Dow Protected Membrane Roof EN - Manual (Page 15)

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Function
The roof deck should:
• Provide structural support to
accommodate both live and
dead loads without significant
deflection.
• Provide dimensional stability by
forming a stable substrate not
affected adversely by cyclical
thermal- and moisture-induced
movement.
• Provide fire resistance as deter-
mined by the building type
and intended use.
• Provide a substrate for the roof
system.
• Accommodate building move-
ment. Where necessary, building
expansion joints and roof area
dividers should be designed
and installed.
• Provide for drainage (either by
sloping the roof deck or using
tapered insulation or both).
The roof surface should be
sound and should drain water
freely within 48 hours follow-
ing a rain. Every effort should
be made to isolate and correct
the causes of any standing
water or ponding on the roof.
CRCA and NRCA recommend
a minimum slope of 1/4" per
foot (2 percent). The
International Building Code
(IBC) also requires a slope of
1/4", except for coal tar mem-
branes that require 1/8" slope.
However, if the roof is
designed to allow ponding,
ensure the insulation is not
adhered to the membrane
and a filter fabric is used.
• Provide suitable roof drains
and gutters. Care should be
taken to prevent ballast from
entering the drains and/or
gutters by using perforated
collars or paving stones.
When concerns exist, a
drainage assessment should
be conducted per SMACNA
guidelines.
The membrane should:
• Provide a continuous water-
proofing barrier to protect the
interior environment.
• If the membrane is tacky, use
a slip or separation sheet (e.g.,
4-mil polyethylene) to mini-
mize adhesion between the
membrane and insulation.
• If there are compatibility issues
with the membrane, such as
with certain PVC or coal tar
membranes, refer to the
manufacturer’s or supplier’s
recommendations. In some
cases, a slip or separation sheet
(e.g., 4-mil polyethylene) may
be required.
The flashing should:
• Provide a continuous water-
proofing barrier when tied
into the membrane to protect
the interior environment.
• Extend well above the expected
high water level (typically 8"
minimum).
Specification
General: The overall system
(including membrane and insu-
lation) should be designed so that
the dew point is located above
the membrane. The system should
be designed so that freezing will
not occur at the membrane level.
Where required, an adequate
thermal barrier should be pro-
vided between the insulation and
the interior of the building. The
thermal barrier may consist of the
deck, a ceiling assembly or an
underlayment board equivalent
to 1/2" gypsum board.
Membrane: Refer to membrane
manufacturer’s literature for
details. The manufacturer or
supplier of the membrane shall
be responsible for determining
compatibility of the membrane
with STYROFOAM
™ extruded
polystyrene insulation.
Roof deck and flashing: Refer
to general roofing specification
for details.
Installation Notes
See the NRCA Roofing and
Waterproofing Manual – Fifth
Edition. Online edition available
at: http://www.nrca.net/rp/
technical/manual/manual.aspx
See the CRCA Roofing
Specification Manual. Details
available at: http://www.roofing
canada.com/ItemsForSale.asp
Components
A L L O T H E R C O M P O N E N T S