Building envelope consulting and design has become one of the prime influencer in developing energy efficient buildings. Its failure can cause an array of safety issues and adversely affect the health and wellbeing of occupants. Building condition assessment and evaluation is the first step towards gauging building envelope performance and identifying the dysfunctional elements, thus working towards improving the energy efficiency of a building.
What is a building envelope?
A building’s envelope is an interface between the exterior environment and interior space of a building. It includes the walls, doors, windows, roof, foundation etc. A building envelope determines how well the inner space in buildings remains protected and conditioned, i.e. it determines the quantity of energy required to regulate indoor temperature and maintain thermal comfort.
“Today, buildings (residential and commercial) consume nearly 70% of the electricity load in US and account for almost 39% of total greenhouse gas (GHG) emissions.”
A building envelop affects energy consumption and hence subsequently GHG emissions in many ways. How? Read on to know
Evaluation and design of building envelopes for existing buildings and making necessary improvements can reduce heat transmission through the interiors to exterior environment and vice versa. Hence in cold climates this reduces the cost of heating and in hot climate it reduces the cost of cooling. Apart from heating and cooling, the envelope design can also be optimized for better ventilation and day lighting. This also improves the light efficiency and hence lowers the light bills as well. Some examples of a well designed building envelope include having a south facing window in cold temperatures and providing shading to obstruct direct sunrays in hot climatic conditions.
Important factors that contribute to a better and energy efficient building design, are materials and products ‘used in and associated with’ a building’s envelope.
The energy required –known as embodied energy- for manufacture, transport, storage and installation of building materials used for the building envelop are the associated factors that contribute to the energy costs of a building. If efforts are made towards making these processes efficient, the energy consumption and CO2 emissions can be reduced and hence the associated costs can also be brought down.
Now, materials and products used in roofs, walls, doors and windows and insulation and air sealing are directly a part of the building envelope. Choosing the right materials and improving envelope is important. Why? Let’s understand.
- Insulation and air sealing:
Heat always flows from a hot space to a colder space. So what does insulation and air sealing do? In summers it does not allow the outside heat to make way into the cool interiors of a building and in winters it prevents the warmth inside a room to go outside. Strategically adding insulation improves the building’s energy efficiency; however care has to be taken that the building is properly sealed no cracks and leaks should be left out.
- Roof design:
Roofing plays a crucial role in reducing the amount of air conditioning requirement in hot climates. Well designed roof reflects solar heat rather that absorbing it, alternatively installing onsite solar energy generation systems on rooftops can also result in a step towards a net zero energy building.
- Walls, windows, doors and skylights:
The materials used for walls, windows, doors and skylights together determine a buildings thermal mass and can affect its thermal properties. Such buildings where the best materials are used for an improved thermal mass absorb energy slowly and then retain it for a longer time, hence maintaining the buildings temperature for a longer time. Windows, doors and skylights in a building are collectively called fenestration. In addition to the material and design; placement of these elements is also very important.
Optimizing window design and glazing specifications can reduce the energy consumption in residential buildings from10 to 50 percent below the acceptable practice. In commercial buildings, improved fenestration reduces the costs for lighting and HVAC by 10 to 40 percent.
Improvements in building envelope significantly affects the energy consumed in HVAC and lighting. By appropriate selection of materials for a buildings envelop and optimizing the design for higher energy efficiency, not only can we reduce the green house gas – GHG emissions but also enjoy better occupant comfort at reduced HVAC and lighting bills, thus leading to long term savings and hence cost efficiency.