Dow Green Roof - Manual (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.
W H AT P R O D U C T S C A N
B E U S E D T O C R E AT E A
D R A I N A G E L AY E R ?
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*
Filter Fabric
Preformed Drainage Sheet
Filter Fabric
STYROFOAM™ Brand
Foam Insulation
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
Planting Layer
Root Barrier Membrane
Convective Loop
Drain
Ballast or
Planting Layer
Filter Fabric
STYROFOAM™ Brand
Foam Insulation
Preformed
Drainage Sheet
Root Barrier Membrane
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
Figure 4: Potential for Convective Looping When Installing the
Drainage Layer Under the Insulation*
Filter Fabric
1'' Pea Gravel
Filter Fabric
STYROFOAM™ Brand
Foam Insulation
Fully Adhered
Waterproofing Membrane
Structural Concrete Deck
Figure 5: Option 1 – Drainage Layer Consisting of 1" (25 mm)
Granular Layer*
Planting Layer
Root Barrier Membrane
®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow
*Not to scale. For reference purposes only.
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.