Slate Roofs Why Learn the Hard Way

All roofing contractors do it at
some point in time, don’t
they? They bite off more than
they can chew by diving into a
project while lacking the necessary
experience. It’s called
“learning the hard way.” Since my area of
expertise is in slate roofing and I only provide
consulting services for such projects, I
have had a golden opportunity to observe
and document the mistakes, big and small,
that contractors make when installing slate
roofs. Many of today’s contractors are inexperienced
in this age-old traditional roofing
system, and even slate specialists make
mistakes. I know this for a fact, as I have
probably made many of them myself over
the past four decades, and I confess to having
jumped into jobs not knowing what I
needed to know beforehand.
By documenting and illustrating some
of the mistakes I have seen in the field, I
hope to help others avoid making the same
mistakes as well as to assist consultants in
recognizing a correctly installed slate roof.
Slate roofs are a wonderful architectural
phenomenon, but poor installations can
hurt the reputation of this excellent system.
Three Basic Components
Slate is a type of stone that readily splits
like a deck of cards, thereby allowing for the
fashioning of flat, long-lasting, and beautiful
stone shingles. In the United States,
slate shingles are typically fastened to
decks using roofing nails. Most roof decks
are made of wood, although a rare few are
made of nailable concrete. The basic components
of a slate roof, therefore, consist of
three elements: the slate shingles, the deck
(typically wood), and the fasteners (typically
roofing nails, but sometimes
slate hooks) that attach the
slates to the deck. Nothing else is
needed for a successful, watertight
slate roof installation –
nothing. This fact has been thoroughly
proven in the field by 150
years of demonstration in the
United States and even longer in
the United Kingdom.
In fact, my region of the
United States, northwestern
Pennsylvania, has more rainfall
than either Port land, Oregon, or
Seattle, Wash ington, not to mention
annual temperatures ranging
from -30˚ F to 103˚ F, and
lots of sleet, snow, and ice during
the winter months. Despite
these conditions, we often do
restoration work on 120-year-old
slate roofs, still chugging away
watertight. These consist of
nothing more than the basic
three elements. There is no functional
underlayment on these
roofs. Figure 1 provides an example
of the longevity of slate roofs
still operating after more than a
century, still watertight and consisting
of only stone, wood, and
fasteners. Incidentally, the fasteners
are almost all hot-dipped
galvanized nails.
Granted, a fourth element is
commonly require: sheet metal
flashings. Flashings seal the
joints and penetrations in slate
roofs, but if no joints or penetrations
exist, no flashing is needed.
Ridges and hips can be made
Figure 1 – These photos of existing slate roofs
attest to the durability, beauty, and longevity of
this natural roofing system.
14 • I N T E R FA C E OC T O B E R 2008
of slate alone. So can valleys.
Nevertheless, flashings tend to be
an important component of most
slate roof systems and are often a
source of problems when installed
incorrectly.
Most American slate shingles
should have an expected longevity
of somewhere between 75 and 150+
years, depending on the type of
slate. Therefore, the three roof
components should also have a
similar longevity. If the slate is
going to last 150 years, the deck
and fasteners should also last that
long. The best slate roofs use a
good quality slate of known origin
and proven performance, which is
fastened with corrosive-resistant
fasteners such as copper, stainless
steel, or hot-dipped galvanized
nails, to decks of solid wood at
least ¾-in thick. Pretty simple. So
what goes wrong?
Slate Selection
Well, let’s start with the size of
slate selected for the project. The
smaller the shingles, the more that
are required to cover 100 square
feet of roof – a “square.” For example, the
largest standard size, 14 in x 24 in, requires
98 shingles per square. The smallest standard
size, 6 in x 12 in, requires 533 shin g –
les per square. Since each shingle is
attached to the roof deck with two nails,
use of smaller slate will require much more
labor during installation. If a contractor is
not aware of this fact, he may choose to
purchase small slates simply because they
tend to be considerably less expensive. In
one case, this proved to be a dire error – the
contractor bought 6 in x 12 in slates for a
reroof on a 12-story building in Kansas,
probably trying to save money on materials;
then he went bankrupt halfway through the
job, no doubt because his labor costs were
sky-high.
