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Serving Alberta's Roofing Industry Since 1961
SS Section 4: Slate Tile Roofing
Slate tile roofing may be applied to wood
decking or to wood battens fastened to metal or concrete decks. For
batten installations follow manufacturer’s written
For reroofing the decking shall be minimum
15.9mm (5/8") thick plywood sheathing. The surface of the plywood
shall conform to a sheathing grade under C.S.A. Standards.
For new construction, ARCA recommends minimum
19.0mm (3/4") thick plywood sheathing to provide a solid nailing
surface free of bounce.
When using thicker, larger or heavier weight
slates, the structural capacity and thickness of the wood
sheathing/decking may have to be increased from the recommended
The roof framing and decking shall be designed
of sufficient strength so that they will support all anticipated
loads, such as construction loads. The roof deck shall be free of
damaged, deteriorated or decayed wood.
When reroofing with slate tiles a letter
from a registered structural engineer shall be made available for
the Regulation Authority. The design shall be in accordance with
the Alberta Building Code and the letter shall state that the roof
will support the dead and live loads imposed.
The surface of all roof decks to which a roofing
system is to be applied shall be sufficiently clean and dry so that
proper attachment may take place.
Roofing over existing roofing material is not
permitted, tear off old materials to expose the decking.
Repair damaged or deteriorated decking with
similar materials prior to reroofing.
For the issuance of the Warranty Certificate the
following requirements apply:
Less than 4:12 (1:3):
Not warranted (See ARCA Manual, Division 1, Slope Chart for
system type acceptance)
4:12 (1:3) to 6:12 (1:2):
Use minimum 75mm (3") head laps.
Greater than 6:12 (1:2):
Use minimum 50mm (2") head laps.
SS-4.2 Roofing Materials
SS-4.2.1 Slate Tiles
Roofing slates shall conform to current ASTM
Standard C406, Standard Specification For Roofing Slate, Grade S1,
having a minimum porosity of approximately 0.15 percent.
Commercial roofing slates shall be minimum 4.8mm
(3/16") thick, machine punched for two (2) nails when applied with
standard 75mm (3") head laps, weighing approximately 41 kg/m2 (850
Slate is a natural product and variations in
colour and texture should be expected.
SS-4.2.2 Protection and Storage
Slates shall be stacked on edge and covered to
Slates should be handled with care and placed to
avoid excessive handling of the material at the job site.
Other roofing materials shall be protected from
moisture which would result in their moisture content being above
the manufacturer’s published moisture equilibrium for that
Rolls of felt shall be stored on end, covered
and out of danger of water penetration.
SS-4.2.3 Application Limitations
No roofing material shall be applied when the
weather or the condition of its substrate is such that the required
installation procedure could not be followed or which would
jeopardize the performance of the roofing system.
Note: Due to the variations and complexities of construction,
obtain ARCA approval for application variations not specifically
identified by ARCA Minimum Requirements.
Follow tile manufacturer’s written
application guidelines which exceed specified ARCA Minimum
Solid copper ten (10) gauge slating
nails are recommended for slate applications due to the long
service life of slate. Nails are to conform to ASTM F1667-13
"Driven Fasteners: Nails Spikes and Staples"
Other fasteners approved by the slate tile
manufacturer may be substituted for the solid copper slating
For most applications, standard sized copper
slating nails with 9.5mm (3/8") large flat heads shall be used. The
length of the slate nails will vary according to the thickness and
exposure of the slate being used.
Slating nails shall penetrate through the
plywood or wood sheathing or a minimum distance of 25mm (1") into
lumber decks or battens.
Standard-sized slates shall be nailed with a
minimum of two (2) nails driven home with their heads just clear of
the slate surface so that the slate hangs on the nails.
SS-4.3 Flashing at Intersections
Sheet metal flashing shall consist of not less
15 kg/m2 (3 P.S.F.) thick lead sheet,
0.68mm (20 oz.) thick copper sheet,
or approved non-corrosive alternates.
SS-4.3.2 Valley Flashing
Open valleys should be used where sloping
surfaces of slate roofs intersect to form a valley.
Open valleys shall be flashed with not less than
one layer of sheet metal not less than 600mm (2’) wide
covering a minimum one (1) ply self adhering S.B.S. modified
Centre minimum 914mm (36") wide sections of
S.B.S. membrane over valley centre line and uniformly adhere to a
clean and dry deck surface. Overlap and seal membrane end laps a
minimum distance of 150mm (6").
Centre minimum 600mm (2’) wide sections of
20 oz copper sheet in the valley angle overlapping valley metal
lengths a minimum distance of 200mm (8").
