John Leeke's Historic HomeWorks™
207 773-2306 26 Higgins St. Portland, ME 04103
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John Leeke's Historic HomeWorks™ |
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207 773-2306 26 Higgins St. Portland, ME 04103 |
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The Vieux Carré Commission in New Orleans, the nation's second oldest historic preservation district, held a telephone conference Jan. 6th with roofing and historic building specialists from around the country. We discussed how to fit new roofing products, such as plastic "slate" into their preservation guidelines as they are adapted to meet the post-Katrina recovery efforts. Lary Hesdorffer, director of the commission, and Alice Krishnan, have asked me to post this summary of comments from the participants here at Historic HomeWorks.
If you would like to join the Slate Substitutes discussion go to the Forum: http://historichomeworks.com/forum/viewforum.php?f=15
This article introduces the topic with technical descriptions of substitute slate materials. It was first published as "Making Sense of Slate Roof Stand-Ins," in the May/June 2005 issue of Old-House Journal.
Slate shingles are traditionally made of natural stone. They are know to last for decades, even a century or more with maintenance and minor repairs. Since the late nineteenth century roofing manufacturers have been combining other materials to produce “composite shingles” with the promise they will last longer, look better and cost less. Can they keep that promise? Sometimes.
The familiar asphalt shingles are composed of felt or paper layers saturated with asphalt and covered with granules of stone. Throughout the twentieth century manufacturers refined and improved asphalt shingles with only occasional lapses like the infamous fiberglass shingle failures in the 1990s. While asphalt shingles typically last only 15 to 25 years, their low initial cost and a reasonable yearly life-cycle cost make them a common choice for the typical home owner. There are other, less common, types of composite shingles.
In this type of shingle Portland cement binds together tiny fibers that act as reinforcements like steel re-bar in concrete, but on a much smaller scale. The mix of cement and fibers were cured in molds under pressure to form a variety of building products, including underground drainage pipes, boards, panels, siding, and shingles. The result was a shingle that was durable to weather exposure for decades and resistant to fire. Some shingle products were formed and detailed to imitate traditional wood and slate shingles.
Asbestos-fiber-cement shingles were first developed in France a century ago. New shingling systems and unique shingles were specifically designed to take advantage of this new material as it was developed in the early 20th century. Those special diamond-shaped shingles were called diagonal pattern or French pattern roofing and are now considered to provide architectural character to historic buildings of that era. Asbestos-cement shingles were common in the 1920s and 1930s. They were out-marketed in the 1950s and 60s with asphalt shingles and the need to eliminate the use of asbestos in the 1970s. In the 1980s new shingle products were developed with fiberglass and cellulose from wood.
The early twentieth century products proved to have good performance and durability of 40 to 80 years. The more recent fiber-cement roofing products are still questioned by independent authorities such as the National Roofing Contractor’s Association. Some of the products were problematic and thousands of roofs failed prematurely. During the 1980s and 1990s several manufacturers have moved in and out of the fiber-single market, indicating that these newer products are still in a development phase.
The early asbestos-cement shingles weather only very slightly at the surface. They are quite brittle making damage from tree branches and falling bricks common and repairs difficult. The recent fiber-cement shingles fail when the cement transfers moisture into the wood fibers which swell up. Freezing and expand water adds to the damage of the binding cement. Resin or paint coatings provide protection, but increase the need for pro-active maintenance. Birds peck at the failed coating exposing the softer core, which then allows rapid deterioration and supports the growth of moss. Cement can react with fiberglass to deteriorate the fibers.
Considering environmental issues, the early fiber-cement shingles were made of abundant resources, which were durable and saved resources. Proper handling and disposal of the asbestos-containing shingles has become a costly health and disposal issue in recent years. If the current roofing manufacturers can develop their products to perform as well as the earlier ones without using scarce or polluting materials they may be able to measure up to the strong reputation of the earlier fiber-cement shingles. When used in non-freezing regions the longer life can save resources.
Particles are bound together with plastic polymer resins such as polyethylene and rubber. Sometimes cellulose or fiberglass is added as a reinforcement. A wide variety of materials are used for the particles including pulverized natural stones such as slate, shale, limestone, and clay. The stone acts as a low-cost aggregate and may help block ultra-violet (UV) radiation from the sun. Recycled materials may be added such as shredded tire rubber to provide flexibility. Carbon-black may be added to block UV rays to slow down deterioration of the resin. The materials are heated and compressed into molds that imitate the shape and textures of traditional shingles like wooden shakes and slates. Some products have layered or laminated construction.
Production and availability of these composite shingles is a recent development, a matter of years, not decades. The manufacturers test their products within accelerated weathering chambers, which scientifically suggests they will have a long life. But, the actual demonstration of long-term performance of these shingles out in the real world is unknown.
