1 Green Roof/ Cool Roof Proposal Summary - Cool roofs and green roofs are proposed as possible roof options for the grocery store and the commercial building - For the commercial building, a cool roof with acrylic white paint coating is recommended. - For the grocery store, three roofing options have been proposed: 1. Cool roof for the full roof area 2. Half and half cool roof and green roof 3. Green roof for the full roof area - With option 1 of having a complete cool roof for the commercial building and the grocery store, energy reduction of 1.7% can be achieved in comparison to an untreated roof, with no installation/material cost due to the Pittsburgh Cool Roof initiative described later in the report. - With option 3 of installing a complete green roof over the grocery store, an energy reduction of 2.4% can be achieved in comparison to a standard untreated roof. Although installing a green roof costs approximately $15-$22 per square foot, the vegetables grown on this roof can bring in revenue to the store. - Another option to reduce the installation cost of a green roof would be to implement this as a student learning project where students can help in the plant installation and help reduce labor costs. Assumptions The rooftop assembly options could take advantage of any combination of white roof or green roof options. The plans below describe the three roofing options: Option 1: Cool Roof Figure 1: Option 1 - Cool roof for the full roof area; Option 2 – Half and half cool roof and green roof
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Green Roof/ Cool Roof Proposal - Carnegie Mellon Universityrachel-carson.arc.cmu.edu/file/student_greenroof.pdf · Green Roof/ Cool Roof Proposal Summary - Cool roofs and green roofs
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Green Roof/ Cool Roof Proposal
Summary
- Cool roofs and green roofs are proposed as possible roof options for the grocery store and the
commercial building
- For the commercial building, a cool roof with acrylic white paint coating is recommended.
- For the grocery store, three roofing options have been proposed:
1. Cool roof for the full roof area
2. Half and half cool roof and green roof
3. Green roof for the full roof area
- With option 1 of having a complete cool roof for the commercial building and the grocery store,
energy reduction of 1.7% can be achieved in comparison to an untreated roof, with no
installation/material cost due to the Pittsburgh Cool Roof initiative described later in the report.
- With option 3 of installing a complete green roof over the grocery store, an energy reduction of
2.4% can be achieved in comparison to a standard untreated roof. Although installing a green
roof costs approximately $15-$22 per square foot, the vegetables grown on this roof can bring
in revenue to the store.
- Another option to reduce the installation cost of a green roof would be to implement this as a
student learning project where students can help in the plant installation and help reduce labor
costs.
Assumptions
The rooftop assembly options could take advantage of any combination of white roof or green roof
options. The plans below describe the three roofing options:
Option 1: Cool Roof
Figure 1: Option 1 - Cool roof for the full roof area; Option 2 – Half and half cool roof and green roof
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Figure 2: Green roof for the full roof area
Figure 3: Recommended option 2 for roof design
We recommend option 2 for maximum rooftop production of edible plants for the grocery, while
maintaining easy roof access and drainage in the rear of the building. This also allows space for
additional planters of vegetables if desired, with green walls to the rear of the building near the lift
access.
Roofing background information:
1. Cool roofs
Conventional roofs are typically dark and retain sunlight as heat. When the temperature rises, these
dark roofs absorb heat, which increases roof and building temperatures, building cooling costs, and local
temperatures in urban settings because of the urban heat island effect. These effects can be reduced by
painting roofs with a white coating, which reflect the suns heat instead of absorbing it.
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Advantages of cool roofs:
- Cool roofs reduces cooling costs
- Cool roofs increases roof durability
- Cool roofs reduces greenhouse gas emissions and pollution by lowering the demand for energy
use
2. Green roofs
Types of Green roofs:
1. Extensive Green roofs: These roofs are generally very shallow in depth of soil or growing media
which is usually 3-6 inch although they can be even 1 inch in depth. Extensive roofs are primarily
used for their environmental benefits such as storm water management and insulating
properties. They do not require irrigation except during the initial growth period and require
little or no maintenance. They are usually not intended to be accessed directly for use as a
garden or open space, by paved walkways and seating areas.
