| off-gassing | materials may give off gases, some of which are toxic. implicated in a variety of ailments, some people are more sensitive than others to these gases. |
| off-grid electricity | electricity produced by small generating units that are not connected to high-voltage transmission lines. |
| offsetting | a way of compensating for the emissions produced with an equivalent carbon dioxide saving, by buying carbon offset credits from emission reduction projects; such projects will prevent or have already prevented the emission, or removed an equivalent amount, of carbon dioxide elsewhere in the world. |
| on site stormwater detention (osd) | onsite stormwater detention (osd) is an option where suds are not practical due to soil and ground conditions. this is normally achieved by installing large diameter pipes, culverts or tanks. the basic principal of on-site storage is that during heavy rain, surface water run-off from roofs, car parks and large paved areas is directed to a storage tank. water is stored and normally discharged to a main sewer using a suitable flow control device. at the end of heavy rain, the storage tank is typically emptied either as a gravitational or pumped system and is then ready for the next storm. |
| oriented strand board (osb) | wood panels made from wood fibers and chips that are mixed with resin and raked to orient them in the long direction of the panel to maximize strength. osb can replace plywood, thus saving timber. a concern, similar to many manufactured products, is outgassing from the resin binder. osb is also known as flakeboard. |
| ozone (o3) | an important greenhouse gas found in both the stratosphere and the troposphere (lowest region of the atmosphere). in the stratosphere, ozone provides a protective layer shielding the earth from ultraviolet radiation and subsequent harmful health effects on humans and the environment. in the troposphere, oxygen molecules in ozone combine with other chemicals and gases (oxidisation) to cause smog. a chemically unstable and highly reactive gas. |
| ozone depletion potential | odp, is an indication of the potential a chemical, or groups of chemicals in a material, has on depleting the planets protective ozone layer. the higher the odp the more damage the chemical does. materials with zero odp should be used. |
| ozone depletion | nitrogen oxides, chlorine oxides, hydrogen oxides, and bromine oxides destroy the ozone layer. chlorine and bromine reactions are the most detrimental, which include chlorofluorocarbon reactions. |
| ozone layer | the region of the stratosphere (lying approximately 15-40 km above the earth's surface) that contains the bulk of the world's atmospheric ozone. |
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