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Mechanical Ventilation Requirements in the IBC2015, IECC2015, and the IMC2015
April 28, 2017
7:43 am
casey archacki
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October 1, 2014
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Hello,

Massachusetts is in Climate Zone 5a.  My question is in regards to buildings which are 4 stories and taller.

April 7, 2017
8:33 pm
troyhodas@gmail.com
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April 12, 2016
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Are the units in a building 3 stories or less?  What climate zone?

November 29, 2016
10:37 am
casey archacki
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Hi Everyone,

I know I might have to post this question directly to the technical opinions board, but I wanted to see if anyone has already come across this issue yet.  My state is close to adopting the International Building Code 2015, International Energy Conservation Code 2015, and the International Mechanical Code 2015.  I was reviewing the books when I came across the following sections:

IBC 2015 Section 1203.1: General. Buildings shall be provided with natural ventilation in accordance with Section 1203.4, or mechanical ventilation in accordance with the International Mechanical Code.

Where the air infiltration rate in the dwelling unit is less than 5 air changes per hour when tested with the blower door at a pressure of 0.2 inch w.c. (50 Pa) in accordance with Section 402.4.1.2 of the International Energy Conservation Code-Residential Provisions, the dwelling unit shall be ventilated by mechanical means in accordance with Section 403 of the International Mechanical Code.

The language is the same in Section 401.2 of the IMC 2015.  Combining these testing requirements with the maximum allowable air leakage rate as shown in Section C402.5 of the IECC 2015 (test to confirm maximum air leakage doesn't exceed air leakage doesn't exceed 0.40 CFM/St. Ft. at 0.3 inch w.c. (75 Pa)), this gives us a small window where natural ventilation is acceptable. 

I spoke to several architects and the biggest concern is if the space is designed with natural ventilation, then the testing is done, and the space doesn't achieve the required 5 ACH, this would be a huge problem as the building is already complete.  Therefore, the safest option would be to provide mechanical ventilation to the dwelling units.  With all that being said, does a 2 speed exhaust fan (continuous low 30 CFM and when the switch is turned on, the fan ramps to 80 CFM) count as a source of mechanical ventilation?  The fan runs continuously and provides enough ventilation for a typical studio or 1-bedroom apartment.

Thank you for providing an insight into this issue.