Strip in the edges of the copper valley flashing
with continuous 200mm (8") wide strips of self adhering S.B.S.
modified bituminous membrane adhered 100mm (4") onto both the
S.B.S. modified bitumen valley flashing and the primed copper
Lap the slates over the sheet metal on either
side, leaving a space between the edges of each slate to channel
water down the valley angle. The width of the valley, or the amount
of space provided between the slate edges, shall increase uniformly
down the valley (taper).
Valley slate application shall start a minimum
distance of 50mm (2") on either side of the valley center line at
the ridge and shall taper away from the center at the rate of 25mm
(1") for every 2440mm (8 lineal feet) of valley length towards the
When adjoining roof areas differ in pitch, metal
valley flashings shall contain a 25mm (1") high centre crimp.
The upper corner of field slates adjoining the
valley line shall be trimmed to reduce the possibility of water
migrating back under each course of slates.
SS-4.3.3 Flashing at Vertical
Intersection of slate tile roofing with walls,
chimneys and vertical surfaces shall be protected with copper step
flashings in accordance with the Alberta Building Code.
SS-4.3.4 Crickets or Saddles
Where a chimney or other vertical surface
projects through the roof surface at a right angle to the slope of
the roof, a cricket or saddle shall be built into the roof to
divert water away from the back of the vertical member. If the roof
is constructed of wood, the cricket shall be of light rafter
construction covered with plywood sheathing, valley flashing and
slated the same as the adjacent roof areas. Open valleys shall be
formed with the main roof. The size and slope of the cricket is
largely determined by the roof condition. The slope of the cricket
shall be approximately the same as the adjacent roof slopes.
SS-4.3.5 Perimeter Drip Edge
The installation shall include 20 oz. copper
rake and eaves drip edge flashings.
The deck flange shall extend a minimum distance
of 75mm (3") on to the roof decking and shall be nailed at maximum
254mm (10") centres. Space vertical flange a minimum distance of
6.4mm (1/4") from face of fascia board.
All exposed flashing edges shall be
SS-4.4 Eave Protection and
SS-4.4.1 Eave Protection
Eave protection shall extend from the roof edge
a minimum distance of 900mm (3’) up the roof slope to a line
not less than 300mm (1’) inside the inner face of the
exterior wall. (See ARCA Technical Bulletin on Ice Dam
Eave protection is not required
over unheated garages, carports and porches
where the roof overhang exceeds 900mm (3 ft) measured along
the roof slope from the edge of the roof to the inner face of the
on roofs with slopes of 1 in 1.5 (8:12) or greater.
Eave protection shall be laid along the eave
edge and shall consist of one of the following materials:
No. 30 asphalt-saturated organic felt laid in two plies lapped
480mm (19") and cemented together with lap cement.
No. 40 glass fiber coated base sheet
Self adhering S.B.S. modified bituminous membranes.
The field of the decking shall be completely
covered with a minimum of one ply of CSA No. 30 non-perforated
asphalt saturated organic felt prior to application of the
The underlay shall be installed parallel to the
eaves with head and end laps not less than 100mm (4”)
staggered and offset from adjacent felts.
Over hips and ridges, felts shall extend at
least 300mm (1’) beyond to form a double thickness of
Underlayment shall consist of one of the
One ply No. 30 asphalt saturated organic felt.
One ply No. 40 glass fiber coated base sheet
A self adhering S.B.S. modified bituminous membrane.
or approved alternates.
SS-4.5 Bedding and Sealants
SS-4.5.1 Asphalt Roofing Cement
Asphalt roofing cement may be used under slates
at hip and ridge locations to help secure slates where nailing
strengths and wind uplift are a concern or as a joint sealer.
SS-4.5.2 Polyurethane Sealant
Polyurethane sealant may be used as a tile
bedding or joint sealant at hips and ridges locations. Exposed
fasteners shall be coated with sealant.
Every roof space or attic above an insulated
ceiling shall be ventilated with openings to the exterior to
provide an unobstructed vent area of not less than 1/300 of the
insulated ceiling area. Vents may be roof type, eave type, soffit
type, gable-end type or any combination thereof, and shall be
uniformly distributed on opposite sides of the building.
Roof vents shall be equally distributed so that
approximately 50 percent of the required vent area is located near
the lower part of the roof and approximately 50 percent of the
required vent area is near the ridge. For exceptions see Alberta
Building Code, Section 9.19.1, Venting.
SS-4.7 Slate Application
The tiles shall be set out with courses straight
and parallel with tiles in each course or in alternate courses kept
in alignment so that the finished roof presents a regular and even
The cutting of tiles at hips, ridges, valleys
and abutments shall be clean and straight to provide a regular and
Test each slate for soundness prior to
No through joints shall occur from the roof
surface to the felt. The joints in each course shall be well
separated from underlying courses as follows:
Where slates of random width are used, the overlapping slate
shall be jointed as near the center of the underlying slate as
possible but not less than 75mm (3") from any underlying
Where slates are of one width, this requirement is attained by
starting every other course with a half-slate or, where available
and practical, with a slate that is one and one-half times the
width of the field slates.
