Spring,
2005: Issue #4
READERS WRITE
I need to find some method
to reliably penetrate a slate roof with a vent
flashing.
Traditional Roofing: First, find the
exact spot on the underside of the roof in the attic and
drive a 16-penny nail through the roof, right through the
slate, from inside out. Then go on top (use a hook ladder,
if needed) and find the nail. Push the nail down and then
pull the slates off the immediate area, using a slate
ripper, until the wood roof deck is revealed. Pull
off enough slates to make the job easy — they're
easy to pull off and to put back (you may need to remove
6-10 slates depending on the size of the slates, maybe
more). Cut the hole in the wood just big enough to allow
the pipe through — use a hand-held hole saw or a
cordless circular saw. Insert the pipe through the roof
from inside. Begin to nail the slates back down from the
bottom course up, cutting them with a slate cutter to fit
around the pipe. If there is a hole needed only in the
center of a slate, draw a circle with a nail on the back
of the slate, then punch along the line with the pointed
end of a slate hammer to perforate the line, then break
out the hole. If you need extra nail holes to nail a slate
back into place (such as two nail holes on one side of
a slate) punch the extra nail hole above the existing hole
with the slate
hammer. Fit the pipe
flashing over the pipe before the top courses of slate
are installed so the slates will overlap the flashing properly,
then trim the top slates to fit around the flashing as
you nail them into place. The very top row of slates can
be installed with either slate
hooks or bibs and nails.
The pipe flashing can be a standard aluminum/neoprene or
copper/neoprene flashing or a custom made lead or copper
flashing (avoid all plastic or all rubber flashings). Lead
pipe flashing fabrication is illustrated in the second
edition of the Slate
Roof Bible. The tools, the book and the copper/neoprene
flashings are available at SlateRoofWarehouse.com or
by calling toll free: 866-641-7141.
****
I am an architect building my own
home using a slate roof. Virtually every roof detail
I can find on slate roofs is for unvented roofs. The Slate Roof Bible as well as the documents linked by the
Jenkins web site make numerous references to slate over
rough sawn lumber as a "breathable roof." It
seems reasonable to me that water vapor is not going
to get trapped underneath a traditionally framed slate
roof. Is this presumption correct? Can you provide appropriate
references regarding the appropriate venting of a traditionally
framed slate roof system? Is it going to need ridge vents,
soffit vents, or an air cavity between the roof deck
and the insulation?
Traditional Roofing: The issue of traditional
slate roofs being “breathable” roofs lies in
the fact that such roofs are typically installed on board
decks. Each board has an air space between it and the next
board. That space may be 1/8” to 6”, depending
on the installation method used. A stone roofing system
nailed over a board deck allows some air penetration through
the roof, but not water penetration. It is water-tight,
but not air-tight. Thirty pound felt underlayment initially
acts as an impediment to air flow, but does not block it
completely. This is why century-old slate roofs with no
specific roof ventilation system, insulated or not insulated,
function quite well, provided that standard principles
of insulating are followed (i.e. warm air is not allowed
to contact cold surfaces). Contrast this to plywood roof
decks covered by self-adhering asphalt roll-roofing and
self-sealing asphalt shingles. There is little opportunity
for air to breathe through this sort of roof system, hence,
roof ventilation systems are imperative.
Generally, you should leave an air space between roof insulation
and the roof sheathing (assuming the insulation is installed
between the rafters) to allow for air flow through that
air space so the space maintains the same temperature
as the outside air. In addition, you should install a
vapor barrier interior to the insulation in cold climates
to prevent moist, warm air from coming in contact with
a cold outer surface such as the underside of your roof
decking. Condensation inside roofs is caused by warm,
moist interior air infiltrating to the underside of the
cold roof sheathing. This is prevented by the aforementioned
vapor barrier, proper insulation, and proper ventilation
of the roof space. Ventilation is most often achieved
by gable-end vents or low-profile roof vents, but can
also be achieved by ridge vents when there is no gable
wall available. There is information illustrating the
installation of vented
slate ridges at slateroofcentral.com. It should be
pointed out that there are many thousands of century-old
slate roofs in the U.S. that never had any ventilation
system incorporated into their design, and that these
roofs are still functioning quite well today — after
a hundred years. This seems like a rather strong testimonial
on behalf of traditional roofing methods and materials,
i.e. board roof decks, 30 lb felt, and stone roof coverings.
****
I am curious to know if you would
consider it a good or bad practice of setting all hips
and ridges in a solid coating of a high quality flashing
cement.
