© 2005 Door & Access Systems
Publish Date: Fall 2005
Author: Joe Hetzel
Page 70

ASK JOE HETZEL

Garage Door = Automatic Ventilation?

Q: I’ve heard that, instead of putting vents in a garage door, the garage door itself meets ventilation requirements. Is this true?

A: Yes. Florida recently issued a “declaratory statement” on this matter. Florida often uses such statements to help interpret the building code.

In this case, Florida examined natural ventilation requirements in the Florida Mechanical Code. Their statement concluded, “The fact that a garage door may be closed a majority of the time has absolutely no bearing … the space need only be openable, not open (italics added).”

Since the square footage of even the smallest garage door is usually greater than four percent of the square footage of the floor area of the garage, the door itself easily meets the code minimum.

Wind Speed Confusion

Q: Are the wind speeds reported with hurricanes comparable to the wind speeds specified in building codes?

A: No. This is a common misunderstanding. The hurricane wind speeds of the Saffir-Simpson Scale, often reported in the media, are measured differently than design wind speeds in today’s model codes.

The Scale winds are considered “sustained” winds and are based on 60-second measurements of wind. Code design winds are considered “peak gust” winds, and are based on 3-second measurements. The conversion chart (below) illustrates the differences between sustained winds and peak gusts.

In a typical 60-second period, the wind will fluctuate and contain some higher gusts. Wind engineers have found that the peak gusts are about 20-25 percent higher than the wind averaged over that period.

So, for a Category 1 hurricane with 74 mph-sustained (60-second measurement) winds, the winds will typically include gusts that peak around 90 mph (3-second measurement). The 90-mph number is the one that should be compared against the design wind speed for the affected area.