Specification:Repair and reattachment of slate roof tiles

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=GENERAL=

DESCRIPTION
 This specification provides guidance for the repair and reattachment of slate roof tiles. This specification has been developed for use on historic properties (defined as any district, site, building, structure, or object that is listed in or eligible for listing in the National Register of Historic Places) and provides an overview of accepted practices. Site-specific specifications will be provided by the Architect when appropriate. All work described herein and related work must conform to the Secretary of Interior’s Standards for the Treatment of Historic Properties. The Contractor shall provide all labor, materials, equipment, and operations required to complete the rehabilitation work indicated herein. All work described herein and related work must have the approval of a Cultural Resources Manager, Conservator, Historic Architect, or other professional who meets the standards outlined in the Secretary of the Interior’s Standards – Professional Qualifications Standards pursuant to 36 CFR 61. Such person is referred to in this document as the Architect. 

SECTION INCLUDES
 Replacement of Individual Damaged Slates Repair of Holes in Slate Shingles</li> </ol>

RELATED SECTIONS
<ol type="A"> Section 07631 – Flashing, Gutters and Drains</li> </ol>

DEFINITIONS
<ol type="A"> Slate: A metamorphic rock typically formed from the sedimentary rock shale, which is made of clay and fine silt. The heat and pressure of metamorphism chemically alter the clay and silt which recrystallize into a fine grained rock. Preferred orientation of the minerals leads to the characteristic platy cleavage of slate. </li> Cleavage: The plane along which the rock or other material tends to fracture or split. In slate the cleavage planes are perpendicular to the direction of pressure during metamorphism. </li> Standard Grade: The most widely used form of slate roof. Composed of slates with regular dimensions, smooth cleavage surface, square ends, and approximately 3/16 inch thickness. The slates contain uniform color and exposure. </li> Textural slate roofs: Incorporate slates of different thicknesses, uneven tails, and a rough texture. </li> Graduated slate roofs: The slates were graduated, with the thickest and largest slates laid at the eaves and the thinnest and smallest laid at the ridge. </li> Open valley: Lined with metal where slates overlap only at the sides. </li> Closed valley: Covered with slate. Contains either a continuous metal lining or metal flashing built in with each course. </li> Round valleys: A closed valley with a concave instead of a V-shaped section. </li> Solid wood sheathing: Usually constructed of tongue and groove, square edged, or shiplapped pine boards of 1 inch or 1-1/4 inches thickness and 6 inch to 8 inch width. </li> Wood battens/Open wood sheathing: Wood strips, from two inches to 3 inches wide, nailed to the roof rafters. Each Slate was nailed to the batten that cross its middle, with the upper end of the slate resting at least one-half inch on the batten next above. </li> Torching or tiering: Placing mortar along the top and bottom edge of each batten to help keep out dust and wind driven rain. This simple mortar was typically composed of straw, mud, and moss. </li> Steel sheathing: In fireproof construction, steel angles substituted for the wood battens. The slates were fastened with wire around the steel angle. </li> Concrete sheathing: Concrete decks contained wood nailing strips embedded in the concrete on which to nail slates. </li> Asphalt Saturated Roofing Felt: Temporary waterproofing installed between solid wood sheathing and slates. This practice started in the late nineteenth century. </li> Headlap: The overlap of each slate on the two courses below it. Normally, slate was laid horizontally from the eaves with a headlap of three inches. Headlap was two inches on Mansard roofs and on slopes greater than 5/3. Headlap was increased to four inches on low pitched roofs with a slope of 2/3 or less. Generally, the minimum roof slope necessary for a slate roof is 1/3. </li> </ol>

SUBMITTALS
<ol type="A"> <li>Schedule of Repair: The Contractor shall prepare annotated photographs of the roof areas to be repaired showing which shingles are to be replaced and/or repaired. Review this document on site with the Architect prior to beginning any slate roof repairs.</li> <li>Product Literature: Submit manufacturer’s product literature for new slate shingles. </li> <li>Samples: The Contractor shall submit the following samples: <ol> <li>Replacement slate shingles. Provide manufacturer’s full range of color samples for selection by the Architect to harmonize with the existing roof. Samples are to be of the same size, shape, thickness, and texture as will be used in the work.</li> <li>Fasteners: Submit samples of each type of fastener to be used in slate roofing repairs and reinstallation.</li> </ol> </li> </ol>

QUALITY ASSURANCE
<ol type="A"> <li>Work Experience: <ol> <li>The Contractor performing the work of this Section shall have demonstrated experience approved by the Architect, ideally a minimum of seven years experience in the repair and installation of slate shingle roofs and shall have successfully completed at least three projects of similar size and scope of work within the previous three years. Submit examples of previous slate roof repair projects completed within the previous three years. He/she shall demonstrate a working knowledge of The Secretary of the Interior’s Standards for the Treatment of Historic Properties with Guidelines for Preserving, Rehabilitating, Restoring &amp; Reconstructing Historic Buildings.</li> </ol> </li> <li>Warranty: <ol> <li>Provide slate manufacturer’s standard 100-year warranty against delamination and softening of the slate body.</li> <li>Roofing Contractor shall return to the site annually for five years after substantial completion of the roof repairs and inspect the roof for cracking, slippage or other failures in new slate. The Contractor shall repair any such failures in his work at no cost to the Owner.</li> </ol> </li> </ol>

MOCK-UPS
<ol type="A"> <li>In the presence of the Architect, all personnel to be assigned to the project shall demonstrate their ability to complete the required work in an acceptable manner. Each mechanic shall remove and replace one slate shingle at a location designated by the Architect. Personnel not completing the sample work in an acceptable manner shall not be permitted to work on the roofing repairs.</li> </ol>

DELIVERY, STORAGE AND HANDLING
<ol type="A"> <li>Deliver materials to the site in manufacturer’s unopened bundles with the manufacturer’s labels intact and product identification visible.</li> <li>Slate materials delivered to the site shall be stored on pallets above grade and protected from the weather. Store slate shingles on edge.</li> <li>The Contractor shall dispose of all packaging, waste materials and construction debris in accordance with local, state and federal environmental regulations. All wood scrap shall be kept separate for recycling. No burning of debris, waste material or trash will be allowed on site.</li> <li>Where possible, slate shingles removed from the roof shall be salvaged for reinstallation. Stockpile salvaged slates in a location designated by the Owner’s representative. Store salvaged slates on edge, off the ground, on pallets or dunnage. Do not stack pallets.</li> </ol>

PROJECT / SITE CONDITIONS
<ol type="A"> <li>The Contractor is responsible for protecting existing adjacent materials during the execution of the work. Provide all necessary protection and work procedures to avoid damage to existing material assemblies not a part of the work of this Section. At a minimum, the Contractor shall: <ol> <li>Provide sturdy, weather-proof protection at all areas exposed during slate shingle repairs and installation. Do not leave interior spaces exposed to the elements overnight. The Contractor shall maintain adequate supplies of protective materials on site at all times in the event of sudden weather changes.</li> <li>Protect roof framing during slate shingle installation by limiting imposed loads.</li> <li>Protect new slate shingle roofing by limiting foot traffic over installed slate shingles and ensuring the use of proper soft-soled footwear by all roofing personnel. Use suspended ladders and/or platforms where possible to avoid damage to roof surfaces.</li> <li>Protect roofing and gutters from damage by ladders or work platforms. Keep gutters clear of debris from slate repair work.</li> </ol> </li> <li>Provide sturdy barriers around the work area to protect other trades and passers-by. At least one entrance must remain accessible during the course of the work.</li> <li>Contractor shall coordinate roofing work with the work of other trades to minimize delays in the construction process. Coordinate roofing with other work including, but not limited to, exterior finish carpentry, flashing and gutter work and chimney restoration. Schedule roof work to avoid traffic by other trades over newly installed areas.</li> </ol> =PRODUCTS=

SLATE PROPERTIES AND PROBLEMS
<ol type="A"> <li>Slate is generally of high strength, low porosity, and low absorption. Its resilience depends on method of fabrication, physical and mineral properties, installation techniques, and maintenance.</li> <li>Layers of slate may flake off the cleavage plane as a part of natural weathering. Slowly the interior layers may delaminate as well. Calcite and iron sulfide impurities may react with weather conditions to form gypsum, thus causing an increase in volume and delamination. These increases in porosity will decrease strength and toughness.</li> <li>Lower roof pitches and areas subject to high water flow are subject to greater deterioration due to the action of ice damming and wind-driven rain.</li> <li>Problems typically occur from a lack of understanding the installation technique. Slate nails should be driven loosely and allow the slate to hang freely. Nails driven too tightly can cause breaks in that slate and the surrounding slates. Insufficient overlap can cause water intrusion in nail holes.</li> <li>Another common culprit of slate loss is nineteenth-century cut nail corrosion. Slates also outlive galvanized nails. </li> </ol>

SLATE SHINGLES
<ol type="A"> <li>Technical Requirements: <ol> <li>ASTM C406-05, Grade S1</li> <li>ASTM C120-90 Standard Method of Flexure Testing of Slate: Min. 9000 psi.</li> <li>ASTM C121-90 Standard Test Method for Water Absorption of Slate: 0.25 percent.</li> <li>ASTM C217-85 Standard Test Method for Weather Resistance of Slate: Mx. .002”.</li> </ol> </li> <li>Slate shingles shall match the color, shape and texture of the existing shingles to remain. New slate shingles shall be high quality from a reputable quarry. The product will be inspected and approved by the Architect. </li> <li>Shingle dimensions (including face dimensions, exposure and thickness) to match those of    the existing shingles to be replaced. Variation in surface face dimensions not to exceed 1/8”. </li> <li>Each shingle shall be pre-punched with two nail holes. Nail holes shall be countersunk to allow nail heads to be set flush with slate surface. </li> <li>The grain of the slate shall run parallel to the length of the shingle. Slates shall be free of knots, knurls, “ribbons,” quartz veins and other defects. Slates with cracks, chipped edges or broken corners exceeding 1 inch will not be accepted. </li> <li>Curvature exceeding 1/8 inch in 12 inches shall be cause for rejection.</li> </ol>

