A Roadway to Success
Permeable pavement is installed on
a different base than asphalt or concrete.
Rather than gravel, clean crushed stone
is used and must be 4-12 inches deep depending on the application and required
strength, notes Dave Ouwinga, president
of the manufacturer Porous Pave.
The good news is that you won’t typically replace an entire parking lot with
a permeable surface. It can be best for
areas with only light traffic or in strips,
As there can be a cost premium for
these paving alternatives, savings are
more readily achieved with new construction because they replace more
conventional stormwater management
features such as retention ponds and
Porous materials can be used in any
climate type. They may also be able to
withstand freeze/thaw cycles better than
conventional surfaces, says Ouwinga.
Properties that experience snowfall
should stay away from sanding as fine
grains can clog the pavement, he adds.
Regular snow blowing and salting won’t
Depending on the manufacturer’s recommendations, some surfacing products
“require regular cleaning with a vacuum
sweeping machine to keep the porous
nature of the paving functional,” notes
Stacey Hanley, a designer with OPN
Architects. Some of the void space will
inevitably be filled over time, but even a
reduced capacity will manage stormwater far better than conventional pavement, she adds.
Beyond reducing stormwater fees,
permeable pavement can benefit
facilities working toward green building
certification, says Ouwinga. Both LEED
and Green Globes offer credits for this
strategy. Porous surfaces can also help a
project achieve net-zero water under the
Living Building Challenge, which requires
that all stormwater is managed on-site.
Because this green feature may go
unnoticed, call attention to it with interpretive signage, Hanley recommends.
Not only can you market your building’s
sustainability, but you can help teach occupants and guests about the benefits of
Redirect your budget and runoff with
permeable pavement rather than idly
watching stormwater fees go down the
Jennie Morton jennie.morton@buildings.
com is senior editor of BUILDINGS.
continued from page 17
The Cedar Rapids Public Library in Iowa is a textbook example of how pervious pavement can work in concert
with other stormwater management features.
Replacing an older building that was destroyed by a flood,
OPN Architects wanted the new municipal facility to set a good
example of how to manage rainwater. The downtown library is
located only a few blocks away from the Cedar River, a watershed that is sensitive to runoff.
“The project wanted to do what it could to limit the amount
of rainwater flowing into the city storm system by retaining as
much on-site as possible. The more we can limit peak stormwater flow, the less infrastructure costs the city will incur and peak
flood crests in the future will be lower,” explains Matthew Stew-
PUBLIC LIBRARY USES PERMEABLE PAVEMENT FOR FLOOD MITIGATION
art, an architect and project manager for OPN. “This prompted
the use of pervious pavement, underground detention basins,
irrigation storage tanks, and a green roof.”
This systems approach to stormwater management starts
with the vegetated roof, which collects rainwater in cisterns for
irrigation, says Stacey Hanley, a designer with OPN. Beneath
the parking lot are underground stormwater detention cham-
bers with a 5,400-cubic-foot capacity. Overflow from the roof
is directed to these chambers via a drain.
Pervious pavement is used over parking stalls while con-
ventional pavement is used for the driving area. A structural
bed of crushed rock below “is tied into a granular backfill that
surrounds the stormwater collection chambers. Runoff stored
in the chambers and adjacent rock is able to
infiltrate into the ground during small storms
through a separate header row of vertical
chambers,” Stewart explains.
A plaza on the opposite side of the building
is constructed with pervious pavers, notes
Hanley. Subdrains are connected to the tree
pits at the site’s edge, ensuring rainwater can
reach their root system for optimal health. The
total site is 43% pervious between the land-
scaped areas, green roof, and paving.
Collectively, these stormwater strate-
gies are designed to retain 90% of normal
annual rainfall and 100% of all storm events
up to 1 inch in a 24-hour period. They also
helped the library earned LEED Platinum,
with points under SS Credit 6. 1, Stormwater
Design – Quantity Control and SS Credit 6. 2 –
Quality Control. EDK