October 23rd, 2012
Using green roofs on our homes is just one way to be environmentally friendly by cooling buildings in summer, insulating them in winter, and reducing storm water run-off. Green roofs have been used for a long time, and now we can update the construction with our modern techniques.
What’s a green roof? It’s what you see on top of Chicago City Hall, lots of tall buildings in Portland, Ore., and the vast 10-acre roof of Ford Motor Company’s assembly plant in Dearborn, Mich.: A green roof is planted with a dense layer of vegetation that absorbs rainwater, filters air pollutants, provides insulation and can create wildlife habitat. If enough buildings with green roofs are in close proximity, the respiring plants even create a microclimate that can cool a city.
There are two basic types of green roofs: An intensive one more closely mimics a lush natural garden, complete with a base layer of 2 to 4 feet of soil. An extensive green roof has only 2 to 6 inches of growing medium (generally not soil), and so is much lighter. See examples of both types of green roofs.
The roof can be neat or more natural. It can be used for homes and offices:
Often, roofs are carpeted with a variety of short plants, but some roofs practically resemble a forest, as at the Coast Hotel in Vancouver, British Columbia. (See: hrt.msu.edu/greenroof). While the U.S. so far doesn’t match Germany’s zeal for green roofs — it’s estimated that at least 10 percent of flat-roofed buildings in Germany are covered with vegetation — the concept has growing cache here. Examples abound, including the Social Security Administration Building in New Bedford, Mass. (tinyurl.com) and Atlanta City Hall (epa.gov/hiri/strategies/greenroofs).
But, will it save money?
Installing a green roof costs more up front, but it can save money in the long run: A green roof can be up to 100 degrees cooler than a traditional roof, and so cuts the cost of a/c by up to 50 percent. Because it can prevent heat loss through the roof of the building, it cuts heating costs by up to 25 percent. A green roof also extends the life of the roofing membrane by protecting it from the elements. And, when you’re ready to resell, a green roof can increase property value by as much as 15 percent.
For quite a number of years, people have also used thatch and bamboo. But how do they compare to green roofs?
Green Home Building has an analysis of them here.
Q: Is there a way for me to make a form or pattern for a terra cotta roofing material made from this South Carolina red clay that is abundant here? I hope you can point me in the right direction. I have this idea to use a pvc pipe to act as a form for the tile and to bake it in an outdoor oven on my farm.
A: I have never done this work, therefore I contacted a friend that has had some experience with this. Here is what she said…..
The typical traditional thing is to use a wooden mold and lay the clay mix for the tile in a slab over it for forming. These molds are usually tapered at one end. I’ve been playing with using a used roof tile, purchased from a building recycling center, as a mold. Depending on diameter and taking into consideration shrinkage of the clay a PVC pipe cut to length should work
just fine. Clay has the great ability to hold shape memory and retain it after it comes off the mold, yet before it is dry. In Mexico we would stack them right into the earthen kiln wet and keep a small fire going to dry them. Once dry they were stacked in a ‘house’ and fired in groups of 2,000 or more for three or four days. There are many ways to do it and the most important thing is to find the right material and mix that can handle the form and fire.
Another great article that also discusses thatch and how to properly vent the roof is here.
Venting the Roof
It is not uncommon throughout cold and snowy places to see the effects of ‘ice damming’ — deadly stalactites of ice hanging from the gutters, threatening to impale unwary passers-by, and causing roof leaking due to water back-up on the roof. What’s happening here is that warm air from the building rises and heats the underside of the roof. This in turns melts the bottom of the snow pack on top of the roof, and the resulting water runs along the roof to the eve, where upon reaching the unheated edge of the roof, refreezes into ice, dripping into massive icicles and blocking the way for the water behind it to run off, which in turn backs up under shingles and flashing. There are two ways of avoiding this: venting your roof, or having a very well-insulated roof. In the latter, one relies on the quality of insulation and air barrier in the roof system to keep any warm air from the house from reaching the roof. This has a benefit of allowing the roof to retain snow (depending on roof type and pitch), which is itself an insulator. An example of this are ‘panel roofs’, which are thick foam-insulated roofing panels crane-lifted onto roof structures (often exposed timber framed roofs). The vented roof refers to a channel of cold, atmospheric air ducted underneath the roofing or sheathing and vented at the eves and gable ends or ridge; this ensures that any warm air that does reach the underside of the roof is vented away, keeping the roof cold. Hence the colloquial name for such as system: the ‘cold roof’. Such roofs are often considered to be the most reliable for avoiding ice damming. Different roofs will call for different strategies, and it should be recognized that one is not inherently better than the other; rather, one is better suited to certain roof and building designs than the other, and both should be considered when making a decision as to what type of roof is right for the building.
Moss Acres has a fun article here describing what green roofs are and how to incorporate one using your existing roof.
Think you would try a green roof?