The following comments and questions
are presented by readers to Joseph Jenkins, author of the Slate Roof Bible and editor of Traditional Roofing Magazine:
Normally I do not bite the hand that
feeds me, and your organization has been kind enough to
send me your magazine which I read. However I am moved
to write concerning the comments made in your Spring 2005
issue’s Top Ten Mistakes article. The characterization of “many roofing contractors” as “somewhere
between cretin and ex-convict” is incorrect, unwise,
and counterproductive. Your continuing description of roofers
as “pathological liars, inept, unintelligent, ignorant,
naïve and drunks” is damned uncalled for.
I have never known a good business person that insulted his
customers; or a poor one that did and got by with it for
long. I have never known a teacher who insulted his audience
and got much of his point across.
I was taught not to sell negative. It does not work well
and it reflects poorly on the seller. You may feel that tearing
down contractors in general builds confidence in your listed
contractors; it cannot but cast doubt on the process and
your association. I will match the quality of our industry
people with any.
The problems in the slate roofing universe are no different
than those of the general roofing business and construction.
Working to improve the industry does not include wholesale
condemnation of the industry or its players.
Years ago I asked my father how he ended up as a roofing
contractor: he answered “Just lucky!” If you
keep this kind of commentary up, you will not remain so lucky.
TR: Point taken. Being a roofing contractor myself since 1970 (I started
contracting at the age of 18), and still working on slate
roofs at the age of 54, I'm allowed to poke fun at the
trade. Too much of the work my company does with slate
roofs involves the removal and replacement of substandard
work that had been done by previous "roofing contractors." Being
a nationwide slate
roof consultant, I see too many slate
roof projects going into litigation. In the past year I
have been involved, either as a consultant or an expert
witness, in nine slate roof litigations and I have looked
at several other slate roofs that are not far from the
courtroom. In most cases, the roofers are at fault. Some
of them belong in jail.
Having said that, I also am aware that there are many intelligent,
conscientious, respectful and responsible roofing contractors,
such as myself and yourself. We are people who want to advance
the trade. But when any Tom, Dick or Harry can get laid off
from the factory and pick up a hammer and call himself a
roofer, quality control becomes a problem. Perhaps this isn't
such an issue with asphalt shingle staplers, but we slaters
make roofs that last a century
or two, and workmanship, tradesmanship,
and integrity are of utmost importance to us. When we install
a slate roof, we know our great-grandchildren will very likely
be around to see it — as adults, long after we have
died. Slate roofing is a serious undertaking that should
be practiced by conscientious craftspeople. When I see slate
roofs being slapped on by uneducated and inexperienced asphalt
shinglers who just want to get their money and walk, I see
the slate roofing industry being damaged and it gets my hackles
I'm currently working toward the establishment of a slate
roofing training center in western Pennsylvania. I also help
teach slate roofing courses at the new Slate Technology
Center in Vermont, plus I speak
nationally on the topic
of slate roofs to architects, home inspectors, roofing
contractors and others. Training and eventual certification
are sorely lacking in the slate roofing trade today (unlike
other types of roofing where manufacturers provide application
training). In time, the roofing trades in the United States
should be as respectable as in Europe where extensive training
via established roofing schools is required prior to employment.
But we have a long way to go.
In our local towns almost all state
roofs have 2 inch headlap, and have worked well for
150 to 200 years. What is the point in 3 inch headlap?
My dad has been roofing for 48 years. I've been at
it 15 years and we would like your reason for 3 inch or
more head lap.
TR: Three inch headlap is considered
standard these days for new slate roof
installations when the slope is greater
than 8:12. When lower than 8:12, 4 inch headlap is recommended.
Many older slate, tile and asbestos roofs (usually with 10:12
or more slope) have only 2 inch headlap and have done fine
for a century or more. Better to err on the side of caution
and stick with a 3 inch headlap, however, rather than a 2 inch headlap when
installing new slate roofs.
Headlap recommendations are difficult to universally apply. For example, why would you need the same headlap in Los Angeles (where it hardly ever rains) as in northwest Pennsylvania where we get over 40 inches a year and a lot of it is ice and snow? Industry headlap recommendations are meant to cover the worst case scenarios. Better to have a nice, tight, slate roof under all circumstances rather than one that leaks under extreme conditions because someone skimped on the headlap during installation.
I was wondering if you know the following
statement to be true or false: Underlayment is recommended
by all slate tile manufacturers and the National Roofing
Contractors Association Roofing and Waterproofing Manual,
and so it follows by the International Residential Code
in R905.1 and R905.6. It is also a requirement set by Underwriters
Laboratories when assigning a fire rating to slate or any
TR: Underlayment is recommended in the United States for
use on new slate roof installations as a protective waterproofing
material to keep the building dry until the slate is installed.
