seen in the RCI Interface
Journal, Nov/Dec 2004; Vol XXII, No. 11, pages 6-10:
of Historic Slate Roofs
With Examples of Wrongful Condemnations
as a PDF
Slate roofs have two unusual characteristics
that set them apart from most other roofs: 1) a common slate
roof will last a long time, even centuries; and 2) slate
roofs are made of removable and interchangeable parts — any
individual slate shingle, for example, can be removed from
the roof and replaced, as can any flashings on the roof.
However, these characteristics can be both a blessing and
Illustration above from the Slate Roof Bible, 3rd Edition
It’s easy to understand the advantages of a simple,
natural roofing system that can last centuries, but there
is also a disadvantage to a slate roof’s longevity.
A century is a very long time, and over a period of 100 years,
a lot of people can get on the roof and do a lot of damage,
euphemistically described as “repair.” Repair
work by poorly qualified roofing contractors, building owners,
maintenance personnel, and others with good intentions but
lacking the necessary skills and knowledge, is a common blight
on historic slate roofs. When a roof consultant inspects
historic slate roofs, he or she will invariably witness a
plethora of chronic slate repair mistakes. In fact, some
historic slate roofs have been so poorly maintained and even
abused by contractors that they are condemned by inspectors
and deemed beyond hope.
However, this is where the second characteristic of slate
roofs comes into play. No matter how poorly repaired and
maintained a slate roof is, if the slate is still good,
the roof can be restored. The bad repairs can be removed,
the tar patches erased, the mis-matching slates replaced,
and the roof returned to its former glory — if the
slate is still good.
It is incumbent upon any professional roof consultant who
claims an expertise in slate roofing to be familiar with
all the types of slate and the characteristics of each,
including the expected longevity. Roof slate, stated simply,
is stone. It is quarried up and down the eastern seaboard
of the United States as well as around the world, yielding
many different types, colors and characteristics.
Roofing slate can last roughly 55 years to maybe 400 years,
depending on the type, thickness, method of attachment,
slope, and other factors. If an historic roof is 100 years
old and has slate on it that is historically proven to
last only 100 years, then the roof is reaching the end
of its life, cannot be restored and should be replaced — with
new slate. On the other hand, if a roof is 75 years old
and has slate on it that is historically proven to last
150 years, then it is only halfway through its life and
is a prime candidate for restoration. After 100 years,
if the stone is sound, why should the entire roof be replaced?
Any leaks can be repaired, any flashings replaced, and
faulty repair work redone while leaving the original stone
in place, providing it is still sound.
An historic slate roof halfway through its life is a very
common scenario in the United States today. Virtually all
of these good roofs will nevertheless be condemned by contractors
and consultants who have little or no experience in slate
restoration. At present, contractors with a vested interest
in roof replacement significantly contribute to the destruction
of many good slate roofs.
The following are some examples of slate roofs that illustrate
these, and other peculiarities.
Ford’s Theater, Washington DC — Almost
If a roof leaks, it must need to be replaced,
right? Ford’s Theater is the historic site in Washington
D.C. where President Lincoln was assassinated in 1865, shortly
after the theater opened. In 1998, the slate roof leaked
in two places. Standing in the upstairs hallway near a front
window, one could see plaster crumbling from the ceiling,
indicating a major leak. There was a vantage point outside
where one could stand on an adjoining building and get a
close-up look at the slate roof on the theater. The slates
looked very old; perhaps they were the originals from 1865.
Apparently, it was time for a new roof. However, just to
play it safe, the author was called in to inspect the roof
prior to putting the project up for bid. That was a smart
In short, the entire roof and all of the copper flashings
had already been replaced and were about 25 years old — quite
young for a Buckingham slate roof, which can be expected
to last at least 125 years. However, when the original
slates were removed, the good ones were saved and recycled
back onto one side, coincidentally at the only place where
the roof could be easily inspected. It appeared from that
vantage point as if the entire roof was still the original
slate, but a closer inspection showed that 80% was new
slate and only about 20% was original. Furthermore, no
current worker at the theater had been there for 25 years
and there was no written record of the roof having been
replaced, so no one knew that it was already new. The leaks?
The front parapet wall copper coping had split at a soldered
seam and was channeling water directly into the building
down the front wall. The other leak was caused by a defective
flashing between the adjoining flat roof and the building
wall. The roof itself didn’t leak at all. From a
slate perspective, it was still a new roof — but
Ford’s Theater - Left
photo: This side of the roof looked old because the original
1865 slates were reused here when the roof was replaced around
1975. The right photo shows the front parapet wall. The arrow
is pointing to the spot where the copper coping had split — right
at the joint — a perfect funnel for rain water.