Employ the standard 75mm (3") head lap for most
slate tile roofing applications.
For steeper roofs, such as the mansard roof and
other roofs nearly vertical in plane, a minimum 50mm (2") head lap
may be satisfactory.
Employing a head lap less than 75mm (3") reduces
the amount of material over which water may be blown and may
increase the possibility of leaks occurring in the roof.
Slates shall be fastened with a minimum of two
(2) copper slating nails per tile. The length and number of slating
nails will vary according to the thickness and exposure of the
slates being used. Slating nails should be driven just clear of the
slate’s surface so that the slate hangs on the nails.
Improperly driven fasteners will damage of break the slate
The “exposure” of a slate is the
portion not covered by the next course of slate above and is the
length of the unit exposed to the weather. The proper exposure to
use for a particular length of slate is calculated by deducting the
head lap from the length of the slate and dividing by two.
For example, the proper exposure for a 508mm
(20") slate is: 508mm (20") - 75mm (3") = 433mm (17") /2 = 216mm
SS-4.7.3 Starter Course
The starter course’s primary function is
to shed water that might migrate through the joints of the slates
in the overlying first course. The starter slates are applied over
the ice-dam protection membrane installed along the eaves.
The length of the starter course is calculated
by adding 75mm (3") to the proper exposure of the field slates. The
width of the starter slate is either the width of the field slate
or twice the width of the field slates.
Starter slates should be laid to extend
approximately 25mm to 50mm (1" to 2") beyond the eave and rake
edges. Where cutters or eaves trough are used the overhang may be
reduced to 25mm (1") from the fascia board.
To establish the proper angle for the field
slates, fasten a tapered wooden cant or lath to the roof deck over
the ice dam protection, just upslope of the eave edge. The lath or
cant’s thickness will vary depending upon the slate’s
thickness and exposure dimension specified.
Punch holes and fasten the starter course with a
minimum of two (2) copper slating nails along a line parallel to
and approximately 25mm to 38mm (1" to 1-1/2") below the top edge of
the starter slates.
SS-4.7.4 Field Slates
Align the butts of the first course of field
slates with the butts of the starter slates. Ensure joints are
offset a minimum distance of 75mm (3") from the joints in the
underlying starter course. Fasten slates to the substrate with a
minimum of two (2) copper slating nails.
Succeeding courses of field slates are generally
started with alternating half-width and full width slates to
achieve an offset application pattern. Most slate patterns are
established by jointing or offsetting slate courses as close as
possible to the centre of the slate below or by a minimum distance
of 75mm (3").
The field slates are continued to a point near
the ridge but held back from the ridge apex to allow installation
of wood lath and nailers. The wood lath and nailers shall be the
same thickness as the abutting field slates and shall be installed
just down slope from the ridge.
So all nails are covered, fasten ridge slates so
their joints overlap and break the joints of the slates in the
An optional copper or felt ridge flashing may be
installed along the ridge line prior to application of ridge
The nails of the finishing slate shall be
covered with sealant.
The ridge slates may be bedded in asphaltic
roofing cement or polyurethane sealant along the ridge joint.
SS-188.8.131.52 Saddle Hips
Saddle hips are formed by fastening a two-piece
wood lath or an 89mm (3-1/2") wide wood cant strip to the wood
decking over the underlayment along the apex of the hip. Field
slates are installed up to the wood lath or cant strip.
Mitered hip slates, which are usually the same
width and exposure as the adjacent field slates, are fastened to
and on top of the wood lath or cant strips. The mitered tile edges
shall align along the hip centre line with butts aligning with the
Fasten hip slates with a minimum of two (2)
slating nails per unit.
The bedding and sealing of hip slates in
asphaltic roofing cement or polyurethane sealant is optional.
SS-184.108.40.206 Mitered Hip
Mitered hips are formed with field slates. Field
slates are applied up to the hip, then hip slates are miter cut so
the mitered edges butt along the hip centre line on both sides of
After cutting, trial fit hip slates to ensure
finished miter joints will be tight. Fasten each mitered hip slate
with a minimum of two (2) copper slating nails per unit.
To improve the long term water shedding of a
mitered hip application, an optional copper hip soaker flashing may
be woven into each course of mitered hips.
Bedding and sealing of hip slates in asphaltic
roofing cement or polyurethane sealant is optional.
© 2019 Alberta Roofing Contractors Association