BCAB #1009 - Ventilation in Crawl Space, Subsection 9.18.3.

June 10, 1988

BCAB #1009

Re: Ventilation in Crawl Space, Subsection 9.18.3.

With reference to your letter of May 10, 1988 regarding the ventilation of a crawl space. This requirement is dealt with under Subsection 9.18.3. of the Code, and in view of the differing interpretations it is preferable that we address the question on a general basis.

Article 9.18.3.1. would appear to be a mandatory statement of principle, requiring that all crawl spaces be ventilated by natural or mechanical means, applicable to both heated and unheated crawl spaces, except as provided in Article 9.18.3.5. This general application, however, is not supported by the specific requirements.

Article 9.18.3.2. specifically requires venting to the outside, unless the crawl space is being used as a warm-air plenum or is vented to an adjacent basement, as provided in Article 9.18.3.5.

Article 9.18.3.3. requires vent covers to prevent the entry of snow into a heated crawl space. In other words, during the heating season the crawl space can be sealed whether or not used as a warm-air plenum, basically ensuring ventilation only during the non heating season.

Article 9.18.3.5. provides two acceptable alternatives for venting to the outside air, but if the crawl space is used as a warm-air plenum then ventilation is only ensured during the heating season, the opposite of Article 9.18.3.3.

In your specific situation the crawl space is heated, and as it is not being used as a warm-air plenum we must conclude that, despite the inconsistency of Article 9.18.3.3., the Code requires it to be ventilated either to the outside air or to a suitable adjacent basement.

While we consider this to be applicable for a normal crawl space, we must qualify our decision in the case of a crawl space ventilated in accordance with Article 9.33.3.1. In such a circumstance, with the space being treated as part of the heated enclosure, we would not regard the application of Subsection 9.18.3. as mandatory. It would seem from the information provided that your system should be readily adaptable to provide for this.

J.C. Currie, Chair