Castle Park Apartment Complex — Wrongfully
The Castle Park building near St. Louis
is a huge, sprawling, five-story building with an 850 square
slate roof built in 1882. The roof suffered hail and wind
damage in the early 2000s and was subsequently condemned
by contractors who offered to replace the roof with asphalt
shingles for ten million dollars. The entire roof was original,
flashings and all, and some leaking was occurring.
An inspection by the author revealed that the slates were
a Buckingham or Peach Bottom variety of exceptional quality.
There was essentially no wear visible on the slates after
120 years. The very steep slopes and the semi-dry conditions
of the area had helped preserve the copper, most of which
was original. The wind and hail damage on the roof was
quite limited and all of it was repairable for less than
3% of the replacement cost. The slates themselves could
be expected to last another century, although the copper
flashings would have to be replaced eventually. The main
leak was in a copper valley and was unrelated to the storm
damage. Although this beautiful slate could last at least
another century, contractors were earnestly attempting
to permanently destroy it.
Castle Park - Left photo: This
is only the entranceway to the huge building which has large
wings emanating in three directions. The slate, at 120 years
of age, is in excellent condition. Roofing contractors, however,
would love to tear it off. Right photo: The minimal wind
damage does not justify replacing the entire roof when the
slate is still in good shape.
Historic Home - Wrongfully Condemned
A residence in an upscale Chicago neighborhood
suffered hail damage to its unique “battered butt” style
75-year-old slate roof. Three firms looked at the roof and
all three condemned it before the owner contacted the author
for an impartial inspection. Hail damage to the mixed Vermont
and Buckingham slate was certainly evident, but it was limited
and all readily repairable by any contractor with a minimum
of slate roof restoration experience. The inspection revealed
about 150 slates needing to be replaced — a couple
days work for experienced professionals.
The condemning roofing contractors were evidently influenced
by the idea that insurance money would pay for an entire
new roof. That may have been a much easier approach for
them than trying to duplicate a slate roof that is a work
of art. But the owner didn’t want a new roof — he
liked the one he had. Yet, if he hadn’t put his foot
down and hired the services of a knowledgeable roof consultant,
he would have lost both his roof and the character of his
Hail damage of this nature
as seen on Chicago area “ragged butt” slate roof
is repairable by simply removing the damaged slates and replacing
them. Most of the slates are undamaged.
Venango County Courthouse — Wrongfully
In 2004, the author was called to consult
on the replacement of a Pennsylvania courthouse roof. The
130-square Vermont “sea green” slate roof was
approximately 72 years old. A county engineer insisted that
the roof was beyond repair and was “absolutely certain” it
had to be completely replaced. The author’s inspection
revealed that most of the problems with the roof were related
to bad repairs in the past, all reversible. The slate itself
was still good and could be expected to last at least another
50 years if not 75 or more. Replacement costs of $358,451
were reduced to restoration costs of $35,000, which included
replacement of virtually all flashings with stainless steel — a
savings to the cash-strapped county of over $300,000.
Venango County Courthouse -
Most of the problems associated with the courthouse roof
were caused by bad repair work over the years. The wrong type and color of slates
were used to repair this roof, indicating the repair contractor
didn’t understand proper restoration techniques. These
will all need to be removed and replaced with slates that
match the original roof. The author counted approximately
700 slates like this on the courthouse roof.
Smithsonian Institute Building — The
The huge Smithsonian building known as “The
Castle” in Washington D.C. has a slate roof measuring
several hundred squares in area. In 2000, the roof leaked
in several places, generating talk of replacement — a
very expensive proposition. An inspection by the author revealed
that the roof had recently been replaced — a scenario
similar to Ford’s Theater. The slate roof on the Castle
was only about 25 years old, having already been replaced
with new Buckingham slates (although some of the original
slates had been reused). The majority of the flashings had
also been replaced with new copper.
Apparently, some of the more important historical buildings
in our nation’s capital had been refurbished around
the time of the bicentennial in 1976. At about that time,
Ford’s Theater got a new roof and so did the Castle.
For some unknown reason, however, not all of the Castle’s
flashings had been replaced. Four main central valleys
and the flashings along two parapet walls had been left
as original, and they now leaked. Furthermore, the maintenance
crew had the habit of tromping on the slate roof in what
appeared to be combat boots, crunching the slates underfoot,
breaking them, and adding to the roof problems. The solutions
were simple and relatively inexpensive: replace the old
flashings with new copper and keep people off the roof
who don’t belong there.