The lack of consistent supplemental watering, shallow soil depth and exposure to intense and
desiccating sunlight and wind require vegetation capable of surviving these harsh, dry
conditions. Generally, plants used for this are known as succulents. Sedums are most often used
for these conditions. Maintenance required for extensive roofs is initial hand watering during
installations and establishments. Occasional weeding, fertilizing and spot repair is required.
2. Intensive roofs: These roofs systems have greater depth of soil or growing medium which allows
for greater diversity in size and type of vegetation. The growing medium is typically 6-8 inches
and can go upto 15 feet or more. Ideally, these green roofs have relatively flat roof surfaces (1-
1.5%) or mild roof slope percentage of 3%. Pathways, terraces, water fountains, ponds and
other architectural features result in beautiful and dramatic spaces that can often be accessed
by people.
Since intensive roofs have greater depth compared to extensive roofs, they are capable of
storing water for longer periods. For this reason, intensive roofs have additional layers such as
protection boards and water retention mats that are usually included in the design to prevent
the roof from any leakage. Due to the increased number of layers intensive roofs are expensive
and require higher maintenance.
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Figure 4: Types of vegetation for green roofs (Adapted from International Green Roof Association)
Special factors for green roof design
1. Load/weight requirements:
The load on a green roof can be of three forms-
- Dead load: actual weight of materials used to construct the roof
- Live load: weight added to the dead load as a result of use of space such as people moving on and off
the roof.
- Other loads: impact of winds, snow or seismic action.
Therefore, the design of a green roof must allow for a safety factor. The total weight of all built
components as a result of all loads must be less than the maximum load permitted by codes. In most
constructions, the majority of the weight is supported at the parapet walls and at points directly over
the intersections of structural beams.
Material Load Requirements
Conventional Roof 7-10 psf
Drainage Layer (Saturated) 2-3 psf
Soil Media (Saturated) 60-95 lb/ft3
Plants 2-3 psf
2. Leak detection:
One of the important steps in the construction of a green roof is to perform the leak detection test.
Methods used to perform the leak detection test are:
- Flood test: Upon completion of the waterproofing layer, verifying water tightness can be accomplished
by flooding the roof to a certain depth. With thermoplastic non-adhered singly ply assemblies, cuts are
made at low points following the flooding to determine if moisture has entered below the membrane
during the flood test. This test can be very time consuming and does not give the exact locations of the
leaks.
- Electric field vector mapping (EFVM): This method involves the installation of waterproofing over a
conductive deck, such as steel or re-inforced concrete. Points of water entry through the membrane
appear as electrical grounds on the surface and can be mapped manually using a voltmeter and quickly
isolated.
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Considerations for Sustainability
1. Roof Insulation
Cool roof
For all assemblies, a high performance insulation system will be employed.
Figure 5: Recommended Roof section with insulation
The roof assemblies can be modified to include 3” of polyisocyanurate insulation (R-19 continuous)
placed above roof deck and 3” of ccSPF (R-19) on the underside of the roof deck after it has been
repaired to create a total roof assembly of R-38. White TPO membrane or Acrymax material can be
applied over the polyisocyanurate insulation to provide a reflective, “cool-roof” rated weather tight
assembly.
Assembly with Green Roof
The same insulation method will be used for semi-intensive
green roof, with an addition of the items above the insulation:
• Drainage medium/root barrier
• Growing medium (6-8in)
o soil in planting areas
o mulch in pathways
• Vegetation
2. Material selection and its environmental impacts
With the advancement in green roof technology, the products used for green roof construction are eco-
friendly products which have zero environmental impacts.
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Recommendations for green roof materials:
1. Growing media: Rooflite intensive certified growing media
(http://www.rooflitesoil.com/rooftop-farming)
2. Drainage System: Rooflite drain
Recommendations for cool roof coatings:
1. Field Applied Acrylic coating by Acrymax Technology – Bright white
(http://www.acrymax.com/roof-coatings.html)
2. Field applied Acrylic coating by Acrylabs – Bright white