Considering the wide range of materials used to make this type of shingle, sometimes from recycled sources, the shingles could have variable characteristics with properties that are not well understood increasing the potential for deterioration. Manufacturers seem to be shifting away from highly variable post-consumer materials to post-industrial materials, which are more consistent. In the shingles up on the roof, the binders breakdown by UV deterioration releasing the particles at the surface. The result is similar to paint that fails by chalking off the surface over time. Shingles of these materials may fail by curling or lifting, so manufacturers try to formulate and design their shingles to prevent this.
When the source of the resin binder used to make these shingles is recycled they could be considered highly environmentally friendly. The variety of materials in the formulations may complicate the high-value recycling of installation waste and of the shingles at the end of their useful life.
Products:
MiraVISTA Slate, cast in molds made from natural slates, no longer on the market
LAMARITE™ SLATE Composite Shingles by TAMKO®; non-absorbent feature is said to prevent moisture related failures, contains fine particles of slate and clay
Majestic Slate, by EcoStar, formulated of recycled TPO plastic resin and EPDM synthetic rubber materials
Dura Slate, by Royal Building Products; made of polymer compound
These shingles are made of a plastic mixture of polymer resins, such as polyethylene or Thermo Poly Olefins (TPO), and sometimes fillers and other modifiers, which are injected into molds under high pressure.
The TPO plastic polymers have been used in the automotive industry since the early 1970s. Their performance and strength characteristics out in the weather are proven and well understood. If the shingle products are well engineered they should last for decades. In the short- to mid-term (3 to 15 years) polymer shingles have proven themselves. The manufacturers test and develop their materials and formulations within accelerated weathering chambers, which scientifically suggests they will have a long life. But, the actual long-term performance of these shingles out in the real world is unknown.
These shingles are not a layered composite and cannot fail by delaminating. They are a solid resin that is “knit” together in long strands at the molecular level. Very limited UV breakdown takes place at the weathering surface.
Environmental ratings are high when these shingles are made from recycled TPO and other post-manufacturing recyclable rubber and plastic materials leftover from other manufacturing. High-value recycling at the end of the useful life of these shingles is engineered into the resin when TPO is used.
Products:
DaVinci Slate, by DaVinci Roofscapes; constructed with ribs and posts underneath to keep them flat; custom colors available at additional cost
Authentic Roof ™, by Crowe Building Products, Inc.; high-value recycling engineered into its PTO plastic resin
Max Slates, by Max Roofing Products; designed with a camber or bow that holds the lower exposed edge down onto the roof
In my work preserving historic buildings I have been able to investigate and compare traditional and modern roofing materials. I apply many of the roofing lessons I have learned from historic buildings to modern roofing needs. Too often roofing decisions are based on the selection of products alone. This is understandable since the building construction industry is driven by product manufacturers and controlled by product marketers and distributors. The skills and methods used in the application of these products have equal, if not greater, importance. Neither the best materials installed poorly nor poor materials installed well result in success. Long lasting roofs that perform well throughout their life are the result of both good materials, good installation and good maintenance methods. A knowledgeable approach to the selection of materials and methods is appropriate because of their expected lifespan. An error in judgment at re-roofing can seriously lower the future value of the major investment made in a building. There are too many examples of failures in new materials and methods to follow a policy of always using the newest, assuming it is the best. Of course, it is the introduction of new products and methods that holds the promise for advancements in roofing. If you are compelled to use new materials, research their application and performance through the manufacturer as well as independent sources of information. Use them on small jobs you can monitor closely over the years to determine their performance and effectiveness. Then use the results of your observations to decide where the new materials and methods can best be used, or if they should be used at all. For critical projects always use materials and methods that have stood the test of time. Is the roof of any building less than critical? This conservative approach reflects my own traditional bias. – John Leeke, Historic Building Specialist
Author:
John Leeke 26 Higgins St. Portland, ME 04103 207 773-2306 www.HistoricHomeWorks.com JohnLeeke@HistoricHomeWorks.comThe molds used imitate traditional thin slate. Made of TPO plastic resin, which has high-value recycling of construction waste and at the end of the useful life of this shingles engineered into the resin.
www.royalbuildingproducts.com
Technology: tiny fibers acting as reinforcements are bound together by Portland cement; much like steel re-bar in concrete, which also uses cement as a binder; cured in molds under pressure to form a variety of building products, underground drainage pipes, boards, panels, siding, shingles. The result: durable to weather exposure for decades, fire resistant building material. Some shingle products are formed and detailed to imitate traditional wood and slate shingles. Companies in Europe are even developing high-tech photo-voltaic units bonded to fiber-cement shingles.
