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Serving Alberta's Roofing Industry Since 1961
MB Section 3: Separator Sheets and Auxiliary Leveling Surfaces
MB-3.1 Separator Sheets
Separator sheets are materials used to separate
roofing system components, to prevent material incompatibility or
to prevent adhesion.
MB-3.1.2 Wood Decks
MB-220.127.116.11 Uninsulated Systems
Direct application of hot bitumen to
wood decks is not permitted. Glass coated base sheet or fire
resistant approved underlayment must be installed on all wood decks
when a modified bituminous membrane is mechanically fastened. There
can be no exposed fasteners.
Follow the membrane manufacturer's
application recommendations when mechanically fastening the screws
MB-18.104.22.168 Insulated Systems
For conventional insulated modified bituminous
roofing systems over wood decks, the vapour retarder membrane will
serve as the separator sheet.
MB-3.1.3 Concrete Decks
MB-22.214.171.124 Cast-In-Place Concrete
Separator sheets are not required over cast-in
Priming of the concrete surface with an asphalt
primer is optional.
MB-126.96.36.199 Precast Concrete Decks
A separator is not required when adhering
modified bituminous membranes directly to precast concrete decks
with hot bitumen, except at deck joints.
Where joints between precast concrete deck
sections are grout filled, a separator sheet shall cover joints.
Installed dry, a 150mm (6”) wide strip of coated or modified
bituminous base sheet shall continuously cover the grouted deck
When precast deck sections do not contain grout
keys, continuously cover joints by installing a one half (1/2) roll
minimum 457mm (18”), width strip of a coated base sheet.
Adhere one side of the separator sheet to within 150mm (6”)
of the deck joint centre line with asphalt or a compatible SBS
MB-3.1.4 Steel Decks
Hot bitumen shall not be used to adhered
modified bituminous membranes directly to steel decks.
Separator sheets are not required over steel
MB-3.2 Auxiliary Leveling
An auxiliary leveling surface is a material used
to provide a smooth substrate to which roofing system components
can be adhered.
ARCA accepted auxiliary leveling
surfaces may be comprised of a minimum 9.5mm (3/8") thick Fibre
Reinforced Gypsum Panel (ASTM 1278), 12.7mm (1/2") thick Glass Mat
Gypsum Substrate (ASTM 1177), 12.7mm (1/2") thick Glass Mat Gypsum
Substrate (ASTM C1396), 12.7mm (1/2") thick plywood, or 12.7mm
(1/2") thick O.S.B. when not used as a thermal barrier.
The existing substrate type and condition will
determine the auxiliary leveling surface type and attachment
Where required by the Alberta Building Code, a
thermal barrier may be used as an auxiliary leveling surface.
MB-3.2.2 Wood Decks
For dimensioned lumber decks an accepted
auxiliary leveling surface shall be mechanically fastened to
completely cover the lumber decking. Hot bitumen shall not be used
to adhere directly to dimensioned lumber deck.
When using roofing nails for attachment, use a
minimum of one (1) nail per square foot of surface area.
When using drywall screws for
attachment, use a minimum of twenty (20) per 1200mm x 2400mm
(4’ x 8’) sheet.
When using screws and plates for
attachment, use a minimum of eight (8) per 1200mmx2400mm (4’
x 8’) sheet.
Mechanical fasteners (nails or screws) must be
of sufficient length to penetrate a sheathing material by a minimum
of 12.7mm (½") beyond the lower surface and a minimum of
25mm (1") into dimensioned lumber.
MB-3.2.3 Steel Decks
For uninsulated and protected membrane designs
an accepted auxiliary leveling surface (excluding perlite and wood
fiber boards) shall completely cover the steel decking prior to
membrane application. SBS modified bituminous membranes shall not
be applied directly to steel decks except as a vapour
The auxiliary leveling surface may be attached
to the steel decking using one of the following attachment methods:
Continuous beads or a full roller coating of an adhesive
applied to the top flanges of the steel deck in accordance with the
adhesive manufacturer’s application rates.
Minimum twenty (20) self tapping drywall
screws per 1200mm x 2400mm (4’ x 8’) sheet fastened
through the top flange of the steel decking. Where drywall screws
break the gypsum board paper covering, install a replacement screw
in approximately the same location. Additional fasteners may be
required to meet wind uplift standards.
When using screws and plates for attachment,
use a minimum of eight (8) per 1200mmx2400mm (4’ x 8’)
sheet fastened through the top flange of the steel decking.
Additional fasteners may be required to meet wind uplift standards.
Attachment method (b) for steel deck is experienced based. ARCA
has not conducted formal wind studies.
To qualify for an ARCA 15 Year Warranty
Certificate, a minimum 12.7mm (1/2”) glass faced gypsum
auxiliary leveling surface shall be mechanically fastened to the
MB-3.2.4 Concrete Decks
An auxiliary leveling surface is not required
over concrete decks.
Damaged and deteriorated concrete decks shall be
repaired to provide a smooth substrate for roofing system
© 2016 Alberta Roofing Contractors Association