Living Roof

LIVING ROOF

Living with the earth instead of just on it has some unexpected benefits, such as the delight we felt when we sold our lawn mower. Before we built here, the land was maintenance-free woodland. After we built, our green roof kept it maintenance-free.

Our green roof provides temperature regulation in and around the house, improved energy efficiency, reduction of the urban heat island effect, storm water management and a very long lifespan. A green roof also integrates the house into the surroundings, improves the look of our property and reduces exterior noise.

If our new house was on the site of our old farmhouse, we would have designed a green roof as a pasture and let the sheep graze it. But, because our house is situated in and among trees, we are designing it to support low-lying forest woodland ground covers. Our intention is to have the roof be part of the forest, as well as support solar thermal panels for our domestic hot water and in-floor heating needs.



The first step was to carefully place 15 cm of sand on top of the waterproof EPDM rubber membrane to protect it. Then we formed and poured parapet caps to seal the top of the ICF walls and to provide an edge to hold the soil on the roof. Since our house is built into a hill, part of the roof is at grade level, so we could back the cement truck close and wheelbarrow the concrete into the forms.

As you can see from the photo, there will be about 45 cm of soil on top of the sand that is already there on this part of the roof.



Once the caps were poured and finished, we were ready to withstand the Canadian winter and plan our next steps.

Our living roof has different levels of soil on different parts, making it somewhat unique. The deeper 60-cm layer could be called intensive. Intensive roofs tend to be more than 15 cm deep to allow for the growth of larger plants, such as small trees and shrubs. With that soil thickness and height of plants, there is more structural loading imposed by an intensive roof, and it may require more watering and feeding. This extra weight and maintenance is what makes these roofs more costly. The plants chosen for an intensive roof tend to be chosen based on visual appeal.

The living roof over our kitchen area is more on the extensive side because it is about 30 cm. Extensive roofs contain smaller plants, including shrubs, sedums (low-lying ground covers) and herbs. They are self-sustaining, except for bi-yearly maintenance, and tend to have lower construction costs. Due to the low level of all the plants, they are often subjected to more weather such as wind and frost. When choosing the plants used for an extensive roof, those that are common to the area and can withstand the harsh conditions are best.

The chart below shows our differing soil depths. However, this is all somewhat academic since we are going for a low-maintenance woodland look on the whole roof anyway. The reason we have more soil on the red-outlined part is for greater insulation and to hide the steel beams necessary to hold the weight. Since we couldn’t hide I-beams in the kitchen, we decided to go for less soil there.



There is a fair amount of flexibility around green roofs as long as you choose your plants carefully for the depth of soil that you have. For example, we will be encouraging native sedums because of their ability to store water in their leaves for extended periods of time in preparation for drought conditions. As well, native dryland and tundra grasses are suitable for use because they can survive the harsh climate conditions a rooftop can experience. Any garden centre can provide advice on drought-resistant, hardy native species, but don’t bother buying plants because they will cost you a fortune. Look for a seeding mixture you can sow instead. It may take an extra year but your pocketbook will thank you.

A living roof with 15 cm or less of soil and proper plants will do a fine job of reducing your maintenance, heating and cooling costs. Plus it is pretty cool to have a picnic on your roof.

A green roof may make sense for you and your roof doesn’t have to be flat to have one. There are modular green roofs in plastic trays and also green carpets that you can just roll out over a traditional roof. Be sure to consult a structural engineer to see what weight your roof can hold.

It makes sense to have the best roof you can and a green roof will perform much better in our climate than the traditional Canadian dark shingles.

Watching Your Waste

Last time I covered waste management, which, I’m convinced, is better than waste covering me. We looked at privies, composting toilets and the environmental problems of septic tanks. This time, as promised, we will investigate the two most responsible ways to handle your waste: peat moss systems and biofilters.

In a peat moss system, water from the dwelling first collects in a conventional septic tank where the solids settle. The clarified effluent then drains, or is pumped, to the peat filter. The peat acts like a sponge, absorbing and wicking the effluent and providing treatment as the wastewater slowly filters through. Eventually the effluent filters to the bottom of the peat where it percolates into the soil for final disposal.



We might not think that filtering through peat would have any treatment effect, but according to the Barnstable County Department of Health in Massachusetts, experimental results show that peat filters are capable of very efficient removal of fecal coliform bacteria, biochemical oxygen demand (BOD) and total suspended solids (TSS). They also appear to be capable of producing a significant reduction of total nitrogen in the finished effluent. This is important because it can avoid unwanted plant growth in the dispersal area.

