Clarifying ventilation

After reading the article "Focus on ventilation," by Dan Perkins, owner of Dan Perkins Construction Inc., Ishpeming, Mich., in the May issue, page 40, I felt it was necessary to address various inaccuracies.

In the third paragraph, Perkins directs readers to Section R806 of the 2003 International Residential Code for the ventilation standard. The article states, "For roof areas over heated or conditioned spaces, a net-free area of 1 square foot per 150 square feet of ceiling area is required."

Nowhere in Section R806 does it state the ventilation requirements are for areas over heated or conditioned spaces.

Section 806.1 states: "Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against the entrance of rain or snow."

The ventilation requirements are for any enclosed attic or rafter space. Section R806 also does not indicate roof ventilation area is based on ceiling area.

Section R806.2 states: "Minimum area. The total net free ventilating area shall not be less than 1 to 150 of the area of the space ventilated ... ."

It does not state ceiling area, which can be less in size than the attic area, depending on how it is measured. In fact, further into the article, Perkins uses a building's width to determine the net free ventilation area.

Perkins also leads readers to believe the 1-150 ratio is the only possibility, which is not correct.

Section R806.2 states: "Minimum area. The total net free ventilating area shall not be less than 1 to 150 of the area of the space ventilated except that the total area is permitted to be reduced to 1 to 300, provided at least 50 percent and not more than 80 percent of the required ventilating area is provided by ventilators located in the upper portion of the space to be ventilated at least 3 feet (914 mm) above eave or cornice vents with the balance of the required ventilation provided by eave or cornice vents. As an alternative, the net free cross-ventilation area may be reduced to 1 to 300 when a vapor barrier having a transmission rate not exceeding 1 perm (57.4•mg/s•m²•Pa) is installed on the warm side of the ceiling."

Since 1977, I have been investigating building problems for various clients. One building problem I have observed on numerous occasions is inadequate roof ventilation. Inadequate ventilation can result in significant damage because of condensation and mold. I do not agree, as Perkins indicates, that a roofing contractor only should ensure ventilation standards are met primarily at the ridge. A roofing contractor may not have the ability to install ventilation at the eave, but it does little good to install the correct amount of ventilation area in the upper roof area (exhaust) without the correct amount of ventilation area in the eave (intake).

A roofing contractor should not let a client believe his building has proper roof ventilation if the intake ventilation area at the eave was not checked. At a minimum, a contractor should inform the client he only has installed the correct ventilation area on the roof (exhaust) and the eave ventilation area (intake) should be checked and corrected as needed by a qualified contractor.

Michael J. Jedrzejewski
Architectural Investigation P.C.
Elk Grove Village, Ill.

Following is Perkins' reply to the article:

It was impressive you analyzed the content carefully and how it corresponded to the wording in the 2003 International Residential Code. You clearly know your business and work with these issues daily.

I also know that when our roof systems don't work, we replace them at our expense. That is why I tend to ventilate to the 1-150 standard and ignore the minimum 1-300 exception. The "inaccuracies" you have found with my reference to the code more likely are misunderstandings, and I apologize for any lack of clarity in my writing.

You noted that nowhere in Section R806 does it mention roof areas have to be over heated or conditioned areas. You are right. However, the code is a residential building code and is written to address the issues associated with these types of buildings. Open attic areas still are areas over heated or conditioned spaces, and the ventilation required for those areas still should meet the 1-150 rule for the ceiling below.

You also are right about the exception allowing for a 1-300 ratio. In a legal battle, a builder or roofing contractor can make a stand on that exception.

My goal is to stay away from legal battles. In the challenging climate of northern Michigan, I need more ventilation to avoid ice-damming issues.

Thanks again for your participation in this debate.


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