Green Roofs - Living Architecture Monitor - Fall 2016 - 24


PROFILES
Different studies have proven that
PV on a green roof has five per cent
to 15 per cent higher output put during hot seasons. (See Table 1.) More
large-scale study (over 20,000 sf),
would likely demonstrate even better
efficiency performance gains because
of even greater reductions in the ambient temperatures. Despite this initial
research, opponents of integration cite
that there isn't enough research, or
the data is based on projects that are
too small-scale. Meanwhile every kid
knows that standing on a parking lot in
summer is much hotter than standing
on a lawn in a park. Maybe these kids
wonder whether the costly search for
even more data might be much better
invested in just doing it.
Another reason is the hesitation of
unrestrained and open-minded collaboration between solar companies, green
roof professionals, architects, landscape
architects, and building owners. A Solar
Garden Roof (combing both technologies) can add more value to relevant
industries, if they are willing to work
collaboratively. Fully integrated systems
can be built on any type of waterproofing without effecting roofing warranties.When correctly engineered and
installed Solar Garden Roofs certainly
out-compete an extensive green roof
without PV or a PV roof without living
green. (See Table 2.)
As the green roof and solar roof
top industries continue to evolve, the
business case for the integration of
these technologies should help drive
the market to much greater use of roof
spaces across North America.
Jörg Breuning is the president of Green
Roof Service, LLC.
(1)
(2)
(3)
(4)
(5)
(6)

Assuming 5% higher output because
of cooler ambient temperatures
Racking system average costs
Includes fully integrated racking
system
Average costs in DC, non-union job,
no roofing company as middle man
Assuming Roofing is done beyond
common industry standards
Average max. temperature on 10
square foot, sunny summer day, air
temperature 85°F

LIVING ARCHITECTURE MONITOR / FALL 2016 / 24

TABLE 2:

COMPARISON OF REFLECTIVE, EXTENSIVE GREEN AND TWO TYPES OF SOLAR
GARDEN ROOF SYSTEMS FOR A GREEN ROOF IN WASHINGTON, DC
COURTESY J. BREUNING

REFLECTIVE
ROOF
(NO PV AND
NO GREEN)

EXTENSIVE
GREEN ROOF
5" DEPTH

SOLAR
ROOF 10°
(NO GREEN)

SOLAR
GARDEN
ROOF
15° ANGLE
5" DEPTH

SOLAR
GARDEN
ROOF 30°
ANGLE
5" DEPTH

MAX. AVERAGE WEIGHT PER
SQUARE FOOT

2 lb / sf

28 lb / sf

10 lb / sf

35 lb / sf

35 lb / sf

ANNUAL WATER RETENTION

0 gal.

14,700 gal.

0

14,700 gal.

14,700 gal.

WATER RETENTION OF STORM
EVENT

0

2" storm

0

Min. 2" storm

2" storm

AMOUNT OF SOLAR PANELS
(PREMIUM 330W)

0

0

270

252

180

PV ROWS (LONG SIDE OF
BUILDING FACING SOUTH)

0

0

15

7

10

SYSTEM
CHARACTERISTICS

PV ORIENTATION

No

No

Landscape

Portrait

Landscape

0.0 kW

0.0 kW

89.1 kW

83.1 kW

59.4 kW

SYSTEM LOSSES (HEAT, TILT,
SNOW, ETC.)

0%

0%

18.63%

14.11%(1)

14.11%(1)

ESTIMATED ANNUAL POWER
OUT FOR LOCATION

0.0 kWh

0.0 kWh

104,012 kWh

105,392 kWh

78,420 kWh

SAVING COOLING / HEATING
ENERGY BUILDING

2%

10%

0%

12%

12%

140°F

95°F

130°F

90°F

90°F

REDUCING HEAT ISLAND
EFFECT

No

Yes

No

Yes

Yes

RACKING SYSTEM REQUIRED

No

No

Yes

No

No

ROOFING SYSTEM EXPOSED
TO ENVIRONMENT

Yes

No

Yes

No

No

ROOFING SYSTEM PROTECTED
AGAINST IMPACT(5)

No

Yes

No

Yes

Yes

ELIGIBLE FOR STORMWATER
FEE REDUCTION

No

Yes

No

Yes

Yes

ELIGIBLE FOR GREEN ROOF
INCENTIVES

No

Yes

No

Yes

Yes

ELIGIBLE FOR SOLAR TAX
CREDIT (30%)

No

No

Yes

Yes

Yes

ELIGIBLE FOR SREC
IF AVAILABLE

No

No

Yes

Yes

Yes

HABITAT FOR PLANTS AND
INSECTS

No

Yes

No

Yes

Yes

MAINTENANCE REQUIRED

Yes

Yes

Yes

Yes

Yes

$14.00/sf

$18.00/sf

$5.00/sf(2)

$21.00/sf(3)

$22.00/sf(3)

$0

$0

$9.45

$8.82

$6.30

$140,000

$180,000

$144,500

$298,200

$283,000

$0

$150,000

$0

$150,000

$150,000

POWER OUTPUT SYSTEM

MAXIMUM SURFACE
TEMPERATURE(6)

ESTIMATED INSTALLED
COSTS W/O PV
PROJECT COSTS FOR PV
INSTALLED PER SF ROOF
ESTIMATED ENTIRE PROJECT
COSTS(4)
TYPICAL DC GREEN ROOF
INCENTIVE

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Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Fall 2016