The great advantage of a peat system is that most of the treatment can be contained in a large, above-ground box with a minimal drainfield. This makes the system ideal for rocky areas where installing a below-ground system with a conventional drainfield is difficult and expensive.

But, you can’t just buy garden peat moss and build a system yourself. The peat must be air-dried, have a very specific moisture content and a precise degree of decomposition. Peat meeting these specifications is mined from peat bogs specifically for use in peat filter systems.

This peat has unique chemical, physical and biological properties that contribute to sewage treatment. The peat bed holds up to 20 times its weight of water, and this stabilizes the internal temperature, nurtures the natural microbial population in the peat when the system is not being actively used and maintains performance even in very cold conditions.

The moist, spongy environment gives the effluent a long residence time in the peat. As the wastewater is wicked through the peat, it flows in a thin film over the surfaces of the peat fibres. This allows the effluent to become aerated, exposed to the acidic chemical environment of the peat and come in close contact with the microbiological community inhabiting the peat. Solids that are larger than the channels in the peat are trapped on the peat fibres as the effluent trickles through.

Within several weeks of use, the peat filter is colonized by a range of micro-organisms and invertebrates from the septic tank effluent and the surrounding soil. These include bacteria, fungi, protozoa, nematodes, earthworms, rotifers and others. Treatment of the septic tank effluent is performed mainly by acid-tolerant bacteria and fungi living in the peat media.

Because of the high organic content, the peat must be periodically replaced. This means physically removing the peat when it has begun to decompose. Life expectancy depends on usage, but 10 to 15 years is average. Make sure your system is designed to make it easy to remove and replace the peat, and have your installer give you a firm quote for maintenance and peat replacement.

A peat system is usually more expensive than a conventional system, but much cheaper than trying to put a conventional system in difficult circumstances. This makes it ideal for small lots and cottages. Plus, a peat system typically provides better treatment and a cleaner discharge than a conventional septic system.



Biofilters act much like peat systems; they rely on the biological treatment of wastewater. Household sewage goes into a septic tank where the solids settle, then through a filter. The clarified effluent is sprayed over non-biodegradable foam cubes that provide a foothold for the bacteria that treat the waste.

The final water that is released is exceedingly clean, which was our reason for going with this system since we are next to the Salmon River. Our manufacturer claims we could drink it, but our confidence level is not quite that high. Nevertheless, we believe that this is the cleanest sewage-treatment method available.

Our biofilter system is housed in a small, above-ground shed 2 metres high, 1 metre wide and 2 metres long above a 3-metre in diameter drainfield. Most biofilters can be installed above or below ground.



Biofilters reportedly have several benefits. We have only had ours for six months and can’t attest to them all, but it has worked well for us so far:

•Low maintenance: The non-biodegradable filter medium normally does not require cleaning or changing for 20 to 30 years.
•Low energy: A small intermittent pump is the only energy requirement.
•Recoverable: Easy to recover if the septic tank fails, unlike sand filters or conventional tile beds.
•Flexible configuration minimizes tree cutting and excavation.
•Small footprint: Effective treatment in an area five to 10 times smaller than that of sand, soil or peat beds; and 10 to 50 times smaller with recirculation or deeper beds, especially useful for larger systems.
•Applicable in many locations: bedrock, clay, swamp or small lot.

The cost of a biofilter is comparable to a high-end, conventional septic system, but because the results are so much better, that cost is justified no matter where you live.

So, we’ve come a long way from using bushes or throwing our night soil out the window in the morning. Both peat and biofilter systems co-operate with nature to process our waste, and that co-operation is always the best way.

Let’s treat the earth as if our lives depended on it.

Waste Not, Want Not

Human waste is a delicate topic, whether you call it ordure, night soil, jakes, dung or guano. When we were nomadic or lived in small, scattered communities, managing our waste was no big deal. But it became a more repulsive problem when it was removed from our backyards and concentrated in rivers and highway ditches as populations converged in cities during the Middle Ages. When Londoners commonly held cut oranges to their noses against the stench of the Thames, enough was enough. The elimination of human sewage in congested residential centres became one of humankind’s biggest engineering agendas, and many parts of the world are still without any sewage systems.