The type of slate is also very important.
Ideally, the slate selected for a project is a
tried-and-proven material with many
decades of outstanding performance in the
field and is manufactured by a company
that takes pride in its product. Most
American and Canadian slates fall into this
category. However, there are many foreign
slates entering the American market these
days with little or no history of performance.
In one recent case, a very large twoyear-
old roof installed with Chinese black
slates faded or changed color dramatically
to create a splotchy, unpleasant black and
white appearance. This entire roof had to be
removed and re –
slated at great cost.
This is not to suggest
that all Chi –
nese black slates
will do this, but
obviously some
will. Selecting the
correct slates can
be very tricky when
the slates come
from another continent
and you can’t
trace their origin
back to any particular
hole in the
ground.
Some Spanish
black slates are
known for their
pyrite content,
which will bleed
red rust stains
down the roof.
Figure 2 shows
such a slate, taken
from a residence in
Florida after only one year on the roof. This
large residential roof had to be completely
re slated at great ex pense. The owner of the
residence selected this slate because he
liked the shade of black on a new sample
piece and did not understand that some
slates will change in appearance with exposure
to weather. When selecting Spanish
slates, it is important to know whether
those being considered are pyrite-bearing, a
condition that may or may not be obvious
by visual inspection. In a recent case on the
east coast, an entire church roof had to be
re slated because the new, Spanish black
slates were bleeding rust down the roof, and
the church people did not like the way it
looked. Again, this is not to be construed as
a condemnation of all Spanish black slates,
as some are quite good.
In another case, Spanish black slates
were ordered for a large roof, but they were
not all of the same origin. Although they
looked the same sitting in the pallets on the
ground, once they were installed on the
roof, they created a slightly mottled look
that was unacceptable to the property
owner. It’s hard to say who was to blame for
this mistake — the supplier, who should
have known he was not sending the same
material to the job site, or the contractor,
who did not reject the slates due to obviously
different pallet markings that suggested
slates of different origins. The con-
Figure 2 – This Spanish black slate leached
rust stains down the new slate roof. This
photo shows the slate after only one year on
the roof.
Figure 3 – Even domestic slates can rust. These Vermont
slates on a high-rise apartment were poor in quality and
should have been screened for pyrite inclusions.
OC T O B E R 2008 I N T E R FA C E • 1 5
tractor also could have
prevented the unsightly,
patchy mottling of
the roof by thoroughly
blending or shuffling
the slates before in –
stalling them. This
would have allowed for
a uniformly mottled
effect that is pleasing to
the eye.
Even if the slate is
from the same source,
different pallets can
contain different
shades of slates, due to
the location of the rock
strata and/or other
factors related to the
quarrying of the material.
Therefore, when the
slate is delivered to the
site, all of the pallets
should be opened from
the outset and slates
should be taken from
each pallet in order to
blend the entire inventory and create a
pleasant appearance on the roof. It is a mistake
to start with one pallet, install those
slates, then open another pallet, install
those slates, etc.
Poor-quality slates occasionally originate
from the United States. This may be due to
the manufacturer’s not culling out rejects,
for example. Shoddy quality control can
lead to rusting pyrites on even the best
American slates. Figure 3 shows Vermont
slates badly rusting down an apartment
building roof. This is very unusual and indicates
a commercial source of roofing slate
that should have been avoided or a bargain
slate that wasn’t worth the money combined
with a contractor who should have
culled the defective slates out but didn’t
know what a bad slate looked like.
Follow Traditional Methodologies
There are other factors related to the
manufacture of roofing slates that can
affect quality and longevity. Direction of
grain and nail hole placement are two
examples. A good manufacturer will be
aware of these nuances and strive to produce
top-quality slate. It pays to buy from
such a slate source.
