My company specializes in cedar roofing and siding here on
Cape Cod, where cedar has long proven its durability even in
severe coastal weather conditions. Correctly installed, a
premium cedar roof can easily last 25 years — and
typically much longer. In this article, I’ll talk about
the specific cedar products and installation procedures we use
to ensure a long service life.
Shingle or Shake?
Although the terms “shingle” and
“shake” are often used interchangeably, they are in
fact two distinct products. Shingles are always sawn on both
faces and are thinner, usually with a 7/16-inch butt. Shakes
have 5/8- to 3/4-inch-thick butts and are split — rather
than sawn — from the log, resulting in a rough, uneven
face. (Taper-sawn shakes are unique in the category in that,
like shingles, they are sawn on both sides. However, for all
intents and purposes, I consider taper-sawns to be nothing more
than thick shingles. Generally, the thicker the shingle, the
longer it lasts.) Whether split or sawn, roofing application
calls for a product with least 90 percent “edge
grain,” meaning grain oriented perpendicular to the
surface. Edge grain produces better stability and minimizes the
cupping and splitting that wood undergoes in the wetting and
Grading. Manufacturing members of the CSSB, the Cedar
Shake & Shingle Bureau (604/820-7700,
rely on a standardized “Certi-label” program,
adopted by the major code agencies, to identify various shake
and shingle grades (see Figure 1). Grading
rules are listed on the CSSB Web site. This is important
information because building codes stipulate certain minimum
standards for wood roofs. Using the wrong shingle could spell
big trouble. The IRC (905.7.4) defers to CSSB grading rules for
approved shingles, which include grades 1, 2, and 3.
Figure 1. Code-recognized grading rules include
strict specifications for cedar roofing shingles. This chart
(top), from the Cedar Shake & Shingle Bureau Web site,
shows the basic grading rules for 18-inch
“perfections,” a premium shingle. Note that as
shingle grade declines from “No. 1-Blue” to
“No. 3-Black,” the allowable exposure shrinks. A
CSSB “Certi-label” (above), required under every
bundle band, confirms a mill’s participation in the
standards program. The one shown above was taken from the
taper-sawn shakes seen in this article.
On our roofs, we don’t use anything but premium grade,
which is 100 percent clear heartwood and 100 percent edge
grain. It’s the best guarantee that the roof will perform
without any problems for the longest period of time. The
shingles we consider suitable for roofing include 18-inch
“perfections” and 24-inch “royals.”
Sixteen-inch “fivex” (5-inch exposure) shingles are
also available and are allowed by code, but we never use them
on the roof.
Finally, while shake roofs are common in the West, I have yet
to install one here in New England. (There are a few
differences between shingle and shake installation, which
I’ll touch upon later.)
Warranties. Although it’s ending this year, the
CSSB has historically offered a warranty program on behalf of
its manufacturing members, made available through CSSB-approved
installers (of which I’m one). In the future, warranties
will still be available directly from the individual
A wood roof is an expensive roof. Two or three years ago, in a
red-hot market, I was paying $300 per square for premium red
cedar shingles. In today’s flat economy, prices are well
under $200 per square, helping to make red cedar a more
attractive alternative to 50-year asphalt shingles.
That’s not to say the two are competitive, exactly; I
generally quote a replacement roof in asphalt at around $375
per square and cedar starting at $600 per square.
New-construction costs are slightly lower.
Wind resistance. Wood shingles are rated for wind
pressures equal to 173 mph, and shakes to 245 mph — a
certain advantage over asphalt shingles in hurricane zones.
Insuring a wood-roofed home can still cost more, though,
because it’s perceived as having a higher value.
Presumably, that perception can also mean a higher asking price
when it’s time to sell.