It’s also a good surface to chalk lines on when installing
slate. Once the slate is installed, however, the underlayment
is effectively obsolete — it’s punctured full
of nail holes and is expected to deteriorate beyond effective
use over time, well before the slate has worn out. Some
people want to argue that because underlayment is recommended,
it must be an important element of a slate roof and therefore
the thicker, beefier and more expensive, the better. A
lot of slate roofs have been installed with no underlayment
whatsoever and are still functioning quite well a century
later. It's pretty hard to argue that underlayment is critical
on a slate roof when you look at one installed 150 years
ago, still in good condition, with no underlayment whatsoever.
It’s anybody’s guess why underlayment would
be required for fire-rating purposes. It's very flammable.
Do you have experience with ridge venting
when installing a slate roof? Is this necessary with a
TR: Ridge ventilation is necessary to ventilate roof systems
that do not allow air flow and have no other means of ventilation,
such as via gable vents or attic vents. Traditionally,
American slate roofs are made of lumber boards covered
with 30 lb. felt underlayment (or no underlayment at all).
This roof assembly, which is easily reproducible today,
allows air transpiration without additional ventilation
in most cases, which is why you rarely see ventilation
systems on older slate roofs. The advent of plywood roof
decking, peel and stick underlayment, and asphalt shingle
roofs has created roof assemblies that prevent air transpiration
and therefore require ventilating systems.
Ridge venting on slate roofs can be achieved by purchasing
ventilation systems designed for slate roofs, such as TopSlateTM
from Castle Metal Products (ph: 847-806-4540). Alternatively,
a low-profile ridge vent can be achieved by using a plastic
vent installed underneath the ridge slates (see Figure1,
below). Read more about ventilating slate roofs with slate ridges.
As a general rule, is it true that roof
nails should be long enough to fully penetrate through
the roof deck? I checked a slate quarry website and found
the following installation spec: “All slate shall
be fastened with two large-head slaters' hard copper wire
nails....of sufficient length to adequately penetrate the
roof boarding.” Without full penetration, the nails
do not have complete “bite” into something,
and risk getting pulled out.
TR: As a general rule, the length of the slate
be twice the thickness of the slate plus one inch (it is
assumed that the roof sheathing will be approximately one inch thick).
This will give the nail a one inch bite, which may or may
not show through the underside of the roof sheathing. A
perfect scenario would have the nail bite through the wood
100% but not penetrate through to the inside.
On the other hand, nails that are too long and stick into
the roof space, puncturing the back out of the roof deck
boards, effectively decrease their holding potential by decreasing
the thickness of the wood where the nail has penetrated (Figure
2, below). Therefore, it is important that the slating nails
be neither too short, nor too long.
Why is soldering with torches considered
so poorly? Is it that it’s often accompanied by poor
workmanship, people are neurotic about fire, oxidation
of materials when flame is directed towards the open seam,
over use of heat annealing the copper, what?
TR: The problem with open flame torch soldering on roofs
is not related to the sweating of the joint, the workmanship,
copper annealing, etc. It is simply that the felt paper
(or even the wood deck) under the metal being soldered
will combust and smolder when subjected to the heat of
an open flame torch — a problem not associated with soldering
irons. The smoldering combustion may or may not
be noticed by the roofer, who may receive a call at three
o'clock in the morning that the building is filling with
smoke. If the combustion is noticed by the roofer, he may
frantically try to put it out, but realize that the smoldering
material is underneath the copper and can't be reached.
A lot of roofers find this out the hard way, and sometimes
it's tragic. Open flame soldering on copper not attached
directly to the roof surface, such as on gutters, is OK.
I am currently taking down a 100-year-old
slate roof in southeast Ireland. I wish to re-use the slate
on a new project, however, someone has tarred the slate roof.
Is there any solvent I can use to remove the tar from the
slate, or can I sand it off? It seems like a terrible waste
of such beautiful slate.
TR: Your options are limited. Other than trying to remove
the tar with a solvent or by power washing (good luck)
you can try flipping the slates over and using the back
side out. You will probably have to hand trim the edges
to reverse the bevel, which is a job in itself.
I have a persistent leak in my slate roof
near the eaves. I had it repaired last year, but it still
leaks in the same place. The previous roofer had removed
the slates from the bottom 3 feet of the drip edge, installed
peel and stick ice membrane, then reinstalled the slate.
It continues to leak. What’s going on?
