[Scpg] More on Rooftop Gardens plus other ideas for using design to grow food in Urban Spaces

[Wesley Roe and Marjorie Lakin Erickson]

 From City Farmer out Vancouver BC Canada and Excellent Resource for idea 
to use in Urban Permaculture Check out their Website


3.3 Rooftop Gardens  http://www.cityfarmer.org/barrsUAvanc.html#4.1
Current Situation - A typical aerial photograph of Vancouver will reveal 
that the city has a vast amount of flat roof space which could be utilized 
as productive growing space in the form of urban gardens. (estimate usable 
roof space in central area alone) There are, of course, number of roof 
gardens in the city although they are seldom, if ever, designed for food 
growing. The lack of roof space probably represents the city's biggest 
waste of potential growing space.

"In some parts of Germany, new industrial buildings must have green roofs 
by law; in Swiss cities, regulations now require new construction to 
relocate the area of green space covered up by the building's footprint to 
the rooftop - and even existing buildings, some hundreds of years old, must 
convert 20% of their roof space to pasture! This has spawned a whole new 
industry which specializes in lightweight growing mediums, filter cloths, 
roofing membranes, plant stock, and how-to books and kits; nurseries, 
designers, consultants, and contractors have been forced to relearn and 
re-adjust in order to compete in the new market, with the result that they 
now have more and varied work."

Benefits - In theory just about any plant can be grown on a rooftop garden 
including small fruit trees. Rooftop gardens can take advantage of the heat 
output of a building which can extend the growing season by as much as 3 
weeks and it is common in winter for the soil of a rooftop garden to be 5 
to 10 degrees Celsius higher than soil in the surrounding landscape. This 
additional heat input makes it possible to grow palms, figs and vines in 
temperate areas. It also improves building insulation and reduces heating 
costs. The presence of vegetation on rooftops can improve the local 
micro-climate and reduces the heat-island effect. The roof acts like a 
sponge and the absorption of rainfall reduces the pressure on the 
storm-water and sewer system. Roof gardens can be places where residents, 
who would otherwise never meet, congregate for social activities and rally 
around the common interest of gardening. Soil can also extend the life of a 
flat roof by protecting the waterproof membrane although careful 
consideration has to be given to the materials used and construction 
methods used.

Considerations - There are a number of factors that need to be taken into 
account when deciding if an existing roof is adequate for installing a 
rooftop garden or designing a new building. These are:

the type of membrane used for waterproofing purposes. Roofing membranes are 
nowadays of high quality and tend to be far more durable than those of two 
decades ago. "If of suitable quality and laid as a three layer system, 
should prove capable of lasting 50-60 years for asphalt and 20 years for 
bitumen.

the load-bearing capacity of the roof - a conventional soil profile at a 
depth of one metre will impose the considerable load of 2 tonnes/m2. 
According to Brownlie "roofs of commercial buildings are generally built 
with the same load-bearing capacity as that of other floors in the building 
and may thus require little, if any, additional structural support for a 
roof garden. Roofs of residential buildings, however, have a relatively low 
load-bearing capacity". When planning a roof garden it should be noted that 
the load the garden will impose depends mainly on the thickness of soil but 
also whether any large trees or rainwater storage barrels will be used 
(large point loading) and whether any live loads in the form of heavy 
machinery or people will be present. Generally live loads can be expected 
to be around 1. 5 KN./m2 giving a total load of around 5KN/m2. Where weight 
is a serious problem that cannot be easily overcome, hydroponic systems can 
be used or we can make use of extremely light growing mediums. It is also 
possible to use the snow-load capacity of the roof which isn't needed 
during the growing season.

irrigation method and drainage - obviously an adequate means of watering 
the garden needs to be in place especially considering that the thinner 
soils and higher winds on a roof garden will facilitate rapid drying. This 
could be either a rainwater collection and storage system, could use 
municipally supplied water, or better still from a sustainability 
perspective, would be to re-use waste-water from the building.

wind protection - roof gardens need protection from the wind especially if 
they are on higher buildings. This is necessary to prevent rapid drying of 
the soil, trap warm air in the garden to facilitate growth and to prevent 
plant damage.

A number of rooftop gardens already exist in Vancouver but few seem to be 
used for growing any food. The ability to grow food producing crops in 
these spaces may well be impeded by the requirement that adequate 
vegetation is planted by the developer prior to completion.