The drier, the better. Steeper roof pitches shed
water more rapidly, reducing absorption and making them the
best candidates for wood roofing. Cedar shingles are not
recommended for roof pitches below 3/12, nor shakes for pitches
less than 4/12. On 3- and 4-inch slopes, I reduce the course
exposure to about 4 inches. On 3-inch slopes, we always fully
cover the deck with self-adhering underlayment. Steeper than
that, 30-pound felt is sufficient (Figure
Figure 2. On this waterfront roof, the builder
covered the entire roof with self-adhering membrane,
eliminating the use of standard #30 felt underlayment. With a
self-adhering membrane and reduced course exposure, cedar
shingles may be installed on roof slopes as shallow as
In the Northeast, red cedar is far more common than Alaskan
yellow cedar, a relative newcomer to our market. Nonetheless, I
prefer yellow cedar; it’s slightly denser than red cedar
and has better resistance to cracking and splitting. Also,
it’s dimensionally stable and has natural oils that make
it highly decay-resistant. While red cedar weathers to a dark,
sometimes uneven shade of gray, yellow cedar turns a softer
silver-gray that closely matches the color of the white cedar
shingles commonly used on sidewalls. When it was first
introduced, yellow cedar was considerably less expensive than
red cedar. However, while prices vary from one region to
another, yellow cedar in this neck of the woods now costs about
20 percent more than red cedar.
Pressure-impregnated red-cedar and yellow-cedar shingles are
also available, — either preservative-treated
(Certi-last) or fire-retardant-treated (Certi-guard), but not
both at once. Preservative treatment can really extend service
life and offers significantly better material warranties, up to
50 years in some cases. These shingles are recommended for use
in high-humidity regions; we recommend their use in
particularly shady locations where the shingles are likely to
remain wet for extended periods of time. Preservative treatment
costs about 7 percent more than nontreated shakes or shingles
— a good bargain when weighed against the extended
Fire-retardant treatment comes in Class C and Class B ratings;
a Class A rating can be achieved by installing a Class B shake
or shingle over a 72-pound mineral-surface fiberglass cap
sheet. Design specifics are best obtained from the specific
treatment company (Chemco, 360/366-3500, chemco.us; or F.S.R.
The CSSB cautions that white cedar shingles are intended for
siding use only. White cedar is softer than either red or
yellow cedar. The shingles are also predominantly flat-sawn,
which practically guarantees that they’ll curl, cup, and
split under rooftop exposure.
Width and grain rules. A good roof-grade shingle will
split straight along the grain when cut with a utility knife
(Figure 3). Generally, if the grain looks too
wavy — as if the shingle had been cut close to a knot
— I toss it. Wavy grain means the shingle is likely to
cup or warp and need replacement. Lower grades permit a certain
percentage of flat-sawn grain and knots above the exposure
line, both dubious qualities on a roof.
The straight grain of a
premium-grade cedar shingle slices cleanly with a utility
blade. Excessively wavy grain can contribute to cupping or
Narrow shingles, or “paint sticks,” don’t
make the cut, either. With shingles less than 4 inches wide,
there’s simply not enough surface area to cover adjacent
keyways and nails. The best range is between 5 and 9 inches
wide. Shingles wider than that will move too much during
wetting and drying cycles and may end up splitting around the
We cull the 10-inch-wide shingles and resaw them to 5 inches.
The very widest ones — those around 12 inches — we
put aside to use for one-piece valley shingles, which saves
time and materials (Figure 4).
Figure 4. The author culls shingles more than 10
inches wide from the bundle and uses them to make one-piece
After establishing an accurate pattern, we cut all the valley
shingles at once, using an adjustable angle fence on the table
saw. On a hip roof, the offcuts can always be used to complete
Because cedar shingles readily absorb moisture, it’s
important to provide a means for air to circulate and speed
their drying. Otherwise, they’ll cup and support fungal
growth and decay.
Many wood roofs today are installed directly over felt
underlayment and plywood sheathing, but that’s not the
best way to go. Although preservative-treated shingles may hold
up well in direct contact, there’s still the possibility
that moisture will be trapped against the sheathing.
