steep roofs such as mansards, or
sidewalls, may use just a 2-inch headlap.
Figure 5.Slates come in many sizes and
thicknesses. To estimate the size needed for a match, measure
the exposed course height, double it, and add 3 inches for a
standard headlap, 4 inches for pitches from 4/12 to
If you repair a graduated roof, you may need several different
sizes and weights. The larger and heavier pieces are placed
along the eaves, and succeeding courses get smaller as they get
closer to the ridge. Be careful to match both the height and
the thickness of the slate.
Flashing, Nails, and
Flashing and fastener failure account for a large percentage
of slate roof leaks. It's important to use materials that will
last as long as the slate, but that isn't always done. Iron
nails rust away, enabling wind and weather to slide slate out
of place. Valleys and metal flashings rust through and have to
be replaced. When repairing a slate roof, you'll seldom go
wrong if you use copper nails and copper, stainless, or lead
flashings. It's often necessary to fabricate and solder
flashings for durable jobs. If you don't have the skills for
that, bring in a sheet metal mechanic.
But for economic reasons, those top-of-the-line materials
aren't always appropriate. On some jobs, budget is a higher
priority than aesthetics, and some repairs are done just to
extend the life of the roof for a few more years. If you judge
that the roof will probably get replaced within 25 years,
aluminum siding nails and .024 or heavier aluminum flashing are
sensible choices. You don't want to install 100-year nails and
flashings on a roof that won't be around for three decades, any
more than you would appreciate it if your mechanic put lifetime
parts on a work truck that's on its last legs.
Tools and Techniques
For most slate repairs, only two specialty tools are required:
a slate ripper and a slate cutter. A regular hammer will do,
but a slate hammer, which has a sharpened upper edge on the
handle for cutting slate and a punch for making nail holes
(instead of the usual claw), is a worthwhile investment if
you're doing slate work on more than an occasional basis.
There are two ways to cut slate. Some experienced slaters use
a slate stake and hammer. But if you don't make your living
doing slate work, you won't appreciate the cost in time and
broken slate it takes to develop this cutting skill —
especially when a slate cutter is much easier to master and
produces great results.
The slate cutter's lever blade shears through slate, much like
a paper cutter (Figure 6). You can quickly learn to get nice,
accurate cuts by feeding the piece into the cutter's blade,
exposed face down, and nibbling through the slate with short,
ratcheting pumps of the lever. As it bites through the slate,
the blade breaks out the edge on the underside of the cut,
producing a scalloped bevel. Cutters retail for about
Figure 6.A slate cutter's lever arm is powerful
enough to readily shear through slate but allows fine control
for careful cutting. Here, slate roofing contractor John Kuhn
uses the tool to nibble out a half circle for a vent pipe
Slate rippers are invaluable in most kinds of slate repair.
They're used to remove the nails holding the damaged slate,
pull out damaged slate, and reinstall slate and flashing. About
30 inches long, slate rippers are forged from round steel. The
flattened blade at the end has a hooked notch on each side for
snagging and pulling out nails and broken slate. The center of
the flat tip also has a sharp notch you can use to shear off
nails that resist removal. Rippers retail for about $65.
Pulling slates. Most slates
are fastened with two nails. To remove a damaged slate, slide
the flat end of the ripper under the slate and push it up until
the hooked end is above the nail (Figure 7). Pull it sideways
and down to hook the nail in the notch of the ripper. A few
taps downward on the perpendicular section of the ripper handle
will usually loosen the nail. Repeat the procedure for the
other nail. With both nails removed, slide the ripper back
under the slate and press down on the top of the slate with
your free hand, sandwiching the slate between your hand and the
tool, and pull down on the ripper to slide the slate out.
Figure 7.Removing a cracked slate is quick and
simple with a slate ripper: The roofer slides the tool under
the slate and hooks the nails out with a combined pulling and
levering action (top left and right). A slate hook driven into
the roof will hold the bottom of the replacement slate (bottom
right). Sometimes the installer needs to punch and grind a
pilot hole for the hook into the crack between the two slates
in the course below (bottom left).
If the whole slate doesn't come out, reinsert the ripper and
pull out any pieces. (If you've ever had to use a "Slim Jim" to
unlock your car through a closed window, you've got the
To install the new slate, simply slide it into place. There
are two ways to fasten the replacement slate. One way is just
to punch a nail hole in the new slate between the edges of the
slates above, midway up the joint. Slightly pry apart the
overlaying slates above, just enough to drive the new nail
Unlike other materials, slate has to be nailed loosely: It is
important to leave the head of the nail slightly above the face
of the slate, so that the slate "hangs" on the nail. Driving
the nail tight against the slate prevents the slate from moving
as it expands and contracts with changes in temperature, which
overstresses the brittle slate and can cause it to crack.
