Complete Guide: Ecological and Green Roofing in Canada

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The complete guide to ecological, vegetated and green roofs in Canada

Green roofs are a type of vegetated roof that is becoming more and more popular in the province of Canada. They offer many benefits to both the building and the environment. Benefits include improved energy efficiency, reduced storm water runoff, reduced heat island effect and improved air quality. Green roofs can also provide habitat for wildlife and can be used to grow fruits and vegetables.

Green roofs for the quality of our environment. An important environmental choice.

Green roofs are only one component among all the sectors of green (ecological) architecture whose four main characteristics aim:

1. Protection of non-renewable energy and natural resources.
2. Improving air quality in buildings and outdoors.
3. Preserving fresh water and improving the quality of drinking water, lakes and rivers.
4. Reducing greenhouse gas emissions leading to climate change.

Roofs have important impacts on the 4 aspects of green architecture and that is why they are particularly targeted during green interventions on buildings.

White roofs: economical and ecological

The main advantage of a white roof is that it reflects light radiation rather than absorbing it and transforming it into heat. White roofs therefore reduce urban heat island effects in cities and allow for a much more pleasant use of roofs in the form of roof terraces or roof gardens. Roof terraces located near asphalt and gravel roofs experience a significant increase in temperature that often inconveniences users. This extreme heat can also be detrimental to the proper development of plants on a roof garden.

Green roofs: ELT, an ultra-lightweight system

It is now possible to create green roofs on existing roofs without adding excessive weight that could cause damage to its structure. It is an ultra-thin system, prefabricated in tiles of about 90 cm X 90cm and using very hardy plants that can withstand prolonged drought. A modified system can also be used to create green walls for the exterior or interior of buildings.

What are the benefits of green roofs?

The concept of a green roof is often confused with that of a vegetated roof. In fact, the green roof is part of the green roof family and is both the most elaborate and the most efficient concept.

However, the green roof is not the only green roof. Sometimes other roofs are preferable depending on water availability (will you need to water during droughts?), maintenance (pulling out the highly allergenic ragweed), or simply spreading your money around in different green areas of green architecture.

Where to invest in an eco-responsible way?

Green roofs are only one component among all the sectors of green (ecological) architecture whose four main characteristics aim:

1. Protection of non-renewable energy and natural resources.
2. Improving air quality in buildings and outdoors.
3. Preserving fresh water and improving the quality of drinking water, lakes and rivers.
4. Reducing greenhouse gas emissions leading to climate change.

Roofs have important impacts on the 4 aspects of green architecture and that is why they are particularly targeted during green interventions on buildings.

Roofs pollute air and water

The average life span of roofs in Canada is very short. For flat roofs it is only 13 years for a common asphalt and gravel roof while for sloped roof asphalt shingles it is about 20 years.

This means that every 13 years, the equivalent of all the asphalt and gravel roofs in the country are sent to landfill. Every 20 years, asphalt shingles go the same way.

These petroleum products consume non-renewable energy resources, emit solvents into the air when exposed to sunlight, and pollute groundwater as they break down.

Roofs increase energy costs

Black or dark colored roofs absorb solar radiation, become hot and re-emit their heat during the evening and night. The surface temperature of an asphalt and gravel roof or an asphalt shingle can rise to 175 degrees F.

In cities, large areas of flat roofs, masonry walls, streets and sidewalks contribute to an increase in air temperature of 3.5 to 5 degrees F (2 to 3 degrees C) compared to areas with little construction. The increase in temperature creates the urban heat island phenomenon.

A very hot roof also increases heat radiation to the interior of the building (only if the roof is poorly insulated and ventilated), further increasing the air temperature in buildings in summer. The combination of these two factors increases the overall cooling energy requirements of all urban buildings by about 10% and sometimes more.

Roofs dry out the soil

In cities, soils are generally in water deficit over a yearly period. That is, they lose more water than they absorb. This has a serious impact on trees and on the stability of soils, such as clay soils. This is the case in the city of Montreal where there has been a chronic annual water deficit since the early 1980s.