Traditionally, wood shingles were installed over spaced boards,
or “skip sheathing,” a practice that allowed air to
circulate under the shingles. The problem with skip sheathing
is that it’s more labor-intensive to install than plywood
sheathing and doesn’t provide the same racking
A hybrid approach, where spaced boards are placed over solid
sheathing, is sometimes used, but the continuous ventilation
product Cedar Breather (800/346-7655,
provides a good, economical alternative without all the fuss
(Figure 5). I always recommend it. A
200-square-foot roll of the random-matrix mesh costs about $110
and is easy to staple down with a hammer-tacker. Installed, it
adds $80 per square to the roof price. The mesh should run all
the way from the edge of the eaves to the top of the ridge. At
rakes, we hold it back about an inch so that the shingles can
be nailed down hard along the edge to close the roughly
1/8-inch gap. The roll-off is imperceptible. If we’re
replacing the roof trim, it’s a simple matter to raise
the rake edge enough to cover.
Figure 5. Ventilating Cedar Breather mat installs
quickly and provides critical air circulation under the
Using Cedar Breather does introduce a thin, springy void under
the shingles, bringing with it some concern for cracking the
shingles underfoot. We take extra care when walking on them and
add staging brackets and planks as needed to minimize direct
foot traffic. With thicker, taper-sawn shakes, this is not as
much of a concern.
Cracked shingles have to be replaced. The good news is that
they’re fairly easy to remove piecemeal, especially if
the roof isn’t at the end of its service life. But
that’s typically when I find myself making temporary
repairs and recommending a new roof. The majority of the wood
roofs we replace are about 25 years old, while roofs 40 and 50
years old aren’t unusual.
Shingles require a three-ply application (Figure
6). Thus, a 51/2-inch exposure calls for 18-inch
perfections to ensure triple coverage. A 7 1/2-inch exposure
will require 24-inch royals to create a three-ply surface.
Unlike shingles, thicker shakes may be installed in two-ply
coverage. For example, a maximum exposure of 7 1/2 inches is
acceptable for an 18-inch shake, and a maximum of 10 inches for
a 24-inch shake. Exposure tables for shingles and shakes on
steep and shallow roof slopes are found in IRC 905.7.5 and
Figure 6. Wood shingles must be installed in three-ply
application. Shakes are typically installed in two plys, but
require an interlay course of #30 felt to prevent wind-driven
moisture from penetrating.
Note that when installing split shakes, there’s an
important added step. The irregular, corrugated surfaces of
shakes prevent them from lying tightly against each other,
which helps with ventilation but makes them susceptible to
wind-driven snow and rain entering under the courses. To
prevent this, shake courses are interlaid with 18-inch-wide
strips of #30 roofing felt. The interlay laps the tips of the
shakes no lower than twice the distance of the exposure up from
the butt and runs up onto the sheathing, effectively creating a
third ply and a baffle against snow and water entry. However,
felt interlay should never be used under shingles or taper-sawn
shakes, which have no inherent ventilation space between the
layers. The felt is absorbent and can hold water, potentially
leading to buckled shingles and early roof failure.
Nails. Although hot-dipped galvanized nails are
acceptable, we use only stainless steel ring-shank nails.
Considering the overall cost of the installed materials,
it’s cheap insurance against failure. In any case, we
never use electroplated fasteners of any kind. The CSSB
discourages their use, and I have to agree. I’ve seen
cedar shingles literally slide off a 7-year-old roof after
these nails rusted away. Whether this was due to corrosive
salt-laden air or a chemical reaction with the natural oils in
the cedar wasn’t clear — but regardless, these
nails aren’t worth taking a chance on.
For shingles, we use 13/4-inch nails, while thicker shakes call
for 2 1/4-inch nails. Stainless steel staples are allowed, but
we don’t use them because I just don’t like the
idea of doubling the number of penetrations. Also, staples are
more difficult to remove should we need to make spot-repairs or
retrofit a skylight. Whichever you use — nails or staples
— don’t overdrive them. Doing so risks voiding the
manufacturer’s material warranty. We adjust the gun
pressure so that the heads are driven just flush with the
The first course is always a double layer. We nail the first
layer a little low, about 5 inches up from the butt, and the
second layer an inch above the exposure line. Metal drip edge
can be eliminated, but the felt underlayment or self-adhering
membrane should always be carried onto the top of the fascia.