History: first developed in France a century ago. New shingling systems and unique shingles were specifically designed to take advantage of this new material as it was developed in the early 20th century. Those special diamond-shaped shingles were called diagonal pattern or French pattern roofing and are now considered to provide architectural character to historic buildings of that era. <see illustration from ICS>; common in this country by the 1930s; out-marketed in the 1950s and 60s with petroleum-based products and the need to eliminate use of asbestos; 1990s new products developed with other fibers such a wood. During the 1990s several manufacturers have moved in and out of the composite shingle market, indicating that these newer products are still in a development phase.
Performance: proven performance and durability (40-60+ years) of the early products; more recent (1990s) fiber-cement roofing products are questioned by independent authorities such as the NatRoofContAssoc
Failure Mode: penetration of moisture into the fibers which freezes and expands to damage the binding cement; coatings mitigate this damage, but increase the need for pro-active maintenance and can fail, especially when the fibers are cellulose, with birds pecking the failed coating and supporting growth of moss
Environmentally responsible: durable, saves resources; made of abundant resources, saves scare resources; non-toxic, lessens pollution
How to identify old and new fiber-cement shingles; photos; not to be confused with “panelized products” like James Hardie's newest siding, Shingleside Heritage
Products: ???
Technology: stone particles (natural slate shale limestone clay) bonded with resin and cellulose or fiberglass reinforcement
History: a matter of years, not decades
Performance: ???
Failure Modes: whitening/chalking over time
Products:
MiraVISTA Slate, cast in molds made from natural slates
LAMARITE™ SLATE Composite Shingles by TAMKO®www.tamko.com (will fax MSDS) www.tamko.com, non-absorbent prevents moisture related failures, made of a colorized polymer (plastic) that is mineral-filled with fine particles of slate and clay
EcoStar's Majestic Slate, recycled building products
Royal Building Product's Dura Slate, www.royalbuildingproducts.com
Table: type product fire rating wind resistance warrantee cost
Technology: Thermo Poly Olefins (TPO) plastic polymer resin made from old tires and other recyclable rubber and plastic materials leftover from other manufacturing; not a composite that can fail when its parts break down, but a “pure” resin that is knit together in long strands at the molecular level.
History: 15 years
Performance: ???
Failure Mode: UV breakdown at the weathering surface;
Environmental Responsibility: high-value recycling at the end of the useful life of this shingles is engineered into the resin.
Products:
Authentic Roof ™,
Crowe Building Products
905-529-6818
www.authentic-roof.com
“Innovators of the world's first recycled and rubber roofing 'slates'. Manufactured from 100% recycled reengineered polymers and rubber materials. The 'slates' are also completely recyclable. These roofing tiles are warranted for 50 years, but have 100 years of life expectancy. Easy installation. No special tools or equipment required. Fastened with standard 1 1/2" roofing nails over standard plywood and is less labor intensive than slate roofing.” -- http://www.ccia-net.com/buscon.htm
Special tools: Porter Cable 6605 Fiber/Cement Shear $215; Makita 5036DWB 6-1/4" Cordless Fiber-Cement Cutting Circular Saw with Dust Collector $400;
Too often roofing decisions are based on materials alone. This is understandable since the building construction industry is driven by product manufacturers and controlled by product marketers and distributors. The skills and methods used in the application of these products have equal, if not greater, importance. Neither the best materials installed poorly nor poor materials installed well result in success. Long lasting roofs that perform well throughout their life are the result of both good materials, good installation and good maintenance methods. A knowledgeable approach to the selection of materials and methods is appropriate because of their expected lifespan. An error in judgment at re-roofing can seriously lower the future value of the major investment made in a building. There are too many examples of failures in new materials and methods to follow a policy of always using the newest, assuming it is the best. Of course, it is the introduction of new products and methods that holds the promise for advancements in roofing. If you are compelled to use new materials, research their application and performance through the manufacturer as well as independent sources of information. Use them on small jobs you can monitor closely over the years to determine their performance and effectiveness. Then use the results of your observations to decide where the new materials and methods can best be used, or if they should be used at all. For critical projects always use materials and methods that have stood the test of time. Is the roof of any building less than critical? This conservative approach reflects my own traditional bias. In my work of preserving historic buildings I am able to investigate and compare traditional and modern roofing materials. I apply many of the roofing lessons I have learned from historic buildings to modern roofing needs. – John Leeke, Historic Building Specialist
Join the discussion on plastic "slate" at the Historic HomeWorks Forum:
http://historichomeworks.com/forum/viewforum.php?f=15
(These comments were compiled and edited by Alice Krishnan)
As an FYI, I thought you might like to know about an "interim" solution that the VCC have approved for certain situations. I am referring to the French Quarter applications that have come from some owners requesting a temporary "fix" while they were deciding (or waiting for insurance or some other rationale for choosing) exactly which type shingle to use. WeatherLock G is an underlayment material made by Owens Corning that supposedly can be left exposed to weather for up to 6 months and still remain sound. We have approved it for "temporary" use (obviously since it is not a permanent roof coating) to give buildings protection until the final shingles are obtained and installed.