Traditional Roofing: Bad. Frankly, the
setting of slates in roof cement creates a long-term problem
related to maintenance and restoration. One unique quality
of a slate roof is that it lasts so long, and one reason
it lasts so long is because it can be taken apart and put
back together — in
other words, maintained and restored. When the slates are
glued to the roof, or to each other, they cannot be removed
without damaging the roof. Every time the slate roof mechanics
at Joseph
Jenkins, Inc. run into a roof where slates have been
glued down with roof cement, they begin uttering a long series
of profanities that usually lasts until the repair work has
been completed. The better approach to the issue of hips
and ridges opening up over the years is to install step flashings under
the hip and/or ridge slates. This is a permanent, effective
solution that allows the roof to be easily repaired or
maintained years later when, for example, a tree branch
falls on it. In short, we discourage the use of roof cement
or other adhesives under slates anywhere on the roof except
in unusual situations, such as: 1) exposed gable edges
subject to wind damage, and 2) small pieces of slate that
require a little extra holding power, which could be a
narrow piece on a gable end, a small piece on a tower hip,
etc. Routinely using roof cement under slates is a mistake.
You can see an example of a slate ridge being installed
with copper step flashing at slateroofcentral.com (click
on “How
to Install a Slate Roof,” then follow the links
to slate
hips and ridges).
****
My concern is the prices of new
slate, which, by my opinion, as with many other contractors,
is quite expensive.
Traditional Roofing: When the price of
the material is compared with the expected life of the
material, and other considerations are included such as
aesthetics, natural vs toxic, etc., then it can easily
be argued that slate is not as expensive as the "cheap" stuff
(which is short-lived and has to be regularly replaced
at increasing cost, creates toxic waste upon disposal,
produces environmental toxins during production, looks
ugly over its lifetime, etc.). When one considers that
almost all average houses in the northeast U.S. had slate
roofs on them at one time, back when people were frugal
and living by modest means, then one might ask what has
changed today. At that time, people bought slate for their
roofs without question because they wanted good, beautiful,
long-lasting roofs. Now, slate roofs are considered by
some to be too expensive. The difference is 1) people today
can buy very cheap roofing materials, and 2) people generally
don't live in the same house very long and therefore don't
care whether the roof will last a long time. I don't think
the solution is to try to produce cheaper slates. I think
the solution is to market slate roofs to those people who
value quality and are willing to pay for it. Remember,
you get what you pay for.
****
I am in the midst of restoring an
1860s home complete with a slate roof. Unfortunately,
the original box gutters were torn out and replaced with
plywood and asphalt shingles. I would like to go back
to the original design and would appreciate any information
you can give me.
Traditional Roofing: There are copper
sheet metal sources in the Slate
Roof Bible, 2nd edition. There is also some information
in the book about replacing box gutters, including drip
edge detail and installation sequence. Slateroofcentral.com has
illustrated information about both installing box gutters as well as installing a copper
snow apron over an area that had once been box gutters
but was replaced with plywood and asphalt shingles, like
your situation. Go to “How
to Install A Slate Roof” and follow the links.
Remember, when installing box gutters, expansion joints
are required every 30 feet or so. If you are installing
expansion joints, end one gutter at a high point and butt
the end against the end of the next gutter section (leave
an inch or so space), then place a copper cover over the
gap. That allows the gutter to expand and contract. This
is also illustrated at Traditional Roofing.
****
Can you tell me what would be the
best nail to use for natural slate roofing?
Traditional Roofing: Copper
nails will outlast galvanized nails and stainless
steel nails will outlast both. If the slates are
new, you should use either copper or stainless. If the
slates are salvaged and not expected to last more than
50 more years, hot-dipped galvanized nails will do. Stainless
nails are stronger than copper and may work better on
some old, hard oak or yellow pine roof decks. However,
stainless nails are also harder than copper nails to
pull out when repairing the roof. Copper and stainless
steel roofing nails are available from slateroofcentral.com
or by calling the phone number at the bottom of this
page.
****
Can you tell me if it is customary
to use or not use an aluminum drip edge on a slate roof?
Traditional Roofing: Aluminum drip edges
are not used on slate roofs. They are designed to prevent
asphalt shingles from sagging over the edge of a roof.
Slates don’t sag. In fact, no metal drip edges were
ever used on traditional slate roofs — neither on
the drip edge nor on the rake edge. The practice of using
metal edges on slate roofs is a recent one that has been
promoted by asphalt shinglers who typically use plywood
roof decks. Metal drip edges do not reflect traditional
slate roofing techniques and can be avoided altogether
by traditional slaters. More about drip edges.