Flat roofs with a central drain and sloped roofs with gutters receive rainwater and direct it directly into the storm sewers. This prevents the soil from receiving much of the water that was intended for it. This is why all measures of rainwater harvesting from roofs are to be encouraged.

Roofs suffocate waterways

Dark, sun-heated roofs are also detrimental to algal blooms in waterways and their impact on marine life. When cool summer rain falls on a hot roof, it heats up the water by several degrees. This warmed water then finds its way into municipal sewers and contributes to the warming of river waters, further activating the phosphate that has accumulated in the water and leading to the growth of algae that obstruct light and kill fish.

Is your roof green?

1. A green roof conserves rainwater and returns it to the soil.
2. A green roof limits the heating of the air in cities and of rainwater.
3. A green roof is made of a sustainable, recycled or recyclable material, which reduces the production of waste and especially polluting waste.
4. A green roof consumes little energy during its entire life cycle, from the extraction of raw materials to manufacturing, transportation, installation and use (maintenance), to removal, transportation and disposal. This is called the grey energy associated with a material. However, the energy consumed during its lifetime must then be divided by the number of years of service to compare it with other products with a different lifetime.
5. A green roof takes the concept of a green roof a step further by allowing organic vegetables to be grown close to where they are consumed, optimizing the use of water and natural fertilizers. The production of biomass for consumption also removes 0.7 pounds of CO2 from the air for every 10 pounds of vegetables produced, thus contributing to the reduction of greenhouse gases and ultimately to climate change.

Green walls and vertical gardens

In general, green walls can be created simply and very economically by using Virginia creeper, which is very hardy in Canada. The walls covered with Virginia creeper provide shade on the exterior walls and help reduce the urban heat island phenomenon. The foliage of the Virginia creeper also reduces CO2 in the air and creates healthier air.

There are popular beliefs that Virginia creeper causes damage to siding. It is believed to damage the mortar joints of masonry walls by holding moisture and seeping into the cracks. In fact, vines protect masonry from summer storms and cannot damage mortar joints in good condition, but they can infiltrate if the joint is already open or crumbling.

The main advantage of vegetated walls using prefabricated panels is that they can be used to create diversified structures that are integrated into the exterior or interior architecture. For example, panels can be installed in the kitchen to grow herbs. Their use remains more aesthetic and friendly.

The short history of green roofs

In China, they want to transform rooftops into rice fields to respond to the rural exodus to the cities and feed the population. In Canada, the urgency to act globally is less but experimentation must be done quickly to find design and technical solutions that meet the expectations of citizens and businesses.

The construction of green roofs is done in a traditional way in several Scandinavian and European countries. The mixture of earth and plants rooted on the roofs allowed to realize relatively well insulated, air and water tight, wind and fire resistant roofs. All of this was done with readily available materials.

In Germany, during the last 10 years, 10% of the roofs have been vegetated. A "bonus" point system grants an environmental tax reduction to real estate developers who use green roofs.

In Japan, the city of Tokyo requires that any building occupying more than 10,000 square feet of land be covered with vegetation on 20% of its surface.

In the United States, green roofs have long been associated with fringe concepts of bio-climatic, buried, earth-covered architecture. This fallout shelter architecture did not gain widespread popularity. The advent of new, lighter growing systems and new environmental issues have revived interest in these roofs. We are now talking about sustainable roofs that add quality of life to urban residential buildings.

In Canada, commercial and residential projects that include green roofs are still few and far between, but the products and expertise are now more available and many baby boomers are dreaming of garden roofs and flowering meadows for their condos and apartments in the city as well as for their homes in the country.

Green roofs: City versus rural

Green roofs offer very different benefits depending on the type of construction and the location of the building. In cities and suburbs, where flat roofs are not seen, the main benefits are related to roof uses and environmental functions. In the countryside, where there is no shortage of land, they are primarily used to integrate buildings into the natural environment.

