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Historic Preservation - Technical Procedures

Spectitle:

Reroofing Using Slate Shingles

Procedure code:

0731503R

Source:

Hspg Prepared For Nps - Sero

Division:

Thermal And Moisture Protection

Section:

Slate Shingles

Last Modified:

02/24/2012

Details:

Reroofing Using Slate Shingles



REROOFING USING SLATE SHINGLES


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on reroofing a slate
         shingle roof.

    B.   See also Procedure 07315-02-S for general information
         concerning slate.  See 07315-04-S for supplemental
         guidelines in repairing and replacing slate roofs.

    C.   Safety Precautions:

         1.   Wear rubber-soled shoes that have non-slip tread
              (preferably sneakers with a high top for good ankle
              support).  Avoid wearing loose clothing.

         2.   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.

         3.   As the work proceeds, keep roof clear of debris and
              water.  Avoid stepping on damaged or crumbling
              roofing materials.

         4.   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.

         5.   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.

    C.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure.  These guidelines
         cover the following sections:

         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)

         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

    A.   Acceptance at Site:  Keep roof materials dry during
         delivery, storage, and handling.

    B.   Storage and Protection:  

         1.   Store materials in stacks with provisions for air
              circulation within stacks.  Protect bottom of
              stacks against contact with damp surfaces.  Protect
              materials against weather.

         2.   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.

         3.   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

    A.   Environmental Requirements:

         1.   Do not apply new or repaired shingle roofs in wet
              weather.  

         2.   Do not remove roofing from structures when rain is
              forecasted or in progress.

         3.   If roofing is to be removed on a clear day, remove
              no more than can be replaced or repaired in one
              day.

1.04 MAINTENANCE

    A.   Whenever possible, make inspection from ground or from
         above if possible.

    B.   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.

    C.   Look for indications that nails are corroding or pulling
         loose.  Loose and missing slates, or metallic stains are
         an indication of this.

    D.   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.

    E.   In addition to scheduled inspections, inspect after each
         exposure to unusually severe weather conditions such as
         strong winds, hail, or long continuous rains.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Slating tools:  

         John Stortz & Sons
         210 Vine Street
         Philadelphia, PA  19106
         215/627-3855

2.02 MATERIALS

    A.   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.

    B.   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.

    C.   Flashing material - match appearance and material of
         existing.  

         1.   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.

         2.   Lead - 2-1/2# to 3#.

         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.

         4.   Galvanized - 24 ga. to 26 ga. depending on type of
              flashing, consult manufacturer.

    D.   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.

    E.   Solder shall be 50% lead and 50% block tin, with rosin
         flux.

    F.   Elastic cement or exterior grade caulk such as "Gutter-
         Seal" (Dow), "Roof Sealant" (Alcoa), or approved equal.

2.03 EQUIPMENT

    A.   25' steel tape

    B.   Hacksaw(s)

    C.   Slate ripper

    D.   Machine punch and hand (or mawl) punch

    E.   Slate cutter

    F.   Hammer

    G.   Slater's Stake

    H.   Nail pouch


PART 3---EXECUTION

3.01 EXAMINATION

    A.   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.
         
3.02 PREPARATION

    A.   Surface Preparation:

         1.   Carefully examine, measure, and record existing
              slate shingle patterns at edges, hips, ridges, and
              other special conditions.

         2.   Remove existing roofing down to the roof deck.
              Salvage original slates for reuse where possible.  

         3.   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.

         4.   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.  

         5.   Remove loose or protruding nails or hammer them
              down.

3.03 ERECTION, INSTALLATION, APPLICATION

    A.   Lay felt over entire deck.  

         1.   Lay felt in horizontal layers with joints lapped
              toward eaves and at ends at least 2".  Secure edges
              with flat head copper nails.

         2.   Lap felt over all hips and ridges a minimum of 12",
              and 2" over the metal of any valleys and gutters.

         3.   Omit felt at valleys, using instead, rosin paper to
              allow for thermal movement of the sheet metal.

    B.   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.

    C.   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.

    D.   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.

         1.   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.  

         2.   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.    

    E.   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.

    F.   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.

    G.   Lay hip slates and ridge slates (or install ridge and hip
         cap flashing) as originally designed.  Consult with slate
         manufacturer for construction details.

         1.   Ridge types (slate): saddle ridge, strip saddle
              ridge, comb ridge, cox-comb ridge.

         2.   Hip types (slate):  saddle hip, mitred hip, boston
              hip, fantail hip.

    H.   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.

    I.   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.

    J.   Fit slate neatly around any pipes, ventilators, or other
         roof penetrations.

                         END OF SECTION