Buildings under pressure -- Part 3

For years building consultants have said air leakage is the chief cause of exterior wall issues including efflorescence, masonry spall,  ice build-up, frozen pipes, wall cavity condensation, high energy costs and poor indoor humidity control.

In our last few posts, we discussed two major causes of building air leaks – wind and stack pressure. Today, we address the third most common cause of air leaks – HVAC fan pressure.

Fan pressure is caused by HVAC system pressurization. Negative fan pressure creates a vacuum effect on the building envelope by drawing in cool, dry air in winter months and hot, humid air in summer months. Conversely, positive fan pressure pushes warm, moist air into the building envelope in the winter and deposits condensation on surfaces within walls and roof enclosures. 

A study released in 2005 by the National Institute of Standards and Technology (NIST) reported that building owners can save 15-40% on HVAC energy costs simply by sealing the building envelope.  The evidence is indisputable:  a properly installed air and vapor barrier system is critical to achieving long-term energy efficiency and indoor environmental quality performance goals.