Page 1
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
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
A protected membrane roof (PMR)
design is an ideal solution for “green”
roofs where landscaping or plantings are used on the top surface.
Preventing leaks is crucial in any
roof, and even more so in a vegetative 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 layers, drainage materials and plantings,
and the assorted equipment used
during the installation process.
WHE RE SHO ULD THE
DRA INA G E L AY ER BE
LOC ATED ?
The drainage layer should always
be above the STYROFOAM
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.
™
Brand
Figure 1: Vegetative Roof PMR*
Landscaping Curb
Ballast
Figure 2: Creating “Diffusion Closed” Situations
(colder areas in North America)*
Vapor Impermeable Surface
Cold Exterior
40°F (4°C), 20% RH
Warm, Humid Interior
70°F (21°C), 40% RH
Vapor
Drive
(standing water, retention mat)
STYROFOAM™ Brand
Foam Insulation
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
Figure 3: Creating “Diffusion Closed” Situations
(warm, high-humidity areas in North America)*
Vapor Impermeable Surface
(standing water, retention mat)
STYROFOAM™ Brand
Foam Insulation
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
Warm, Humid Exterior
90°F (32°C), 50% RH
Cool Interior
70°F (21°C), 40% RH
Vapor
Drive
lanting Layer
P
ilter Fabric
F
rainage Layer
D
shown: preformed
(
rainage sheet)
d
STYROFOAM™ Brand
Foam Insulation
Root Barrier Membrane
ully Adhered
F
aterproofing Membrane
W
Structural Concrete Deck
®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
*Not to scale. For reference purposes only.
Page 2
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
Installing the drainage layer under
the insulation can potentially minimize
the overall benefits of the insulation
by creating a convective loop below
the thermal insulation (Figure 4). In
this case, air can move through the
drainage layer and reduce the overall
insulation value. Installing the drainage
layer above the insulation ensures
that the insulation value is maximized.
IMPORTANT: When scheduling or
weather conditions delay installation
of plaza, patio deck or vegetative roof
PMR areas, care must be taken to
ensure that dark-colored products,
such as black plastic drainage boards
(dimple boards) or dark fabric, are
not placed over the insulation and
then left exposed. Dark-colored
products can lead to extremely high
surface temperatures, increasing the
potential for distortion of rigid foam
boards.
If STYROFOAM
™
Brand Extruded
Polystyrene Foam Insulation is already
installed, cover it with a white opaque
polyethylene film to protect it during
the delay. Otherwise, schedule the
insulation installation for a time when
the entire installation process can be
completed in a timely manner.
Figure 4: Potential for Convective Looping When Installing the
Drainage Layer Under the Insulation*
Ballast or
onvective Loop
C
Drain
Planting Layer
Filter Fabric
STYROFOAM™ Brand
Foam Insulation
Preformed
Drainage Sheet
Root Barrier Membrane
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
Figure 5: Option 1 – Drainage Layer Consisting of 1" (25 mm)
Granular Layer*
lanting Layer
P
Filter Fabric
'' Pea Gravel
1
ilter Fabric
F
STYROFOAM™ Brand
Foam Insulation
Root Barrier Membrane
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
WHAT PR O DUC TS C A N
BE US E D TO CRE AT E A
DRA INA G E L AY ER?
A number of products can be easily
incorporated, depending on the
drainage requirements, budget and
other preferences. The main
categories of products include:
• 1" (25 mm) (min) layer of pea gravel,
free of fines, with a filter fabric
above and below the ballast
(Figure 5)
• 3/8" to 1/2" (12 mm to 12.7 mm)
dimpled, preformed plastic drainage
sheet. Where possible, specify a
product that minimizes contact
with the insulation (e.g., place
dimpled side down) (Figure 6)
• Any other product that provides
adequate drainage while providing
minimal direct contact on the
underlying insulation (Figure 7)
Figure 6: Option 2 – Drainage Layer Consisting of a Preformed
Plastic Drainage Sheet*
Planting Layer
Filter Fabric
Preformed Drainage Sheet
Filter Fabric
STYROFOAM™ Brand
Foam Insulation
Root Barrier Membrane
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
*Not to scale. For reference purposes only.