****
I have been told that one can judge
the quality of a slate by tapping it with a metallic
object. The harder slates have a ring, and softer slates
sound duller. Is this an accurate test of (1) the quality
of the slate or (2) the useful life remaining in a slate?
Traditional Roofing: The answer to your
question is complex. There are subtle nuances involved
in determining the quality of used slates. The ring is
part of it, but many older slates (100 years old) do not
ring like new slate does. New slates should always ring
well, unless they're cracked. The best way to know if an
older slate is any good is to know
what type it is, what approximate age it is, and
then examine it visually for surface delamination and
softness. Punching a nail hole in the slate with a slate
hammer or cutting it with a slate cutter will reveal
the hardness or softness of the slate, although an experienced
slater can tell the quality of a piece of slate by simply
holding it and looking at it. Even a reputable, old,
hard slate with a degree of softness can last many decades
re-nailed to a roof. Slates that are notorious for not
being reusable when old are some PA black slates (while
other PA black slates have quite high degrees of longevity).
Some Vermont sea green strains can also become soft after
115 years, although most don't. Generally, if it’s salvaged American
slate and it looks like a good, smooth piece of dense stone
while holding it in your hand, then it will most likely
make a good roof.
****
About two years ago, I purchased
an 80-year-old home with a Vermont “sea green” slate
roof. Last spring I noticed a leak, and as I am not as
young as I once was, I decided to look for a contractor.
To make a long story short, I was very dissatisfied with
the work this company performed. My objective in writing
this is two-fold: first to let you know the working ethics
of at least one of the companies you recommend on your
web site, and second, any pressure you may be able to
exert on the roofing company on my behalf will be greatly
appreciated.
Traditional Roofing: We do not recommend
any roofing contractors on our nationwide online Directory
of Slate Roofing Contractors. We once had a list compiled
from voluntary submissions that were simply posted on our
website for the convenience of the public. There had never
been any charge to any contractor for inclusion on that
Directory and none of the contractors were screened in
any way. We posted a large, bold disclaimer to
this effect right on the top of the Directory.
That said, please be aware we have discontinued our voluntary
contractor directory at slateroofcentral.com. Instead,
we have replaced it with a Directory
of Slate Roofing Contractors Association members who
pay a fee to be included in the Directory and who fill
out an extensive membership application revealing their
level of experience and other important aspects of their
contracting capabilities — information that is
posted on the Directory as a Contractor Profile. We are
now only listing roofing contractors who are willing
to be scrutinized, willing to abide by a Code
of Ethics, willing to allow their Contractor Profile
to be publicly displayed on the website, and willing
to pay a fee for this service. This has knocked out a
lot of the dead wood from the old, original Contractor
Directory.
****
I hired a contractor to replace
my copper valleys. Thanks to your advice I told him I
did not want him to slip the new valley over the old
valley which he mentioned was an option to save money
and time. While he was removing the slate, he was breaking
almost every piece. The next day, when I came home from
work, I noticed he had done three dormers in the same
time it took him to do one the first day. I climbed up
on the hook ladder to check out the work and discovered
he had given me the VALLEY SLIP and he also broke over
70 pieces of hard Vermont slate. I called him up and
told him to get his stuff and get off of the job. He
said he used the slip method only because he was breaking
too many slates. He told me that at this rate he would
have used up my remaining 150 pieces to do 75 feet of
valley. How many slates can I expect to replace because
of breakage on an average hard Vermont thick slate roof
that’s 90 years old when an experienced slate roofer
is replacing valleys?
Traditional Roofing: A hard Vermont slate
roof should experience little if any breakage when valleys
are being replaced. However, if the valleys are tarred,
or if they have been walked on over the years, breakage
will increase. Typically, a hard Vermont slate roof may
have 5% breakage along a valley, if that. Sometimes there’s
no breakage at all. Sounds like your contractor had no
idea what he was doing. He should have read the Slate
Roof Bible (which has an entire chapter on valleys
and valley replacement) before he dove into that project.
****
My roof expert says that New York
has adopted national codes and that self-adhesive asphalt
ice shield on a pitched roof is now code. Can you tell
me if this is so?
Traditional Roofing: You need to look
at the code yourself and see what it actually says. The
International Building Code of 2000 states that in areas
where the average daily temperature is 25 degrees Fahrenheit
or less, a double layer of felt cemented together or a
layer of self-adhesive ice
shield are required at the eaves. However, traditional
slate roofs were never installed in this manner unless
there was a particular need for a heavy underlayment, meaning
an extraordinary expectation that the roof would leak.
