INTRODUCTION Peak U.S. domestic slate roofing production occurred in the years surrounding the turn of the twentieth century, from about 1885 to 1925.1 Much of this slate is now nearing the end of its expected service life. This article addresses key aspects of assessing the condition of existing slate roofs, with a focus on what to look for with regard to the slate itself, slating nails, and flashings. The condition of roof underlayments for slate roofs will be explored as well.2 ASSESSING THE CONDITION OF THE SLATE SHINGLES In assessing the condition of slate shingles, it is helpful to have knowledge of the type of slate present on the roof3 and the date the shingles were installed. This information, combined with knowledge of the estimated service life of the slate, can provide insight into the expected remaining service life of the roof. Be aware that this is just an initial understanding, which must be tempered by a complete look at the condition of the slate, slating nails, and flashings as outlined herein. The estimated service life of slate shingles depends on the geology of the slate—its mineral composition, and the heat and pressure it was subjected to during its formation—a process known as metamorphosis. Based on past history, different roofing slates thus have varying estimated service lives, according to the region of the country from which they were derived (Figure 1), and assuming all other things associated with the roof are equal. These estimated service lives are shown in Table 1. Of course, all other things are never equal, and such factors as roof slope and orientation, the presence of shade trees, runoff from low-slope roof areas located above the slate, foot traffic, the quality of the original installation, and maintenance activities, all impact the longevity of the roof system. As an example, if the roof is covered with Vermont unfading green slate installed in 1925, and the current year is 2020, that means the slate is 95 years old and could have an expected remaining service life of approximately 30 years, depending on the factors discussed previously and the findings of an on-site condition assessment. If the roof slope is found to be only 6:12 and the slate not very well maintained, the roof could be nearing the end of its service life. If, on the other hand, the slope is 14:12 and the roof was installed well to begin with and regularly maintained over the years, it could have an expected remaining service life of 40 years. During the field survey portion of the condition assessment, broken and missing slate shingles can generally be seen from afar—from grade using the naked eye and/or binoculars. It is important to observe the slate up close as well, to look for such things as cracked slates, exposed nails within the bond lines of the slates (Figure 2), wear holes caused by the heads of the 38 • IIBEC InterfaceCEMarch 2020 Figure 1 – The principal commercial slate deposits in the United States are situated along the Appalachian Mountain chain. The Glendyne Quarry, producer of North Country Black slate, is located just east of the northernmost tip of Maine, in Saint-Marc-du-Lac-Long, Quebec, Canada.8 slating nails working their way through overlying slates (Figure 3), and delamination. Delamination occurs when impurities contained within the slate (primarily calcite and iron sulfides, such as pyrite and marcasite) react, in association with hot/cold and wet/dry cycling, to form calcium sulfate (gypsum) molecules that take up slightly more volume than the original minerals.4 This gradually pushes the slate apart along its cleavage planes, eventually manifesting itself as the paper-thin laminae we observe on the exposed and hidden faces of the slate (Figure 4). As the slate delaminates, it becomes softer and more prone to breakage. It also tends to hold moisture longer, thus becoming susceptible to freezing and thawing damage. The Slate District Estimated Service Life Monson (Piscataquis County, Maine) 100 years New York/Vermont (Washington County, NY/Rutland County, VT) 125 years +/- Pennsylvania Soft-Vein (aka Pennsylvania Black; Lehigh and Northampton Counties, PA) 60 years or more Pennsylvania Hard-Vein (aka Chapman; Northampton County, PA) 100 years +/- Peach Bottom (York County, PA /Harford County, MD) 200 years or more Buckingham (Buckingham and Fluvanna Counties, VA) 175 years or more North Country Black (Saint-Marc-du-Lac-Long, Quebec, Canada) 100 years +/- Table 1 – Estimated service life of various slate. Figure 2 – Exposed copper slating nail within a bond line; in this case, the result of the use of a narrow slate and insufficient