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[[Category:Done 2015-04-01]] 
[[File:Control_function(good)3.png|400px|right|framed|Figure 1. Illustration of different environmental effects controlled by the building envelope, also taking into account the internal environment.<ref>"Control Function" by Augustine Musa.</ref>]]

<onlyinclude>The '''control function''' refers to one of the three functions a [[building envelope]] serves, and it 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.</onlyinclude><ref name="R1">Building Science Corporation. (March 20, 2015). ''The Building Enclosure'' [Online]. Available: http://www.buildingscience.com/documents/digests/bsd-018-the-building-enclosure_revised</ref> 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.<ref name="R2">National Institute of Building Sciences. (March 20, 2015). ''Function and Performance'' [Online]. Available: http://www.wbdg.org/design/env_introduction.php#fap</ref>

In terms of the control function, the main purpose of the building envelope is to maintain a specific, comfortable internal climate dispite changing conditions in the external environment. Its purpose is to make a building comfortable and livable, and thus ensuring the control function of a building is satisfactory is of the utmost importance. Specifically, the flows that are most vital to control between the external and internal environments or within the internal environment itself are:<ref name="R3">National Institute of Building Sciences. (March 20, 2015). ''Building Enclosure Design Strategies'' [Online]. Available: http://www.wbdg.org/resources/buildingenclosuredesignstrategies.php</ref>

# '''Heat''': Controlling [[thermal energy|thermal]] (heat) exchange between inside and outside environment
# '''Air''': Controlling air flow due to leakage, wind [[pressure]], or internal partitioning
# '''Moisture''': Controlling moisture transfer due to rain, vapour diffusion, or condensation
# '''Sun''': Controlling solar transfer from [[fenestration]] (windows, doors etc.) or dealing with insufficient natural lighting
# '''Sound''': Controlling ambient sound, excessive sound, or sound due to vibrations
# '''Fire''': Control the spread of fire within a home from the inside or outside through the use of fire doors and windows

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.<ref name="R3"/>

==Controlling Heat==
Controlling heat in a home is mainly done through the [[HVAC]] system ensure that air at a comfortable temperature is spread throughout the building. This requires the proper use and installation  of [[furnace]]s and vents. Improvements to home energy efficiency can be made using natural heating through [[passive solar heating and cooling|passive solar heating]] and the use of [[trombe wall]]s, [[solar wall]]s, or [[solar chimney]]s and through the selection of proper [[insulation]] to prevent undesirable temperatures inside.<ref>Building Science Corporation. (March 20, 2015). ''Thermal Control in Buildings'' [Online]. Available: http://www.buildingscience.com/documents/digests/bsd-011-thermal-control-in-buildings</ref>

==Controlling Moisture==
Controlling moisture is one of the most important functions that the building envelope serves, due to the fact that the harmful effects of water in building materials is extensive. Mold and rot are two of the most harmful effects of moisture intrusion in a house. Although in many instances the water by itself is not harmful - only becoming an issue 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 control of moisture in building enclosures generally takes precedence over other measures.<ref name="R3"/> 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.<ref>US Department of Energy. (March 20, 2015). ''Moisture Control'' [Online]. Available: http://energy.gov/energysaver/articles/moisture-control</ref>

==Controlling Air==
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 weather stripping, 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.<ref>Rick Quirouette, B.Arch. (March 20, 2015). ''Air Pressure and the Building Envelope'' [Online]. Available: https://www.cmhc-schl.gc.ca/en/inpr/bude/himu/coedar/upload/Air-Pressure-and-the-Building-Envelope.pdf</ref>

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