August 9, 2012
To Vent or Not to Vent - Perhaps No Longer an Option
There has been a strong push to increase the energy requirements of the International Energy Conservation Code (IECC) since 2006. Along with some of these changes come some unintended consequences, such as the potential for reduced indoor air quality as a result of more tightly air sealed homes. In an attempt to address this issue, a number of changes were made to the 2012 I-Codes that effectively mandate the use of mechanical ventilation in residential dwellings. But, before we get into the details of requirements, let’s step back to understand why there may be a need for mechanical ventilation.
The general thought is that the air quality outside the home is better than the air quality inside the home. Inside a house there are often higher concentrations of VOCs, moisture, ordors, dust, and bacteria than outside. So any air exchange with the outdoor air will dilute the contaminants and improve indoor air quality.
The 2012 IECC increased the need for mechanical ventilation by dramatically reducing the allowable building air leakage for all low-rise residential buildings (three stories or less) which went from 7 air changes per hour at 50 Pascals of pressure difference (ACH50) in the 2009 IECC to 5 ACH50 in Climate Zones 1 and 2 and 3 ACH50 in all other Climate Zones. This reduction in natural ventilation increased the need for mechanical ventilation.
Code changes were made in the residential section of the 2012 IECC and the International Residential Code (IRC) which require mechanical ventilation for virtually all one- and two-family dwellings and in the International Building Code (IBC) for multifamily buildings three stories or less. For multifamily buildings four stories or higher, mechanical ventilation is required except when there is more than 4% openable area and the unit has not been tested to an air tightness level less than 5ACH50.
The 2012 IRC requires mechanical ventilation for any dwelling tested tighter than 5 ACH50 and the 2012 IECC requires all dwellings be tested to 5 ACH50 or tighter in climate zones 1 and 2 and 3 ACH50 or tighter in all other climate zones. Technically, a house in climate zone 1 or 2 which is tested to exactly 5 ACH50 would not need mechanical ventilation; however, it is difficult to know in advance what tightness the building will meet. So it is not anticipated that builders will not install mechanical ventilation hoping to achieve exactly 5 ACH50
There are four requirements for the installation of mechanical ventilation systems that a builder needs to be aware of:
- It must meet the ventilation rate requirement of the code (e.g. ,75 CFM for a 2,500 square foot, 4-bedroom house)
- It must meet the efficacy requirements (e.g., 2.8 CFM/watt for any 90+ CFM fan)
- It must be vented to the outside (not to an attic)
- It must have a user-operable, manual override on/off switch
The simplest solution to meeting the requirement of the 2012 I-Codes would include a high efficiency exhaust fan installed in a bathroom with sufficient air flow, a wall switch, and vented to the outside. It should be noted that this solution has the potential to depressurize a house which could be problematic when there are combustion appliances within the building envelope that have the potential to backdraft the flue gasses. Common solutions which would significantly reduce the backdraft potential would include direct vent appliances, supply mechanical ventilation (rather than exhaust) or balanced ventilation (e.g., Energy Recovery Ventilators).
The Home Innovation is always on the forefront of what’s happening in the building code arena and are happy to help builders and manufacturers navigate the imminent changes and those more on the horizon.
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February 12, 2013 2:45 PM