In the city: for green spaces and the environment

In urban areas, green roofs are mainly appreciated for the creation of useful green spaces for the population and for their technical advantages to protect the environment:

• Add green spaces. They give back to the city and its occupants the use of a green space used for the construction of the buildings. These green spaces can be used for relaxation (reading, swimming in a shallow pool, sunbathing) or for gardening according to the needs of the occupants. These areas can be designed as a personal refuge or as a meeting place. Given the high cost of land in cities, the investment is largely offset by this use as green roofs replace the function of private or common yards. They have the advantage of adding continuous sunlight and a better view for all. Montreal's flat roofs are also very dangerous for the spread of fire through the roofs. A complete earth covering would greatly reduce this phenomenon and increase fire safety.
• Environmental protection. This green space reduces outdoor air temperature in the summer, filters air pollution and creates some rainwater retention during storms, reducing the number of overflows from water treatment plants. They can also double the life of roofing membranes, reducing bituminous waste from roofing repairs by 50%.

Why a green roof in the country?

At first glance, when looking at the social and environmental benefits of green roofs, one wonders how they can be useful in rural areas where there is no lack of land.

• When a building is less than 20% of the land area, there is no need to add greenery on the roof for climatic, air quality or water retention reasons.
• In rural areas, sloped roofs can be more easily and cheaply covered with other durable materials such as concrete, aluminum, fiber cement, or other tiles.
• In rural areas, green roofs add a lot of land maintenance that is already significant in general. The low cost of land does not justify the high costs of a green roof as an additional use for a single family.

This reality must however be adjusted to the type of dwelling planned. Is it a single-family home on a large, flat, cleared lot, or is it a resort condominium in the forest on mountainous terrain?

Condos and mountainous terrain

Resort condominium projects are very popular in mountainous areas. These projects bring important investments to these regions but they are often the target of citizens who criticize them for their poor visual integration and the destruction of natural environments.

In such a context, green roofs can be used to conceal their mass and integrate them visually into the environment.

This "Green Marketing" does not aim to deceive citizens but to meet their expectations of architectural integration. Medium density condominiums (4 to 6 stories) are much more environmentally friendly than single family detached homes which require 4 to 5 times more deforestation per unit.

In addition, the consolidation of green space into a larger mass creates a much more sustainable ecosystem than planting a few trees on individual lots. Clustering also creates a much more controlled management system for green space, wastewater treatment and recycling, and overall common environmental practices.

In a tiered condominium project, one owner's roof can become another's terrace and create a private personal space or even a small vegetable garden.

Suburban or country single-family home

Symbolism is always very important when choosing a house. Many people buy old historical wooden houses that will cost them a lot of money to renovate, heat and maintain simply because of its cachet and its belonging to the history and culture. In the same way, the green roof represents the symbiosis of man with the natural environment. It is a beautiful image that can be used to sell the idea of integration and environmental protection to the whole society. In this sense, "Green Marketing" is very important, but it must not distort the meaning of the product it sells.

Indeed, this image can also remain a simple "architectural style" where vegetation is used as an exterior finishing material. Many American architects took this trend in the 80's and 90's covering their buildings with grass as well maintained as a golf course. This is the worst avenue, one that emphasizes a stylized design that adds maintenance, watering, fertilizers and chemicals at the expense of the environment.

For the single family home in the country or suburbs, the green roof can instead become a rooftop garden with much better sun exposure than if it were located on the ground and protected from the many animals that sometimes become impossible to dislodge from the garden (skunks, raccoons, bears, deer, etc.)

Materials and techniques

The addition of a growing medium and plants requires a sufficiently strong roof structure, perfect waterproofing, a relatively low slope and easy access for maintenance during the first years.

Roof structure. The addition of a lightweight 6 inch (15 cm) high growing medium creates a 30 to 40 lbs/ft2 surcharge when the soil is saturated with water. Canadian roof structures are generally designed to accommodate a uniform snow load of 40 psf.

