[GBlist] low tech green roof?

["Richard Nelson" <ricknelson@videotron.ca>]

Hi Alan,

I agree with low-tech, but I prefer the combination of
high-science/low-tech - which is not a revival of traditional green roof
practices from pioneer days - but a modern implementation that integrates
the production of living plants into solar roof design. I have proposed such
a building integrated approach in the solaroofgarden concept.

This is a lightweight weatherproof roof system. It is suited to wide-span
"superstructures" that actually span over the top floor level (think of this
as the "conventional" opaque roof cover) of interior buildings, as well as
courtyards, atria, pedestrian malls and other common spaces between
buildings. It is a very suitable approach to multi-residence developments
where greater value will be added to roof gardens and terraces and common
spaces because they are sheltered for year around, all weather use. The
solaroofgarden becomes the roof level of the building. The existing roofs of
buildings that are enclosed become top floor levels and can be developed as
climate controlled living/garden spaces with the outdoors/indoors feel. This
is like putting a greenhouse shell over the conventional roof. But the
design is advanced as compared to greenhouse concepts.

There are two versions of the solaroofgarden - one for the "south" (tropical
& subtropical) and one for the "north" (cold winter seasons & snow). At the
website below you can see a description of both. For the DC Region you could
consider going with the south version. The south-design has a two layer roof
envelope that is carried by a lightweight, wide-span array of Open Web
Joists, or Parallel Chord Trusses. These trusses are placed at 10' on center
(other spacing is possible) and can span 30 to 60 feet or more @ ten foot on
center spacing. The trusses carry an inner roof layer that is a translucent
weatherproof architectural fabric. The outer layer of this roof envelope is
a light-gauge welded-wire mesh. Low-tech/high-science plant growing
methods - generally known as "hydroponic" systems - are used to grow
ornamental or food crops (in season) above the roof fabric layer. These vine
type plants spread their leaf canopy over the mesh support and the
developing fruit hangs through the mesh and can be picked from below. The
truss construction allows a person to ride on a rolling platform along the
truss (it is a 4 foot deep space) between the mesh and the fabric.
Additionally, one can similarly travel over the top of the roof on rolling
platforms that travel on the top chord of the trusses on walking on the wire
mesh roof itself (conventional code requirements pose no problem).

Is this strange living roof worth while? Yes! Absolutely! First of all, it
is low cost - a galvanized steel framing kit will cost less than a dollar
per square foot. The fabric roof cover adds about half a dollar. Second, it
is a great modular, pre-engineered, pre-fabricated, mass-production roof
system. The bolted construction is foolproof and is a great DIY
(DoItYourself) project - or, for builders - there is the advantage of lower
cost unskilled labor (where union & trade regulation permits). Certainly for
the tropics and subtropics of the developing world this is a cost-effective
roof. Lastly, the capital and operating cost of buildings under the
structure (which are in a climate-controlled space) are greatly reduced.

The hydroponic systems will cost another dollar per square foot - but, what
a payback! You can produce some ten pounds of fruit per square foot per year
on your rooftop! The hydroponic irrigation systems assure the best quantity
and quality (and you can use organic nutrients and eliminate chemicals) that
will fetch the highest market price. Local production = minimum
transportation cost. Why use heavy, old-fashioned, soil based (we are
talking very heavy) roof gardens? The building beneath these traditional
systems is similar to an "underground" structure. On the other hand, the
growing channels of the hydroponic solaroofgarden only occupy 10% of the
roof surface. This provides the opaque covered "root growth zone" that
protects the sensitive roots from the sunlight. The rest of the 90% of the
roof area is open to the translucent roof fabric, which lets daylight
through to the sheltered space below (top stories of buildings and ground
level spaces that are enclosed by the solaroofgarden superstructure). On the
top-floor of the buildings and ground level space you can grow more plants
if you like. Rather than feeling that you are "underground" you feel like
you are sheltered under a leaf canopy - just as the tree leaf canopy of the
forest shades the under-story plants. Now the rooftop crop can be selected
to give a dense or a light shade canopy. Because the fabric roof cover is
transparent (and is shaded by the leaf canopy overtop) this waterproof cover
will not get "hot in the sun". It is not only the shading but the fact that
the top side of the cover is normally wet due to the intermittent irrigation
of the root growth zone" growing channels. The drain down "gravity" water
that will not stay on the roots will flow back over the roof fabric to the
irrigation water reservoir. Rainwater will also drain off the roof fabric to
the storage reservoir. There are no toxic material exposures or any
contamination of this "water working" (meaning of the term "Hydroponic")
system.

The last word is - if you want to grow sod on your roof you will spend allot
and you can keep a goat - but if you want to grow food you can pay off the
solaroofgarden in less than one year. You will conserve water, obtain a good
use of daylighting and own a roof that will remain at 60F to 70F through the
sunny mid-day, even in the tropics!. This concept is coupled with using
water cooled roof systems and district cooling resources like the DOW and
COW technology (more great low-tech/high-science knowhow - see the "energy
solutions" navigation link at our website below) that together make up the
BlueGreen revolution.

Together we can BUILD a sustainable future.

Richard Nelson
www.solaroofgarden.com
rick@solaroofgarden.com


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