Green building incorporates a tripod of attributes; energy efficiency (both in material selection and actual energy use), healthy living including indoor air quality, and careful resource management. Green building does not require any architectural style. It doesn’t have to look earthy or organic. It doesn’t have to be expensive to build, nor does it have to look “different”. It can be designed in any style, or any shape. The main focus of green building is to provide benefits to the occupants. These include:

Less expensive to heat and cool
Greater comfort
Healthier, particularly for children
Greater durability
Less maintenance

A green building is a building that is designed, constructed, and operated utilizing a whole-system design approach, with the goal of enhancing the overall environmental performance of the building and the site on which it sits.

A House as a System

A building is a very complex system, wherein each part of the system affects every other part of the system. Consequently, and in turn, each individual sub-system is made up of components. Each component is further made up of individual products, technologies which dictate how the products function, and particularly the relationships between the different products. How things function as a whole is the focus of our investigation.

To begin, lets’ use the analogy of a building envelope (herein referred to as the cumulative parts of all the systems) being similar to the human body. Our bodies have a cooling system, a heating system, both of which require energy, and a waste system. They all work together. In order to maintain personal health and comfort, we all must cool down when we are too hot, heat up when we are too cool, and get rid of waste. Just as our bodies use energy to maintain equilibrium, so must our homes in which we live.

As we breathe, so do our houses. As we sweat when we’re too hot, or shiver when we’re too cold, our houses act in a similar fashion. This is probably the most important factor to understand when following the above analogy. The walls, roofs and foundations in our homes (ie: the skin on our bodies) are the most important parts of the building envelope (our bodies). They regulate the temperature and overall condition of what is inside, and is directly related to how the inside reacts to the outside, the external environment.

Building should work to utilize the benefits of the surrounding environment. Instead of using the same building plans for projects in completely different climates, homes should reflect their surroundings. Responding appropriately to these varied climates will result in more efficient home building.

Whereas temperature, humidity, and wind are some of nature’s characteristics which affect us personally (and dictate how well we feel and how our body reacts), they also affect our homes to much the same degree.

Though there are many important factors to keep in mind, here are the basics. Houses should:
• Designed to fit the surrounding climate
• Control heat, air, and water vapor flow
• Control rain penetration, and water infiltration
• Control light and solar radiation
• Control noise transmittance between rooms and from the outside
• Be durable, strong, and rigid
• Be economical to construct, and maintain
• Be aesthetically pleasing
• Meet the psychological and social needs of its’ inhabitants

Building Science 101

Let us start by explaining heat. Heat flow can flow in any direction (in or out), though it always flows from hot to cold. When we apply this to buildings, and the basic physics that always applies, heat is transferred in any of three main ways: conduction, convection, or radiation.

Conduction: the flow of heat through solid materials due to a temperature difference across the material. Think of a frying pan. Would you rather pick up a hot cast iron pan or a wood handled one? We all knew the answer to that one when we were 2 or 3 years old. Wood is a better insulator than iron. Insulation is a better insulator than wood.

Convection: occurs when gases and liquids are able to move and carry heat with them. Think of a cold draft on your feet on a winter’s night. Hot air rises and cold air is heavier so it falls. When you have both at the same time it creates a draft.

Radiation: occurs when heat is transferred from one surface to another without contact (conduction) or air movement (convection). An object that possesses more heat energy will radiate the heat through space to an object that is colder as we mentioned above. On a hot summer day would you rather stand in the sunshine or in the shade? The air temperature is the same but the experience of heat is a result of the radiation from the sun.

Water movement is just as important as heat flow:

Moisture Movement

Moisture flow is a very important factor, when our goal is to maintain durable and healthy living spaces, as it directly affects our thermal comfort. Moisture can exist as a gas, liquid, or solid. Water vapor, the gaseous form, is always present both on the inside and outside of house. Though it is commonly referred to as relative humidity, being the relative amount of water vapor in the air, at any one time, water vapor has a correlation with the air temperature, and thus our comfort. Warmer air holds more moisture, and colder air holds less. We know about dew in grass after a cool night. Moisture turns from vapor to liquid at the dew point, a temperature at which air can no longer hold the moisture.

Water

Water comes in three forms; solid, liquid or gas. In all forms, it is a major enemy of the building world. A large part of the construction process focuses on keeping moisture out of a building. Rain and snow work hard to find their way under the shingles and siding. It can wreak havoc causing rotting, mold and other damage. It is key to prevent moisture from entering the building in order to create a healthy project that will stand the test of time.

There are many important building methods that will help prevent water infiltration. While water always flows downhill, through capillary action, water can also travel up through porous materials causing additional problems.
Builders should always put felt paper on the roof from the eaves to the ridge with the upper course overlapping the lower course. The same holds true for building wrap under the siding. If it is applied incorrectly, moisture will seep through and rot the sheathing.

Diffusion

Water (like heat) always flows from areas of higher concentration to areas of lower concentration. If there is moist, wet soil on one side of a foundation wall, it will try to find a way through the concrete foundation wall and into the dry, warm basement. It is very important to correctly waterproof foundations and install footing drains to move moisture away from the building. Damaged to foundation is difficult and expensive to repair, and can cause a whole host of other house problems.

Capillary Action

Water can be sucked or pulled through many building materials. It can actually travel uphill and cause unseen rot under siding or under shingles. Builders have to think like water and carefully seal the smallest of gaps in a structure. Proper flashing and detailing is key to help prevent this problem.

Airflow

If air can get into a wall cavity, so can moisture. As building occupants, our daily activities such as showering, cooking and even breathing create a lot of moisture. A plastic vapor barrier applied to the studs under the drywall helps prevent mold from growing in the wall. It is important to put a system in place to catch this moisture and controlling its movement. Good quality exhaust fans and making sure that the dryer vent is correctly installed are both important steps. Better yet, eliminate the cavity, or the space between the studs, that holds insulation that allows air flow. Spray cellulose or spray urethane foam do this job well.

The science just makes sense. The aspects that compose the idea are not that complicated or new. We need these methods to become building norms. Careful planning and detailing at the start of a project will enrich and make the project much simpler. Builders spend just months building a home, but if it’s done correctly, the final product should last for generations to come.

Source:- http://www.greenbuilding.com/knowledge-base/what-green-building-science