It doesn't cause any appearance problems for the VCC since it must be covered by the roofing material … but it serves its purpose as temporary protection and is especially useful if the approved material of choice is back-ordered or temporarily unavailable, like slate from a quarry that has closed for the winter. It also pre-empts the need for a second complete installation (as a cost savings) since the Weatherlock G can stay in place as the underlayment for the final shingle installation.
In addition, here are the proposed VCC roofing guidelines that were being considered at the time of the January 2006 conference call:
INSERT VCC ROOFING GUIDELINES
Again, thank you so much for your participation in this process.
-- Lary P. Hesdorffer Director, Vieux Carre Commisson 334 Royal Street, Second Floor New Orleans, LA 70130 lhesdorffer@cityofno.com
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I am or member of the consulting engineering firm of Simpson Gumpertz & Heger Inc., and we specialize in building technology and failure investigations of buildings, especially roofs. This is my super-short summary of my opinion on the telephone conference on the slate roofing problem in New Orleans.
1. The repair of slate roofing designed and specified should be by a licensed engineer or architect with specific experience in roofing/slate technology. Bypassing this specification stage and contracting with a roofer directly can lead to problems. 2. When design is complete, with detailed specifications, it should be offered for bidding to experienced slate roofers only, on a competitive basis. 3. Only natural slate should be used. Quality second-hand slate should be considered, if available. My experience with some of the artificial slates shows that they do not function as well as the natural and (outlawed) asbestos slates. Many artificial slates self-destruct in a very short-time. 4. Not all natural slates are the same. Experience and lab tests should be used to pick the right one. Another reason a licensed designer should prepare full plans and specifications. 5. Questions of vapor drive and flashing are important considerations in the design of the work. 6. Buy quality design and construction. 7. Have you considered importing craftsmen from other parts of the country? The prices I heard are too high.
Lots of luck! With best wishes,
-- Werner H. Gumpertz Simpson Gumpertz & Heger Inc. Boston, MA January 2006
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This is my opinion regarding the issues of synthetic versus natural slate. Of course, I prefer natural slate be put back on a building which originally had slate. The issues regarding the proper re-roofing with slate can be best solved if there are a sufficient number of roofing contractors with adequately experienced personnel.
Synthetic slate can be considered as a less than permanent, but perfectly adequate, solution. As roofing, this material can easily be replaced, in turn, with slate some time in the future when the pressure to use authentic slate, applied by experienced mechanics, is not overwhelming the marketplace due to the effects of a natural disaster.
It is more important to replace damaged roofs sooner than later. In fact, I would not hesitate to allow asphalt shingles in such a situation, simply to get a serviceable roofing system in place.
Of course, these questions have implications with regard to subdivision and historic district covenants, approving agencies, boards of architectural review, and insurance settlements. In response to a natural disaster, it would seem that all parties would be flexible in allowing some leeway in the re-roofing of buildings so that the building structure, contents, interior finishes and materials, will be protected from water damage and extremes in temperature.
It seems that such flexibility would help to expedite repairs to buildings which might otherwise be demolished as a result of a prolonged fight over this one issue.
-- David C. Fischetti, PE Cary, North Carolina January 2006
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Thank you very much for the opportunity to participate in the conference call Friday. I commend you for seeking national input on such an important topic and think that we, too, can learn from your approach.
Both as a structural engineer specializing in engineering for historic preservation and as a member of the City of Charleston's Board of Architectural Review, I advocate not permitting a permanent change from natural to artificial slate on any buildings in your Vieux Carre. Please let me cite six examples of buildings on which I have done significant Hurricane Hugo (1989) repair work here in Charleston. Several of these are National Historic Landmarks, so are of a quality and importance similar to those you encounter in New Orleans.
St. Michael's Church - 1751 St Michael's was roofed in slate some time in the 1750's. The slate roof was repaired during and after the Civil War (the steeple of the church was used as a target for Union shelling from Ft. Sumter) and repaired after our great earthquake of 1886. In the late 1930s, the roof was severely damaged by a tornado. In the subsequent repair, new slate was randomly mixed with old to render a mottled appearance. After Hurricane Hugo, we reroofed completely, moving the remaining good slate to the portico roof and randomly mixing slates of several carefully selected colors over the remainder of the roof. We have every reason to think that a number of the slates which we put back down on the portico roof have been in use for just over 250 years.