The Smithsonian Institution
Building known as the Castle had already been replaced with
new slate, but some of the original flashings had been left
in place, and they leaked. The author is inspecting the roof
in the photo above.
Cathedral in Arkansas — Rightfully
(But Replaced with New Slate)
A slate roof will wear out, of course,
and at the end of its life, nothing can save it. This was
the case with the Cathedral of St. Andrew in Arkansas. The
Cathedral roof was made up of Pennsylvania black slates and
Vermont unfading green slates mixed in an ornate pattern.
At 120 years of age, the PA black slate had simply worn out — become
soft, flaky and falling apart, especially on the south exposure
and on the main body of the church. The Vermont unfading
green slates showed almost no wear at all despite their age
of 120 years.
The original roof was inspected by the author to determine
its condition and to draw up specifications for replacement.
The new slate roof was subsequently installed by Midland
Engineering of South Bend, Indiana, to match the original
roof. This time, however, Vermont unfading green slates were
mixed with Welsh black slates from Cwt-y-Bugail. All of the
copper flashings were replaced with terne coated stainless
steel (some 4-lb. sheet lead was also used). The new slate
roof is expected to last at least 150 years.
The Cathedral of St. Andrew
in Little Rock, Arkansas, had worn out its black Pennsylvania
slate after 120 years (above top). The Cathedral's new roof,
installed by Midland Engineering in 2003, is likely to last
150 years. Vermont unfading green slate mixed with Welsh
black slate and terne-coated stainless steel flashings should
out-perform the original roof.
Private Residence - Wrongfully Condemned
For what it’s worth, even newer slate
roofs fall prey to unscrupulous roofing contractors. A house
just outside New York City had a ten-year-old Vermont mixed
slate roof. In the spring of the year the owner found some
slates on the ground, along with some snow guards. A local “third
generation slate roofing expert” was called to the
scene. He promptly condemned the 100 square roof and offered
to replace it for $450,000. The owner then called the author
for a second opinion. The author’s inspection revealed
that the snow guards had let loose due to severe weather
that winter combined with an inadequate number of snow guards
for the size and slope of the roof. Each snow guard was hooked
onto a slating nail causing a slate to be pulled out with
the snow guard. The damages amounted to a maximum of $10,000
and all of it was covered by homeowner’s insurance.
Otherwise, the roof was fine. So much for “experts.“
Ten year old slate roof on
a private residence condemned by roofing contractors. The
nominal snow guard damage, however, was covered by homeowner’s
insurance — the roof did not need to be replaced at
Remember one simple rule regarding the restoration of slates
roofs: if the slate is still good, the roof can usually
be repaired and/or restored. One can visually inspect the
slate to determine its condition. If the surface is smooth,
the slate is probably still good. If the surface is crumbly
and flaky and if there are slates sliding off the roof
here and there, you may be looking at a roof that is ready
to retire. It certainly helps to be able to identify the
type of slate that is on the roof.
In summary, slate roofs are in a world of their own. They
require specific knowledge and expertise. Genuine experts
in the field are rare and there are many “pretenders” whose
advice should be taken with a grain of salt. A second opinion
can be very valuable if it’s coming from the right
Joseph Jenkins, in the preservation trades
since 1968, directs Joseph
Jenkins, Inc. in northwestern Pennsylvania that provides
national slate roof consulting
services, slate roofing publications and
slate roofing tools
and supplies. He has personally worked on over a thousand
slate roofs, many with an average age of one century. Jenkins authored and
self-published The Slate Roof Bible, which has been recognized in four national
book award competitions
and presented with the National Roofing Contractors Association
Gold Circle Award. The research for this book involved travel
around the world. Jenkins has been a presenter on the topic
of slate roof restoration at many International
Preservation Trades Workshops. He has also conducted slate
roofing presentations at the Natural Building Colloquium
in Maryland, for the Roof Consultants Institute, the Restoration
and Renovation Trade Show, and many other venues. Jenkins
was on the Board of Directors of the National Slate Association
(SlateAssociation.org) and founded the Slate
Roofing Contractors Association of North America (SlateRoofers.org).
Jenkins also maintains a web site at SlateRoofCentral.com which
provides information on slate and tile roof repair, lists
industry contacts and sources of
materials, sells tools and maintains a message
board on slate, tile and asbestos roofing. His website
at SlateExperts.com provides more
Slate roofing tools,
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