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Serving Alberta's Roofing Industry Since 1961
BUR Section 6: Primary Membrane
Built-up bituminous primary membranes may be
comprised of three (3) or four (4) plies of organic or inorganic
felt adhered with interply applications of hot bitumen.
Built-up bituminous membrane systems can be
categorized as a conventional design, membrane applied above
insulation, a protected membrane design, membrane applied below
insulation, or a combination design, membrane applied between two
For all designs the built-up membrane shall be
uniformly adhered to and supported by an accepted substrate
including cant strips at vertical junctions. The primary membrane
shall be joined and sealed to the vapour retarder membrane
extension at perimeters and penetrations.
Application of built-up roofing systems must not
be undertaken when the air temperature at roof level is colder than
-18°C and a wind velocity of more than 14.5 km/h, or an
equivalent wind chill factor of 1300. Built-up roofing systems
shall not be applied during periods of rain, snow or similar
BUR-6.2 Design Considerations
Roof assemblies must meet the standards
as set up by the authority having jurisdiction.
When developing a BUR system design, the design
authority shall take the following items into consideration:
BUR-6.2.1 Drainage Provision
The Warranty Certificate does not warrant the
roof drainage system.
The Warranty Certificate covers the watertight
integrity of the primary membrane and the seal of the roof flashing
component, e.g. lead flashing, drain or scupper flange. The design
authority shall ensure that the drainage system is designed in
accordance with the governing Plumbing and Building Code to provide
positive drainage and accommodate minimum roof drainage slopes as
Some isolated ponding water can be anticipated
when drainage slope is provided.
ARCA recommends that emergency or overflow
drainage be incorporated into the roof drainage systems. The
Warranty Certificate requires that emergency drainage be provided
in designs using “flow control” type roof drains.
Splash pads shall be installed beneath drain
outlets discharging water onto lower roofs to prevent the erosion
of the membrane protection and damage to the primary
BUR-6.2.2 Roof Slope
The maximum slope for a BUR system is 1:6
BUR systems incorporating organic felt plies
must provide for the back nailing of the felts on slopes exceeding
BUR systems incorporating inorganic felt plies
must provide for the back nailing of the felts on slopes exceeding
Protected membrane and combination designs do
not require the back nailing of the felts plies regardless of
whether the felts are organic or inorganic.
Back nailing of felt plies for insulated
conventional roof designs will require the installation of nailers.
Please refer to Section 5, Insulation, Subsection 5.2, for the
requirements for spacing and installation of
Enclosed roof sections that include
photovoltaic equipment shall be independently drained and shall
have positive drainage with a minimum slope of 1:50 (2%).
BUR-6.2.3 Temporary Membrane
A minimum two (2) ply vapour retarder comprised
of roofing felt adhered with hot bitumen may be used as a temporary
membrane. A separator is required over wood decks and an auxiliary
leveling surface is required over steel decks prior to application
of the temporary BUR membrane.
For two-stage construction the installation of
the vapour retarder membrane is the first stage. The vapour
retarder membrane shall be inspected and repaired prior to the
remaining roofing components being installed.
Uninsulated conventional and protected membrane
designs do not qualify for two-stage construction.
BUR-6.3 Built-Up Roof Membrane
The bitumen used to adhere BUR membranes may be
roofing asphalt or coal tar pitch. Asphalt is the most common
bitumen used in Alberta and shall be manufactured in compliance to
CSA A123.4-04. Coal tar pitch is rarely used and shall be
manufactured to ASTM Standard D450, Type 1.
Bitumens must not be heated in excess of their
Final Blowing Temperature, i.e. the temperature at which the
bitumen was oxidized.
Equiviscous Temperature (E.V.T.) is the
recommended application temperature range for bitumen and shall be
measured at the point of application. E.V.T. is provided by the
bitumen manufacturer and may differ with the bitumen type.
Coal tar pitch and roofing asphalt are not
compatible with each other.
Roofing asphalt is available in three types or
grades. The selection of the asphalt type to be used is based on
the roof slope and is determined as follows:
Type 1 Asphalt: For slopes 1:25 (1/2”/ft.) and
Type 2 Asphalt: For slopes 1:12 (1”/ft.) and less
Type 3 Asphalt: For slopes 1:6 (2”/ft.) and less
Asphalt is applied in a full application
(coatings) to the membrane substrate and between felt plies at its
Equiviscous Temperature (E.V.T.) application range. For organic
felts it is applied at the approximate rate of 1.0 kg/m²
(20lbs/100sq.ft.). For inorganic felts the approximate rate is 1.2
kg/m² (25lbs/100sq.ft.). The asphalt may be applied by hand
with a roofer’s mop or mechanically with an asphalt
applicator. The asphalt shall be applied with sufficient coverage
to ensure full adhesion of the felt ply.
Coal tar pitch use is restricted to a maximum
roof slope of 1:25 (1/2”/ft.).
Pitch shall be applied at an approximate rate of
1.5 kg/m² (30lbs/100sq.ft.) in full application to the
membrane substrate and for interply mopping. Only perforated pitch
saturated felts may be used.