Cathedral Church of St. Luke and St. Paul - 1814 Some time before 1989, the Cathedral had had its slate roof replaced with an asbestos shingle roof. In Hugo, much of this roof was completely lifted off of the building, leaving the bare major trusses. The roof now on the building is a roughly 16 year old artificial slate (Supra-Slate) which has faded to an entirely too uniform silver color. We're just about to start major repair to the roof trusses and are going to extremes, in doing the repair work, not to touch the roof, knowing that we could not possible match what's there now in the repair of small areas.
William Mason Smith House - 1820 This house, in which our family lives, has what we believe to be much of the original slate on the main roofs. The slate roof over the hyphen was replaced about 1887, after the hyphen virtually collapsed in the earthquake of 1886. It is in near perfect condition, untouched, today. The slate on the main roofs is weathered, no longer in very good condition. We have seen the receipt which the architect, William Jay, signed for that slate in December of 1820, just over 185 years ago.
St. Philip's Church - 1835 St. Philip's was roofed in standing seam terne metal from the earthquake of 1886 (or perhaps earlier) until Hurricane Hugo in 1989. We replaced the roof with standing seam copper in 1994 (yes, hurricane repairs can be slow), with our BAR approving that change as an upgrade. It's not slate, but it's the focus on long term quality which is important here.
21 Legare Street - c. 1840 After Hurricane Hugo, the slate roof over the main house was replaced with asphalt shingles, not being visible from a public right-of-way. The roof over the dependency in the rear, being visible, was replaced with slate having a high iron content, reportedly Chinese. In just a few years, this slate has deteriorated severely. It is hoped that a new owner will be replacing both roofs in a high quality slate.
Grace Church - 1846 The original roof, of purple slate, lasted until the earthquake of 1886. After the earthquake, the original slate was reused but mingled with blue slate to replace damaged slate. Between 1887 and 1989 repairs used Buckingham slate. This church roof was completely replaced in Welch Royal Purple slate in 1991. It's in perfect condition today.
The lessons we've learned are these: - High quality materials are an excellent value. Slate is a superb value. - Skilled installation is paramount. - Prices will come down in time, but it might take five years. - Temporary roofs (90 lb. rolled roofing, fully adhered EPDM membrane, etc.) are entirely acceptable, and - Lower quality permanent roofs should not be allowed.
Members of the VCC, keep your standards high. You will regret doing otherwise. Thank you.
-- Craig M. Bennett, Jr., PE 4SE, Inc. Charleston, SC January 2006
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Our comments probably will repeat and overlap the comments of other participants. We think this should be taken as a sign of how significant some comments are, and indicate how much they should weigh in your equations.
Temporary Protection and Comments by Others We listened to the conference call and read the early comments posted by e-mail. We agree with many of the comments and observations made in support of using natural slate shingles and not using artificial slate shingles. John Leeke's article, in particular, is a very good summary. We also cannot disagree with Pat Sparks' plea for quick action, as few conditions are so harmful to a building as having inadequate weather protection, or no roof at all. Temporary protection may be vital to saving numerous buildings. The availability of substantial quantities of new, good-quality slate may be problematical, resulting in the need for many temporary roofs.
Underlayment The idea of installing a waterproof membrane that later may be used as the underlayment for a shingle roof was one of our first thoughts as well. But we caution that experience has shown that vapor barrier materials may lead to wood decay in the roof timbers and sheathing due to insufficient ventilation. Granted, the conditions of vapor drive may be more pronounced in our northern climate than at the Gulf Coast, but New Orleans experiences higher levels of relative humidity for longer periods. The effect of vapor barrier roofing should be very carefully examined before its widespread use is encouraged.
Sheathing Sheathing should be substantial and traditional - 5/4-inch-thick boards of naturally rot-resistant wood is highly recommended. The common use of skip sheathing attests to early builders' desire for a breathable roof system. We believe that plywood sheathing should not be used under shingles. Plywood vibrates too much when shingling nails are being hammered into place, reducing control over this relatively delicate work. Plywood sheathing also has been known to delaminate and deteriorate under shingle roofs. If plywood is placed in a continuous "diaphragm" it can act as an effective vapor barrier. Deterioration of the plywood - its relative impermeability may cause moisture to accumulate - may also cause premature failure of a slate or imitation slate roof.
Material Quality Regardless of whether natural or artificial slate shingles are used, their quality should be beyond question. Manufacturers' and suppliers' claims, including the submission of test reports, should not be considered absolutely reliable. The tests may be outdated, or may have been performed on materials that do not represent the majority of the actual products available when ordered. To avoid sub-grade products, both natural and artificial shingles should be subjected to testing by independent testing laboratories. There will need to be some assurances that the tested materials are representative of the actual construction stock, or current production runs, and selected at random. It is our understanding that Chinese, Spanish and some Pennsylvania slate is of inferior quality.