The nail in the seam is exposed and has to be weatherproofed.
Cut a 3-inch-wide piece of flashing long enough to reach the
top of the new slate and cover the nail by approximately 2
inches. Bend a 90-degree flange at the top of the flashing
slightly shorter than the thickness of the slate. Using your
slate ripper as a push stick, push the flashing in place until
the bend "snaps" into place over the top of the new slate. Now
reorient the two slates above, and you have an invisible repair
(see details in Figure 5).
Slate hooks are another way to hold the new slate in place.
With the damaged slate completely removed, drive the pointed
end of the hook into the roof deck, leaving the crook of the
hook in line with the bottom of the replacement slate. Push the
new slate into place over the hook and pull it down to lock it
in. The exposed portion of the hook is usually invisible from
the ground. If the roof is visible from a dormer window,
however, I like to use the nail-and-flashing method because it
is much less apparent.
If you need to replace multiple slates in a small area, go
ahead and pull off a whole pyramid-shaped section and re-cover
the area from the bottom up. This minimizes the number of
slates you have to install with hooks or face nails and
Slate pieces usually come from the quarry with prepunched
holes, but when you cut slate to size, you may need to make new
holes. With practice, you can learn to do it quickly with the
slate hammer. But a slate hammer is not essential: You can do
the same thing with your usual hammer and 3/16-inch nail set.
Lay the slate face down on a uniformly supported surface, place
the punch tip where you want the hole, and strike a quick, hard
tap. This will make a neat round hole on the underside, but it
blows a tapered hole on the face side for the nail head to seat
into. It looks just like the round hole a BB gun makes in plate
Slaters are kind of like pilots: "There are old ones and there
are bold ones, but there are no old, bold ones." Slate roofs
tend to be steep and slippery. Accessing the work area safely,
without damaging the good slate, is one of the difficulties of
slate repair. It takes patience — rushing things is
dangerous for both you and the roof.
Slates are very hard, but they are also brittle and crack
easily. A soft-soled shoe is a must. Avoid walking directly on
slate if possible; if you must step on the roof, walk only on
the bottom of the exposed course where it's not spanning the
If the repair area is within arm's length of an eaves or gable
edge, a ladder will provide decent access. But more often, you
have to cross a sect ion of existing roof to get to the work
area. The idea is to spread your weight over several slates
— similar in concept to using kneeling boards to work on
fresh concrete. My preference on a slate roof is to work off
chicken ladders. I like to make my own, for the same reason you
pack your own parachute (Figure 8).
Figure 8.The author likes to build his own
"chicken ladders" to allow access to the areas that need work.
The ladder spreads his weight across a section of roof to
prevent the cracking that foot traffic can cause. The ladder is
made with straight-grain, clear 5/4 or 1x4 stock, with steel
brackets and a 2x6 bolted onto the top end for a ridge
I use clear straight-grain fir for the rails and rungs and
space the rungs 12 inches apart. At the top of the ladder, you
can bolt heavy, 6-inch, 90-degree flat metal brackets to the
top ends of the rungs with the bracket leg facing down, then
bolt a 2x6 to the bracket legs that will lay over the ridge to
keep the ladder from sliding.
Chicken ladders work efficiently on gable roofs, but hip roofs
offer a different challenge. The farther down you are from the
ridge intersection, the farther in you are from the hip.
Sometimes it works well to use a chicken ladder to get to the
right elevation, then you can install a roof jack close to the
hip and plank across.
Whenever you climb a roof, a rope and harness are a good idea;
in many cases, OSHA will expect it. The meaningful word when
you approach a slate repair is "forethought." No one method
will work in every situation, so plan each job the way a good
climber plans a cliff ascent. It often takes more time to set
up the job for safety and efficiency, and to demobilize
afterward, than it takes to do the work on the roof — but
the risks involved are just too great otherwise.
Norm Yeageris a contractor and construction
supervisor with more than 30 years' experience in the trades.
Thanks to John Kuhn and Tom Netzer of John Kuhn Copper for
assistance with photography for this story.
www.slateassociation.orgJenkins Slate Roofing Services
www.jenkinsslate.comPublisher of theSlate Roof
online tool store
Vermont Slate and Copper Services, Inc.
www.vermontslateandcopper.comPublisher ofThe Slate
source for slate tools and