These are not nearly so labor-intensive as intensive green roofs. They do still need occasional maintenance, such as: irrigation during extreme drought, weeding until the plants become well established, and occasional application of fertilizers. Extensive green roofs are usually installed more for environmental benefits rather than for the enjoyment of the general public.
The soil depth for extensive green roofs is much shallower than most intensive green roof: 3″ to 7″ as opposed to 8″ to 4′. Because of the extreme conditions of many roofs the plants for extensive roofs are typically low growing and very drought and sun tolerant. The plant foliage is usually 2″ to 6″ long and designed to provide maximum ground cover, water retention, erosion resistance, and respirative transpiration of moisture.
Click on the thumbnail for larger view of the diagram.
These roofs can be installed over various roofs, but it must first be inspected to ensure that it can bear the load of a green roof. If it is installed on a flat roof another layer must be added to drain the excess water away from the root zone. The best roof slope for extensive green roofs is between 5 degrees and 20 degrees, but, if a grid system is used, they can also be installed on slopes up to 45 degrees.
In general, there are two types of green roof: intensive and extensive. Occasionally a third, semi-intensive, is added to that list. The depth of the planting medium and the amount of maintenance required determines which category the roof falls under.
Generally intensive roofs are characterized by thick soil (8 inches to 4 feet), heavy weights, and elaborate plantings. The plants usually include shrubs and trees. Rooftop ponds, incorporated into the overall design, would also fall under this category. Intensive green roofs are installed primarily over concrete roof decks to enable them to withstand the weight requirements. The roof needs to be able to support from 80 to 150 pounds per square foot.
Intensive green roofs require significant maintenance, but they are beautiful. These are what generally come to mind when you mention green roofs in the city. They are usually park-like and accessible to the general public.
Green roofs, also known as eco-roofs, vegetated roofs, living roofs, and greenroofs, are becoming increasingly popular, although the market is weak and still underdeveloped in North America. They incorporate high quality waterproofing, root repellent system, drainage system, filter cloth and lightweight growing medium to make an economically sound, and psychologically easing environment right in the middle of the city. Rooftop ponds are another form of green roofs. These are often used to treat greywater. Vegetation planted in containers on the roof are not considered true green roofs, but there is some debate in this area.
Overall, green roofs are expected, when build and maintained properly, to increase the roofs life span two or three times! However, they do have much higher structural demands than traditional roofs; not all buildings can be retrofitted with green roofs.
These roofs can retain up to 75% of the rain water and gradually release it back into the atmosphere. This significantly cuts down on the pollution that goes back into the surrounding ecosystem. Installing a green roof isn’t cheap. The cost is five to thirty-five dollars a square foot and more. There are many benefits though. Not only is it aesthetically pleasing, but it also reduces sound, and can reduce your summer cooling and winter heating losses by 26%!
“… efficiency isn’t something that you can just stop the production line for a few hours, change a few parameters, and start the production line up again.” HERE.
Presidential candidate, Senator John McCain, calling for more energy efficient government as a model to the people of the United States. HERE.
Edmonton, Canada gets new energy-efficient trains. HERE.
Energy-efficient housing community for low-income, chronically-homeless families. HERE.
Cork is commonly used as an underlayment for hardwood and ceramic floors. It is also used under wall coverings, in ceilings, and around pipes. This is mainly because of its amazing resilience and acoustical benefits. It has the bonuses of not deteriorating over the years, repelling insects with the inherent substance suberin, being fairly waterproof because of that same substance, and being resistant to mold and mildew.
Cork forests are threatened with the decline in demand for natural cork bottle stoppers. With that threat comes threats to the already-endangered species: the Iberian Lynx, Barbary Deer, and Imperial Iberian Eagle. The cork industry employs 30,000 people in various jobs, and it would be economically detrimental in the extreme if the industry were to shrink. In some places cork forests are being replaced by the more lucrative, less sustainable, more nutrient-demanding eucalyptus. This is a very hazardous change as the soil will be much more prone to erosion, and will make it very difficult to establish native plants there in the future.
Cork, in all its various forms, is derived from the Cork Oak (Quercus suber) tree which is native to southwest Europe and northwest Africa. Half of all cork production is done in Portugal. The bark of the cork oak is harvested entirely by hand with the first cut being when the tree is about 25 years old. Harvesting can continue after that every 6-12 years, and is only done by local craftsmen. The trees live 150-250 years, and there are usually 12-15 cuts per tree throughout its lifetime.
Granules of cork can be mixed into cement to increase energy absorption, low thermal conductivity, and low density. It has been used in rocket technology because of its fire resistance, and it can also be made into bricks for the outer walls of houses.
