Dow Green Roof - Manual

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*Not to scale. For reference purposes only.
A protected membrane roof (PMR)
design is an ideal solution for “green”
roofs where landscaping or plant-
ings are used on the top surface.
Preventing leaks is crucial in any
roof, and even more so in a vege-
tative roof, because repairing this
type of roof can be costly.
In a vegetative roof PMR, typically
a fully adhered membrane is installed
over a concrete deck and the desired
thickness of STYROFOAM
™ Brand
Extruded Polystyrene Foam Insulation
and a root barrier are installed above
the membrane (Figure 1).
This layer of insulation serves a
dual function of providing both
long-term thermal insulation value as
well as mechanical protection of
the crucial waterproofing membrane
during the installation of the roof
landscaping, including drainage lay-
ers, drainage materials and plantings,
and the assorted equipment used
during the installation process.
W H E R E S H O U L D T H E
D R A I N A G E L AY E R B E
L O C AT E D ?
The drainage layer should always
be above the STYROFOAM
™ Brand
Extruded Polystyrene Foam
Insulation to ensure that any water
is quickly drained away and the full
value of the insulation is maintained.
In vegetative roof PMR deck
designs, a drainage layer above the
insulation allows water to drain off
the top surface of the insulation,
creating a “diffusion open” assembly.
If the insulation is sandwiched
between a vapor retarder (e.g.,
saturated drainage felt) and the
underlying membrane, vapor cannot
escape, so there is the potential for
it to be driven back into the insulation
(Figures 2 and 3). To create a “diffusion
open” layer, ensure that the top surface
of the insulation has a ventilating air
space as well as provides a good
slope for drainage.
Note: Never install a polyester
mat or moisture retention blanket
directly on the insulation. If used,
ensure a clear drainage layer
separates the moisture retention
blanket and the insulation.
V e g e t a t i v e R o o f P M R – A D e s i g n P r i m e r
I N F O R M A T I O N . C O M M E R C I A L . U S / C A N A D A
Figure 1: Vegetative Roof PMR*
Landscaping Curb
Ballast
Planting Layer
Filter Fabric
Drainage Layer
(shown: preformed
drainage sheet)
Root Barrier Membrane
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
STYROFOAM™ Brand
Foam Insulation
Cold Exterior
40°F (4°C), 20% RH
Vapor
Drive
Vapor Impermeable Surface
(standing water, retention mat)
Fully Adhered
Waterproofing Membrane
STYROFOAM™ Brand
Foam Insulation
Structural Concrete Deck
Figure 3: Creating “Diffusion Closed” Situations
(warm, high-humidity areas in North America)*
Figure 2: Creating “Diffusion Closed” Situations
(colder areas in North America)*
Warm, Humid Interior
70°F (21°C), 40% RH
Vapor Impermeable Surface
(standing water, retention mat)
Fully Adhered
Waterproofing Membrane
STYROFOAM™ Brand
Foam Insulation
Structural Concrete Deck
Warm, Humid Exterior
90°F (32°C), 50% RH
Vapor
Drive
Cool Interior
70°F (21°C), 40% RH