offset. Figure 3 – Cracked and broken slate shingles, as well as holes caused by slightly projecting slating nails working their way through overlying shingles in this c. 1966 Pennsylvania Black slate roof. Figure 4 – Severely delaminated slate shingles. The relatively low slope of the roof (5:12) helped to accelerate the rate of deterioration. March 2020 IIBEC InterfaceCE • 39 moisture retained in the slate can also begin to cause the wood roof deck to rot, especially if the original felt underlayment is in poor condition. The lower the slope of the roof, the greater the rate of weathering and deterioration, as the slates tend to stay wet for a longer period of time after each precipitation event. In addition to observing the exposed portion of the slate shingles, a random sampling should be removed in order to observe the back sides of the shingles and allow for sounding the shingles. While the slates are out, headlap can be verified, and the type and condition of roof underlayment(s) and slating nails can be observed as well (Figure 5). Removing one to two slate shingles per slope is generally sufficient to draw conclusions, although on a large roof or particularly large roof area (e.g., on the order of 3,000 to 5,000 sq. ft.), removal of additional slates may be necessary. Removed shingles should be reinstalled upon completion of observations. It is important to observe the back side of the slate shingles because it will sometimes be found to be in “worse” condition—that is, exhibiting a greater degree of delamination—than the exposed portion (Figure 6). Sounding a slate is an excellent method by which to gauge its integrity and confirm one’s visual observations. The method is simple: Grasp the slate in one hand, and then tap the exposed face with a knuckle or metal object, such as a slating hammer. Good-quality slate will emit a distinctive ring when tapped in such a manner. A dull thud, similar to that which might be emitted by a piece of wood, is usually indicative of a very weathered slate that is delaminating. A rattling sound typically indicates a cracked slate, or a slate containing a loose fragment separated from the main body of the shingle along its cleavage plane. The presence of oxidizable iron pyrites in slate shingles can cause rust staining on the surface of adjacent shingles and appear unsightly. The condition, sometimes called “rusting out,” occurs most often in New York/Vermont weathering green slate, but it is typically isolated to a relatively few slates. When in an advanced state, the affected area can be flakey and soft, due to the increased volume of the oxidation product compared to that of the original pyrite (Figure 7). Replacement of the slate is required to prevent further deterioration and staining. As a general rule, based on past experience, if 20 percent or more of the slate shingles on a roof are broken, cracked, missing, sliding out of position, severely delaminated, or suffering from inappropriate Figure 5 – Test opening in a 90-year-old roof with a slope of 14:12 and covered with slate shingles from the Monson District, Piscataquis County, ME. The slate, hot-dipped galvanized slating nails, and felt underlayment were all found to be in good condition. Figure 6 – The exposed portion of this slate (left) exhibits little to no delamination. The unexposed face (right) exhibits a good deal of delamination, especially around the nail holes, where the loss of section is significant. 40 • IIBEC InterfaceCEMarch 2020 Figure 7 – Oxidized iron pyrite in an isolated New York/Vermont Unfading Green slate on a dormer cheek wall. past repairs (e.g., face-nailed, undersized), then it is often more practical and cost-effective to replace the roof than to attempt individual repairs (Figures 8 and 9). This assumes that the deteriorated slates are randomly located, rather than being concentrated in one or two locations. March 2020 IIBEC InterfaceCE • 41 Figure 8 – Sometimes it is necessary to count slates to determine the percentage of broken or otherwise deteriorated shingles present on a roof. Here, roughly 72 of the 369 slates captured in this photograph (19.5%) are in need of repair. Figure 9 – Widespread severe delamination in these 120-year-old New York/Vermont unfading green slates, combined with broken, cracked, and missing slates; face-nailed and undersized slates stemming from inappropriate repair work; slates sliding out of position; and the corroding terne metal open valley, make roof replacement a straightforward decision. This brand-new edition is available only in digital format.Pre-order now and download after March 31, 2020. IIBEC Manual of Practice – 3rd Edition Pre-Order Now and Save Pre-Convention Special:Member: $295 Nonmember: $375Convention Price:Member: $325 Nonmember: $399After March 31, 2020 Price:Member: $349 Nonmember: $429 ASSESSING THE CONDITION OF THE SLATING NAILS Various types of nails have been used to secure slate shingles over the years. Copper and stainless steel slating nails will typically be found to be in good condition (Figure 10). Steel cut nails and steel wire nails, and the electroplated versions of these, with only a minimal zinc coating, will often be found to be in poor condition with either their heads corroded off (Figure 11) or that portion of the shank located just above the roof deck corroded nearly through. A common manifestation of corroded fasteners is individual slate shingles sliding out of position (Figure 12). It should be verified whether fastener corrosion is widespread or localized in areas subject to concentrated water flows, such as below dormer valleys or below where a low-slope roof drains onto the slate roof. If the condition is typical and widespread, it is likely time to replace the roof, lest more shingles continue to slide downslope, or the shingles become subject to blowoff in high winds. If the corrosion is localized, removal and reinstallation of the slates may be possible. With longerlived slates such as Peach Bottom and Buckingham, it is possible for the nails to have failed due to poor selection, while the slate shingles themselves still have decades of service life remaining. In such cases, salvage and reinstallation of the slate shingles can be considered. If this course of action is selected, the slate should be re-laid using the same, or less, exposure as the existing to mitigate the visual impact of ghost lines, indicating the original exposure of the slate, on the reinstalled roof (Figure 13).5 Keep in mind that exposure and headlap are inversely related and that the change in headlap will always be two times the change in exposure. Increasing headlap beyond that required is acceptable (within limits, of course), whereas reducing headlap is not (see Figure 13). 4 2 • I I B E C I n t e r f a ce Ma r c h 2 0 2 0 Figure 10 – Ninety-year-old copper wire slating nail (left) and 120-year-old bronze cut nail (right)—both in good condition. Figure 11 – Corroded steel cut nails on a 145-year-old slate roof. Figure 12 – As a result of the corroded nails shown in Figure 11, numerous shingles on this Peach Bottom slate roof had slid out of position. Figure 13 – Example of ghost lines on the exposed face of slates that have been reinstalled above a new standingseam copper roof. In the case of partial removal, salvage, and reinstallation of slate shingles, it is also important to match the original exposure of the slate in order to maintain the intended headlap. In this case, the extra ½ in. of exposure resulted in the loss of a full inch of headlap, from a 3-in. headlap down to a 2-in. headlap. Two-inch headlap is insufficient for the 9:12 slope of the roof. Note, too, the lack of patina formation in that portion of the copper roofing located along the drip line of the slate shingles. ASSESSING THE CONDITION OF FLASHINGS A full discussion of flashing assessment is beyond the scope of this article.6 Suffice it to say that most slate roofs, should they leak, tend to do so not in the field of the roof, but rather around their edges, at roof penetrations, and at changes in plane— instances in which flashings are (or should be) present. Flashings are critical to the integrity and weathertightness of all roofs, including slate roofs. Those most susceptible to wear occur at areas of concentrated water flow—valley flashings, both open and closed; followed by gutters and base flashings (sometimes called step flashings). The condition of flashings can be assessed by pushing the butt ends of the slate shingles slightly to one side (e.g., at the centerline of a closed valley; Figure 14), or by removing slates located atop flashings (Figure 15). In areas of c o n c e n t r a t e d water flows, copper flashings often turn a golden orange color before they actually wear through (Figure 16). This color is an indication that the copper is paper-thin (to the point where one can easily push a finger through the material) and in need of replacement. This condition must be distinguished from the duller copper color that indicates a patina 4 4 • I I B E C I n t e r f a ce Ma r c h 2 0 2 0 Figure 15 – A slate shingle was removed in order to get a better look at the condition of the base flashings located along this gable end wall. Figure 14 – Despite