Mpls library-greenroof

Minneapolis Central Library Green Roof Tour
Minneapolis Central Library Green Roof

Green Roof Technology
and
L. Peter MacDonagh, R.L.A.
Adj. Asst. Professor, University of Minnesota
The Kestrel Design Group, Inc.
by
Loren Abraham, A.I.A.
Adj. Asst. Professor, University of Minnesota
Abraham + Associates Architects
1313 5th St. SE, Ste 334
Minneapolis, MN 55414
labraham@abrahamarchitects.com

WHY green roofs?
 7 Key Water Quality Problems and BMPs
 Roof longevity and energy savings
 LEED and B3 Standards
WHAT is green roof technology (GRT)?
 Components of green roof systems.
 Plant selection and research
 Irrigation and management
HOW are green roofs installed?
 Photo History of Minneapolis Library Green Roof
 Step by Step Process
The finished product
 The first year
 The second year
WHO designed and installed the Green Roof?
 Architects and Landscape Architects
 Contractors
Outline

Why Green Roofs?

Why Green Roofs?
1. Excess Peak Runoff Volume
2. Floatables
3. Suspended Solids
4. Bacteria
5. Phosphorus
6. Chlorides
7. Nitrogen
7 Key Water Quality Issues
Green Roofs help prevent

Problems Associated with Impervious Surface
Why Green Roofs?
20%
shallow
infiltration
15% deep
infiltration
10%
shallow
infiltration
25%
shallow
infiltration
21% shallow
infiltration
5% deep
infiltration
25% deep
infiltration
21% deep
infiltration
40% evapotranspiritation 38% evapotranspiritation
35% evapotranspiritation 30% evapotranspiritation
Natural Ground Cover 10-20% Impervious
75%-100% Impervious35-50% Impervious
10%
runoff
20%
runoff
30%
runoff
55%
runoff
“The number one cause
of water pollution is
paving over earth.”
Environmental
Protection Agency
Relationship Between Impervious
Cover and Surface Runoff (adapted
from FISRWG 1998 In Low Impact
Development Strategies 1999)
Source: Minnesota Urban Small Sites BMP Manual

Problems Associated with Impervious Surface
Why Green Roofs?
Large storm
Higher base flow
Small storm
Streamflowrate
Higher and more rapid peak
discharge
More runoff volume
Lower and loss rapid
peak
Gradual recession
Time
Predevelopment
Postdevelopment
Adapted From: Protecting Water Quality in Urban Areas. Best management Practices for Dealing with
Storm Water Runoff from Urban and Suburban Developing Areas of Minnesota. MPCA 2000.

Water Resources Benefits of GRT
Why Green Roofs?
Water Resources Focus:
 Provides sustainable stormwater
management—
absorbs, slows, cleans and
moderates temperature of runoff
 Adds wildlife habitat
Other Benefits:
 Lowers energy costs for heating and
cooling building
 Improves urban air quality-reduces
dust and smog levels
 Extends roof life
 Lessens urban heat island effect
 Provides sound insulation
 Improves aesthetics which
produces psychological benefits
Effect of green roof thickness on
stormwater absorption
Surface % Stormwater
Retained
1‖ moss/sedum
layer + 2‖ gravel
58%
2.5‖ sedum/grass
layer
67%
4‖ grass +
herbaceous
vegetation
71%
Green roofs are most
beneficial for volume and
rate control in areas with
precipitation patterns like
those found in Minneapolis:
low annual precipitation
short, high intensity storms
(i.e. cloudbursts) that occur
during dry weather periods

Water Resources Benefits of GRT
Why Green Roofs?
Building on
this
research, the
Twin Cities
Metro is one of
the BEST
locations in
this country
for extensive
GRT
Source: Patrick Graham, Marian Kim, Evaluating the Stormwater Management Benefits of
Green Roofs Through Water Balance Modeling, 2003.

What is Green Roof Technology?
Type 1: EXTENSIVE
 Lower weight: (17-30lbs/sf saturated)
_often additional structural support is not
required.
 Lower capital cost: $15-$30 per s.f.
Depends on area, steepness, soil depth
 Relatively Shallow Depth: 1" to 5―
 Substrate: lightweight
 Low maintenance: inspection 1-2 times/year
 Supply of water and nutrients mainly by
natural processes
 Native, natural plant selection (plants
adapted to drought and heat and wind)
 Access: not designed for public use but can
be accessed via walkways or for routine
maintenance

Type 2: INTENSIVE
 Increased weight: 30-100 lb per s.f.
 Increased capital cost: $30+ per s.f.
 Depth: usually 12‖ or more
 Substrate: higher amount of organic material
in layers >100 mm
 Increased maintenance: depends on plant
selection, e.g., mowing, fertilizing, watering,
weeding
 Intense planting: manicured
landscapes, ornamental
lawns, flowers, shrubs, trees, even organic
gardening
 Access: can be used as public park or
building amenity
 …and can include ponds, play
areas, decks, patios, even a miniature golf
course, etc.
 Often found over underground garages.