Once the correct slate has been selected
and delivered to the job site, it’s time to
begin installation. Styles and methods of
installation can vary greatly, but one important
point needs to be emphasized: if it’s
longevity that’s de sired, then the in –
stallation system should be based upon
known methods and
materials that have
proven longevity. A
solid, nonlaminated
wood roof deck, with
the emphasis on correct
slate and flashing
installation and not on
underlayment, has pro –
ven to provide exceptional
longevity. Such
traditional methods
and materials can easily
be replicated today,
yielding the same
degree of success.
Modern asphalt
roof installations rely
on plywood decks and
self-ad hered modified
bitumen or other heavy
underlayment, creating
a roof deck system that
strays widely from traditional
slate roofing
systems. Tra ditional
systems made of board
decks and slater’s felt (30-lb felt) allow for
the transpiration of air through the roof
deck, which enables the roof to “breathe,”
Figure 4 – Traditional slate roofing systems, despite their incredibly
successful performance, are being largely abandoned in favor of plywood
roofs with peel-and-stick underlayments.
Figure 6 – No slate lies flat on a slate roof. Every slate is angled, which is why it
should not be walked upon and why the starter course requires a cant.
16 • I N T E R FA C E OC T O B E R 2008
Figure 5 – The starter course should be flipped over and laid upside down as
shown on the right in this illustration. This cre ates a clean drip edge and allows
for correct nail countersinking.
allowing it to dry out should water ever penetrate the roof covering.
The boards won’t wick moisture through wide areas as laminated
decks will, so that if the roof deck becomes water damaged, it can be
re paired easily. The thin, temporary felt underlayment on a traditional
slate roof will slowly disintegrate over time, allowing for the
free use of the slate-ripping tool, which slides under the slate and is
so essential to the repair and maintenance of the roof. Heavy underlayments
can dry up and crack underneath the slate, impeding the
use of the slate ripper, making repair and long-term maintenance a
nightmare.
Figure 4 shows a 150-year-old slate roof
being replaced in Boston. Although the roof
was still functioning at the time of replacement
and the existing roof system – made of
slate, 1-in boards, 30-lb felt, and nails –
had demonstrated a 150-year performance,
the contractors who replaced the roof completely
abandoned the existing system and
replaced it with one that had no proven
longevity, emphasizing underlayment and
completely eliminating any chance of air
transpiration. The original 1-in roof board
deck, still sound, was covered with ½-in
plywood, then self-adhered modified bitumen,
then 30-lb felt, and then slate. Will
this new roof system last 150 years? Time
will tell, but why reinvent the wheel? A
chain is only as strong as its weakest link.
Traditional, 3-link slate roofing systems
have already proven themselves, are less
expensive, are more environmentally friendly,
and take less time to install. If one wants
to guarantee that a slate roof will last a century
or two, traditional methodologies
should be followed.
Common Installer Errors
Let’s look at how traditional slate roofs
are correctly installed, and let’s identify
where contractors go astray, beginning with
the starter course. The starter course is the
very first row of slates to be installed.
Starter slates are invisible once the roof is
completed, because they’re hidden underneath
the first course of slate.
There are several common mistakes
made when installing starter courses. For
one, the starter course slate should be
installed face down, unlike all the other
slates on the roof, which are installed face
up. Technically, this is not a significant
functional mistake because the roof will still
perform correctly whether the starter slate
is face up or face down. However, nail holes
on starter course slates are punched at the
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OC T O B E R 2008 I N T E R FA C E • 1 7
Figure 7 – Note that the starter slate is laid backside up and
is propped up by a cant strip.
quarry with the intention that the slates are
to be installed face down. This allows for a
clean edge where the starter slate meets the
first course (Figure 5). The reason it’s important
to know this information is because the
orientation of the starter course is an indication
of whether the slate installer has had
much experience. Inexperienced installers
often put the starter course face up.