Page 3
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
igure 7: Option 3 – Drainage Layer Consisting of a Commercially
F
Available Mat and Filter*
Planting Layer
Filter Fabric
Drainage Layer
Filter Fabric
STYROFOAM™ Brand
Foam Insulation
oot Barrier Membrane
R
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
WHAT TYPE OF STYROFOAM
BRAND INSULATION SHOULD
BE SPECIFIED?
The insulation must be able to perform
long term under both sustained (dead
loads from plantings, planters, etc.)
and cyclic loading (live loads from
maintenance vehicles, foot traffic,
etc.). Because the design of each
vegetative roof is unique, it is important that the designers calculate
both the live and dead loads created
on the insulation layer. STYROFOAM
Brand Extruded Polystyrene Foam
™
™
Regardless of the type of insulation,
where more than one layer of insulation
is required, follow these guidelines:
• The bottom layer of insulation (the
layer directly on the root barrier)
must be at least 2" (50 mm) thick.
• The bottom layer must be the
thickest or, at minimum, equal
to the top layer (e.g., 3" [75 mm]
bottom and 3" [75 mm] top).
• Lay succeeding layers of insulation
unbonded or unadhered.
• Stagger or offset all joints from
those of the underlying layer.
Insulation is available in a range of
compressive strengths from 35-100
psi (240-690 kPa) to address the
specific design loading requirements
for each project.
For a vegetative roof PMR that is
exposed to limited pedestrian traffic
and minor landscape maintenance
using light power tools, typically
STYROFOAM
™
Brand ROOFMATE
™
Insulation or STYROFOAM™Brand
HIGHLOAD 40 Insulation may be
specified, depending on design loads
from the planting layer and other
dead loads. Where vehicular traffic
or large design loads are anticipated,
STYROFOAM
or STYROFOAM
100 Insulation may be required.
STYROFOAM
™
Brand HIGHLOAD 60
™
Brand HIGHLOAD
™
Brand PLAZAMATE
TA BL E 1: RE QU IRE D BA LL A ST AR OU ND P E RI ME TER S
AN D PEN ET RATI ONS
STYROFOAM™ THICKNESS, REQUIRED WEIGHT OF APPROXIMATE THICKNESS
IN (MM) STONE BALLAST, LB/FT2(KG/M2) OF BALLAST, IN (MM)
Up to 2 (50) 12 (60) 1-3/4 (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)
™
Insulation (U.S. only) is also available.
Note: These are guidelines only;
it is the responsibility of designers and/or engineers to calculate
and accommodate live and dead
loads in a vegetative roof PMR
design. If required, contact a Dow
representative for additional
information on the live and dead
load design limits for STYROFOAM
rand Extruded Polystyrene Foam
B
Insulation.
WHAT AR E T HE WEI GHT
REC OMM E NDATI ONS FOR
BAL L A ST AN D T HE
PLAN T ING L AYE R ?
When designing a vegetative roof
PMR, the stone ballast typically
specified in a PMR is effectively
replaced by the planting layer to
minimize any potential for flotation.
As detailed in Dow literature and
Tech Solutions 508.1 (Ballast Design
Guide for PMR Systems [U.S.]), the
minimum stone ballast requirement
of 10-12 lb/ft
replaced with a similar weight of a
dry and unsaturated planting layer,
with additional ballast required
around any penetration(s) and the
roof perimeter. Refer to Table 1 for
either weight or thickness of additional ballast, depending on the
thickness of insulation. For additional
literature, visit www.dowpmr.com
or call 1-866-583-BLUE (2583).
2
(50-60 kg/m2) can be
™
®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
*Not to scale. For reference purposes only.
Page 4
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
C A N THI S P MR TY P E QUA L IFY F O R LEE D C RED I TS?
A vegetative roof PMR can provide valuable credits when obtaining the
U.S. Green Building Council’s LEED** (Leadership in Energy and
Environmental Design) rating. Refer to Table 2 for examples of possible
redits.
c
For more details, refer to the “STYROFOAM
and Green Roof Assemblies” brochure (Form # 179-05082/178-00698)
at www.dowpmr.com.
For more information on LEED, refer to www.usgbc.org (U.S.) or
www.cagbc.org (Canada).
