Dow Protected Membrane Roof EN - Manual (Page 14)

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Components
A L L O T H E R C O M P O N E N T S
Description
MEMBRANES
The membrane is the flexible
or semi-flexible waterproofing
layer on the roof deck. In a PMR
application, the membrane is
sandwiched between the roof
deck and the insulation.
Membranes fall into three
general categories: built-up roof
(BUR), two-ply modified bitumen,
single-ply (sheet) or liquid
membranes.
Note: PMR assemblies should be
installed with adhered membranes
only.
BUR membranes are semi-flex-
ible, multi-ply roof membranes,
consisting of plies or layers of
saturated felts, coated felts, fab-
rics or mats between alternate
layers of bitumen, either asphalt
or coal tar based.
Modified bitumen membranes
are similar to BUR membranes,
but instead are manufactured in
a production facility, using
asphalt modified with various
additives. The membrane is fully
adhered and the seams overlap
to provide an uninterrupted
waterproof layer.
Sheet or single-ply membranes
are prefabricated sheets of polymer-
based material, such as thermo-
plastic (e.g., PVC), elastomeric
(e.g., EPDM) or modified bitumen
with polymer modifiers. Single-
ply roofs can be:
• Fully or partially adhered: The
membrane is fully or partially
adhered to the underlying sub-
strate with a flood coat.
• Loose-laid: The membrane is
not attached to the substrate
except at the perimeter and at
penetrations. In a PMR assem-
bly, the loose-laid membrane
is held in place with full ballast.
(See “Ballast” on page 10 for
details.) Care must be taken to
ensure that air infiltration
underneath the membrane is
prevented.
• Mechanically fastened: The
membrane is attached at
defined intervals to the sub-
strate. Mechanical fastening
may use various fasteners and/
or other mechanical devices,
such as plates or battens.
• Self-adhering: The membrane is
adhered to a substrate and to
itself at overlaps without the
use of an additional adhesive.
This is usually accomplished
with a surface adhesive pro-
tected by a release paper or
film that prevents the mem-
brane from bonding to itself
during shipping and handling.
Note: With some membranes,
manufacturers may recommend a
slip sheet (e.g., 4-mil polyethylene
film) over the membrane to prevent
adhesion of the foam to the
membrane or plasticizer migration
(e.g., chemical attack) to the
STYROFOAM
™ extruded poly-
styrene insulation. Consult the
membrane manufacturer for
recommendations.
Liquid membranes are applied
in-situ as a liquid that hardens or
sets into a continuous, monolithic
membrane over the substrate.
These liquids are generally
applied by spraying or with
rollers and include:
• Hot-applied rubberized
asphalts, a blend of asphalt,
mineral fillers, elastomers, virgin
or reclaimed oil. Some versions
consist of two coats of rubber-
ized asphalt with a polyester
mat in between (fully reinforced
or two-ply system).
• Cold-applied liquid com-
pounds consist of emulsions
and solutions of resins, elas-
tomers (e.g., polyurethanes,
silicones, acrylics, etc.) and
bitumens and/or modified
bitumens.
FLASHINGS
Flashings are materials used
to weatherproof or seal the roof
system edges at perimeters,
penetrations, walls, expansion
joints, valleys, drains and other
places where the roof covering
is interrupted or terminated. For
example, membrane base flash-
ing covers the edge of the field
membrane, and cap flashings
or counterflashings shield the
upper edges of the base flashing.
ROOF DECK
The roof deck (including
drains and gutters) is the struc-
tural component of a building’s
roof. The deck must be capable
of safely supporting the design
dead and live loads, including
the weight of the roof systems
and the additional live loads
required by governing building
codes.
Decks are either non-com-
bustible (e.g., corrugated metal,
concrete or gypsum) or com-
bustible (e.g., wood plank or
plywood), and provide the sub-
strate to which the roofing or
waterproofing system is applied.