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Serving Alberta's Roofing Industry Since 1961
BUR Section 9: Protected Membrane and Combination Designs
A protected membrane roofing design is an
insulated and ballasted roofing system in which the primary
insulation is applied above the membrane and retained in place by
A combination roofing assembly is comprised of a
conventional insulated membrane system where the primary membrane
is covered with insulation held in place with ballast.
Protected membrane and combination designs do
not require back nailing of the primary membrane plies for roof
slopes 1:8 (1 1/2"/ft.) and greater.
For protected membrane and combination designs
the drainage slope shall be a minimum 1:50 (1/4"/ft.).
The maximum roof slope is restricted to 1:6
When flow control drains are incorporated into
the roof drainage system, membrane level scuppers shall be provided
at the roof perimeter as emergency drainage. Roof drains and
scuppers must have gravel screens installed when gravel ballast is
specified. Drainage openings are not permitted through expansion
BUR-9.3 Penetrations and Perimeter
Except for roof drain and pedestal fall
protection roof anchors, all membrane penetrations shall be
contained within or supported by a curb secured to the structure or
Roof parapets, roof/wall junctions and membrane
penetrations including curbs, area dividers, equipment supports and
pedestal fall protection anchors shall extend a minimum distance of
200mm (8") above the surface of the insulation when using gravel
ballast or above the surface of concrete pavers when they form the
Pedestal fall protection roof anchors
may be waterproofed with an ARCA Warranty Ltd. approved one-piece
manufactured metal specialty flashings. The one-piece metal
specialty flashing shall incorporate a minimum 100mm (4”)
wide integral flange. The flashing flange shall be mechanically
fastened to the structure or decking over the primary membrane
prior to the application of the membrane flashing.
Roof area dividers are not required for
protected membrane designs.
BUR-9.4 Membrane Flashing
A minimum of three (3) plies of organic felt
membrane flashing, adhered in applications of hot bitumen, and
shall be installed at internal roof drains, parapet, curb and wall
junctions. For alternate membrane flashing types refer to Section
7, Built - Up Roofing Membrane Flashings.
When gravel ballast is specified, the vertical
extension of the membrane flashing shall terminate a minimum
vertical distance of 200mm (8”) above the surface of the
For concrete pavers or concrete topped
insulation systems, the vertical extension of the membrane flashing
shall terminate a minimum distance of 200mm (8”) above the
top of the concrete surface.
BUR-9.5 Bitumen Flood Coat
A bitumen flood coat shall serve as a barrier
against moisture infiltration and shall completely cover the field
of finished primary membrane.
The bitumen flood coat shall be applied in two
(2) separate applications for a minimum combined bitumen mass of 3
kg/m² (0.6 lb/ft²).
BUR-9.6 Separator Sheets
When set, the bitumen floodcoat shall be
completely covered with a minimum of two (2) mil thick loose-laid
polyethylene separator prior to application of the Type 4 primary
insulation. The polyethylene separator prevents the insulation from
bonding to the bitumen floodcoat.
Separator sheets, including filter fabric, shall
have minimum 300mm (12”) wide side and end laps.
At perimeters, curbs and wall junctions the
separator sheet shall extend to the surface of the primary
When gravel ballast is specified, a loose-laid
filter fabric shall completely cover the surface of the Type 4
When concrete paver ballast is specified, the
use of a filter fabric is optional.
The roof insulation shall be Type 4 extruded
polystyrene insulation loose-laid over a polyethylene separator
sheet. The insulation provides ultraviolet light protection for the
bitumen, as well as the thermal resistance for the roofing
Roof insulation 100mm (4") thick and less shall
be installed in a single layer.
For multi-layer insulation applications, the
base layer of insulation boards shall not be less than 100mm
(4”) thick. When using more than one insulation layer, the
board joints shall be offset a minimum distance of 300mm
(12”) from the joints of the previous insulation layer.
Poured-in-place concrete topping ballast is not
accepted for Warranty Certificate issuance.
The ballast may be comprised of rock or concrete
Gravel (rock) ballast shall be
relatively free of fines and other foreign matter, shall contain
gravel sizes between 19.0mm (3/4") and 38mm (1 1/2") in diameter
and shall conform to ASTM D7655 "Standard Clasification for Size of
Aggregate Used as Ballast for Membrane Roof Systems".
A minimum ballast mass of 50 kg/m² (10
lbs/ft.²) is recommended over the field of the filter fabric
and loose-laid insulation system. With the minimum gravel ballast
mass, the filter fabric may be visible. For thick insulation
layers, consult with the insulation manufacturer for ballasting
For concrete paver ballast, the weight of
individual pavers shall not exceed 45 kg (100 lbs.) in mass. When
using a paver ballast system, the pavers shall be elevated above
the insulation to provide an air space between the paver and the
primary insulation. Pedestals or insulation strips shall be
employed to elevate the concrete pavers above the surface of the
Type 4 insulation boards. Paver ballast shall not be placed on a
The design parameters of the roof structure
itself must include the weight of the newly installed ballasted
roofing system. The structure must be capable of supporting the
weight of the roofing system plus the specified ballast without
encroaching on the necessary live load allowance and without
creating or aggravation water ponding problems. A design
professional should be consulted to certify that the structural
system will support these loads.
BUR-9.9 Sheet Metal Flashings
Gravel stop flashings are not accepted for roof
For a gravel ballast system, the sheet metal
base flashings shall contain a minimum 50mm (2”) wide
horizontal leg that rests on the top surface of the primary
With paver ballast, the 50mm (2”)
horizontal base flashing leg shall rest on the surface of the
© 2016 Alberta Roofing Contractors Association