TA BL E 2: PO TE NTI AL LEED P OI NT S F OR GRE E N RO OF
SY S TE MS BA SE D ON LE ED REFE RE NCE G UI DE FO R
GR E EN BUIL DI NG DE SI GN A ND CO NS TRU CT ION 2 00 9
ED I TI ON
REDIT NUMBER CREDIT NAME NUMBER OF POINTS
C
SS Credit 5.1 Site Development, protect or 1
SS Credit 5.2 Site Development, maximize open space 1
SS Credit 6.1 Stormwater Design, quantity control 1
SS Credit 6.2 Stormwater Design, quality control 1
SS Credit 7.2 Heat Island Effect, roof 1
WE Credit 1 Water Efficient Landscaping 2-4
EA Prerequisite 2 Minimum Energy Performance Required
EA Credit 1 Optimize Energy Performance 1-19
MR Credit 3 Material Reuse 1-2
MR Credit 4 Recycled Content 1-2
MR Credit 5 Regional Materials, 10%/20% extracted, 1-2
EQ Credit 7.1 Thermal Comfort, design 1
ID Credit 1.1 100% green roof for exemplary performance 1
ID Credit 1.2 Green roof accounts for 40% of the project 1
ID Credit 1.3 Green Roof area doubles the requirements 1
restore habitat
(post consumer+1/2 preconsumer)
processed and manufactured regionally
of SS Credit 7.2
site area for SS Credit 5.1
of SS Credit 5.2 depending on local zoning
open space requirements.
™
Brand Insulation, LEED
WHAT P R ODU CTS CAN
BE USED IN MA IN TAINING
THI S P MR T Y PE?
Often chemicals are used in maintaining a vegetative roof PMR,
including fertilizers, pesticides and
herbicides. Because of the many
different components in the roof
assembly, it is recommended that
chemical compatibility be checked
or each component (e.g., filter
f
products, preformed drainage layers
and membranes). In general, for
STYROFOAM
Polystyrene Foam Insulation, always
use a solvent-free product. Contact
your Dow representative or call
1-866-583-BLUE (2583) for more
information.
™
Brand Extruded
www.dowpmr.com
Technical Information
1-866-583-BLUE (2583) (English)
1-800-363-6210 (French)
The information in this document is not intended to replace the need for design by appropriate professionals such as architects or engineers.
NOTICE: No freedom from infringement of any patent owned by Dow or others is to be inferred. Because use conditions and applicable laws may differ from one location to another and may change with time, Customer is
responsible for determining whether products and the information in this document are appropriate for Customer's use and for ensuring that Customer's workplace and disposal practices are in compliance with applicable laws
and other government enactments. The product shown in this literature may not be available for sale and/or available in all geographies where Dow is represented. The claims made may not have been approved for use in all
countries. Dow assumes no obligation or liability for the information in this document. References to “Dow” or the “Company” mean the Dow legal entity selling the products to Customer unless otherwise expressly noted. NO
WARRANTIES ARE GIVEN; ALL IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE ARE EXPRESSLY EXCLUDED.
STYROFOAM™ Brand Extruded Polystyrene Foam Insulation
CAUTION: This product is combustible. Protect from high heat sources. A protective barrier or thermal barrier may be required as specified in the appropriate building code. For more information, consult MSDS, call Dow at
1-866-583-BLUE (2583) or contact your local building inspector. In an emergency, call 1-989-636-4400 in the U.S. or 1-519-339-3711 in Canada.
WARNING: Rigid foam insulation does not constitute a working walkable surface or qualify as a fall protection product.
Building and/or construction practices unrelated to building materials could greatly affect moisture and the potential for mold formation. No material supplier including Dow can give assurance that mold will not develop in any
specific system.
Printed in U.S.A.
Sales Information
1-800-232-2436 (English)
1-800-565-1255 (French)
®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow Form No. 179-05268X-0713MCK
IN THE U.S.
THE DOW CHEMICAL COMPANY
200 Larkin
Midland, MI 48674
IN CANADA
DOW CHEMICAL CANADA ULC
450 – 1st St. SW . Suite 2100
Calgary, AB T2P 5H1
178-00590X-0713MCK
McKAY219304
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