Sola Roof Garden

The Problem: Hot Roofs?

Throughout the Tropical Climates and in Hot Climates in general, both humid and arid, one of the most prevalent methods of residential roof construction is that of galvanized sheet metal, painted metal, clay tiles or fiberglass shingles applied over non-insulated wood frames. Light steel joist structures are typically covered with sheet metal roofs for commercial and industrial buildings. Another common roof construction is that of a steel reinforced concrete “slab-roof” which is often used for residential and commercial buildings.

All of these conventional types of roof construction suffer from excessive mid-day overheating due to the high solar radiation incident on their surface area. The larger the roof area, the greater is the difficulty in controlling the overheating of the building interior. The interior ceiling temperature will measure within a few degrees of the exterior roof temperature, often exceeding 80 degrees Celsius. The hot roof overheats the interior environment both by conductive and radiant heating. Furthermore, these opaque roof structures prevent the use of daylight within the building (unless the roof incorporates expensive skylight systems).

The Solution: Sola Roof Garden

I propose a new version of the Sola Roof system designed specifically for the tropics, which can overcome these problems and limitations. This version, called the Sola Roof Garden is a simplified Sola Roof that uses a single translucent or transparent covering, with the purpose of transmitting daylight within the structure. Additionally, this system provides a shade factor and cooling mechanism suitable for maintaining a comfortable environment for the human occupancy space beneath this shelter.

Unlike conventional roofs the Sola Roof Garden will not overheat, because its design incorporates three methods of cooling:

  1. The Top Grid? of this structure supports a Sola Net?, which carries the plant Leaf Canopy? that spreads over and covers the entire roof area;
  2. The Mid Grid? space is equipped with a water spray cooling system and plant root zone spray with nutrient solution (aeroponic growing); and,
  3. The Bottom Grid? of the structure supports a Sola Fabric?, which is weather proof cover that will not overheat due to its radiative transparency.

The single Sola Fabric? cover collects rainwater to a water reservoir used for conventional garden production at the Top Floor? and Ground Floor? spaces below as well as for the Roof Level? aeroponic Sola Roof Garden. The Sola Net? that covers the rooftop is strong enough to walk on and can easily support a crop heavily laden with fruit. The Sola Net? and Sola Fabric? components are both prefabricated and install easily on the prefabricated aluminum frame structure. The Sola Roof Net? supports, at the mid span, a continuous growing channel (an aeroponic root zone environment) for growing food and horticultural crops.

As these plants grow their Leaf Canopy? will spread out over the Sola Net? and shade the Sola Fabric? membrane below. Such a leaf canopy is self-cooling and provides the high shade factor that is ideal for protection from the intense midday sun of the tropics and subtropics. Standard roofs or shade materials used in standard roof construction are generally opaque and operate to block solar radiation and produce “shade”. However, the problem is that this solar radiation absorption, in equilibrium with the radiative emissivity will cause these materials to become hot in the midday sun.

Reflective white roofs minimize this problem, but not over the long term, since they will get dirty. Metal roofs or metalized shade materials are not a good choice because the very low emissivity will cause these roofs to be the hottest, even while they do reflect most of the radiation. At this time our leaders of building design subscribe to the idea that reverting to the use of white roofs (which were the rule before the days of air conditioning) is a great advance over the prevalent use of dark colored roofs – however in reality this is just a return the common sense choice that was know decades ago.

The big problem with reflective roofs is that (while I acknowledge the 20-30% load reduction compared to dark roofs) they completely reject the incident solar energy. This energy could be used for day lighting (provided it is cool, diffuse daylight with a good shade factor as is provided by a leaf canopy) and for energy conversion by photosynthesis into Bio Fuels?. The advantage we can get out of this approach is that our built environments can (at a lower cost than conventional roofs) be used for producing food/biomass and fresh water.

Unlike Photo Voltaics?, plant Photo Synthesis? can use sunlight to convert a CO 2? enriched atmosphere into hydrocarbon. There is no energy storage problem, no scaling up problem, a low cost of multiplying the plant materials (poor people cannot afford PV even at FUTURE lower cost) and an extremely low incremental cost for implementing the food/biomass production system. The value of the products produced by a Sola Roof Garden is multiples over the production cost (mostly labor) – that is to say – it is very profitable right now.

Roofs, concrete and asphalt surfaces have turned our urban landscape into a Grey Zone? that is dead, and like a desert, is the cause of a hot microclimate referred to as the Heat Island Effect?. It is well known that trees are the best remedy to combat this problem and to halt the spread of deserts. However reforestation is a very slow process and rather incompatible with the Urban Environment?. The SOLAROOF solution is to use lesser plants that are fast growing and which can quickly establish a Leaf Canopy that will intercept the solar radiation before it is absorbed by any other material.

This deceptively simple design specification assures that we are using the plant leaf canopy as the receptor of the solar radiation before it impinges on the building or after it enters the building through the transparent SOLAROOF. Here I will say something that needs a lot more validation and scientific understanding – ONLY a living plant canopy has the ability to transform (at ambient temperature and pressure) the peak solar load into the latent energy of water vapor through the Phyto Mechanism? of transpiration.

The Sola Roof Garden is an “external” crop and leaf canopy that is grown over the rooftop, while my proposed “Phyto Technology?” is roof level controlled environment system to harness this wonderful capability of plants and to enhance their performance as the engine of a solar energy utilization process that accomplishes the building climate control and initiates an effective process of thermal heat rejection or capture. In addition to the benefits of cooling and shading, the Sola Roof Garden can produce a further benefit of revenues generated by harvesting the crop produced at the roof level of the building. The cost of production of crops by this method is very low and therefore the profits generated by the high yield Bio Ponic? technology will pay for the entire Sola Roof within about two years.

Individual buildings of various types can produce income from their unutilized roof areas. The Sola Roof Garden is a method for Urban Agriculture? that is applicable to residential, commercial and industrial Gray Zones? and Brown Fields?. With reference to the Sola Roof Garden drawing above, one can see how the modular Sola Roof structure assembles to create large roof areas. The Sola Roof Garden can span over interior structures to create shaded top floor terraces and covered, cool ground level living – working – recreational - or garden spaces. Commercial and industrial projects can generate additional income. Municipal and community based projects can become self-funding through the additional revenues generated by the roof level aeroponic gardening. Estimated gross revenues of 5 to 15 dollars (U.S.) per square foot will net about 3 to 9 dollars profit per square foot.