Air Leakage or "Accidental Ventilation" as we like to call it. Air leakage in a building represents 5-40 % of the space-conditioning cost. Air leaking in is often referred to as infiltration, and air leaking out as exfiltration. Controlling air leakage is one of the most important functions and often the most difficult for existing construction. For new homes, it is very important to address air-sealing techniques and strategies during construction. Some of the principals and functions of air leakage control are to: • Save energy. • Increase the comfort of the occupant. • Protect insulation’s thermal performance and integrity. • Reduce direct cooling or heating of people and building components by outdoor air. • Avoid moisture migration into building cavities. • Reduce vermin’s access into the interior shell. • Reduce flow of air pollution from external sources. • Reduce moisture leakage. • Enhance fire safety. Pressures driving natural and internal air leakage come from: • Wind pressure – Windward side of the building experiences a positive pressure for infiltration, and on the leeward side can create a negative pressure for exfiltration. • Stack-effect pressure - The draft established in a building from air infiltrating low and exfiltrating high • Exhausting devices such as furnace blowers, clothes dryers, bathroom fans and stove exhaust hoods Direct air leakage occurs at windows, doors and other concentrations of seams and building component integrations. These types are leaks obliviously easier to locate and seal, indirect leaks on the other hand can be very challenging to locate and seal. The air can penetrate the shell in one area, flow through the building cavities and emerge at different location. Prominent among hidden indirect air leaks are those found in intermediate zones like attics, porches, attached garages, or crawls spaces. Blower Door testing can be very beneficial in locating these leaks and also estimating the size of the leakage areas. To find out more about Blower Door Click Here Building materials can also be a source of air leakage that is not often recognized. Concrete block, brick, perforated felt and most insulation materials (especially fiberglass) have relatively high air permeability and can’t be consider air barriers. For more info on air sealing from the EPA, Click Here (You will need the free Adobe Acrobat Reader) Keep in mind that air leakage can alter the performance of the insulation products that are being used to achieve thermal continuity in the building.. It is very important that the pressure (air leakage) and thermal boundaries of the building system are in alignment.