Cork use in building has declined in the past 20 years. This is mainly because of a change in fashions since the ’70s, some difficulty with building regulations, and poor quality cork sold in the ’80s and ’90s. Cork marketing is changing however, and we may soon see a revival of cork use everywhere. Cork flooring is already readily available, and it is possible to obtain cork insulating boards.
In the previous article, I mentioned the two possible insulating concrete form construction techniques: pre-formed, interlocking blocks; and separate panels which are tied together using plastic or steel ties. As well as different construction methods there are also three main shapes within these two techniques:
Flat — This form gets an even thickness of concrete throughout the wall, like a conventional poured wall.
Grid — The grid system creates a waffle pattern. The concrete is thicker is some places that in others.
Post and Beam — Also called “screen grid,” this shape forms horizontal and verticle columns of concrete. It offers significantly less fire resistance than the previous two systems.
Insulating concrete forms, or ICFs, are basically just forms for poured concrete that stay in place permanently as a part of the wall. The forms are constructed of foam insulation, and are either pre-formed, interlocking blocks or separate panels that are connected with plastic ties.
Houses built with ICFs are fire-resistant, and wind-resistant. Obviously they are better protection during tornadoes than traditional wood-frame houses. This type of building material is highly sound resistant, making for a peaceful home in even the busiest areas. They also provide R-values of between R-17 and R-26, higher than wood-frame construction R-values (R-12 to R-20). This cuts energy consumption by up to 40%. ICF buildings require very little repair and maintenance. They are about 0.5 to 4% more expensive than conventional building techniques, but this is quickly recuperated with the savings in energy.
Poured earth is a very similar technique to concrete. The primary difference is that it uses ordinary soil as aggregate instead of sand or gravel. Poured earth also uses Portland cement as a binder, but it generally uses much less. It can be considered a moderate strength concrete. Minimal maintenance is required on a poured earth structure since it has very high resistance to the weather.
The ideal soil is low in clay, and somewhere between silt and three-eighths inch aggregate. Testing needs to be done on the material to assure the quality of the product. It must be tested for shrinkage and compression strength. The mix needs to have little or no shrinkage in the drying process, and it needs to have compressive strength of 800 to 1200 psi.
Poured earth buildings have an added benefit of being capable of having a steel insulating grid within the wall. This increases the thermal mass and overall strength of the structure. However, because of iis rather customized nature, a poured earth house is usually ten to twenty percent more expensive than traditional construction.
Slipform stone masonry is a cost and energy efficient way of building a beautiful, fire-proof, and weather-proof home. If you use stones from your area the cost is quite low. In addition, most inspectors accept slipform houses as a form of masonry, and that’s covered in all building codes.
When building using slipform the form is placed on either side of the wall, up to two feet high, to serve as a guide. Then the stones are placed with the good faces against the form, and concrete is poured behind them. Rebar is added for strength. The stone can be on one or both sides depending on your resources and desires.
However, this type of construction is extremely labor intensive, and rather slow, since you have to wait for the wall to set before “slipping” the form up to the next spot. If you’re willing to work and wait you will eventually have a beautiful stone home.
There are some good stories out there by people who have built or are building slipform stone masonry houses:
This is one of the newest alternative building material in the green building world. It is basically re-pulped paper fiber mixed with a little concrete and sand. Occasionally clay is used instead of concrete; this is called paper adobe or padobe. The overall cost of papercrete houses can easily be less than a dollar a square foot.
The paper used for papercrete can come from anywhere, even those slick magazines. In fact, those are perhaps more desirable because they have clay in them. Once the paper is collected it is sometimes soaked in water before being placed into a large mixer with the concrete or clay and sand. It is then shaped into blocks, like adobe, or poured into slip forms, like rammed earth. Occasionally the earthbag technique is used too. It can also be used as a plaster for other alternatively built houses. This is perhaps, the better way to use it.
Papercrete has several problems to work out. It is such a new concept that it hasn’t been tried long term (over twenty years) yet. It is extremely susceptible to moisture because it essentially acts as a sponge unless it is plastered or coated. Even then, if moisture gets past the plaster, it creates an ideal habitat for mold. Some early papercrete houses are already uninhabitable because of mold problems. Papercrete houses also pull moisture from the ground if it is in direct contact with the earth. Again, not a good idea.
This is one of the oldest building technique that is still in use today. It has many advantages, but specifically being vermin-, dust-, fire-, flood-, insect-, bullet-, and rust-resistant. It is also easily cleaned with a sponge, and requires minimal maintenance. Because the materials used are non-toxic, adobe buildings are non-allergenic.
Adobe is basically just mud mixed with a bit of straw. The best adobe soil is 15 to 30% clay with the rest being mostly sand or larger aggregate; it is occasionally stabilized with cement or asphalt emulsion. This mixture is then shaped into blocks to either form walls by stacking, like bricks, or to be just stacked to create a structure over time. The buildings need large eaves to protect the walls and foundation from the weather.
