Even with a very good envelope, a building will still loose heat in cold weather and gain it when it is hot outside. Your basic cost-saving objective is to minimize the cost to correct these loses and gains. In the book “The Energy Efficiency Guide for Businesses, Industry, Government and Institutions” Third Edition on their segment titled “Envelope”, the objectives to minimize energy costs caused by unwanted heat loss and unwanted heat are clearly stated.
These objectives are to: stop infiltration, reduce heat transfer, control humidity, and control sunlight.
Prevent the leaking in of outside air, and likewise prevent the leaking out of inside air you have paid to heat or cool, through openings such as cracks in walls around windows, and where doors don’t fit or close properly.
Reduce Heat Transfer:
Minimize the transfer of heat through materials in the building envelope by conduction and convection. Heat always flows from a warmer environment to a colder one. All materials conduct heat, but some, such metal or a single pane of window glass, conduct it faster than a substance such as fibreglass, which is a poor conductor and therefore a good insulator.“R” value is a measure of resistance to heat flow; the higher the “R” value number, the higher the resistance. There are various ways you can increase the “R” value of your roof, walls, floor, and windows, to reduce the transfer of heat from one side to the other.·
Control the movement of water vapour in and out to achieve appropriate humidity levels. For health, comfort, and protection of materials such as wood, relative humidity should range between 30-60%. Vapour barriers and ventilation can prevent condensation and associated rot and mildew problems.
By letting in the sun’s light and heat or blocking them out when not wanted, you can reduce levels of artificial light, heating, ventilating, and air conditioning loads.