Cob Construction

Cob is nothing but the earthen construction, known by different names in different cultures. The word 'COB' meaning 'a lump or loaf' in old English, refers to the mud building system common in old Britain and former English colonies like Australia and New Zealand, which uses no form-work, no wooden supports and no bricks.

Cob is made from sand, straw and clay based subsoil mixed with water to produce moist and malleable building material. It is quite similar to adobe but here higher straw percentage is mixed in. Instead of creating the uniform blocks, cob is normally applied by hand in large gobs where it can tossed by one person to another during the building process. Traditionally cob was mixed by stamping the ingredients together bare feet, but it can also be combined by hand or mechanically by using the backhoe for mixing. This stiff mud is then built up into walls while still wet in courses. Each of the course was sewn into the prior one while both are still pliable. As the bottom of the wall becomes firm and dry, more cob is added on top until desired height is reached taking along the windows, doors, elect. conduits, plumbing, cabinet anchors etc.
This gives a strong, hard and monolithic earthen wall reinforced with interwoven high tensile strength straw fibers.
Advantages :-
1. Durable, resulting in buildings that will last for 100s of years.
2. weather resistant even in harsh climate of Britain coastal line.
3. more resistant to earthquakes as no mortar joints.
4. walls don't burn, rot or get eaten by insects
5. enormous thermal storage capacity, making it ideally suited to passive solar designs.
6. extreme fluidity of forms, cob can be shaped into expressive sculptural forms.
7. Made entirely form natural and recyclable materials, consuming virtually no energy and producing no pollution in manufacture.

Disadvantages :-
1. Extremely thick walls, impractical for smaller plots or tight corners.
2. slow to build with since each layer of 450-600 millimeters takes 3 to 4 days to dry.
3. Variability of applicable soil types requires slightly different ratios of mix ingredients.
4. Cob is susceptible to water damage.
5. Must be built on a masonry foundation to protect against rising damp, and gutters, drainpipes and an overhang roof must be properly maintained to prevent excessive moisture penetrating the walls.

Passive Solar Cooling

In Passive Solar Cooling, Solar Building Design does not aim at using the gained solar energy, but rather it aims at slowing the rate of heat transfer into a building in summer, and improving the removal of unwanted heat.

Passive solar cooling is much easier to achieve in new constructions rather molding the existing ones. Lets see some of the strategies to achieve passive Solar cooling in new designs.

In Hot climates like here in Arizona, North facing walls should have as many openings as possible whereas totally avoiding the south facing wall. This will enhance the light and ventilation and will also reduce the heat absorption. In Cold and temperate climate, South facing walls should have large number of windows for greatest solar gain in summer, But these windows should be protected from high angle midday sun by providing overhangs, awnings or operable slatted shutters. South exposure windows should be operable. Casement windows offer the best airflow. Awning (or hopper) windows should be fully opened or air will be directed to ceiling. Awning windows offer the best rain protection and perform better than double hung windows. If a room can have windows on only one side, use two widely spaced windows instead of one window.

East and west facing walls, which receive low angle sunlight in morning and late afternoon, should have less openings. Best effect can be gained by shading these openings by trees or high shrubs.

Passive ventilation can be effective when windows and vents will be opened to bring in outside air when temperatures are cool mainly in early morning and late evenings. If the outdoor air is very humid or if temperatures don't get much below 65F at night - this may not be much effective.

Solar Chimney can enhance the ventilation though. A Vertical dark colored shaft protruding well above the roof, heats up during the day, pulling the air upward and thus creating the breeze in room below. Another way to achieve ventilation is providing the wholehouse fan, which will draw the air from entire house pushing it out through the vent. As other strategy, make the outlet openings slightly larger than the inlet openings. Even Placing the inlets at low to medium heights will provide airflow at occupant levels in the room, making it more comfortable for occupants.

Applying Low Emissivity film to window glasses can also reduce the heat loss in winter and also the heat gain in summer. Selection of this film is to be done carefully considering the climate conditions.

Reflective and light colored roofing will also reduce the heat gain helping to reduce the cooling costs.