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Mohamed Hage, founder and president of Lufa Farms Inc., runs a greenhouse that is built on top of a commercial building in Montreal.Graham Hughes/The Canadian Press

Nothing's more down to earth than farming, but a new urban farm in Montreal is inspiring designers to think of growing in the clouds.

Lufa Farms, on the roof of a commercial building near Montreal's Marché Centrale, is a 32,000-square-foot hydroponic greenhouse that's producing more than 453 kilograms of vegetables every day, all year round.

With demand growing for local produce and a shortage of open fields in urban areas, the concept is attractive. But Lufa Farms founder Mohamed Hage has found that it is way more complicated to be a rooftop farmer than setting up a glass house and planting seeds.

It took him five years just to find a suitable building, convince the owner and the city building department to allow it, and to design and build it. And it took an investment of almost $2-million to get it off the ground and into production.

But it's an example that is inspiring other rooftop farms, says Aaron Quesnel, founder of Sky Harvest Inc., a startup in Vancouver that's also planning a rooftop greenhouse farm.

While roofs represent as much as 30 per cent of the surface areas of major cities, only about 10 per cent of commercial rooftops in Canada could support the weight of a greenhouse farm, Mr. Quesnel says.

In a study of urban farming Mr. Quesnel co-authored while a student at a technical institute in Sweden, he found that even those buildings whose roofs can carry the load are often off limits because they're already built to the maximum height for their zoning.

But he sees great potential for using what's basically wasted space at this point. "In cities where you have astronomical real estate costs it makes increasing sense to use this amazing resource," he says. Growing locally is also preferable because of the monetary and environmental costs of shipping food long distances.

Sky Harvest has been doing engineering studies on a number of buildings but has yet to choose the site of its first greenhouse in Vancouver. "Every building is different, so you can spend a lot of time doing engineering assessment only to find out it's not feasible. While some buildings could be retrofitted to bear the load, in most cases that's not economically viable," Mr. Quesnel says.

The rooftop farming movement is being pioneered in Montreal and New York. He knows of groups in Calgary, Boston, New York and Seattle as well as abroad in London that are looking at rooftop farms.

"The costs are still relatively high but as worries grow about the risk of the sustainability of the food-supply chain it will become more of a trend," Mr. Quesnel predicts.

Sky Harvest co-owner Dirk Gibbs says he's found there is a great deal of investor interest in funding rooftop farms. That's important because the development costs add up even before a site is chosen.

With a farm on the ground, it's relatively easy to begin cultivating. But the costs of doing engineering studies on rooftops, for example, can be astronomical even before you start installing equipment, Mr. Gibbs explains.

"There are very few ideal spaces in a city. You need to have a roof built with materials that are designed to carry at least 10 per cent more weight, depending on where water and crops are stored." Engineers also have to take "live load" into account; that's the ability to carry the number of people moving around the roof to tend the crops.

Construction costs can also go beyond the fabrication and lifting of components onto a roof that may be in a crowded urban area. Building codes for workplaces generally require more than one exit, and the tops of commercial buildings are designed for machinery and don't often have elevator access for moving people and equipment to the greenhouse, Mr. Gibbs notes.

But he predicts that as greenhouse roofs become more mainstream, new buildings will be engineered to accommodate the trend.

One under-utilized source of strong roofs is parking structures, which are built to hold the weight of cars and trucks. One community garden in Seattle has set up on the roof of a parking garage, he adds.

The urban farm concept is different from existing attempts to grow vegetables on "green roofs," Mr. Hage explains. Being in operation year-round, a hydroponic greenhouse on a roof provides environmental benefits of cooling a building in the summer and holding in heat in the winter.

The green pluses include being able to grow with natural pest control, such as using ladybugs to eat aphids.

Lufa Farms' glass enclosure produces 40 types of vegetables and herbs in a variety of growing media, moisture and lighting conditions. There are two macro-zones and several micro-zones. Tomatoes, for instance, grow best in the sunny south-facing part of the greenhouse while lettuce does better in the cooler, northern portion of the roof.

Crops are harvested each day by six employees who work in the greenhouse. The produce is boxed and taken to pick-up points for customers who have pre-ordered custom selections of vegetables. (A small basket suitable for one or two people is priced at $22, and a large one suited for three or more sells for $44.) Lufa Farms employs 30 people, including sales people and logistics staff.

So far, demand for the produce is growing faster than supply. Mr. Hage says the company hopes to open two more greenhouses, another in downtown Montreal and one in Laval, Que.

"This is an idea whose time has come," Mr. Hage says. "Big cities like Montreal, Toronto and Ottawa are basically food deserts; most of the year you can't find locally grown sustainable food and we have to rely on imports."

Lufa Farms facts

  • Greenhouse completed in 2011.
  • Dimensions: 80 by 43 metres, and 4.2 metres high.
  • Weight of greenhouse: 1.8 kilograms per square foot.
  • Load capacity of building roof that supports it: 45 kg per square foot.
  • Modifications needed: Two staircases from the floor below to the roof and a small freight elevator; a water supply and irrigation pipes.
  • Number of plants: About 3,000 plants of 40 types of vegetables and an herb garden.
  • Yield: 450 to 680 kg of food per day.
  • Number of farmhands: Six work daily in the greenhouse.

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