Repair of slate roof tiles

Technical procedures are supplied by GSA only as a reference. All procedures have been reviewed for general consistency with federal standards for rehabilitating historic buildings. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location.

References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.

Part 1 – General

1.01 Description

1. This specification provides guidance for the repair and reattachment of slate roof tiles.
   1. 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, when appropriate, will be provided by the Architect.
   2. All work described herein and related work must conform to the Secretary of the Interior’s Standards for the Treatment of Historic Properties.
   3. The Contractor shall provide all labor, material, equipment, and operations required to complete the rehabilitation work indicated herein.
   4. 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.

1.02 Section includes

1. Replacement of Individual Damaged Slates
2. Repair of Holes in Slate Shingles

1.03 Related sections

1. Section 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections and should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from GSA Historic Preservation:
   1. Safety Precautions
   2. Historic Structures Precautions
   3. Submittals
   4. Quality Assurance
   5. Delivery, Storage and Handling
   6. Project/Site Conditions
   7. Sequencing and Scheduling
   8. General Protection (Surface and Surrounding)
   9. Historic Building Treatment Procedures

1.04 Quality assurance

1. The contractor performing the work described in this Section shall ideally have 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 & Reconstructing Historic Buildings.
2. Warranty
   1. Provide slate manufacturer’s standard 100-year warranty against delamination and softening of the slate body.
   2. 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.

1.05 Submittals

1. The Contractor shall submit to the Project Team or GSA Approving Official:
   1. 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 Project Team prior to beginning any slate roof repairs, and mark all tiles for repair with blue tape or chalk.
   2. Product Literature: Submit manufacturer’s product literature for new slate shingles.
   3. Samples: The Contractor shall submit the following samples:
      1. 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.
      2. Fasteners: Submit samples of each type of fastener to be used in slate roofing repairs and reinstallation.
   4. A project safety plan to include at minimum: any personal protective equipment to be used by the contractor’s staff such as disposable clothing, gloves and safety glasses, procedures for emergencies and accidents, documentation of staff training in use of equipment and/or chemical products as required by the manufacturers.

1.06 Testing and mockups

1. Contractor, at inconspicuous locations designated by the Project Team and GSA Historic Preservation, shall perform a sample in a small area prior to performing full scale mockup. Testing will determine the best method(s) to perform the work and ensure that the chosen products do not cause harm.
2. Following testing, mockups shall be created (mockups may incorporate successful test patches) using the chosen methods. Size and location of mockups shall be determined by the project Team and GSA Historic Preservation.
3. Personnel to be assigned to the project shall demonstrate their ability to complete the required work in an acceptable manner as reviewed by the Project Team. Each mechanic shall remove and replace one slate shingle at a location designated by the GSA Historic Preservation. Personnel not completing the sample work in an acceptable manner shall not be permitted to work on the roofing repairs.
4. Approved replaced tiles shall become part of the work and shall serve as the quality standard for all similar work.
5. Any testing, demonstrations, or mockup that is rejected by the project team shall be removed in its entirety without damage to the surrounding masonry and a new demonstration/mockup shall be performed for the project team’s review.

1.07 Delivery, storage, and handling (as applied to products and materials)

1. The Contractor shall:
   1. Deliver materials to the site in manufacturer’s unopened bundles with the manufacturer’s labels intact and product identification visible.
   2. Slate materials delivered to the site shall be stored on pallets above grade and protected from the weather. Store slate shingles on edge.
   3. 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.
   4. 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.

1.08 Safety

1. The contractor shall isolate the work area with cones, tape or similar means as possible for the duration of the project, to prevent unauthorized individuals from entering.
2. For any work required on elevated surfaces (4 feet or more above the ground) the contractor shall install and use any ladders, scaffolding or platforms in accordance with OSHA regulations (29 CFR Subpart M).

1.09 Project/site conditions

1. 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:
   1. 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.
   2. Protect roof framing during slate shingle installation by limiting imposed loads.
   3. 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.
   4. Protect roofing and gutters from damage by ladders or work platforms. Keep gutters clear of debris from slate repair work.
2. 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.
3. 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.
4. If applicable, the Contractor shall coordinate work with the other trades involved in exterior and interior restoration work, including but not limited to masonry restoration, sealing, and painting.
5. All Contractor personnel performing treatment operations shall be provided by the Contractor with gloves, respirators, protective clothing and any other personal protective equipment (PPE) as recommended by the manufacturer of the products used during the work and required by local, state, and federal regulations.

Part 2 – Products

2.01 Slate shingles

1. Technical Requirements: ASTM C406-05, Grade S1
   1. ASTM C120-90 Standard Method of Flexure Testing of Slate: Min. 9000 psi.
   2. ASTM C121-90 Standard Test Method for Water Absorption of Slate: 0.25 percent.
   3. ASTM C217-85 Standard Test Method for Weather Resistance of Slate: Mx. .002”.
2. 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.
3. 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”.
4. 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.
5. 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.
6. Curvature exceeding 1/8 inch in 12 inches shall be cause for rejection.

2.03 Nails

1. 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.
2. 3d nails for slates 18 inches long or less.
3. 4d nails for slates 20 inches long or more.
4. Nails for slates on hips and ridges.

2.04 Roofing felt

1. Roofing felt shall be ASTM D 226-89, Type I or Type II, 30-pound or heavier, unperforated, asphalt saturated felt.

2.05 Accessory materials

1. 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.
2. Use of roof cements or sealants is not acceptable on historic slate roofs and is a sign of an inappropriate repair.  

Part 3 - Execution

3.01 General

1. 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.
2. 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.
3. Roofing Contractor shall transport and store slate in such a way as to avoid overloading the roof framing during the slate shingle installation.

3.02 Removal of existing slate tiles

1. 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.
2. 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.

3.03 Replacement slate installation

1. Main method
   1. 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.
   2. 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.
   3. 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.
      1. 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.
      2. 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.
   4. 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.
   5. 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.
   6. 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.
   7. The Owner shall be furnished with a stock of 2 percent extra slates for future roof repairs.
2. Alternative Method: THIS METHOD SHOULD NOT BE USED IN NORTHERN CLIMATES WHERE SNOW AND ICE COULD CAUSE TAB TO UNBEND.
   1. Remove damaged slate as directed above.
   2. Cut a copper tab approximately 1 inch wide by 8 inches long. Double over bottom 4 inches and bend up to form an “L” shape.
   3. Nail top of tab to roof deck using a copper nail. Daub nail head with non-corrosive, non-staining elastic roofing cement.
   4. Slide replacement slate into place so that bottom of slate rests on copper tab. Bend doubled portion of tab up and over the bottom of the slate to hold it in place. Approximately 1 inch of the tab should be visible.

Part 4 – Final report

4.01 Final report

1. The Contractor Shall:
   1. Provide a final report of completed work, including all approved submittals and photographs of the areas repaired that were taken before, during, and after the work.
   2. Provide a written summary of the project and results upon final inspection and approval. The summary shall include a discussion of steps taken or new findings not specified in the initial documentation. Summary should also include any applicable ongoing care and warranty requirements.