NAILS
<ol type="A"><li>Nails for fastening slate shingles shall be large-head, smooth shank, #10 solid copper slater’s nails. Verify that nails are long enough to penetrate the lath at least 1/2 inch to 3/4 inch. No ferrous nails are to be used.</li> <ol> <li>3d nails for slates 18 inches long or less.</li> <li>4d nails for slates 20 inches long or more.</li> <li>6d nails for slates on hips and ridges.</li> </ol> </ol>

ROOFING FELT
<ol type="A"> <li>Roofing felt shall be ASTM D 226-89, Type I or Type II, 30-pound or heavier, unperforated, asphalt saturated felt.</li> </ol>

ACCESSORY MATERIALS
<ol type="A"> <li>New sheet metal for patching nail holes shall be 28 gauge Type 304 dead soft stainless steel coated with 50 percent zinc / 50 percent tin alloy to a thickness of 20 microns. </li> <li>Although some manufacturers recommend roof cements or sealants, use of these products is not acceptable on historic slate roofs and is a sign of an inappropriate repair. </li> </ol> =EXECUTION=

GENERAL
<ol type="A"> <li>With proper installation, slate roofs require relatively little maintenance and will last 60 to 125 years or longer depending on the type of slate employed, roof configuration, and the geographical location of the property. The pattern, detailing, and craftmanship of slate roofs are important design aspects of historic buildings; it is important to repair historic slate roofs rather than replace them.</li> <li>Examine all framing, sheathing and lath, where applicable, for any conditions that may affect the repair and reinstallation of the slate shingle roofing. Notify the Architect if any framing and/or decking is found to be unsuitable for roofing.</li> <li>Roofing Contractor to coordinate roof repairs with chimney restoration, flashing and gutter work if required to ensure that eave configurations and shingle projections are suitable to receive new gutter work and that flashing and other items may be installed prior to shingle installation.</li> <li>Roofing Contractor shall transport and store slate in such a way as to avoid overloading the roof framing during the slate shingle installation. </li> </ol>

REMOVAL OF EXISTING SLATES
<ol type="A"> <li>Pull the nails from damaged or mismatched slate shingles using a slate ripper. Gently remove the shingle without damaging the edges of adjacent shingles to remain.</li> <li>Where two or more adjacent shingles must be replaced within the field of the roof, remove additional shingles in the courses above, pyramid-fashion, to minimize the number of bibs required for the replacement shingles.</li> </ol>

REPLACEMENT SLATE INSTALLATION
<ol type="A"> <li>Sound all shingles prior to installation by tapping. All shingles should ring clear. Shingles that rattle or produce a muffled sound when tapped are likely defective and shall not be used.</li> <li>Nails shall not be driven so as to produce strain on slates. Nails shall be driven so that the head is flush with or below the surface of the slate. The slate shall be loose when fully nailed. If this is not executed properly, building movement could draw the nail head through the slate. </li> <li>Spot replacement of damaged, missing or non-matching color slates shall be done using the bib method (also known as “slip flashing”) using copper nails and bibs. <ol> <li>Slates are put in place, the nail location marked between the two shingles in the course above and then the slate removed and the nail holes punched. After punching the nail holes, reinstall the slate, nail in place.</li> <li>Cut a sheet metal bib approximately 3 inches wide by 8 inches long and insert under the course above to cover the nail hole in the new slate. Friction from the upper course of slate should hold the bib in place.</li> </ol> </li> <li>Replacement ridge slates shall be laid in to match the pattern of the remaining slates. Ridge slates may be rotated 90 degrees and cut to match the width of the field shingles. Nails of the combing slates shall pass through the joints of the slates beneath. </li> <li>Exposed nails at the top courses shall be appropriately covered with ridge tiles. The use of roofing mastic or elastic cements will cause future cracking problems and is not approved. </li> <li>Entire surfaces of all roofs, except as noted, shall be covered with slate in a proper and weatherproof manner. Upon completion, all slates must be sound, whole and clean. The roof must be left watertight and neat in every respect, and subject to the Architect's approval. </li> <li>The Owner shall be furnished with a stock of 2 percent extra slates for future roof repairs.</li> </ol>

FINAL REPORT
<ol type="A"> <li>The Contractor shall submit a final report of the completed repairs including all approved submittals, photographs taken before, during and after construction and written warranty.</li> <li>The Architect shall develop an effective maintenance and repair program for the slate roof that can be retained for future use. </li> </ol>