BUR-188.8.131.52 Polymer Modified
Polymer modified roofing asphalt shall be
manufactured in compliance with ASTM D-6152, "Standard
Specification for S.E.B.S. Modified Mopping Asphalt Used in
Polymer modified asphalt use is restricted to
the application of the membrane protection floodcoat and shall not
be used to adhere membranes.
To prevent moisture infiltration roofing felt
rolls shall be poly bagged during shipment and storage out of
doors. Store felt rolls on end and on pallets above the roof/ground
surface. Do not install roofing felts when their moisture content
exceeds the felt manufacturer’s equilibrium moisture
BUR plies shall be applied in a full application
of hot bitumen, true to line, without wrinkles and vapour locks.
Each ply of felt shall be carried to the top of cant strips at
horizontal to vertical transitions.
When nailers are required the membrane plies
shall be adhered in a full application of bitumen, in a straight
four (4) ply application installed perpendicular to the direction
of the nailers. Additionally, membrane plies shall be mechanically
fastened to each nailer with a minimum of one (1) galvanized
roofing nail placed approximately 50mm (2”) down from the
leading edge, of each felt ply.
BUR-184.108.40.206 Organic Felt
Organic felts shall be either No. 15 asphalt
saturated perforated felt manufactured to CSA A123.3-05, or No. 15
coal tar pitch saturated perforated felt manufactured to ASTM
The following organic asphalt saturated roofing
felts meet the requirements of CSA A123.3-05 and are accepted for
issuance of the built-up roofing Warranty Certificate:
- No. 15 Asphalt Felt - Perforated
Pressure shall be applied to each organic felt
ply with a broom or squeegee during application to assure complete
contact with the hot bitumen.
The specified number of felt plies, together
with the membrane protection shall be applied each day. Organic
felts shall not be left unprotected. If, due to exceptional
circumstances, the application cannot be completed, the organic
felt surface shall be sealed with a light (visible) glaze coat of
BUR-220.127.116.11 Inorganic Felt
Inorganic felt shall be either Type IV or Type
VI asphalt saturated fiberglass roofing felt manufactured to CSA
A123.17-05 (ASTM D2178).
The following inorganic asphalt saturated
roofing felt meet the requirements of CSA A123.17-05 and are
accepted for issuance of the BUR Warranty Certificate:
- IKO Glass Type IV Ply Sheet
Due to the unique properties of fiberglass felt
the following application techniques form part of the BUR minimum
requirements for Warranty Certificate issuance.
The use of mechanical bitumen spreaders is not permitted for
fiberglass felt applications.
For fiberglass felt BUR application, a straight four (4) ply
application shall be the preferred application method. The 2 + 2
application method is permitted but must be completed within the
same working day. The ganging of multiple rolls of felt is
For proper adhesion, individual felt plies must be hand mopped
with hot bitumen applied at the high end of its equiviscous
temperature (E.V.T.) range.
Fiberglass felt rolls shall be kicked out from either the
insulation or deck sides of the roof. Refrain from walking on the
newly applied fiberglass felts until the bitumen has set. Bitumen
set times will vary with changes in the ambient temperature, from
15 minutes in cool weather to several hours during extremely warm
temperatures. Point loading of material or equipment on the
completed fiberglass membranes is not allowed. Personnel are not to
walk on or push equipment over the newly installed membrane until
the bitumen set time has been achieved.
The brooming of fiberglass felt into the hot bitumen during
application is not required.
Fish mouths occurring at membrane edge laps must be
immediately cut and pressed into the hot bitumen.
Roof transitions occurring at drain and scupper sumps,
crickets, saddles, valleys and other changes in roof slope /
elevation shall be reinforced with a minimum of one (1) ply of No.
15 organic felt adhered in hot bitumen. Application of the organic
felt ply precedes the application of the inorganic felt primary
Fiberglass felts cannot be used for the membrane flashing
plies. The membrane flashing shall be comprised of a minimum of two
(2) plies of modified bituminous membrane or three (3) plies of No.
15 organic felt.
Night cut-offs waterproofing fiberglass primary membrane
terminations must be completed using No.15 organic felt glazed with
The completed fiberglass felt primary membrane must either be
glazed or have its membrane protection installed within the same
Cants must be installed at all vertical roof
junctions to support the membrane plies and to reduce their
Cants shall incorporate a nominal 89mm
(3½") wide 45º sloping face.
Wood fiberboard, perlite, fire resistant mineral
board or wood may be used to manufacture cant strips. No other
material may be used unless approved by ARCA Warranty Ltd.
Cants may be uniformly adhered to their
supporting substrates with hot bitumen or be mechanically
Wood cants must be mechanically fastened to wood
blocking supported by and fastened to the structure or the
BUR-6.4 Membrane Protection
The membrane protection may be comprised of a
bitumen floodcoat with embedded roofing gravel or a smooth surfaced
emulsion or aluminum coating.
No other solution of bitumen dissolved in a
solvent may be used for the membrane protection.
