Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. 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.
- This procedure includes guidance on reroofing a slate shingle roof.
- See also Procedure 07315-02-S for general information concerning slate. See 07315-04-S for supplemental guidelines in repairing and replacing slate roofs.
- Safety Precautions:
- Wear rubber-soled shoes that have non-slip tread (preferably sneakers with a high top for good ankle support). Avoid wearing loose clothing.
- Wear a safety belt or harness and secure it to a substantial chimney or other substantial object secured to the building. Leave only enough slack to work comfortably in one area. Move and adjust as required to work on other sections of the roof.
- As the work proceeds, keep roof clear of debris and water. Avoid stepping on damaged or crumbling roofing materials.
- On slopes where the roof is steeper than 4 inches rise per foot, special consideration must be given to footing and handling of materials. Chicken ladders or cleats should be used on the roof as required for adequate footing.
- Do not work on shingled roofs when wet or snow- covered.
- 6. Carrying and transporting of materials should be limited to a safe amount so that balance and footing are not impaired.
- See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing this procedure and should be followed, when applicable, along with recommendations from the Regional Historic Preservation Officer (RHPO).
1.02 DELIVERY, STORAGE AND HANDLING
- Acceptance at Site: Keep roof materials dry during delivery, storage, and handling.
- Storage and Protection:
- Store materials in stacks with provisions for air circulation within stacks. Protect bottom of stacks against contact with damp surfaces. Protect materials against weather.
- When the slates are stored in an open yard, cover the piles with overlapping boards or use tar paper weighted down. Adequate protection prevents the slates from being frozen together. While slates are of ample strength when used in their proper place, reasonable care should be used in the handling of the material.
- Slates up to and including 20" X 11" may be safely piled up to 6 tiers high. Slates of a larger size should never be piled more than 4 tiers high. Closely piled, 100 commercial slates average 20" to 24".
1.03 PROJECT/SITE CONDITIONS
- Environmental Requirements:
- Do not apply new or repaired shingle roofs in wet weather.
- Do not remove roofing from structures when rain is forecasted or in progress.
- If roofing is to be removed on a clear day, remove no more than can be replaced or repaired in one day.
- Whenever possible, make inspection from ground or from above if possible.
- Inspect roof for broken or missing slates, delamination or flaking of surfaces, slate particles collecting in valley flashing, staining, or other manifestations of slate failure.
- Look for indications that nails are corroding or pulling loose. Loose and missing slates, or metallic stains are an indication of this.
- Inspect the underside of the roof deck from the attic to detect leaks. Inspect at all flashing points carefully for evidence of leakage such as water stains.
- In addition to scheduled inspections, inspect after each exposure to unusually severe weather conditions such as strong winds, hail, or long continuous rains.
- Slating tools: John Stortz & Sons 210 Vine Street Philadelphia, PA 19106 215/627-3855
- Slate/substitute material: roofing units used for replacement should match existing slate in thickness, color and texture. Individual slates should be pre- punched for nailing. See Procedure 07315-02-S for complete list of manufacturers of natural slate and substitute materials.
- Large flat-head hard copper wire nails not less than 7/8" long. Length should be twice the thickness of an individual slate plus 1 inch.
- Flashing material - match appearance and material of existing.
- Copper - 16-oz. soft copper; occasionally 20-oz. required, consult manufacturer. All edges to be soldered shall be tinned 1-1/2" on both sides.
- Lead - 2-1/2# to 3#.
- Terne - 20# or 40# depending on type of flashing, i.e cap and base flashing, 20# or vertical and horizontal surfaces, 40#. Consult manufacturer.
- Galvanized - 24 ga. to 26 ga. depending on type of flashing, consult manufacturer.
- 15-lbs asphalt-saturated rag felt underlayment with Commercial Standard Slate; with graduated roofs use 30-lb for 1/4" slate, and 45-lb, 55-lb, or 65-lb prepared roll roofing for heavier slate.
- Solder shall be 50% lead and 50% block tin, with rosin flux.
- Elastic cement or exterior grade caulk such as "Gutter- Seal" (Dow), "Roof Sealant" (Alcoa), or approved equal.
- 25' steel tape
- Slate ripper
- Machine punch and hand (or mawl) punch
- Slate cutter
- Slater's Stake
- Nail pouch
- Inspect the deck to determine whether it is sound. Make whatever repairs are necessary to the existing roof framing to strengthen it and to level and true the deck. Replace rotted, damaged, or warped sheathing or plywood.
- Surface Preparation:
- Carefully examine, measure, and record existing slate shingle patterns at edges, hips, ridges, and other special conditions.
- Remove existing roofing down to the roof deck. Salvage original slates for reuse where possible.
- Use a slate ripper to remove the nails of slates in good condition which can be reused. Use care in the removal and stacking of slates to avoid damage.
- Be careful not to damage old metal wall and vent flashings that may be used as a pattern for cutting templates. If metal cap flashings at the chimney and other vertical masonry wall intersections have not deteriorated, bend them up out of the way so that they may be used again. Carefully remove slate shingles in these areas to avoid damaging reusable base flashing.
- Remove loose or protruding nails or hammer them down.
3.03 ERECTION, INSTALLATION, APPLICATION
- Lay felt over entire deck.
- Lay felt in horizontal layers with joints lapped toward eaves and at ends at least 2". Secure edges with flat head copper nails.
- Lap felt over all hips and ridges a minimum of 12", and 2" over the metal of any valleys and gutters.
- Omit felt at valleys, using instead, rosin paper to allow for thermal movement of the sheet metal.
- Determine exposure of slate: subtract 3" (standard head lap between alternating courses) from overall length of slates being used. Divide this number in half to determine final exposure.
- If required by slope of roof, nail cant strip at bottom eaves, even with edge of sheathing, to slightly raise first courses of slate. Thickness of cant strip allows second course of slate to be laid correctly. A 1/4" taper is usually sufficient.
- Lay under-eave starter slate. Butt of slate shall project 2" beyond cant strip or bottom edge of sheathing, and 1" beyond the edge of the sheathing at gable ends. Under-eave slate is shorter than other slates. Determine length of under-eave slates by adding 3" to the exposure as determined in B. above. Secure each slate with two nails.
- Drive the nails into the punched holes until heads just clear surface of slate. The slates should "hang" on the nails, not be driven in so far as to produce a strain on the slate.
- Use 3d nails for standard-thickness slates up to 18 in. long. Use 4d nails for extra-long slates, and 6d nails on hips and ridges.
- Lay full first course with bottom of slate even with bottom of under-eave slate. Position joints between slates so that there is a minimum 3" off-set between the vertical joints of the under-eave slates below.
- Lay second full course of slate using the exposure as determined in B. above. Off-set vertical joints a minimum of 3" from the vertical joints in the course below. Continue to lay main field of slates in this manner.
- Lay hip slates and ridge slates (or install ridge and hip cap flashing) as originally designed. Consult with slate manufacturer for construction details.
- Ridge types (slate): saddle ridge, strip saddle ridge, comb ridge, cox-comb ridge.
- Hip types (slate): saddle hip, mitred hip, boston hip, fantail hip.
- Build in and place all flashing pieces furnished by the sheet metal contractor. Valley design shall match original construction. Valleys may be open, closed, or round. Consult with slate and/or sheet metal manufacturer for construction details.
- Slates overlapping sheet metal work should have the nails so placed as to avoid puncturing the sheet metal. Exposed nails should be permissible only in top courses where unavoidable.
- Fit slate neatly around any pipes, ventilators, or other roof penetrations.