TR: The problem was not a lack of ice
membrane. Think about
it — why would water be penetrating the slate in
the first place? No water should get past the slate and
flashings. If slate roofs routinely leaked, they would
be failures as roofs and such roof systems would have been
abandoned generations ago. It makes no sense to think that
water will penetrate the slate and therefore what is underneath
the slate is what really keeps the roof from leaking. When
roofing contractors can't find a leak, they resort to desperate
measures, such as removing slates and installing ice shield.
But it's often a waste of time and money.
You will likely find that your leak is being caused by a specific
fault in the slate or flashings. That fault must be identified
and repaired. It could be something as simple as a cracked
slate, exposed nail head, or even a hidden leak, such as
a too-close sidelap and a nail head too closely positioned
underneath the lap joint (which would only leak during ice
dam conditions or heavy rain, but can be repaired in minutes
with a copper bib flashing). [Editor's note: In this case the problem turned out to be faulty step flashings
on a low dormer.] The roofers who looked at and "repaired" the
roof probably didn't know how to replace step flashing on
a slate roof. They certainly did not know how to diagnose
Furthermore, if water is penetrating a slate roof
at the eaves and there are no faults with the slate or flashings,
then the headlap along the eaves could be too small. This
is a problem that would have plagued the roof from the beginning,
however. When eaves leak intermittently at one location,
the problem is probably not headlap. For example, if there
are repair slates in the leaking region, say on a roof with 20 inch long slates, and they used 18 inch long slates for the repairs, you
would not be able to see that the slate is 2 inches too short
and therefore has little or no headlap. That is called a
"hidden leak." You need to find an experienced slater to find
the problem with your roof. Don't waste your money on red
herrings like the lack of peel and stick.
When installing a new slate roof, if you want to tighten
up the roof along the eaves, increase the headlap along the
bottom 3 or 4 feet of the roof (Figure 3). You can’t
rely on peel and stick underlayment (or any underlayment)
for long term effectiveness on a slate roof because the stone
roofing just lasts so much longer.
In my area there are many hardwood trees.
We are in contact with a local sawyer to apply rough-sawn
deck sheathing. What do you think is the most desirable wood
and thickness to use as roof decking?
TR: I have often used hardwood sheathing for roof decking.
However, the trick to using hardwoods in rough construction
is to use them green (undried). Once they dry, they become
very hard, so forget about nailing them without drilling
holes for the nails. The most desirable thickness, in my
opinion is 1 inch, which also happens to be the most common
thickness traditionally used on slate roofs. Any hardwood
will work — tulip poplar, oak, cherry, ash, maple, etc.
Oak sheathing has a high longevity, but put it on green.
You can air dry it somewhat to get rid of the wetness,
but green — right off the stump — is OK too
if the lumber is able to dry out in position. If not, air
dry it first. My preferred roof sheathing right now is
local hemlock or pine, also green, but we do air-dry the
lumber when we can. A word of caution: you can not use
green lumber in buildings that allow no way for the lumber
to dry out in place (it can cause mold).
We are in the first phase of installing
our Vermont slate roof. The slater is butting the slate at
the hip and ridge and relying on the tar paper underneath
the slate to prevent leakage. Should this not be flashed?
Also, the valley has 2 foot copper sheets (one foot on either
side of the lowest point of the valley) and the slate does
not cover that much of the copper. Therefore, a lot of copper
is showing — at least more than I think should be.
Is there a rule of thumb on how much slate is brought over
onto the copper flashing?
TR: Traditionally, slate was often installed without flashing
on the saddle hips and ridges. Flashing does a better job,
however, so we usually use it when installing
slate hips or ridges. The procedure is shown at slateroofcentral.com.
Your contract documents should detail the flashings that
are used. Typically, on residences, valley exposure is
6 inches (six inches showing), sometimes 8 inches on larger
roofs (assuming an open valley rather than a closed valley).
The valley metal should go underneath the slate a minimum
of 5 inches on each side. When you overlap more of the valley
with the slate, you're just nailing holes through the metal,
which is self-defeating.
Keep in mind that there is not one hard and fast rule to cover all situations. What is the slope? Lower slopes need more overlap. Some roofers like to widen the valley as it descends down the roof. Some like to leave a wide open valley along the bottom to help drain out ice and snow more quickly.
I hope that this question is not the
absolute dumbest one you have ever received but.... Is
it possible to paint or stain old slate to more closely
match some adjacent new slate that was installed after
some storm damage? The older slate is in good condition
and so the insurance company will not replace the undamaged
tiles but there is a noticeable contrast in coloration.