BUR-6.4.2 Roofing Gravel
Roofing gravel shall be approximately 9.5mm
(3/8”) nominal diameter, washed, crushed or rounded rock,
relatively free of fines. Roofing gravel should be opaque, light
coloured, non- porous and reasonably free of moisture.
BUR-6.4.3 Floodcoat and Gravel
Roofing gravel embedded in a floodcoat of
bitumen is the most common form of membrane protection application
for conventional BUR systems. Polymer modified asphalt may be used
for the bitumen floodcoat with asphalt adhered membranes The
floodcoat and gravel may be applied using either a single or a
double application method as follows:
The single application method shall be comprised of a minimum
bitumen floodcoat of 3kg/m² (60 lbs./100 sq. ft.) and
approximately 20 kg/m² (400 lbs. /100 sq. ft.) of roofing
gravel applied while the bitumen in hot. To reduce the effects of
wind scour at the outside corners, single applications shall
incorporate a double application extending out from the corner a
minimum distance of 1200mm (4ft.) in each direction.
The double application method is restricted to a maximum roof
slope of 1:25 (1/2"/ft.). A double application shall be
proportioned so that the combined mass of the completed membrane
protection is 5kg/m² (100 lbs./100 sq. ft.) of bitumen and
approximately 30 kg/m² (600 lbs. / 100 sq. ft.) of roofing
gravel. The first application should limit the amount of gravel so
that the majority of the gravel is embedded in the hot bitumen and
little or no loose gravel to be swept away. The second application
shall follow the first as soon as possible to prevent dirt or
moisture from entering the system between applications. Both
applications shall be applied within the same working day.
Emulsion application is restricted to minimum
roof slopes of 1:25 (1/2”/ft.) and temperatures above
Bituminous emulsion coating shall conform to
CGSB 37-GP-28M or 37-GP-31M.
The surface of the built-up membrane, whether
organic or inorganic felt, shall be covered with a glaze coat of
bitumen prior to the application of the emulsion coating. The
emulsion shall be applied in two (2) coats so that the combined
application rate is approximately 2L/m² (4 gal/100 sq.ft.).
The first coat shall be allowed to set prior to the second
BUR-6.4.5 Aluminum Coatings
Aluminum coatings shall be restricted in use for
roof slopes of 1:25 (1/2”/ft.) and greater.
Aluminum coatings shall conform to CGSB
37-GP-42M, Type 2.
Apply aluminum coatings in accordance with
manufacturer’s application rates over a glaze coat of bitumen
or over an emulsion coat applied to the BUR membrane. Follow the
coating manufacturer’s recommendations for bitumen or
emulsion set-up and curing times prior to the application of the
BUR-6.5 Membrane Load Protection
Under no circumstance shall any equipment load
be supported directly on the surface of an unprotected primary
For roof mounted equipment exceeding
91kg (200 lbs.) in mass or when roof loads exceed 5kPa (105 p.s.f.)
they shall be supported on minimum 200mm (8”) high structural
curbs, structural sleepers or structural pedestals attached to the
structure or decking. Roof mounted equipment includes antennae,
signs, service lines, skylights, hatches and walkways. For new
construction where H.V.A.C. equipment is elevated above the roof
membrane, a minimum clearance of 300mm (12”) shall be
provided beneath the equipment to permit installation of the
roofing system. Equipment supports shall be designed by a
structural engineer and shall conform to the Alberta Building
Equipment loads 91Kg (200 lbs.) or less in mass,
may be supported by free floating sleepers or support pads loose
laid over the roofing system. Free floating sleepers shall be
pressure preservative treated wood, precast concrete, metal or
specialty product. Free floating sleepers or pads shall be placed
on a minimum 25mm (1”) thick layer of Type 4 insulation
attached to the base of the supports without the use of mechanical
fasteners. A ply of mineral surfaced roofing adhered to the primary
membrane in an application of hot bitumen may be substituted for
the Type 4 insulation protection layer.
When guy wires are used to anchor roof mounted
equipment their anchorage points shall be waterproofed with 200mm
(8”) high curbs or with gum boxes.
H.V.A.C. units, skylights and hatches shall be
supported by insulated metal or wooden curbs supported by and
fastened to the structural deck and extending a minimum distance of
200mm (8”) above the surface of the roofing system measured
at the highest point.
To protect the primary membrane from concrete
paver and/or walkway damage, a minimum 25mm (1") thick layer of
Type 4 insulation shall be placed between the walkway/pavers and
the finished gravel roof surface. Place the Type 4 insulation so
that the roof drainage is free to flow under the
BUR-6.6 Accepted Fully Adhered
Built-Up Roofing Membrane Systems
Organic No. 15 Perforated Asphalt Felt
||Separator + 3 plies or 4 plies
|Uninsulated Auxiliary Surface
|Protected Membrane Design
|Combination Design Insulated
Inorganic Asphalt Felt Systems
||Separator + 3 plies or 4 plies
|Uninsulated Auxiliary Surface
|Protected Membrane Design
© 2016 Alberta Roofing Contractors Association