If you live in a city with a municipal sewer system, you are pretty much limited to hooking up and using it because most cities frown on do-it-yourself sewage treatment. Unfortunately, municipal systems are incredibly expensive to build, use vast amounts of water, break down in heavy rains and are unsustainable in their present forms. For your cottage, though, or if you live in a more rural area, there are many choices including a privy, a composting toilet, a traditional septic tank, a peat moss tank or a biofilter.

The privy is just a hole dug in the ground to hold biological waste, whether you call it an outhouse, backhouse, thunderbox, biffy, dunny, long-drop or kybo. If sufficient moisture is available, natural bacteria within the waste materials, earthworms, amoebas, moulds and flying insects slowly decompose the wastes and form a compost pile in the pit.

This decomposition is slow but generally effective if the new wastes do not exceed the decomposition rate of the old ones. Where the percolation rate of water through the soil is slow and where there is not a large amount of waste entering the pit, the wastes can slowly decompose and be rendered harmless without causing groundwater contamination.

In sandy soils with a fast rate of percolation, or where the base of the pit penetrates topsoils and goes directly down to underlying gravel and fractured substone, waste liquids entering the unlined pit may quickly seep deep underground before bacteria and other organisms can remove contaminants, leading to groundwater pollution. This pollution can be slowed or prevented in newly dug privies by lining the base of the pit and the walls with a thick mat of grass clippings or other absorptive material. This material then decomposes and becomes part of the compost pile lining the pit that continues to act as a moisture sponge.

A composting toilet is a well-controlled version of a privy. Models range from simple twin chamber designs to very high-tech advanced systems with rotating tines, temperature and moisture probes, and electronic control systems.

They are effective biological converters of human and household “waste,” saving money and energy for you and your community. They initiate the regeneration of the Earth’s environment that is long overdue.



The benefits of composting toilets are many:

• Reduce water use by 20 per cent to 50 per cent;
• Lower water and sewer costs;
• Reuse the small amount of end product;
• Reduce the load on municipal sewage systems;
• Eliminate sewer back-ups;
• Reduce nutrient load on nearby watercourses;
• Can be used in difficult sites: rocky, high water table, no water storage, environmentally sensitive, close to running watercourses, and swampy ground.

Plus there is no odour. This is a decentralized method of sewage management to seriously consider.

In North America, approximately 25 per cent of the population relies on septic tanks; this can include suburbs and small towns as well as rural areas. In Europe, they are generally limited to rural areas only.

The term “septic” refers to the anaerobic bacterial environment. Wastewater enters the first chamber of the tank; solids settle and scum floats. The settled solids are anaerobically digested by bacteria and reduced in volume. The liquid flows through the dividing wall into the second chamber for further settlement and then drains in a relatively clear condition into a drain field.



Pumping the tank every four to five years is required to remove the irreducible solids that settle and gradually fill the tank.

Septic systems have problems:

• Excessive dumping of cooking oils and grease can cause the inlet drains to block;
• Flushing non-biodegradable hygiene products such as sanitary napkins and cotton balls will rapidly fill or clog a septic tank. These materials should not be disposed of in a septic system;
• The use of garbage disposals for waste food can cause a rapid overload of the system and early failure;
• Pesticides, herbicides, bleach, paint or solvents will damage the working of a septic tank;
• Excessive water entering the system will overload it and cause it to fail;
• Biofilms develop on the pipes of the drainage field and can lead to blockage;
• Septic tanks are ineffective at removing nitrogen compounds that can potentially cause algal blooms in receiving waters.

There are also environmental issues with septic systems:

• Byproducts include carbon dioxide, methane (a greenhouse gas 20 times worse than CO2) and hydrogen sulfide — a pungent and toxic gas;
• The discharge from a septic tank into the environment can trigger prolific plant growth including blooms of algae and potentially toxic cyanobacteria;
• Sandy or coarse soils adjoining water can become saturated with phosphate, posing a threat of oxygen depletion to nearby surface waters;
• In areas with high population density and septic systems, groundwater pollution often exceeds acceptable limits;
• Trees in the vicinity of a concrete septic tank have the potential to penetrate the tank as the system ages and the concrete begins to develop cracks and small leaks. Tree roots can cause serious flow problems due to plugging and blockage of drainpipes, but the trees themselves tend to grow extremely vigorously due to the continuous influx of nutrients into the septic system.

There are ways to handle your waste responsibly. Installing a composting toilet is one. Next time we will talk about two more sustainable methods: peat moss systems and the one we installed for our earth-sheltered house on the river: a biofilter.