CEMP-ET
TI 809-53
01 May 1999
5-3.DESIGN CONSIDERATIONS AND ALERTS.
a. Attachment. Modified bituminous membranes require strong and uniform attachment to the
substrate. The use of the nail-one, mop-one technique to install thermal insulation is a good way to
achieve that.
b. Phased Construction. All components from the top of the roof deck through the completed
membrane (excluding surfacing) should be completed in a single day. Just installing a base sheet to
protect the substrate then returning later to install the MB capsheet is called phasing and is to be
avoided.
c.
Adhesion Type. Use torch, mop, or cold mastic techniques as required by system choice.
d. Walkways. Protective walkways are needed if more than occasional roof traffic is expected.
Polyester reinforced SBS modified cap sheets may be used as a walkway. This layer is in addition to
the membrane specified.
e. Equiviscous Temperature. The EVT concept may be inappropriate for MB application. Follow
the minimum bitumen temperatures specified by the proprietary specification, typically 230C (450F)
or higher.
f.
Flashings. Specify two-ply, not single-ply base flashings.
g. Overlay Boards. Require protective cover boards with taped joints to be installed over EPS
insulation to prevent melting of the EPS.
5-4. CONSTRUCTION CONSIDERATIONS AND FIELD ALERTS.
a. General. Materials must be delivered to the job site and ready to install when work begins.
MB roofing is a continuous process and everything from vapor retarder through roof membrane must
be installed in a single day. While it is tempting to delay the capsheet until an entire roof area is
completed, this can result in delamination and blistering.
(1) Storage.
Materials must be stored off the ground and protected from weather and
(2) Bitumen Temperatures.
Bitumen for hot-adhered systems must be heated and
transported to meet the temperatures required at the point of application. Generally temperatures to
apply MB products will be higher than EVT.
(3) Vapor Retarders. Vapor retarders (when used) must be protected with insulation as soon
as installed to avoid construction damage.
(4) Edge Seals. Roof edges and end of day work must be sealed off to protect against water
penetration.
(5) Surfacings. If field applied surfacings are used, they should not be installed until the
entire roof area is completed. Manufacturers may recommend long delays for some coatings to allow
the MB to stabilize.
(6) Material Compliance. Read labels on roll goods and verify compliance with specifications
and UL and FM requirements.
b. Pre-Roofing Conference. A pre-roofing conference should be held prior to construction.
Representatives of the designer, user, roofing contractor, general contractor, materials manufacturer,
5-6
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