Recommendations:

Conduct a study into the feasibility of rooftop gardens on existing 
residential and industrial buildings. This should examine the ecocomic 
expenditures and the structural adjustments necessary.

Encourage/require the inclusion of rooftop gardens on new flat-roofed 
residential developments, commercial buildings, and industrial building.

Allow flexibility in height restrictions and FSR for the purpose of rooftop 
greenhouses.

Provide advice and guidelines about how to develop a rooftop garden, 
capture and use rainwater, re-use grey-water on rooftops and grow food 
plants (i.e. useful species and cultivars that can tolerate shallow soil 
profiles)


Figure 3-3 Example of recent rooftop garden design (Not available here)
3.4 Vertical Gardens

Current Situation - A group of young people are looking into the 
possibility of growing vertical gardens in dense urban spaces - on walls 
and balconies. They have already experimented with hydroponic container 
gardens on Downtown rooftop spaces and are now examining designs for 
containers that they can build themselves from local timber rather than 
purchasing expensive, pre-manufactured containers. Their goal is to obtain 
a piece of land with property and use it to demonstrate the feasibility of 
urban food production and at the same time generating a viable business 
form the idea. The group have received enthusiastic support from a number 
of business people and community leaders. This type of approach is crucial 
for urban agriculture. Because space is limited in the city we need to 
devise ways of using vertical space more efficiently to produce food. Just 
as buildings get taller in areas of expensive land so too must food growing 
areas. As long as the requirements for sunlight, nutrients and access for 
harvesting can be met, plants can be stacked vertically to create greater 
yields from the same land area. Growing food on vertical walls, trellises, 
and in vertically stacked containers could be a significant contribution to 
food production if the techniques necessary can be acquired.

Recommendations:

Promote the work of the Living Wall Project as a good example of combining 
Community Economic Development with the principles of sustainability.

Consider the use of vertical (wall) space and solar access to these spaces 
when reviewing landscape proposals and building designs.

Figure 3-4 Vertical garden concept (Not available here)
3.5 Street Trees/Orchards

Current Situation - Vancouver Park's Board Street Tree Department is 
responsible for the planting and maintenance of the city's 1,400 km of 
streets with over 100, 000 street trees currently on them. These trees 
represent approximately 55% of potential planting sites in the city. Each 
year a further 4,000 street trees are planted, one third of which are 
replacements for trees that are lost to disease, old age, development or 
storm damage. There are a potential 90,000 sites for new trees in the city 
which represents an incredible opportunity for urban food production. 
Redbud, Crabapple, Cherry and Plum are all on the list of recommended 
street trees for Vancouver but generally the non-fruiting cultivars are 
used. There is the potential., if the will exists, to replace many existing 
non-fruiting trees with cultivars that could produce an abundance of food 
for bird, animal and human populations. The current street tree policy of 
not planting fruit-bearing trees however, means that this does not happen 
at present. The problem of mess is a real one and innovative approaches to 
stewardship by local residents are needed to ensure that pruning is 
undertaken correctly and harvesting is done at the right time. A block or 
neighbourhood group could negotiate a contract with the city whereby it 
would agree to manage the trees for a number of years. In return the group 
would derive the benefits of the fruit harvested from the trees including 
the right to sell any surplus not required by the group. At Village Homes 
in the City of Davis, California, the residents now produce and sell enough 
fruit from their street trees to be able to pay for the maintenance of 
their remaining public open space. Many people have expressed an interest 
in including street orchards on the Ridgeway Greenway currently under 
development. Some cities also grow fruit trees in their parks - Stockholm, 
Prague, and Bangalore grow up to 25% fruit trees in their urban parks.

Recommendations:

Adopt a policy of planting fruit-bearing trees where this is appropriate - 
on new sites and as trees need replacement.

Encourage the formation of neighbourhood stewardship groups who would take 
on the responsibility of pruning and harvesting in return for keeping the 
fruit.

Begin a policy of planting fruit trees in Parks.


3.6 Inside Buildings

Although most forms of urban agriculture require good solar exposure in 
order to promote photosynthesis, mushroom growing can happen inside 
buildings as long as the requirements for warmth and moisture are met. 
Herbs and salad crops can be grown in window sills or in hanging baskets. 
This type of production has the added benefit that plants purify the air in 
a building.