Dow Protected Membrane Roof EN - Manual (Page 10)

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Description
Crushed stone or washed,
rounded riverbed rock, with a 1"
(25 mm) clear size, free of fines
or stones smaller than 5/8" (15 mm)
or larger than 1-3/8" (35 mm).
Most stones should be 3/4" to
1-1/4" (19 mm to 32 mm) size.
Function
Prevent uplift and prevent
flotation: Ballast is required to
prevent negative flotation and is
based on the total thickness of
STYROFOAM
™ Brand Extruded
Polystyrene Foam Insulation and
the type of membrane used.
Adhered membrane (e.g.,
membrane attached to deck):
When a suitable UV-resistant filter
fabric is used over a membrane
attached to the deck, the amount
of required ballast is 10 lb/ft
2 (50
kg/m 2 ) regardless of the insulation
thickness, except around the
perimeter and penetrations, and in
areas of high winds. See Table 2 for
amount of ballast required for
perimeters and penetrations, as
well as PMR assemblies installed
without a fabric.
It is critical that the membrane is
properly attached to the deck when
using 10 lb/ft
2 (50 kg/m 2 ) ballast
and a suitable filter fabric to prevent
the possibility of any ballast falling
under the membrane during times
of ponding and air infiltration.
Areas of extra ballasting: Extra
ballast, required to overcome high
wind loads and restrain insulation
during heavy rainstorms, should be
considered in the following locations:
• Perimeter edge – 4' (1.2 m)
wide band running along the
perimeter edge of the roof
insulation.
• Penetrations through the
insulation – 2' (0.6 m) wide
band around any roof penetra-
tion greater than 4' (1.2 m) in
any direction (e.g., skylights,
equipment pads, etc.).
• Corners – Concrete pavers
and/or parapets may be
required. See “Pavers” on page
12 for additional information.
• Building exposure – Consider
the surrounding terrain and its
potential effect on overall
wind exposure (e.g., nearby
woods versus shorelines).
Prevent wind scouring: The
wind performance of stone-
ballasted PMR assemblies has
been excellent. Only a few iso-
lated minor scouring problems
have occurred, typically limited
to small areas in and around
corners. In these few cases, the
ballast has been blown inbound
by about 4' (1.2 m) and piled up
on the filter fabric, creating
additional weight. In these
instances, concrete pavers
should be considered. See
“Pavers” on page 12 for details.
Prevent UV degradation of
the insulation: Most PMR appli-
cations use a filter fabric that
typically incorporates a UV sta-
bilizer. However, if no fabric is
used, the insulation must be
totally covered by the ballast to
prevent UV degradation. The
quality of the ballast is critical
in these types of applications.
Too small (fines not more than
10 percent of mix) and the
stones may work into the insula-
tion joints or be moved by the
wind; too large and the ballast
may not provide adequate cover
to protect from UV light.
Provide a Class A fire-resistant
roof cover: Class A roof covering,
as defined by ULC S107, ULI 790
and ASTM E108. (See “Fire and
Wind Ratings” on page 20
for details.) The requirements for
Class A roof construction cover
the performance of roof assem-
blies and roof covering materials
when exposed to a fire originating
from sources outside a building.
The stone ballast provides the
Class A fire rating.
Components
B A L L A S T
T A B L E 2
Required Ballast Around Perimeters and Penetrations, and for Standard PMR (Without Fabric)
Insulation Thickness, inch (mm) Required Weight of Ballast, Approximate Thickness of Ballast,
lb/ft 2 (kg/m 2 ) inch (mm)
Up to 2 (50) 12 (60) 1-1/2 (40)
3 (75) 17 (84) 2-1/4 (60)
4 (100) 22 (108) 3 (75)
5 (125) 27 (132) 3-1/2 (90)
6 (150) 32 (156) 4-1/4 (105)
7 (175) 37 (180) 5 (125)
8 (200) 42 (204) 5-1/2 (140)