Ice damming problems are often caused by a lack of insulation
in the roof of a heated building. The ice and snow melts
from the roof, then freezes at the unheated eaves causing
an ice build-up that can allow water to penetrate the roof
at the eaves, especially at weak points. It's much better
in ice-dam prone climates to properly insulate the roof
and to reinforce the eaves during the roof installation
by increasing the headlap there. Beefing up the underlayment
is a temporary waterproofing measure that will not last
nearly as long as the slate itself. It is unwise to rely
on the underlayment to keep a slate roof water-tight. A
properly installed slate roof requires no underlayment
to be completely water-tight during its lifetime. [Read an article about how to install ice dam resistant eaves on a slate roof.]
****
I am having my roof installed next
week. I ordered the slate myself and ordered random width.
Is there anything special the roofer should know regarding
installation of random width vs uniform?
Traditional Roofing: Random width slates
are not hard to install. The slater has to keep an eye
on the sidelaps, but that's about the only additional thing.
The guy bringing the slates up to the roof has to make
sure he's blending the widths according to the proportions
available. For example, if you have 20% 8" wide, 40%
10" wide and 40% 12" wide, then he should bring
up two 10" and two 12" for every one 8" slate.
Other than that, there's not much else to it. [Read an article about installing random widthslate roofs.]
****
My roof was constructed at an 18
degree pitch with 38x38mm battens covered with underlayment
and the slate tiles nailed to the battens. It's leaking
so badly that there is sagging of the battens. Please
correct me if I'm wrong but what I would like to do is,
1) Remove tiles, underlayment and battens; 2) Apply new
battens nailed directly to roof trusses; 3) Apply slates
tiles to battens with copper nails. Please advise if
the above exercise will work, if not please can you suggest
an alternative!
Traditional Roofing: Minimum slope for
slate roofs is 4:12. (around 18 degrees). You must have
4" of headlap on the slate at that slope, or more.
If you re-lay the slate with the proper headlap and don't
allow anyone to walk on it during installation or after,
you should be OK. Replacing the battens with boards will
help (you can use 1" rough sawn lumber or 3/4" planed,
kiln-dried lumber — either will work fine). 30 lb
felt paper over the boards and under the slate, half lapped
(i.e. two layers), would also be a good idea at this low
slope.
****
I am a professional engineer called
upon to determine whether or not a hailstorm caused damage
to a slate roof. I should note that it appears to me
(from your guidance in "How To Identify Your Slate" at
slateroofcentral.com) that the roof is a blend of Vermont
greens and gray with a little New York red mixed in.
I found a broken piece of slate on the ground (approximately
4" long along the bottom edge by 3" irregular)
that has a distinct circular (3/8" diameter) rusty
deposit on the underside within 1/2" of the lower
edge. Can it be that the nails have pushed out, similar
to nail pops in drywall, to cause enough stress to fracture
the slate?
Traditional Roofing: Vermont slate is
pretty resistant to hail damage. Hail damage is indicated
by holes with the back of the slate broken out, i.e. the
holes have clean edges (not beveled) on the impact side
of the slate (the side facing the sky). Holes in slate
originating from inside the building (from gunshots, for
example), would have the beveled edges showing on the outside
of the slate. Yes, nails will push against the underside
of the slate and sometimes wear a hole in the slate. In
this case, the beveled edges also show on the top (outside)
of the slate. This phenomenon happens when the slate underneath
was "under-nailed," (the nail was not driven
down far enough), or when the nail was driven into a knot
in the wood (for example) and the nail was then forced
back out a little as the wood dried. It's unlikely that
the nail stress would have "popped" or broken
the slate. Typically, the nail simply wears a clean hole
in the slate, as shown in the Slate
Roof Bible, 2nd edition, page 220 (which is a drawing
made from a photograph). Below is a photo of hail damage
on a 75-year-old mixed-color Vermont slate roof which suffered
massive hail impact a few years ago. Notice how beat up
the metal vent is, but of all the slates around it, only
one slate was perforated by the hail. This is what one
typically sees when a slate roof is hail damaged — spotty
damage to the slate here and there that can be repaired
by simply replacing the damaged slates. The bigger issue
is whether the flashings need to be replaced. If so, this
can usually be done without removing and replacing the
entire roof. [Read an article about hail damage.]
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