Typical Native Soil Profile vs. Typical Green Roof Soil Profile
(Source: Zinco)
1. Components
Example 2:
Xeroflor Prairie
System
Example of Typical GR Drainage System:
Wet weight of system = 4.7 lb/ft2
Wet weight of 6‖ pea gravel = 60 lb/ft2
Source: Zinco Brochure
Drainage element:
 Recycled polyethylene
 Water troughs on top side hold
0.1 gallons water/s.f.
 Retained water is released into
soil by evaporation or root
uptake.
 Holes in tops of troughs allow for
air circulation, evaporation, and
ventilation of soil and roots.
Moisture Retention Mat:
 Recycled polypropylene fibers
 Retains 0.12 gallons water per
square foot to promote root
growth

 Tailor to structural loading
capacity of building
 pH, nutrients, porosity and
water permeability needed
by plants
 Deep enough to protect
plants from frost and
compaction, and have a
stable structure for root
anchorage.
 Resistant to wind and
water erosion
 Using pure native
garden soil often
results in
problems when
the soil
degenerates
from compaction
and acidification.

 Perennial or self-
seeding plants
 Shallow, fibrous mat
roots
 Require no
maintenance
 Survive in shallow soil
 Provide no ambient
heat
 Endure drought
 High winds
 Extreme sun exposure
3. Plants for EXTENSIVE Green Roofs

Ruellia humilis
Wild Petunia
Source: http://www.prairienursery.com
Tradescantia occidentalis
Western Spiderwort
Source: http://www.prairienursery.com
Minnesota Plants Adapted to Green Roof Conditions

European Green Roof Species
Sedum floriferum
―Weinstephaner’s Gold‖
Sedum album
―Coral Carpet‖
Sedum ellacombianum
Source: Intrinsic Perennials

4. Irrigation
 Irrigation is primarily for
Plant Establishment &
Building Cooling
 Temporary Establishment of
Plants is 2-3 Seasons
(Spring, Summer, Fall)
 Offers Peak Load Cooling
on Flat Roofs in Summer
(e.g., 1 story flat roofs)

4. Irrigation for Plant Establishment
 Plants need at minimum
1‖ of water per week
June, July, August
 Pan Evaporation is 2‖
per week
June, July, August
(MSP)
 ¾‖ pipe = 2 to 3 GPM; 1‖
pipe = 5 to GPM

Project Description
Minneapolis Central Library Details
 GR installed summer
2005.
 3 roofs on two levels:
 5th floor roof
 Two on 2nd floor
 Rainwater is collected
and stored in two
7,500 gal. cisterns for
irrigation.
 All are extensive roofs
that can be seen from
inside the library and
surrounding buildings.
 Planting design
includes 18 European
and 39 native species.

Photo History
Photos
 Roofing Installation
 Flood Test
 Insulation
 Root Barrier
 Drainage Membrane
 Irrigation Systems
 Growing Medium
 Erosion Blanket
 Plants - Plugs
 Plants - Cuttings
 Finished Roof
Minneapolis Central Library

Photo History
Roofing Installation
 Roofing Membrane
 Flood Test
 Insulation
 Edge Tiles
 Green Roof Edging

Photo History
Green Roof Layers
 Root Barrier
 Drainage Membrane
 Irrigation Systems
 Growing Medium
 Erosion Blanket
 Plants

Photo History
Irrigation Systems
 Drip System
 18‖ Grid
 Supported mid-
height
 Emitters 18‖ spacing
 Zoned valve boxes
 Moisture sensor
control
 Spray (Pop-up)
 Used on 2nd Floor
roof – Facing South
due to reflected
sunlight intensity
 18‖ high
 Heat sensor control

Photo History
More Green Roof
Layers
 Growing Medium
 Erosion Blanket

Photo History
Planting
 Plants – Plugs
 Sedums
 Native plants
 Plants - Cuttings

Photo History
Finished Roof
 First Year (2005)
 Second Year (2006)
 Third Year (2007)

Photo History
Finished Roof
 Third Year (2007)

Building Architects
 Pelli Associates, Design Architect
 Architectural Alliance, Architect of Record
Green Roof Architect
 Abraham + Associates Architects
 Loren Abraham AIA, LEED AP, Lead Architect
Landscape Architects
 Kestrel Design Group, Inc.
 L. Peter MacDonagh, R.L.A., Lead Landscape Architect
 Nathalie Hallyn, Project Manager
Roofing Consultant
 Ambe Ltd.
 Rick Grobovsky, Roofing Consultant
Construction Manager
 Mortenson Construction
Roofing Contractor
 Rosenquist Constrution
Irrigation Contractor
 Green Acres
 John Fiegle, Project Manager
Planting Contractor
 Aloha Landscaping
 John Darsow, Project Manager
Project Team

Mpls library-greenroof

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