Roofing

This article is about house construction that consists of beams and an outer weatherproof skin, as found on most domestic architecture. Such roofs may take a number of different shapes. The rafters, tie beams and joists serve to transmit the weight of the roof to the walls of the building. There are a number of structural systems employed to facilitate this, including the use of wall-plates set at the top of the wall, hammer-beams, which spread the weight down the wall and create an equilibrium between outward and upward thrust, king posts which transfer the weight of the roof ridge, and various types of trusses.

A simple ridged roof consists of inclined rafters that rest on horizontal wall-plates on top of each wall. The top ends of the rafters meet at the horizontal ridge plate or ridge beam. Horizontal purlins are fixed to the rafters to support the roof covering. Heavier under purlin are used to support longer rafter spans. Tie beams or ceiling joists, are connected between the lower ends of opposite rafters to prevent them from spreading and forcing the walls apart. Collar beams or collar ties may be fixed higher up between opposite rafters for extra strength.

The related idea of a living machine is based on the most basic cycle of gardening: using wastes (organic waste and sewage), appropriately broken down, usually in some specialized container, on the soil, and harvesting food which, when processed, generates biodegradeable waste, and when eaten, generates sewage. In most of the world, this kind of very tight closed loop gardening is used, despite certain health risks if necessary precautions are not taken. Composting human or pet waste should achieve thermophilic conditions and age for at least a year before being used. Manure from herbivorous animals is safe without these measures.

Cool roof can also be used as a geoengineering technique to tackle global warming based on the principle of solar radiation management, provided that the materials used not only reflect solar energy, but also emit infra-red radiation to cool the planet. This technique can give between 0.01-0.19W/m² of globally-averaged negative forcing, depending on whether cities or all settlements are so treated. This is generally small when compared to the 3.7W/m² of positive forcing from a doubling of CO2. However, in many cases it can be achieved at little or no cost by simply selecting different materials. Further, it can reduce the need for air conditioning, which causes CO2 emissions which worsen global warming. For this reason alone it is still demonstrably worth pursuing as a geoengineering technique.

A green roof is a roof of a building that is partially or completely covered with vegetation and soil, or a growing medium, planted over a waterproofing membrane. This does not refer to roofs which are merely colored green, as with green roof shingles. It may also include additional layers such as a root barrier and drainage and irrigation systems. Container gardens on roofs, where plants are maintained in pots, are not generally considered to be true green roofs, although this is an area of debate. Rooftop ponds are another form of green roofs which are used to treat greywater.