Installation We cannot stress enough that shingle roofing of any kind requires installation by workers who are qualified and experienced in this particular trade. Roofers who have experience only with contemporary systems such as asphalt shingles and membrane roofs may produce sub-standard shingle roofs that require replacement after a relatively short amount of time. This would be a tremendous waste of scarce resources and compound the emotional stresses suffered by the hurricane victims. Make sure that workers only install the types of systems with which they are familiar, even if it results in less-than-desirable asphalt or membrane roofs. These roofs may be considered long-term temporary, until proper slate roofs can be installed.
Regardless of the materials specified, consideration must be made for both the historic appropriateness and the performance of the roof under "normal" and "storm" conditions. It is irresponsible to require that historic roofing materials be used on buildings where the structure, roof geometry, etc. will result in a failure in a similar storm. Predictions for the next several years are for storms of similar magnitude; losing a new roof that is historically accurate but practically inappropriate risks the loss of cultural resources (the historic structure), economic resources (the income generated by taxes and fees on occupied buildings), and human life (danger to persons from flying slates, lost income, etc.) - in no particular order.
Flashings It is important to note that shingle roofs of all kinds require impeccable flashings. As with proper installation of quality roofing, proper flashings are also of paramount importance to a good roof. We favor heavy-weight copper sheet flashing with 30 lb. underlayment. Good flashing materials also must be installed by knowledgeable and experienced craftsman.
Structure The structural capacity of the roof framing must be considered for the following cases:
(a) where slate is to be installed on a roof that historically featured slate, but where it had been removed at some time in the past and replaced with a lighter material (asphalt, sheet metal, etc.); (b) where imitation slate is to be installed on a roof that was clad in slate prior to Hurricane Katrina; (c) where slate is to be installed on a roof that had slate prior to Hurricane Katrina, but where the structure is undersized (by observation or analysis) or compromised as a result of the storm, insect or fungal infestation, or alteration.
There may be other general cases for which the structure must be considered. In ALL cases, the structure must be evaluated at each building for the existing geometry and conditions observed; while many buildings may be similar architecturally they should not be considered "typical" structurally.
Very truly yours,
-- Eric Hammarberg, Director of Preservation, Vice President Derek Trelstad, Associate Bruce Popkin, Senior Project Director Thornton-Tomasetti Group, Inc. LZA Technology Division New York, NY January 2006
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I wanted to add to the lively discussion about slate roofs a comment I heard at the latest International Preservation Trades Workshops this past October: "The best textbook is an old house," a comment offered by Japanese timberframers.
This comment particularly resonated with me because I gained the bulk of my knowledge about slate roofs by studying slate roofs on old houses (over a thousand of them).
Surely there are slate roofs in New Orleans that are a century old and successful. It would be advisable to look at how they were assembled, then replicate the assembly, with obvious improvements such as copper nails and flashings. This is a quick way to put to rest the contentious issue of decking materials and underlayments.
Also, we are setting up a small slate roof training center (not yet operating) here in western Pennsylvania via my company and there is another getting off the ground in Vermont - the National Slate Technology Center, where I will be on the faculty and have a two day course for architects scheduled for March 23-24, 2006 (http://www.nationalslatecenter.org/course_offerings.html).
Furthermore, there is a great resource center for slate roofs on the web at slateroofcentral.com (http://www.slateroofcentral.com/).
-- Joe Jenkins Joseph Jenkins Inc. Contracting, Consulting, Publishing, Retail Sales Grove City, PA January 2006
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Thank you for holding the conference call. (I had to bow out after the first hour.) I think one of the important issues to arise in the discussion was of how current roofing choices will affect the building in the decades to come. Plastic shingles are lighter that slate shingles: does the building need the weight of slate to hold the roof structure down? The use of WeatherLock G underlayment may be a good temporary treatment, but if left in place will it trap moisture in the attic and roof structure causing decay?
It is my experience that long-term damage too often results when modern building materials are introduced into historic buildings. This conflict between modern building technology and traditional building technology must be considered in each case. You orders of building importance and appropriate roofing materials seems to reflect this. I'm wishing you the best of success as you incorporate plastic shingles into the orders.
Rather than asking,
Should plastic shingles be used?
Are plastic shingles good or bad?
or even,
How long will plastic shingles last?
Which plastic shingle is best?
we must ask,
What kind of roofing does this building need.
also, some of my clients are now asking about the socio-economic issues,
Must I support the corporateering petro-chemical industry with my shingle purchase, or are there viable alternatives from family-owned businesses that will support local economies and the continuation of traditional materials, trades and crafts?
-- John Leeke, Preservation Consultant Historic HomeWorks (www.HistoricHomeWorks.com) Portland, ME January 2006
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I thank the commission for allowing me to participate in an interesting and informative discussion on alternative materials for the replacement of historic roofs within the Vieux Carre. I commend the commission for assembling a wide variety of experts for the discussion.
As a conservation scientist specializing in cultural materials conservation, I provided some insight into possible deterioration problems and appropriate testing of these alternative materials.
Regarding any materials used in historic preservation, there are three main questions - 1. Will the material deteriorate? 2. How fast will the material deteriorate? 3. Will the deterioration affect its form and function?
Any petroleum based products, such as Lamarite from Tamko, Co. will undergo deterioration over time upon exposure to UV light found in sunlight. The exposure to UV differs based on longitude and latitude as well as elevation. Thus a product that performs well in South Dakota, may not perform as well in Tampa Florida. In order to stabilize petroleum based products UV stabilizers are added, hence my question to the Tamko representative regarding stabilizers.
How fast a material deteriorates can be tested in the laboratory and through long-term exposure. Laboratories use artificial weathering to test rates of deterioration. In general, artificial weathering cannot predict the lifetime of a material. Instead, it can determine relative rates of deterioration. For example, artificial weathering can determine if product A deteriorates faster than product B under certain conditions. There are standards for artificial weathering including those established by the American Standards for Testing Materials (ASTM).
In order to have a better understanding of how a material performs over time, scientists usually perform both long-term weathering in natural environments and a series of performance tests to determine when and how a material fails.
When evaluating a product, I recommend asking the manufacturer for data on how the product has been tested. Are ASTM standards or other standards used to evaluate the material? What are the results of those tests? How are the warranties determined? Have other organizations other than the manufacturer tested the material? What do we know in general about the material? For example, fiber reinforced concrete materials may be more susceptible to acid rain in urban environments. How are the colorants added? Are there dyes, which may be more fugitive upon UV exposure, or are there mineral pigments that are less susceptible to fading? Is the colorant throughout the material or added as a coating? If it is a coating, then we are really talking about the performance of a composite of materials. The composite will only perform as well as its weakest link.
I hope that these comments provide you with a better understanding of some of the questions to ask when considering these materials as replacements for slate roofing and other historic roofing materials. You may also wish to review the National Park Service Preservation Brief #4 on Roofing for Historic Buildings. It can be found at http://www.cr.nps.gov/hps/tps/briefs/brief04.htm.
In my closing thoughts, I wish to emphasize the need to preserve as much original historic material as possible. In situations where only a portion of slate roof is damaged, I would encourage the property owner to replace the damaged sections with matching slate. In situations where the entire roof must be replaced and costs are considerable, I would carefully weigh slate with alternative materials, keeping in mind that in many cases slate has withstood the test of time.
-- Mary F. Striegel, Ph.D. Chief, Materials Research, National Center for Preservation Technology and Training Natchitoches, LA January 2006
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I won't be available for the conference call but my personal experience with slate substitutes has not been good--although other alternatives (such as metal) may be appropriate for less significant locations I do not feel anything other than natural slate or clay tile (new or salvaged) would be appropriate for the Quarter. Such materials are proven to have the best longevity and are aesthetically superior.
-- Neal Vogel Restoric LLC Evanston, IL January 2006
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I wouldn't call myself an expert on the subject, but we have used synthetic slate which was replaced within 10 years because it faded so much. Sorry I will not be available for the conference call.
-- Eugene Surber Surber Barber Choate & Hertlein Atlanta, GA January 2006
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My input (I may not have time for the call): Mississippi was hit directly by this storm, and the damage there is extreme. 65,000 homes were completely destroyed. Countless more were damaged. FEMA failed to properly tarp hundreds of historic buildings because of 'hard' roofs. The techniques and material are available to correct this failure, now and in the future.
The use of substitute shingles, or whatever, is not so important as getting a decent compatible roof back on the houses as soon as possible. I would, and do, recommend that most people put on dimensional shingles NOW, to get it DONE, and so that they have more money to do other things to the house. Regarding the reuse of asbestos shingles, I say DON'T, EVER.
Regarding natural slate and tile, you just have to follow good techniques and be sure they don't come off the next time. In a hurricane zone, putting a waterproofing membrane under every roof is the best thing to do, especially any slate, tile, or metal roof. If you do this, you stand a much better chance of surviving the next time.
-- S. Patrick Sparks President, Sparks Engineering, Inc. Mississippi Field Office January 2006
(Mr. Sparks attached the below case study as an example to share with the group.)
Recommendations Regarding Stabilization of Hancock County Courthouse November 2005
Observations: There is extensive hurricane wind damage to roof, gutters, downspouts, windows, etc., as well as flood damage to the interior, windows, and contents. The main roof of the courthouse is constructed of historic slates nailed to 1-inch pine lumber deck on timber framing. The slates were not directly visible due to the tarps. I estimated the loss of slates at least 50% based on observations from the attic. The additions to the courthouse have low-slope built-up roofs that were also damaged.
A FEMA blue-roof tarp has been installed but is somewhat ineffective due to the roof configuration (internal gutters, multiple hips/valleys, etc) and difficulty in nailing over remaining slates. The tarp sheets are not fully lapped, are not wrapped over the eaves and roof edges, and there is water ponding in the gutters. There is insufficient nail penetration through the slates. I also noted multiple holes in the tarp. It is probably not feasible to tarp this roof for long-term stabilization.
The slate roof area of the courthouse should be fully restored using natural slates and copper flashings, gutters and downspouts.
Immediate Repairs: The most important thing is to prevent water infiltration into the building. For the main roof area, I recommend maintenance repairs of the tarp until the stabilization phase is complete (see below).
The low-slope roof areas are independent of the main roof and can be re-roofed or temporarily repaired now. Protection of some of these roof areas will be required during the replacement of the main roof.
Stabilization: As soon as possible, stabilize the building envelope as follows: 1. Remove and salvage slates, remove flashings, gutter linings, etc. 2. Repair damaged roof deck (not extensive) with exterior grade plywood to match thickness of existing deck. This is important so that slates will lay flat. Remove existing nails, snags and other irregularities. 3. Install granule-surface self-adhering waterproofing membrane (such as Carlisle WIP 100) over entire roof area, including gutters. Assure adhesion, using manufacturer's recommended primer as required. This membrane will provide a waterproof covering for the roof prior to the installation of the slates.* It will also form a permanent waterproof barrier under the slates. 4. Cover damaged window and door openings. 5. Provide for active ventilation of the courthouse to control moisture. Because of the warm humid climate, a small amount of conditioned or dehumidification should be considered.
* The manufacturers of these waterproofing membranes usually recommend limiting the duration of exposure of the membrane prior to installing the finished roof. However, the membranes generally perform very well for extended periods of time (several months), provided they receive routine inspections and repairs as necessary.
Roof Restoration: A full set of design documents should be prepared for the slate roof restoration. These documents should show the scope of the work, flashing details, and provide slating specifications. The contractors should be prequalified based on documented experience with slate and copper roofing.
Specify new flashings, gutter linings, conductor heads, downspouts, etc., lightning protection as required, and reinstallation of slates. Only sound undamaged slates and new matching slates of the best quality should be used.
Particular consideration must be give to wind resistance. The use of stainless steel ring-shank slating nails is recommended. The installation in a hurricane zone usually requires the use of slate hooks and/or adhesives on the slate edges.
The attic should be actively ventilated.
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1) I don't think we are talking about recycled milk bottles here.
Use more oil! An environmental debate on crap?
2) I love false and manufactured materials... the more kitsch the
better. (That is why one of our last contracts was to remove aluminum
and refurbish the underlying wood. If you leave scrap aluminum out on
the sidewalk in Greenwich Village it is scarfed up before the sun
raises. Though I think it odd that the church complains considering how
humanitarian & environmental the leaving behind crap on their sidewalk is.)
3) Proven technology - do we actually know that the plastic slate
will have the durability and performance characteristics of the
'natural' slate that it replaces. (How will it hold up in the next lvl
5? Or will it blow off in large sheets like so much of the tin roofing
now littering the woodlots of the Gulf region?)
4) On that note... is the recovery post-hurricane for plastic slate
higher than for natural slate? Why not go w/ fully adhered black EPDM?
Leastways EPDM is black, gets rid of the ugliness of a whole lot of
little squared lines, has a performance history and would be less
expensive economically and possibly environmentally than plastic slate.
(We recently installed inauthentic fully adhered EPDM to the lead coated
copper - even the llc was not authentic to the history of the structure
- to the gutters on a mansion of a signer of the Declaration. You can't
see it unless in an an ultra-lite or with a ladder and the report is
that it does not leak -- thus saving the wood structure from rot and the
enclosed collections.)
5) As an aesthetic, does authenticity of appearance and tone matter
to the French Quarter? Plastic slate DOES NOT look like natural slate.
Is the intention a DynseyFiction of History?
6) Lastly... even if natural slate is used will it be of the same or
similar quality to the original? Chances are it would be easy for the
pundits to substitute Spanish or Chinese slate that is cut thinner than
traditional American w/ it in mind to maximize the square surface area
contained in a shipping container. Nowadays technology of slate/stone
cutting makes it easier to produce thinner slate -- well suited for the
McMansions. And, as we are no longer in a slate heyday there are not too
many folks who can tell the difference, or care, between a good slate
and a crap slate.
][<
-- Ken Follett,
friend & fellow Preservation Trades Network member from PCLS
Join the Slate Substitutes discussion at the Forum: http://historichomeworks.com/forum/viewforum.php?f=15
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