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Historic Preservation - Technical Procedures
Reroofing Using Slate Shingles
Hspg Prepared For Nps - Sero
Thermal And Moisture Protection
Reroofing Using Slate Shingles
REROOFING USING SLATE SHINGLES
A. This procedure includes guidance on reroofing a slate
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
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-
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
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
1.03 PROJECT/SITE CONDITIONS
A. Environmental Requirements:
1. Do not apply new or repaired shingle roofs in wet
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
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
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.
A. Slating tools:
John Stortz & Sons
210 Vine Street
Philadelphia, PA 19106
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
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
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
F. Elastic cement or exterior grade caulk such as "Gutter-
Seal" (Dow), "Roof Sealant" (Alcoa), or approved equal.
A. 25' steel tape
C. Slate ripper
D. Machine punch and hand (or mawl) punch
E. Slate cutter
G. Slater's Stake
H. Nail pouch
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.
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
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
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
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
J. Fit slate neatly around any pipes, ventilators, or other
END OF SECTION