The shingles should overhang both eaves and rakes by 1 1/2
To start, we nail shingles at wide intervals along the eaves,
overhanging by about 4 inches to catch a chalk line and
establish a straight, 1 1/2-inch overhang (Figure
7). We then tack-nail lengths of strapping to the line
to guide the first course. The projecting shingles are later
To start the first course, the crew
nails a guide strip to a chalk line snapped at the 1 1/2-inch
overhang (above). Fence boards ripped to the exposure width
guide the successive courses (right).
To guide subsequent courses, we rip fence boards to the
exposure width — typically 5 1/2 inches — and
tack-nail them to the face of the previous course with 1
1/4-inch box nails. These nails don’t fully penetrate the
shingles, and the holes self-heal. Every 10 courses or so,
we’ll measure back from the ridge at both ends and center
to make sure the courses are remaining parallel. If need be,
we’ll snap adjusting lines. Don’t use red chalk for
this or you could be looking at an accidental line for a long
time to come.
Side laps over “keyways” — the joints between
shingles — must be at least 1 1/2 inches and thoroughly
cover the nails. Nails should be driven about 1 1/2 inches
above the exposure line and no more than 3/4 inch in from
either edge of the shake or shingle. We’re extremely
careful about placing and covering the nails, since this is
where shingles are most likely to split. If a split lines up
with a keyway, a leak is pretty likely to develop.
For the same reason, it’s also important to make sure
that no two joints align vertically within three successive
courses. According to CSSB standards, a maximum 10 percent
alignment is permissible — but to the experienced eye
these stacked keyways tend to stand out like a sore thumb. We
don’t allow them at all.
To accommodate expansion, we maintain a 1/4-inch spacing
between shingles. (Between shakes, keyways should be about 3/8
inch wide.) However, if the shingles are noticeably wet coming
out of the bundle, we tighten the spacing on the assumption
that the shingles are as swollen as they’re likely to
get. Those keyways will only widen, not buckle.
Valleys. A wood valley can be installed closed, with
the two sides cut to fit against each other, but I feel that
this makes it more difficult to keep nails far enough away from
the center line and prevents the butts from drying promptly. On
open valleys, we snap guide lines between 3 and 4 inches
off-center, depending on the length of the valley and the
expected volume of water (Figure 8). We always
line valleys with a 36-inch-wide self-adhering membrane first.
I buy preformed W-valley 12-ounce copper flashing in 10-foot
lengths from a local sheet-metal fabricator. We overlap all
joints by 6 inches and solder them tight.
Figure 8. A time-tested waterproof valley is
made from preformed W-valley copper flashing.
Hip and ridge caps. While a ridge board is the fastest
method for finishing the roof, a woven cap using shingles or
shakes really puts the icing on the cake (Figure
9). We save considerable time by buying ready-made hip
and ridge units through our roofing supplier. These are made to
order to suit specific ridge and hip pitches. Since the joint
orientation should alternate from one cap to the next, the caps
come in left- and right-hand units. This helps prevent the
possibility of a running seam developing over time.
The author buys these made-to-order
hip and ridge caps through his roofing supplier, greatly
speeding installation. A strip of self-adhering membrane adds
another layer of protection under the cap.
Before installing the caps, we cover the hips and ridges with a
6-inch-wide piece of self-adhering membrane.
Maintenance. Ensuring that the roof will stay as dry
as possible is critical to long service life. Wood fungus leads
to rot and forms most aggressively in areas where the roof
stays wet for long stretches of time. Valleys, gutters, and
downspouts should always be kept clear of debris. Overhanging
branches should be trimmed back and shade trees minimized. A
simple way to help prevent moss from gaining a toehold is to
install a narrow strip of lead or copper under the ridge board
or cap, leaving about an inch of metal exposed. Then, when it
rains, trace amounts of the metal will leach and wash over the
roof, killing mold spores before they become established.
Chris Yerkes owns Cedarworks in South