Often, the cant or shim strip is missing
underneath the starter course. Starter
slates must be angled on the roof in order to
match the angle of all the other slates in the
field of the roof. No slate lies flat on the roof
because every slate is overlapping other
slates, as shown in Figure 6. Since the
starter course does not have a course of
slate underneath it, something else must be
Figure 8 – The starter course should be overlapped by the second
course by at least three inches. In this case, it is not overlapped at
all. This is a serious but common mistake. Note also that the starter
slate is incorrectly laid backside down. This is an indication that
the installer was inexperienced in laying slate.
Figure 9 – Headlap is a critical detail on a slate
roof. Lack of headlap will cause an entire roof to be
condemned.
Figure 10 – This is an example of inadequate headlap
on a shopping center roof in Louisiana.
Figure 11 – When the slate courses are spread too far apart
vertically, negative headlap can result. Although this requires
fewer slates to cover the roof, it also creates holes all through the
roof. There is no remedy for an egregious error such as this other
than to remove the entire roof and start over.
OC T O B E R 2008 I N T E R FA C E • 1 9
installed under it to create the proper angle. Typically, this is
done by installing a wood strip (Figure 7), but it can also be
achieved by using a metal drip edge with a cant formed into
the metal, or even by raising the fascia.
Another very common mistake on starter courses is a lack
of headlap, especially when the field slates are turned sideways
and used for starter slates. The second
slate course must overlap the starter
course by a minimum of 3 in. Inexperienced
slaters often overlook this important detail.
Since the bottom of the roof has more water
running over it than virtually any other part
of the roof, it is imperative that the headlap
on the bottom courses of slate be correct.
An example of a starter course lacking
headlap is shown in Figure 8.
Speaking of headlap, this is one of the
first details that a roof consultant should
look for on a new slate roof installation. If
the headlap is missing or inadequate, the
roof is probably going to be condemned.
Headlap is the overlap on each course of
slate by the second course above it (Figure
9). This overlap is what prevents the roof
from leaking. Three inches is standard, but
headlap can vary according to the slope of
the roof. Figure 10 shows a newly installed
shopping center roof in Louisiana with
about an inch of headlap on the field slates.
The overlap should be 3 in. There is no fix
for this inadequacy other than to rip off the
entire roof and start over. Figure 11 shows a
university building roof in Pennsylvania
with a new slate roof – and, incredibly, negative
headlap. This is the same as having
holes all through the roof. It’s hard to
believe that roofing contractors can make
Figure 12 – “Sidelap,” or lateral overlap, should be a
minimum of 3 in. Here we see no lateral overlap at all.
This entire roof had to be removed and reslated, as it
also had no headlap.
Figure 13 – Each slate side-butt should be stag –
gered so as to break the course below down the
center. Instead, these slates were butted directly
over the underlying slating nails, ensuring leakage.
20 • I N T E R FA C E OC T O B E R 2008
such drastic mistakes, especially on institutional
buildings, but seeing is believing.
Lateral overlaps or sidelaps should also
be 3 inches minimum. However, don’t be
surprised to see slates with no lateral overlap
at all, as shown on an historic building
in Georgia (Figure 12). Incorrectly placed
sidelaps can leave the butt joint directly
over the slating nails, as shown on an historic
Pennsylvania State Park building in
Figure 13. This will allow direct water entry
through the nail holes.
Another common installation mistake is
the overnailing and undernailing of the
slates. Slate nail holes are meant to be
crater shaped to allow the nail head to sit
down inside the slate (Figure 14). Other –
wise, the nail head will protrude and rub
against the overlying shingle, eventually
creating a hole (Figure 15). When the nail is
not driven far enough, this is known as
undernailing. Overnailing, on the other
hand, is when the nail is driven too far and
breaks through the slate. This leaves the
slate hanging on one nail or sliding out altogether
(Figure 16).