Unfortunately, adobe, while it has good thermal mass, doesn’t insulate very well. This is sometimes fixed by making a double wall with an air space or insulator in between. Insulating materials can also be on the exterior.
This is a building technique that was thought up by Michael Reynolds. He realized that any material, be it cans, bottles, or old tires, could be extremely energy efficient if it was filled with earth.
Earthship is a method of energy efficient building that uses rammed earth and tires as the bulk of the construction material. There is quite a bit of information about this type of construction on the internet, and it is gaining popularity.
The first consideration that must be taken with earthship construction is the land. It needs to be south facing to allow the earthship to catch the southern sun in the winter. Once you’ve got your land it’s time to begin construction.
Tires are the main building material. They are filled with earth which is then packed with either a sledge hammer or a pneumatic tamper. This process usually takes between fifteen and thirty minutes per tire. Once they are packed the tires weigh up to three hundred pounds which creates a very sturdy wall. The tires are stacked or staggered like bricks, and concrete blocks are used on the ends of rows where full tires can’t be used.
Rooms are created by placing the tires in large U shapes with the open side of the U facing south. For this reason the rooms in earthships are not called “rooms” but “U’s.”
This type of alternative construction is also known as sandbag. It is very resistant to severe weather, but also to bullets and bombs.
When researching earthbag houses one name that you invariably come across is Nader Khalili. He used his familiarity with Middle Eastern architecture to create a more modern earthbag building technique. His “super adobe” method was first used in the Persian Gulf War for emergency shelters for refugees.
Traditionally, burlap bags have been used, but they eventually rot. Polypropylene bags are used today. They are more durable, if they are kept away from the sun.
The building procedure is quite simple:
Fill bags or tubes using suitable pre-moistened earth.
Close, fold, and pin the bags to make neat, square-cornered rectangles similar to grocery-store brown bags.
Lay the finished bags in a masonry-style running board.
Thoroughly compact with hand tampers after the row has been laid.
Lay two strands of four-point barbed wire, held down with bricks, between every row. This acts as a “Velcro mortar,” cinching the bags in place and providing exceptional tensile strength (resistance to lengthwise stress) while allowing the rows to be stepped, creating corbelled domes and other unusual shapes.
Over the earthbag, apply exterior and interior plasters.
This is an alternative building option that is, obviously, best in wooded areas that can take advantage of the local supply. It is also know as cordwood masonry, stackwall construction, and stackwood construction. It is a very aesthetically pleasing, rustic type of building.
This takes that basic idea of stone walls and applies it to cordwood. Short lengths of cordwood or debarked tree are laid crosswise with cob or mortar. The walls are generally between twelve and twenty four inches thick. The cost is significantly less than the initial cost of stick frame houses if the labor is mostly done by the owner and/or volunteers.
There are certain types of wood that are more acceptable than others: Pacific yew, the new growth of bald cypress, cedars, and junipers. However, Douglas fir, western larch, Eastern white pine, spruce pine poplar, tamarack, and Monterey pine are also alright. Less dense, airy woods are superior because that type of wood wouldn’t shrink or expand as much. Most woods can be used though if they have been properly dried and acclimated to the area’s humidity. Logs from the same species and source are preferred because any shrinking and expanding they will do will be closer to the same.
This type of alternative building is also known as pisé de terre or pisé. It can be built for no more than two-thirds the cost of a standard frame house.
Rammed earth is a building technique that employs damp soil mixed with some sort of stabilizer, lime or animal blood in ancient times, concrete today, and poured four to ten inches thick into a framework. A pneumatically-powered backfill tamper is then used to compact material to about half its original depth. The process is repeated until the wall reaches the desired height. The forms can be removed immediately because the walls are so solid. If wire-brushing, to add texture, is desired then the forms must be immediately removed: the wall becomes too hard to brush after an hour.
The framework is most commonly made of reinforced plywood, but sheet metal and glass fiber can also be used. The forms can be reused. Re-bar, wood, or bamboo can be used to reinforce the walls to help prevent failure during earthquakes and strong storms.
Cob is a type of building that is centuries old, and recently enjoying a revival in interest. Cob material consists of clay, sand, straw, water, and earth. These ingredients are mixed up traditionally with hands and feet. It is then tossed from one builder to another in clumps, and piled up to form a wall. The builders allow one layer to dry before trimming and shaping and adding another layer. In this way, cob building is very labor-intensive, however, the cost of labor is offset by the overall cheaper cost of the finished building.
Cob is fireproof, resistant to rain and cold, and resistant to seismic activity. However, it will hold up much better if it is built on a large foundation, and if the roof overhangs quite a lot.
Cob walls are generally twenty four inches thick. This makes it ideal for passive solar construction. In fact, cob is a better insulating material than adobe. This type of building lends itself to being artistically shaped:
