The control function refers to one of the three functions a building envelope serves. This function is vital to the overall performance of the envelope. The control function refers to the ability of a building envelope to control and moderate the exchange of mass (air and moisture) and energy (heat and sound) due to the separation of interior and exterior environments. A building envelope has a set of functional requirements that must be met, and the control functions are a subcategory of these overall functional requirements.
In terms of the control function, the main purpose of the building envelope is to maintain a specific, comfortable internal climate despite changing conditions in the external environment. Its purpose is to make a building comfortable and livable.
The following are important exchanges between the external and internal environment (or within the internal environment itself):
Experience indicates the control of moisture movement is most fundamental. When this is satisfied, the other control requirements are either simultaneously satisfied, or more easily satisfied.
Controlling heat in a home is mainly done through the HVAC system to ensure that air at a comfortable temperature is spread throughout the building. This requires the proper use and installation of furnaces and vents. Improvements to home energy efficiency can be made using natural heating through: *Passive solar heating
Controlling moisture is one of the most important functions that the building envelope serves, since the harmful effects of water in building materials is extensive. Mold and rot are two harmful effects of moisture intrusion in a house. Although in many instances the water by itself is not harmful (only when combined with other effects) it is vital to control water and moisture inside a building to prevent costly repairs and improve effectiveness of insulation efforts. For this reason, addressing the moisture in building enclosures generally takes precedence over other measures. Since water usually gets into the home through air currents, diffision, or heat transfer it is very simple to control moisture. Properly sealing cracks and paths that air can come in prevents moist air from entering the home. Choosing effective building materials for siding and insulation helps prevent rain or moist air from penetrating the home. As well, the use of vapor barries in walls prevents water coming in through diffusion. Finally, sloping of the ground away from the foundation and the proper use of weatherstripping and caulking in fenestration prevents excess water from entering the home.
Finally, controlling air flows in a building can work to manage both heat and moisture flows as it is very closely connected to the other two phenomenon. Through the use of an HVAC system to control air flows inside the building in an efficient way while ensuring that a home is properly sealed with weatherstripping, caulking, and proper insulation prevents unwanted air flows from the outside from entering a building. As well, methods to ensure that changes in pressures do not greatly effect how well a home is sealed should be taken into account as it is desireable to have a well sealed home in a number of conditions.