Nail length is an issue that is commonly
off the radar screen of the average roofing
contractor. The slating nails should barely
penetrate the roof deck boards. If the nails
are too long, they break through the back of
the boards and splinter out of the wood,
reducing the board thickness where the nail
is located and undermining the effective
holding power of the nail (Figure 17).
A very common error with new slate roof
installations is what I call the Bigfoot
Syndrome – roofers walking on the slates
during installation, as shown in Figure 18
on a new bank building in Kansas. An experienced
slating crew will make every effort
to keep off the slates during installation by
staging the roof correctly (Figure 19). When
Bigfoot walks all over the slates, the shin-
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Figure 14 – A good slater has no problem nailing slates correctly. When properly nailed, the nailhead just sits down inside
the slate. When undernailed, the protruding nailhead, over time, can damage the overlying slate. When overnailed, the slate
being nailed will crack, break, or cock awkwardly on the roof.
OC T O B E R 2008 I N T E R FA C E • 2 1
Figure 15 – A protruding nailhead can eventually wear
a hole in the overlying slate.
Figure 16 – This slate was nailed so tightly
that the nails broke through the slate and
the slate is now sliding out of place.
Figure 17 – When the slating nails are too long, the
back of the roof decking breaks out. This reduces the
effective holding power of the nail. A longer nail,
therefore, does not mean more holding power. The best
nail length just barely penetrates the roof deck.
Figure 18 – It is a mistake to walk
on a slate roof during installation.
22 • I N T E R FA C E OC T O B E R 2008
order to prevent leakage through the corner. If a corner isn’t
folded or soldered, as shown in Figure 22, then the only thing
keeping it from leaking is caulk or sealant, which do not have
adequate longevity. An incorrectly folded chimney corner is
illustrated in Figure 23. This is a leak waiting to happen.
Dormers also often have corners that need to be flashed.
Without folded or soldered corners, a dormer can be left wide
open and waiting for the first good rainstorm (Figure 24).
Figure 20 (left) – Slate roofs that are walked on
during installation will shed slates after the roof
has been installed, perhaps for years.
Figure 21 – Uphill flashing should always lap on top of
downhill flashing. Negative overlap, as shown, will leak.
Figure 22 (left) – Chimney corner flashings should be either
folded or soldered. If neither is evident, then the corner is
either sealed with sealant or not at all. In either case, this is
a leak waiting to happen.
Figure 19 – A correctly staged slate
roof will enable roofers to install the
slate without needing to walk on the
shingles.
OC T O B E R 2008 I N T E R FA C E • 2 5
Common on many slate roofs are built-in gutter systems. “Box gutters”
require expansion joints, but they’re often installed without any allowance for
expansion whatsoever. This becomes evident by the failure of the solder joints
(Figure 25), which are then often roof-cemented after they start leaking in order
Figure 24 – This is a case in which
the corner flashing is neither folded
nor soldered, leaving a large hole in
the roof and clearly showing how
corners need special attention in
order to prevent leakage.
Figure 23 – This chimney corner flashing (left), although folded, was
installed incorrectly and will surely leak. A properly folded corner
flashing must account for the water that runs down the chimney as
well as the water that runs down the roof. In effect, the flashing
should create a “miniroof” over each corner.
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to alleviate the water penetration (Figure
26). Expansion joints (Figure 27) can be
added after the gutters are installed, but it’s
a lot easier to install the gutters correctly in
the first place.
A common sight on new slate roof
installations is incompatible metals, often
steel and copper used together (Figure 28).
The copper will “eat” the steel, causing steel
fasteners to degrade at an accelerated rate.