TR: If the work had been done correctly, the slates used
in the repair work would have been salvaged, not new. There
is no way to now match the original slates in your situation
other than to remove the new slates and replace them with
salvaged slates. Painting or staining will only make matters
We are installing a Buckingham 16 inch long x
random width slate roof for a client in northern Maine.The rake
slates are overhung 1 ½ inches past the gable fascia.
Could you give me your experienced opinion please?
TR: A 1 inch overhang on the gable (rake) ends is standard in the
trade. 1.5 inches should be plenty.
I am planning on purchasing S1 VT weathering
Gray 12x8 slate from [X] slate company. Are there any reasons
that you are aware of that would cause you to recommend
for or against this slate, this slate size, or this company?
TR: The slate size is very small and the installation will
therefore be labor intensive. For a less labor-intensive
installation, use larger slates. Make sure the slate is
punched for nail holes, not drilled, and contains no iron-bearing
inclusions that will leach rust down the roof after installation.
You should order the slates with these provisions guaranteed,
I will be installing symmetrical valleys
and I was planning on open valleys using valley flashing
because it appears the most basic. What width flashing
do you recommend? Do you recommend the V or W for an 8/12
roof where the two roof faces meet at a 90 degree angle?
TR: An open valley style is fine. You will need 5" of
slate overlapping the valley meta, so if you’re installing
a 6 inch open valley, you can use 16 inch stock at that
slope. We don't use V or W valleys unless there is a reason
for it. We just use flat stock and force it into place to
make a rounded valley bottom. That was the most common way
to install a valley on traditional American slate roofs. “W” valleys are designed for use when two assymetrical roof planes are
draining into each other, or when a large roof plane is draining
into a small one. “V” valleys fit nicely into
a new roof, but won’t fit well into old roof valleys
that have some sag to them. We use 20
ounce copper for valleys. Pre-fabricated “V” and “W” valley
stock in 16 ounce copper is available at the Slate Roof Warehouse.
Do you recommend using metal drip edges on slate roofs
and if so what size and material do you recommend?
TR: We rarely use metal
drip edges on new slate roof installations.
Metal drip edges became popular when asphalt shingles became
widely used because such shingles can sag over the edge
of the roof and must be supported. This is not an issue
with slate, which is why traditional slate roofs rarely
use metal drip edges. On the other hand, copper drip edges
are becoming more popular on slate roofs for stylistic
purposes as well as to protect fragile substrate edges
when laminated roof decking is used. You can also form
a cant into a copper drip edge, thereby eliminating the
need for a wood cant strip). Read an article about drip edges on slate roofs.
Can I staple the felt paper or do you
recommend nails only in the pattern you describe in your
TR: You could staple it if you're going to slate over it
immediately. Otherwise it will blow off. It can also rip
loose when you're working on it if it's just stapled.
What headlap do you recommend using on
the roof over a porch that has a slope of 4/12 and a rake
length of 9 feet 6 inches? Will 4 inches be adequate?
TR: Four inches of headlap should work, although you need to
make sure snow and ice will not be falling off an upper
roof onto the porch and damaging the porch slates. Also,
if a downspout drains onto the porch from an upper roof,
it can create problems by draining too much water onto
one spot. In addition, where is your roof located? Tucson, Arizona where it never rains? Or Pittsburgh, where it rains a lot? Also, will people be walking on the porch roof? I hope not, because if they do, it will leak.
It may take me a month to finish my roof.
Do you recommend sealing over the nails holding the felt?
If so, should I use roofing cement or silicon?
TR: If you seal the nails, use roofing cement — it's
a lot cheaper, it only has to work temporarily, and it can
be applied thinly with a trowel so it will not interfere
with the laying of the slate later. You may want to consider
installing the felt half-lapped (i.e. two layers) for added
protection. Then, you may not have to seal the nails if you're
only waiting 4 weeks. However, if you have a valuable interior,
you should either seal the nails or slate the roof ASAP. Or try caulk.
TR: Different hammers have different purposes. For example,
German style slating, such as is shown on the turret in
the article on page 7, requires the slates to be trimmed
on the job site. Therefore, a slate hammer with a slate
cutting shank is preferred by Germans. Such a hammer
has a lot of its weight in the shank (Stortz and Freund make such hammers). When the hammer is being
used to primarily beat on a slate ripper, pound nails,
or punch holes in slate, such as during slate roof repairs
or restoration, the weight of the hammer should be mostly
in the head. The solid shank restoration hammer is best used for this purpose.
If you are installing slate roofs and have a slate cutter
and don’t need a hammer for trimming slate, use a Freund
These have most of their weight in the head and are ideal
for pounding nails and punching nail holes in slate. All of these tools are available at SlateRoofWarehouse.com.
