I TI
Roof Rainwater Harvesting
Questions
nswered
y Anne K Goedken
Previous generations collected water in bar rels and used the contents for watering gar
ing a project
dens and plants. Today, water is being har vested and reused on a much larger scale to save money, earn LEED points, and tell a
th thee safe safest st wat ater er poss possib ible le..
stor story y abou aboutt sust sustai ain n abil abilit ity y in acti action on..
best suited for new construction.
ultraviolet treatment
ing, but according
Just as it does in any building, the roof serves as the collec
and
What is it used for? The primary application
How do does es it work? rk?
Filtering
of the rainwater are also needed to produce
for rainwater
is usually toilet flush
to Yudelson, it varies depending
on the loca
tion and type of building. Because of the ratio of roof area to restrooms, low- to mid-rise commercial buildings are the best
tion point for rainwater. A roof washer is installed to remove dirt, rt, lea eave vess, and debris ris from rom the the roof perio eriod dica callly ly,, ensurin ring clean lean
candidates
water. Gutters or downspouts still carry the water away, but instead of depositing water to the ground, the gutters carry the rainwater to a storage tank. All we re really doing is taking
building, which would have a large surface area and few toilets to flush. In high-rise buildings, rainwater can also be used for
[the roofl system
(which is in place and designed
into every
building), intercepting the run-off, and diverting it to a storage tan ank k, explain lainss Jer errry Yudel elsson, sustain ainab abiility ity direct recto or at Inter ter face Engineering Inc. in Portland, OR. Yudelson is the author of Dev Develop elopin ing g Gr Gree een: n: Stra Strate tegi giees for for Suc Success cess
a primer on green
mark market etin ing g fo forr de deve velo lope pers rs.. The storage tanks are typically located underground ing garages or basements precast
concrete,
in park
and made of epoxy steel, fiber glass,
polyethylene,
or poured-in-place
concrete.
for a roof rainwater
system.
rai rainwater ater,, up to 80 perc rceent of rai ain nfa falll can be collected and used in a build ing. You re just not going to get it all, all, Y Yud udel elso son n emph emphas asiz izes es.. Tota Totall co col l lection
is impossible
due to negli
to collect 600 gallons of water per 1,000 square feet of roof area. The delivery and treatment system requires installation of a
Where does it work? Th The very first thing you try to do as you integrate a building design is [ask], What s nature me for for fre free? The Northwest
........... .......... RAIN
..........
of
Although it s difficult to say how much water can be saved by reusing
Tank size is based on a mathematical equation, keeping this guideline in mind: For every inch of annual rainfall, it s possible
system em,, typi ypically ally mak akiing roo roof rain rainw water harv rves estt-
would be a
required fire-suppression storage by simply up s iizzing the tank, in incu curr rrin ing g mini minima mall extr extraa cost costs. s.
gible rainfall when the water pools and evaporates on the roof or when ov over erfl flow ow occu occurs rs duri during ng heav heavy y rain rain..
dual al-p -pllumbing ing
Irrigation
more suitable use for rainwater collected on a warehouse-type
for rainwater
going to give
Yudel elsson ex exp plai ain ns. is an ideal climate collection
because
Some mun Some munici icipal paliti ities es require buildings to label any source of ra rain inwa wate terr .
it
comes in fairly regularly and fairly gently. H Ho owever, many other areas of the country also receive enough rainwater to make harvesting it an option. According to (www.weather.com). Orlando, FL, receives an average of 48 inches of rain per year; 37 inches of precipitation falls yearly in
COOLING
•
BLACKWATER
PRODUCED
•
POTABLE
•
NO N P PO OTABLE
•
R AI NW AT ER
WATER
SUPPLY
WATER SUPPL Y
Dallas. Northerly cities like Chicago (38 inches per year) and New York City (46 inches per year) receive enough rainfall to make a harvesting system possible, but frozen precipitation needs to be taken into account. In extremely dry climates, such as Phoenix, where rainfall is less than 10 inches per year, rain
TOWER
water harves rvestting
CU.P.
is not as pra ract ctic ical al..
How much does it cost? One dollar per gallon of the tank s storage capacity is a simple cost cost esti estima mate te for for inco incorp rpor orat atin ing g a roof roof ra rain inw wat ater er-h -har arve vest stin ing g syst system em into a new-construction project. The bulk of the expense comes from the storage tank and the dual-plumbing ha hand ndle le th thee wate water. r.
system needed to co conti ntinu nued ed pa page ge
24
BUILD ILD IIN NGS
Augu sstt 2006
www. bu build ild in ings. co com
6
.••• .••• 11 ::11 11
Although rainwater systems are considered more of a LEED po poin intt-ge gett tter er th than an an econo economi micc building measure at this point, there are some cases when they make financial sense. Yudelson
RAINWATER
0.5
G ROU NDWA TER
AS NEEDED
SUMMER
~
WATER
FROM
J
CITY
•••
points to Portland as an exam ple of one city whe herre stormwater hook-up fees are climbing dra matically. If you can avoid the hook-up fee, that can often pay for for the the en enti tire re syst system em,, he st stat ates es.. When looking at sustainable meas measur ures es,, Yu Yude dels lson on reco recomm mmen ends ds that building owners ask them selves, What s for free here that I can harvest, that s going to be there forever, and that I m not going to have to pay for over and overr agai ove again? n?
R EC lA IM ED
MGY
IRRIGATION
COOLING T OW OW E ER R
F IX IXTU R RE E
MA AK KE EU UP
US SE E
P A R RK K BL LO OC CK KS 1. 2 MGY
1. 7 MGY
1. 5 MGY
FUTURE
BIO-REACTO BIO-RE ACTOR R
SEWAGE SEWAGE
TREATMEN TREATMENT T
5 MGY
MGY
=
MIL MIL LIO LION N
GA GAL L LON LONS S //Y YE EAR AR
SA AN N IT IT AR AR Y
What are the benefits? Wha The most obvious benefit of a rainwater system is LEED certification; up to 7 points can be garnered by installing a system in a new building. The process itself is inherently green - reusing rainwater reduces the stress on groundwater supp supplly an and d help helpss cu curb rb run un--off off and and er eros osio ion. n. Yudel udelso son n says says that that one of the most important benefits is using the process as a
a
SE EW WE ER R
MGY
B IO IO- S SW W Al Al E E..
W ET ET llA AN DS DS
TREATMENT
DISPOSAL
te teac achi hing ng op oppo port rtun uniity for bu buiildin lding g occu occupa pant ntss an and d st stak akeh ehol old d ers. You can talk about a rainwater system, you can di diaagram it, [and] you can show it to people; you can even have cut outs where people see the rain. It s one of the [most] easily grasped sys ysttems that you can put in a buildi din ng [and have] the aver averag agee pers person on under underst stan and. d. .B. nne
K
Goedken
[email protected]
pr prod oduc ucts ts ed edit itor or at Bu Buil ildi ding ngss maga magazi zine ne
is new