the presence of debris, wear holes are still quite evident along the centerline of these 65-year-old copper closed valley flashings. Figure 16 – Painted copper open valley flashing. The golden orange color indicates that the copper is paper-thin. Arrows point to where the copper has already worn through. Figure 17 – Corrosion holes along a soldered seam in a copper flashing. is not being formed due to frequent, often concentrated, water flows, but where the copper still has sufficient section, as can be seen below the drip line of the slate in Figure 13. Other conditions to look for include punctures, cracked soldered seams, fatigue cracking, pitting/pinholes along the edges of soldered seams (Figure 17), exposed fasteners, and base flashings that are not consistently spaced,7 are too short, or are not well counterflashed (Figure 18). The list of possible counterflashing issues is quite long and includes: •Insufficient lap of one counterflashing over an adjacent counterflashing •Reglets that are too shallow •Inadequate spacing of lead wedges tosecure the counterflashings in place,or lead wedges placed too close tothe outside face of the reglet •Failed sealant or mortar in the counterflashing reglet •Counterflashings that are too shortto adequately cover the underlyingbase flashings (see Figure 18) •Torn, bent, displaced, loose, andmissing counterflashings •Counterflashings that are set tooclose to the roof surface or steppedincorrectly, thereby limiting theheight of the underlying base flashings (see Figure 18) •Counterflashings secured withexposed fasteners, especially whenthose fasteners also penetrate thebase flashings Whether or not the poor condition of a roof’s flashings merits replacement of the entire roof requires professional judgment and is dependent on several factors. If, for example, the slate and slating nails are in good condition and have an expected remaining service life of 20 or more years, and the roof plan is fairly straightforward (i.e., few changes in plane and a limited number of dormers, chimneys, and skylights—all things that require flashings), then a flashing replacement project may be most practical. If the slate only has an expected remaining service life of ten years, and/or the roof is “cut up” (i.e., containing many valleys, dormers, chimneys, and penetrations), it may be that by the time enough slate is removed to replace all of the deteriorated flashings, it is simply more practical to replace the entire roof (Figure 19). UNDERLAYMENT CONDITION One-hundred-year-old asphalt-saturated organic felt underlayments often lack integrity, or have nearly turned to dust, crumbling or breaking apart when handled. The question often arises: When does the poor condition of underlayment require that the slate roof be replaced? Every roof is different, so the answer is, it depends. Here are a few typical scenarios that can be used as a guide: •The underlayment is in poor condition, but the slate shingles, slatingnails, and flashings are in good condition and the roof does not leak, even in the worst wind-blown rains. This is a good indication that the roof may be retained and, perhaps, monitored with increasing frequency as it continues to age. •The underlayment is in poor condition; only two percent to five percentof the slate shingles are broken,missing, cracked, or otherwise deteriorated; but the shingles have anexpected remaining service life of March 2020 IIBEC InterfaceCE • 45 Smarter Testing. Faster Response.™ only 10 to 15 years, and the roof leaks, but only in heavy or wind-blown rains. This is an indication that it might be prudent to replace the roof. • The underlayment is in poor condition, and the slate and flashings are in good condition and have an expected remaining service life of 30 years, but leaks occur in the field of the roof during most rain events. This is an indication that something else is going on, such as insufficient side lap, insufficient headlap, or the slate shingles are generally too small for the given roof slope and/or climate conditions (e.g., 16 x 8 slates laid on a 6:12 slope in the Pacific Northwest). Further investigation may be required to determine whether roof repair or roof replacement is the most practical course of action. SUMMARY This article examined the key aspects of assessing the condition of existing slate roofs, including the slate shingles themselves, slating nails, flashings, and underlayments. The end result of an assessment is often a written report containing a discussion of existing conditions, recommendations for addressing noted deficiencies, and associated construction cost estimates. When