Is the slate for the starter course usually
sold separately or are the holes not already punched in
TR: You should order the starter slates separately and have
the holes punched on the front (not on the back as is done for
the field slates because the starter is laid front side
down). The quarry should already know how to do this. They
will also supply hip and ridge slates. See the article
on starter slates in this issue, page 3. There was an article
on hip and ridge slates in TR Issue #4. All articles are
posted on the web at traditionalroofing.com after the print
version has been circulated. More about starter courses on slate roofs.
We are re-doing an asbestos tile roof
and are in need of the copper tie-down hooks which are
designed to prevent the wind from lifting the tiles. Do
you carry this item or would you know a supplier?
TR: I know of no source other than maybe Ebay (readers?). some roofers may have some lying around. The copper clip used on asbestos
roofs is shown in Figure 5.
To achieve credits for LEED we need to
provide data for the solar reflectivity of slate (it’s
ability to absorb and release heat). Do you know if such
research has been done?
TR: We get this question more frequently, however, I know
of no data available about this. The solar reflectivity
of slate roofing would, I assume, vary according to the
color of the slate. Some slate is dark, some lighter. However,
on the whole I would think the reflectivity is quite low.
My guess is that LEED is concerned about highly-reflective
roofing types such as some metal roofing or even white
single-ply or white asphalt shingles. I think with slate
it's a non-issue, but as I say, I do not have the hard
data to back it up. Slate, being a stone, does absorb heat
and releases it back out to the atmosphere as it cools.
How this would negatively impact the environmental characteristics
of a building, I do not know. If the roof is insulated,
the heat does not penetrate into the building. Any of you
readers have the answers?
I am currently reading your book, “The
Slate Roof Bible.” The diagrams always show the starter
course slates as having only one hole (which would make
a lot of sense to me). Is this correct? If instead these
starter course slates are just like all the other ones
only turned sideways (with 2 holes), how do you keep the
second hole near the eave from filling with water during
ice backups in winter?
TR: All slates are nailed to the roof with two nails, including
the starter slates. You don't use the bottom hole if you're
turning a field slate sideways and using it for a starter
slate. You punch a new hole in the correct location. It
is important that the starter slate course be laid correctly
to prevent stray holes from ending up where you don’t
want them. See the article
in this issue about slate starter courses.
I know you do not recommend IWS and believe
a 4 inch headlap will protect a slate roof from winter
ice creep up under the slate roof. How does that work?
It seems to me the ice as it melts creeps up the roof from
underneath the slate, so the boards underneath get wet
and over time must be replaced. Am I missing something?
TR: Obviously, if slate roofs allowed water to penetrate
through them, they would be failures as roofs and would
have been abandoned long ago. Slate roofs are watertight.
The underlayment serves no long-term useful purpose after
the slate has been correctly installed. Water does not
creep through the slate and wet the boards underneath unless
the slate has been improperly installed such as with inadequate
headlap or is on an inadequate slope, or if the slate has
holes or other faults, or if the slate along the eaves
has been damaged by gutter installers or roofing contractors.
Granted, we have had some BAD ice-damming years lately, where some slate roofs are essentially under water. I personally have a 4:12 slate roof being drained onto by an upper 10:12 roof and on which are located two large skylights. I had six inch thick ice backed six feet up the roof over the bottom of the skylights, with 18 inches of snow on top of the ice. My roof leaked. I knew it was a poor design when I built it in 1983, but I wanted to see what would happen. It didn't leak for 30 years until the ice dams from hell came upon us. Ironically, immediately adjacent to this roof is another 4:12 being drained onto by an upper 10:12, with NO skylights, and it has never leaked.
The solution in a case like this is to install a soldered copper snow apron at least 8 feet up the roof from the eaves, or make the entire roof a soldered flat-lock or even double locked standing seam roof. I have installed heat cable, hoping it will create drainage channels for water to drain off at the eaves under the ice. This is a stop-gap measure until I replace the roof with something that will not leak when under water.
I’m installing a slate roof. Should
I use copper
nails or stainless steel screws to fasten
the slate? My roofer says I should use screws.
TR: Please DO NOT use screws. The beauty of slate roofs
is that they can be taken apart and put back together over
time, when needed, for repair and maintenance. Screws will
make it impossible to take the roof apart because a slate
ripper will not be able to pull them out.
Have questions, comments, rants or raves?
Send us mail at Traditional Roofing, 143 Forest Lane, Grove
City, PA 16127 USA, or email us at firstname.lastname@example.org.