Existing Canadian flat roofs are therefore generally not designed to support the combined substrate and snow loads of 70 psf. Green roofs are therefore mainly intended for new buildings, especially those with a reinforced concrete structure as found in Europe where green roofs are more popular.

For existing buildings, the strategy of greening the roofs is more like roof gardens where the plantations are made in containers and are located in certain areas of the roof, near the load bearing walls. This requires a case-by-case study where a building professional evaluates the bearing capacity according to the existing structure and its condition. This is especially important for residential wood roofs where the aging structure may have point weaknesses.

After plant root formation, the growing medium holds up very well with slopes up to 4 in 12 (4 vertical units for 12 horizontal units). Generally speaking, however, green roofs are best suited for low slope roofs of 1 in 12 or less.

The elements of a green roof

A green or vegetal roof is essentially composed of five components. Starting with the roof support, there are:

• A waterproofing membrane.
• A drainage and water reserve layer.
• A filtration membrane.
• A growth substrate.
• A vegetation layer.

The waterproofing membrane

The realization of a green roof and its implementation takes a few years and requires important basic investments. It would be ridiculous to make a green roof on a damaged membrane or one that is more than 10 years old because the risks of water infiltration in the medium term would be high.

All standard synthetic waterproofing membranes (elastomeric, PVC, EPDM, etc.) can be used. Multi-layer membranes with asphalt are not recommended for durability reasons.

The drainage and water reserve layer

An embossed polyethylene drainage membrane is used to create a drainage space that directs rainwater to the roof drain or exterior gutters. This drainage membrane is embossed to retain a reserve of water essential to plants in times of drought.

The filtration membrane (geotextile)

The drainage layer is covered with a geotextile filter that holds the soil and allows water to drain away without filling the soil drainage layer. This non-woven geotextile also absorbs the water that passes through it providing a moist environment for plant roots.

Unfortunately, the non-woven geotextile offers little resistance to certain roots that could penetrate it and reduce its effectiveness. It is therefore necessary to cover it with another anti-root geotextile made of woven polyethylene whose role is only to block the roots.

The growth substrate

For many years, landscape architects have recommended a minimum of 12 inches of soil on green roofs to maintain an acceptable environment for plant growth. Unfortunately, soil becomes very heavy when saturated with water (about 100 lbs/cu. ft.) sometimes causing structural damage to buildings and waterproofing. The soil also tends to compact, evacuating the oxygen necessary for the survival of plants. Past mistakes have taught us not to underestimate the importance of the substrate that supports plant life.

The substrate must be light and resistant to compaction while retaining water. Its composition is generally made of vegetable compost of leaves or bark mixed with aggregates of light and absorbent stones having a diameter of 1/8 to 1/2 inch (3 to 12mm). Volcanic stone, expanded clay and sometimes brick debris recovered from demolition sites, then crushed, are used as materials to recover waste destined for landfill.

The aggregates represent a volume varying from 40 to 70% of the substrate of culture according to the thickness of substrate, the irrigation and the type of culture wished. The total thickness of the substrate can thus be reduced to only 4 inches (10 cm) high. This minimum thickness will suit some very frost resistant plants, but in general it is recommended to use a thickness of 15 cm or more to allow the cultivation of a larger variety of plants.

The vegetal layer

Technically, all plants can be grown on rooftops, but some may require constant care to protect them from constant sun, frost and high winds. In general, perennial and native plants that are highly resistant to temperature extremes and will establish quickly to cover soil surfaces to reduce its drying out by sun and wind should be preferred. Ground covers also have the advantage of leaving little room for weeds and reducing maintenance. Alpine plants and those adapted to zone 3 are well suited for this purpose.