Another incompatible metal error involves copper rivets. Many roofing supply
outlets sell copper rivets with copper-plated steel mandrels. When the rivet is
installed, the steel mandrel breaks off inside the rivet, lurking inside to eventually
rust and create a hole in the flashing. These rivets look like they’re made of
copper, but they aren’t. Check them with a magnet to be sure. Copper is not
magnetic, but steel will stick to a magnet like glue, so if your rivets are magnetic,
don’t use them with copper. Copper rivets should have non-magnetic
brass mandrels, not steel.
Figure 27 – Expansion joints allow built-in gut –
ters to move when expanding and contracting,
thereby relieving the stress on the solder joints
and prolonging the life of the gutter.
Figure 28 – Metal fasteners should always be
compatible with the metal they are fastening.
Steel fasteners on copper, as shown, will
deteriorate.
Figure 25 – This is a perfect example
of a new built-in gutter showing failed
solder joints because not a single
expansion joint was installed in the
gutter system.
Figure 26 (above)
– Box gutters
require expan –
sion joints; oth –
er wise, the sol –
der joints will
crack under
pres sure. This is
evidenced by
solder joints
that have been
covered by roof
cement, a
common sight on
box gutters, both
new and old.
OC T O B E R 2008 I N T E R FA C E • 2 7
Open-flame torches should never be
used to solder flashings, so if you see a
worker on a roof soldering a box gutter with
an open-flame plumber’s torch, say something.
The flame is too hot and will ignite
the substrate, be it felt paper or rosin sheet,
which will then smolder underneath the
metal, perhaps unnoticed until it’s too late.
If the smoldering is noticed, panic will
ensue because there is no way to get to the
fire without first ripping out the flashing.
The correct tool for a soldering job is a
closed-flame soldering device or a heavyduty
electric soldering iron. Open-flame
devices can be used on external copper gutters,
however, when the metal is not in con-
Figure 29 – Ideally,
the outer edge of
external rain
gutters should be
hung below the
plane of the roof to
prevent damage to
the gutters from
sliding ice and
snow.
Figure 30 – This
gutter is just waiting
for a snow avalanche
to knock it off.
Figure 31 –
Snowguards must
be installed in
adequate quanti –
ties, or they will get
knocked off in the
first bad ice storm,
damaging the roof
in the process.
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tact with the roof.
Speaking of gutters, they’re often hung
too high. The outer edge of external gutters
should be below the plane of the roof
(Figure 29) if the gutters are in locations
where snow or ice could slide down the roof
and knock them off. The gutter in Figure 30,
for example, will not last long.
Snow retention systems are another
source of problems when they’re installed
incorrectly. One of the tricks for a proper
snowguard installation is to use enough of
them. Otherwise, they won’t be able to hold
the weight of the ice and snow and will rip
out, taking slates with them. A poor snowguard
installation is shown in Figure 31.
Insufficient snowguards on this large roof
caused many of the devices to rip out during
an icy winter. Follow the manufacturer’s
guidelines when installing these important
slate roof elements.
Incorrect tools can be the downfall of
many a would-be slater. Slate roofing has
its own unique set of tools and equipment.
For example, slates should be cut with –
you guessed it – “slate cutters.” A slate cutter
will leave a beveled edge on the shingle,
thereby allowing it to match all the other
shingles on the roof, all of which have
beveled edges. If a diamond blade is used to
cut the slates, a square edge remains,
which can stick out like a sore thumb and
get a roofer into big trouble if the property
owner doesn’t like the look of it. Figure 32 is
Test your knowledge of building envelope
consulting with the follow ing ques tions devel –
oped by Donald E. Bush, Sr., RRC, FRCI, PE,
chairman of RCI’s RRC Examination Develop –
ment Subcommittee.
1. What is the definition of
a monomer?
2. What is a micron?
3. What is a Newton (N)?
4. What is olefin?
5. What is the formula for
determining the percent
of water by volume in a
sample?
6. What is the formula for
determining the percent
of water by weight?
7. Steel deck design re –
quires special attention
to which four items?
8. What are the three basic
wind-speed deter mi nants?
