Water

Greenroofs

Resilience

Independence

Gulf Coast Green – Houston – May 2012

to save energy

to sustain our and our children’s lifestyles

to inflict less damage on our environment

to rid our inhabited realm of chemicals, additives and

supplements that harm

to improve our living environments

to conserve the most valuable asset on the planet –

water

Better known as – save the planet!

Evaporation – accounts for the movement of water to

the air from sources such as the soil, canopy

interception and water bodies.

Transpiration – accounts for the movement of water

within a plant and the subsequent loss of water as vapor

through stomata in its leaves.

Evapotranspiration – a key element or part of the water

cycle – describes the sum of evaporation and plant

transpiration from the Earth’s land surface to the

atmosphere.

Acre-foot – a unit of measure denoting one acre of

ground (a chain x a furlong – 60’ x 660’) x one foot

depth of water. 325,851.4 gallons. Historically

visualized as the amount of water a suburban family

household will use in a year.

1 kWh = 3413 btu

Evaporation – 1 gm of H2O = 580 calories

1 btu = 252 calories – 1 ton = 72,576,000 calories

1 gallon = 3783 grams

1 cf = 7.4805 gallons

75% of the surface is water

25% of the surface is land

Of that 25%, 50% is habitable

Of that 50%, 50% is arable

98% of the water is in the oceans

2% of the water is fresh but 1.6% is locked in polar ice caps and glaciers and .36% is underground in aquifers and wells

0.036% is actually found in rivers and lakes

Water is in a constant cycle – we never lose it

Two (2%) percent of the surface of the earth is

comprised of cities

Fifty-three (53%) of the population of the Earth lives in

cities

Sidenote: thirty-five (35%) of those residents live in

slums with minimal or no services – e.g. no running

water, sewage conveyance or storm water controls

Five intensive green roofs constructed

Roughly 1.40 acres (.6 hectare)

Design/build approach

Anticipated - Energy Star and LEED certification

So far – three Platinum certifications

Goals

◦ Minimum 50% less energy usage

◦ Unique identity within the community

◦ Control long term costs

◦ Radically lessen impacts by and to water

Firstly

reduce stormwater run-off

improve water quality

decrease overall water use

reduce the heat island effect

conserve energy

reduce sound reflection

create wildlife habitat

improve the aesthetics of the roof

Long term investment

Long term maintenance and operations are crucial

components dwarfing the initial cost of the facility

Long term utility requirements and energy needs

present a serious case for understanding and pursuing

sustainable design and building

Greatest water impact opportunities

First, third and fourth buildings – composite framing

Second building – pre-engineered steel frame + bar joists with concrete deck

Fifth building – steel frame + bar joists with concrete deck

Composite system – reinforced concrete slab diaphragm with steel girders + shear connectors

Unanticipated benefit – 24 tons less steel at roof with composite system at roof

Our loads – 50 psf live load + 30 psf (saturated) soil mixture + 25 psf dead load (the structure)

All roofs - intensive

Average depth – 9 to 10 inches; maximum depth 12”

Repeated floor system at roof = minimal cost impact

Composite system inherently rigid

Intensive – less complicated wind resistance

Extensive – wind uplift issues; complicated anchorage

Intensive – more robust plantings

Extensive – smaller scale plantings

o 15,741 sf green roof (based on Bush rainfall rate)

o 8” soil depth results in run-off of 133,085 gallons

o 8” soil depth results in retention of 329,985 gallons

o 15,741 sf green roof (based on Hobby rainfall rate)

o 8” soil depth results in run-off of 182,355 gallons

o 8” soil depth results in retention of 360,035 gallons

o Bush retention equates to 44,113 cf = 1.013 ac-ft

o Hobby retention equates to 48,130 cf = 1.105 ac-ft

o These quantities never impact the storm system

Texas Water Development Board

Texas Manual on Rainwater Harvesting

Texas Rainwater Calculator, Version 2

Garden Roof Storm Water Run-off/Detention Estimator

Run-off and Irrigation worksheet

Innovative Water Technologies

Evaporative cooling off-setting solar radiation

based on month of June

Average direct solar radiation – 1443 btu/sf/day

Equates to 363,550 calories/sf/day

Equates to 626.81 grams/sf/day

Equates to 2607 gallons/day on total roof

Resultant required evaporation = 6.7477mm

Equivalent tons of ac avoided = 78.85

Power saved = 6655 kWh

Cost savings at $0.12/kWh = $798.60

Evaporative cooling based on average Eto

(inches/month) again using June (6.57”)

Equates to 0.219 inches/day

Equates to 2,149 gallons/day over entire roof

Equivalent tons of ac avoided = 65.001

Power saved = 5,486 kWh

Cost savings at $0.12/kWh = $658.34

Resultant kBtu/sf (of building/day) = 13.215

Average resultant kBtu/sf = 8.93

Resultant cost savings/sf = $0.11

Evapotranspiration data

ITC – Texas ET Network found at texaset.tamu.edu

Rainmaster.com – provides evapotranspiration data by

zip code

Roof top retention

Underground cistern approach

Above ground cistern approach

Side benefits – detention system and opportunity to

retain stormwater + reclaim

Capture condensate

Filter out/settle out suspended particles and phosphates

Absorb storm events

Hold 2.52 – 2 year storm events before discharge

Gulf Freeway cistern system holds 395,000 gallons

Gulf Freeway facility – 1.0127 acre-feet never leave

the site or enter the storm system thanks to the green

roof

Total site holds 2.2238 acre-feet (725,000 gallons)

before any impact on storm system

• Net Zero Water: One hundred percent of occupant’s

water use must come from captured precipitation or

closed loop water systems that account for downstream

ecosystem impacts and that are appropriately purified

without the use of chemicals.

Ecological Water Flow: One hundred percent of storm

water and building water discharge must be managed

onsite to feed the project’s internal water demands or

released onto adjacent sites for management through

acceptable natural time-scale surface flow, groundwater

recharge, agricultural use or adjacent building needs.

The gaps between our current building design and the

Living Building requirements include the processing of

water for potable use onsite for a true closed-loop

system and some potential minor additional capacity

during dry seasons.

Recreational rooftop garden – 20%

Productive rooftop garden – 7%

View onto a green roof – 4.5%

Adjacent properties – range of 2 to 7%

Source: Monetary Value of the Soft Benefits of Green

Roofs – Canadian Mortgage and Housing Corporation

Particulate matter removed from atmosphere – 1 square

meter (10.76 sf) absorbs .2kg/year (644#’s)

Oxygen production – 1.5 square meters (16.15 sf)

produces enough oxygen for 1 person per year. A

person uses 6 pounds of oxygen per day (975 people)

Sound attenuation – dependent upon roof assembly

reductions can range from 10 db to 40 db.