The plants to be favored can be:

• Flowering plants: smooth oregano (Origanum laevigatum 'Herrenhausen'), chives, which also have the advantage of being a condiment, a mixture of field flowers to create a flowering meadow, Spanish grass (Armeria maritima), irises (Pumila), clumped bellflower, etc.
• Ground covers: reclining carnation (Dianthus deltoides), creeping gypsophila (Gypsophila repens), white thorn (Sedum album), thyme, etc.
• Grasses: blue fescue (Festuca glauca), amethyst fescue (Festuca amethystina).
• Green plants: silverbush (Iberis sempervirens ' Schneeflocke'), Schmidt's mugwort (Artemisia schmidtiana), scabious knapweed (Centaurea scabiosa), etc.

Automatic watering system

During the first three years of plant establishment, the plants need more watering to create their roots and cover the soil. Without systematic watering, the plants will dry out and can become the cause of fire propagation from one building to another.

Dry soil that is poorly consolidated by roots also becomes lighter and more volatile in high winds. This is why an automated watering system is practically essential for large areas and especially for extensive plantings with a low soil thickness and low water retention capacity.

Green roofs / green roofs: extensive or intensive planting

Depending on the thickness of the substrate and the degree of watering desired, the planting can be extensive, semi-extensive or intensive.

Plantation extensive

This is a type of thin substrate planting (4 to 6 inches) that you don't necessarily want to water unless there is a prolonged drought. This planting uses mostly very hardy ground covers that can withstand droughts and expand quickly to shade the soil and stabilize it with their roots. Its growing medium will contain up to 70% porous aggregate, by volume, to conserve as much water as possible.

Plantation semi-extensive

It is also a thin plantation (6 inches) with an automatic drip irrigation system with small pipes located under the growing medium between the filtering geotextile and the anti-root geotextile. This is why the filter geotextile must also be an absorbent geotextile. It absorbs water drops to moisten the roots without reducing the oxygenation of the roots. This system is also very water efficient, creating almost no evaporation. This type of culture can mix ground covers, flowering or foliage plants, vegetables and even small shrubs or climbers like Virginia creeper or honeysuckle. The substrate for a semi-extensive crop is usually composed of about 50% porous aggregate.

Plantation intensive

It is a type of cultivation in containers up to 1 or 2 meters deep. The intensive culture can accommodate trees such as decorative crabapples or ash trees. In general, it is recommended to install guy wires to resist high winds. These systems should always be equipped with automatic watering to ensure the survival of the trees. The aggregate volume is often reduced to 40% to make room for more nutrients.

What is the best choice

The current trend in Canada is to reduce the thickness of the substrate to reduce its weight and structural costs. This trend is very much at odds with the social benefits sought by the implementation of green roofs:

• The water retention to relieve the purification plants is much less.
• This weakens the survival of the plants during the first years and during droughts. In the event that the plants die, the roots will no longer hold the soil and it can be swept away by water and wind. A large area of dried plants also becomes a high flame spread factor that can blow away and spread a fire to other buildings nearby.
• This limits the function of the green roof. It is no longer a vegetable garden for the occupants but only a ground cover requiring maintenance and weeding against allergenic plants like ragweed.
• The energy efficiency is lower for heating and cooling. Among the products offered, the ultra-light system stands out from the others. It is prefabricated and easy to install by neophytes.

The best choice seems to be a varied approach on the same building. A combination of extensive and intensive planting, with spot planting in containers, generally better meets the needs of the occupants while diversifying the design possibilities.

The cost of building a green roof in Canada

Costs

The cost of a vegetated roof varies greatly depending on the thickness of the substrate, the size of the vegetated surface and the type of plants. For an extensive roof of 1,000 sq.ft. fully covered, you should budget $17/ft. For a small terrace of 200 sq.ft. the total cost will be less but will be more expensive per square foot, approximately $25/sq.ft.

Who can do it?

No roofer has the expertise to build rooftop growing systems. It is generally necessary to have the roofing membrane made by the roofer and to give the green roof contract to a landscaper experienced in this field.