9. Which four basic varia –
bles are identified as
crucial to the final
design wind-uplift
pressures?
Answers on page 30
Figure 32 – Diamond blades cut a square edge on slates, making them stick out
like a sore thumb.
Figure 33 –
Slate roofing
requires the
correct tools to
do the job right.
There is no
excuse for the
sort of work
shown here.
OC T O B E R 2008 I N T E R FA C E • 2 9
a perfect example of square edges exposed
at the wrong place on a slate roof. These
square edges could be dressed with a slate
hammer and stake to give them the proper
appearance, but one first must have these
tools in the toolbox. When the proper cutter
is not on hand, a roofer may resort to drastic
measures to try to cut slates, as shown
in Figure 33, where it looks like the slates
were chewed off. This brand new roof, by
the way, also had to be completely removed
and reslated, causing the property owner
much expense and grief.
Hopefully, you’ve gained some knowledge
from this little sampling of slate roof
mistakes. Slate roofing is not rocket science,
and any reasonably intelligent person
who takes the time to become informed
about the topic will be able to successfully
install a roof sure to last for many generations.
There are plenty of slate roof resource
materials available, both in print and on the
Internet. A couple hours of research can
save a roof installer a lot of problems,
including ulcers and litigation. Slate professionals
long for the day when every slate
roof is installed free of major defects. In the
meantime, they won’t be holding their
breath waiting.
Resources
• Joseph Jenkins, Slate Roof Bible,
2nd edition. Available from josephjenkins.
com, amazon.com, rci-on –
line.org, or via any major bookseller.
• Traditional Roofing Magazine – a free
magazine supported by advertisers
and focusing on slate roofing but
also including other traditional roofing
systems. All articles are posted at
www.traditionalroofing.com after
the print version has been circulated.
Sign up for a free subscription at
traditionalroofing.com.
• Slateroofcentral.com – Source lists,
contractors, tools, materials, supplies,
public message board, in –
struc tions, illustrations, and more.
• Slateroofers.org – the official Web
site of the nonprofit Slate Roofing
Contractors Association of North
America.
• Josephjenkins.com – source of tools,
materials, supplies, and equipment
related to the slate roofing trade.
All photos by Joseph Jenkins.
Answers to questions from page 29:
1. A simple molecule that is
capable of combining with
a number of like or unlike
molecules to form a
polymer.
2. A unit of measurement
equal to 10-6m (0.000001
m) or 10,000 Angstrom.
3. The SI unit of measure for
force.
4. An unsaturated, open-chain
hydrocarbon containing at
least one double bond:
ethylene or propylene.
5. Volume of water in sample
Volume of sample
6. Sample weight wet – sample weight dry
Sample weight dry
7. Side-lap fastening, end-lap
detail, span, and thickness.
8. Geographic location, local
topography, and elevation.
9. Wind velocity and building
size, shape, and wall
openings.
Reference: Manual of Low Slope Roof
Systems, Edition 4.
Glossary (Questions 1-6),
Chapter 4 (Question 7), and
Chapter 7 (Questions 8 and 9).
Joseph Jenkins, president of Joseph Jenkins, Inc., near
Grove City, PA, has been involved in the slate roofing trade
since 1968. His company provides slate roof consulting services
nationwide, slate and tile roof contracting in northwest
Pennsylvania, and slate roofing publications, tools, and supplies
internationally. Jenkins also speaks on the topic of slate
roofs in the U.S. and abroad. During his career as a contractor,
Jenkins has personally installed and restored over 1,000
slate roofs. He authored and self-published the award-winning
Slate Roof Bible in 1997, now in its second edition, and edits and publishes the
Traditional Roofing Magazine. He founded the Slate Roofing Contractors Association of
North America, Inc. in 2005 and is a member of RCI.
Joseph C. Jenkins
x 100
x 100
30 • I N T E R FA C E OC T O B E R 2008