If all goes as planned this will be the first in a series of articles about sustainable building. I have happened upon many interesting quandaries in my attempt to come up with a good design for a roof, so I will start there.
A roof that functions properly is extremely important for the longevity of a structure. The main function of any roof is to keep water away from the occupants and more importantly away from the walls and floor. After all, it is much easier to towel off a Dancing Rabbit than dry a 30 foot long wooden timber encased in stucco. Secondary roof functions include keeping heat in during the winter and heat out during the summer, which of course means providing a location for overhead insulation. An important aspect of roofing, that is sometimes overlooked in "eco-building", is ease of maintenance. Even the most conscientious home-owner will overlook a leaky roof until it is too late and the damage is done. So these criteria, plus weighing the environmental impact of a roofing system, gives us a definite bias when looking at our roofing options.
The most widely used roofing method used in the United States involves virgin lumber rafters set at a 25 to 45 degree pitch. These rafters are then connected together by 1/2 inch plywood for sheathing and covered with a layer of tarpaper and then a layer of tar/asphalt shingles. These shingles need to be replaced approximately every ten years. In addition ,every spring the roof should be walked, looking for damaged shingles or other spots where water can penetrate. This method traditionally uses no recycled materials, uses petroleum products, and virgin lumber. This method is undoubtedly unsustainable, not to mention uneconomical. However, it is very effective for all of our criteria except the earth-friendly category.
Ways to make this method a little more friendly to Mother Nature include using reused rafters from old buildings, reused siding from old barns as a sheathing, and recycled corrugated steel as a water proofing barrier. With these changes come different maintenance protocol. The steel has to be inspected for rust especially around the holes that are made to fasten it to the sheathing. Besides steel, old tires, clay tiles, wooden shakes, or phragmites (reed thatching) can be used as a water proofing barrier. These all have their special environmental impact and maintenance problems.
One issue that I have not brought up is the architectural consequences of having a triangular shaped roof. Aesthetically it breaks up natural lines present on almost any building site (mountainous regions excepted). It also tends to catch air (I do not mean this in the rad skate boarding hip kind of way). I mean that it gets bombarded by wind and weather which sucks heat and cold from a structure as if it were beer in the hands of a college student on a Saturday night (yuum beeeer). So with this in mind we move to the flat roofs and almost flat roofs.
Let's start with the architectural benefits. A flat roof in combination with earth berms can really allow a building to be protected from beer guzzling winds. I mean heat guzzling winds. Ideally the berm would be on the north side of the house (or on the side in which prevailing winter winds blow). The structure would face generally southward. The almost flat roof with a pitch of 7 to 14 degrees could pitch towards the back of the house or towards the front.
The framing for a flat or almost flat roof can be framed in several ways. I will not go into the common methods of using virgin lumber 2 x 12 laid in a joist-like manner, however, I will say that with reused lumber this is a more attractive option. Making mono-trusses, which are web like joists, provides an option that can use scrap lumber and provide a large space that can be super insulated. Timber framing is also a likely option. Using posts and beams from torn down barns could provide the heavy duty structure needed if, for instance, a living roof is desired.
So let 's talk about living roofs. A living roof is characterized by having actual soil on top of the roof and plants growing to keep it there. A living roof helps blend a structure into its natural surroundings and with a little landscaping can cause a building to disappear entirely. The earth on the roof also acts as a blanket insulating the house from the elements. The major concern with a living roof is with the water proof membrane that goes under the soil. The membrane has to be absolutely water tight and allow for no maintenance which requires removing the earth. Since most small structures are not designed for earth moving equipment this work has to be done by hand. Digging up a roof every couple of years is extremely frustrating and not recommended by the people who have had to do it. So what are the options for water tight membranes? Unfortunately, the best options are petroleum products such as polymer based bitumen membranes or PVC membranes (which may have a recycled aspect). One of the most exciting options is bentonite clay. Bentonite is a natural clay that is mined mainly in the South. It is traditionally laid in sheets or sprayed on, and expands when it comes in contact with water making it impermeable to any more H2O. The clay must remain moist to retain its impermeability, so use of bentonite is limited to non-arid regions. Exactly how non-arid I do not know. Bentonite must also be laid on something that can handle damp clay sitting on it for one hundred years, such as concrete. Wood would quickly rot. I have always liked the idea of living roofs, and here in Scotland county there is salvage wood aplenty, so I have a problem to solve. How can I use bentonite clay on my wooden roof? One possibility that needs to be flushed out is light weight concrete. Developed for use in wood frame apartments, light weight concrete deadens noise on upper story apartment floors. Exactly how earth friendly it is warrants more research. Oh, one more concern with using bentonite is that roots can grow through it disturbing the integrity of the clay as a membrane. I here tell laying down a layer of soil fabric eliminates this concern. However, soil fabric is made up of creosoted nylon burlap (enough said).
So there are two questions to answer. What is light weight concrete all about? And what is a Mother Nature friendly way to keep roots out of my water proofing membrane? If you have any solutions to my problem or great ideas I didn't even mention, you can e-mail me directly at halle@gte.net or write to us here at the farm.
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