determining the condition of slate roofs, it is prudent to take a holistic approach and examine other building 4 6 • I I B E C I n t e r f a ce Ma r c h 2 0 2 0 ISSUE SUBJECT SUBMISSION DEADLINE July 2020 The building enclosure April 15, 2020 August 2020 Technology May 15, 2020 September 2020 Trends June 15, 2020 October 2020 Structures as part of design July 15, 2020 November 2020 Raising the bar in standards August 15, 2020 December 2020 The building enclosure September 15, 2020 Publish in IIBEC Interface INTRODUCTION In evaluating building enclosure problems, the author has encountered many newly constructed, wood-framed, low-slope roofs and exterior balconies and decks that exhibit excessive/sustained ponding of water (Figure 1). These conditions can lead to interior water damage through premature deterioration of roof coverings and/or excessive deflection of roof framing members. The ponding (and associated creep of the framing) can be so significant that it may ultimately lead to failure of the roof framing. The purpose of this article is to provide insight into the most likely causes of these problematic ponding conditions as they relate to commonly accepted design and construction methods. 36 • IIBEC IntErfaCE OCtOBEr 2019 Figure 1 – Excessive ponding water on a roof. Figure 2 – Ponding typically occurs prior to reaching discharge points. INTRODUCTION The concept of building for resilience has been increasingly adopted by various organizations over the past five years. Organizations use different definitions or phrases to describe resilience and the hazards that are included in resilient design. These definitions from six sources are compared and a single definition incorporating these is developed. RESILIENCE AS DEFINED BY SELECT ORGANIZATIONS Industry Statement Twenty-one organizations, including the U.S. Green Building Council (USGBC), the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), the American Institute of Architects (AIA), the American Society of Civil Engineers (ASCE), the Building Owners and Managers Association (BOMA), and the National Institute of Building Sciences (NIBS) issued an industry statement on resilience[1] that stated (the bold or red text is theirs): Representing more than 750,000 professionals, America’s design and construction industry is one of the largest sectors of this nation’s economy, generating over $1 trillion in GDP. We are responsible for the design, construction, and operation of the buildings, homes, transportation systems, landscapes, and public spaces that enrich our lives and sustain America’s global leadership. We recognize that natural and manmade hazards pose an increasing threat to the safety of the public and the vitality of our nation. Aging infrastructure and disasters result in unacceptable losses of life and property, straining our nation’s ability to respond in a timely and efficient manner. We further recognize that contemporary planning, building materials, and design, construction, and operational techniques can make our communities more resilient to these threats. Drawing upon the work of the National Research Council, we define resilience as the ability to prepare 8 • IIBEC IntErfaC E SEptEmBEr 2019 This article is reprinted with permission from Advances in Civil Engineering Materials, Vol. 7, No. 1, 2018, copyright ASTM International, 100 Harbor Drive, West Conshohocken, PA 19429 www.astm.org. IIBEC Interface journal is seeking submissions for the following issues. Optimum article size is 2,000 to 3,000 words, containing five to ten high-resolution graphics. Articles may serve commercial interests but should not promote specific products. Articles on subjects that do not fit any given theme may be submitted at any time. Submit articles or questions to Executive Editor Kristen Ammerman at 800-828-1902 or kammerman@iibec.org. Figure 18 – Above, base flashings, which are interwoven with each course of slate, are consistently spaced, but counterflashings are too short and not providing sufficient cover over the base flashings. On the right, base flashings, although concealed, are known to be too short due to inappropriate layout of the stepped counterflashings. Extending the counterflashings to the right would have allowed for a full 4-in. vertical leg in the base flashings instead of the 1¾ to 2 in. that was achieved (see double-arrowed line). materials and systems that may be impacting the slate roof, or which may need to be treated at the same time as the slate roof. Such other materials and systems include rainwater conduction systems, masonry parapets and chimneys, dormer wall cladding, architectural woodwork at eaves and rakes, skylights, roof decking, and roof framing. For example, when a slate roof must be replaced, masonry restoration work at chimneys should take place prior to replacement of the slate, rather than afterwards (so as not to risk damaging the newly installed slate). REFERENCES 1.For more information on slate production, see the National SlateAssociation’s Technical Bulletin No.5, “Historic Production Data,” available at www.slateassociation.org. 2.Although there are many additional research-related, technical, andlogistical tasks associated with performing a proper condition assessment, such as assembling surveyrecord materials (e.g., roof plans andelevation drawings), interviewingthe building owner regarding pastmaintenance practices and problemareas, researching prior to surveying, and access and safety considerations, these are beyond the scopeof this article. For more informationon the subject of condition assessments, one place to start is ASTME2018, Standard Guide for PropertyCondition Assessments: BaselineProperty Condition AssessmentProcess, first published in 1999. Thestandard outlines the purpose andscope of building condition assessments, including such things aswalk-through surveys, interviews,document reviews, identifying andrecording deficiencies, and the contents of assessment reports. 3.Descriptions of the roofing slatefrom the various commercial slatedeposits of the U.S. and Canadacan be found in the National SlateAssociation’s Slate Roofs: Design andInstallation Manual, 2010 Edition,pages 7-10. Color photographs ofmany different roofing slates can befound in the Member Project Galleryon NSA’s website, www.slateassociation.org. 4.D.W. Kessler and W.H. Sligh.“Physical Properties and Weathering Characteristics of Slate.” Bureau of Standards Journal of Research. Vol. 9 (Washington, D.C.: U.S. Department of Commerce, Bureau of Standards, 1932). p.401. 5.Reinstallation ofslate shingles withthe same exposure as the originalinstallation is notalways possible. Inthe past, it was notunusual for slateshingles to be laid with insufficient headlap. Thus, for example, if the slate on a roof with a slope of 12:12 which was laid with a 2-in. headlap is to be salvaged and re-laid, it will have to be reinstalled with a 3-in. headlap in order to meet the requirements of modern-day building codes (and good practice). This will reduce the exposure of the shingles, thereby hiding the ghost lines of the previous exposure. If, on the other hand, salvaged slate originally laid with a 4-in. headlap is to be re-laid with a3-in. headlap, the exposure will begreater and the ghost lines of theoriginal exposure will be visible. 6.Additional information on theassessment and maintenanceof roof flashings can be found inArchitectural Sheet Metal QualityAssurance Guide, First Edition,Sheet Metal and Air ConditioningContractors’ National Association,Inc. (SMACNA), Chantilly, VA, 2015. 7.Inconsistent spacing of base flashings can result in insufficient lapsand the potential for leakage duringprecipitation events. 8.Quarries in other regions of the U.S.operated sporadically and for shortperiods of time in the late nineteenth and early twentieth centuries,primarily when demand for slateshingles was high. These quarriesincluded those located in Rockmart,GA; Monroe County, TN; Sussex County, NJ; Baraga County, MI; near Placerville, CA; and in Slate Canyon, near Provo, UT. For more information on minor slate deposits in the U.S., see the National Slate Association’s Technical Bulletin No. 3, “Lesser Known Slate Deposits of the United States,” available at www.slateassociation.org. March 2020 IIBEC InterfaceCE • 47 Jeffrey Levine is a roof consultant and associate principal in Wiss, Janney, Elstner Associates’ Philadelphia office. He has served as project manager for over 350 roof repair, replacement, and rehabilitation projects fora large variety of building types, including academic, commercial, and ecclesiastical buildings. Levine is chair of the National Slate Association’s Installation Standards Committee and editor and co-author of its Slate Roofs: Design and Installation Manual, its Mobile Field Guide, and several technical bulletins. He may be reached at jlevine@wje.com. Jeffrey Levine Figure 19 – The slating nails on this roof were found to be in good condition, with the slate possessing a potential remaining service life of several decades. All flashings and gutters, however, were deteriorated. Given the quantity of slate that would have to be removed to replace all the flashings and gutters, the owner decided to replace the slate as well.
