Heavy stuff weighs on roofs

MANASSAS, Va. -- The older the home or business, the more likely it will hold less snow, according to International Building Code.

Any structure built between 1975 and 1990 is required to handle up to 25 pounds of snow per square foot; any building built after that time is required to handle 30.

But as evidenced by Mother Nature's fury, newer isn't always safer.

On Saturday, the area was pounded with nearly two feet of snow after 20 inches fell a week before Christmas. The weight of the snow from this weekend's storm collapsed the roof of the Prince William Ice Center, which was built in Dale City in 1996.

On Monday, Manassas city officials deemed Mayfield Intermediate School unsafe after the roof started to show signs of collapse.

According to city schools spokeswoman Al Radford, a structural engineer has evaluated the situation and determined that the building cannot be used until the entire structural system is evaluated and the compromised structural trusses replaced.

This will require, at least for the next several weeks, that the Mayfield Intermediate School students and staff be housed elsewhere. Staff are working on alternatives regarding instructional settings. Mayfield serves approximately 1,000 fifth and sixth grade students.

Mayfield was constructed before the 2006 school year and houses more than 500 students, according to the school's Web site.

Most residential structures are built with a sloped roof, which helps shed the snow. Roofs that are constructed with a flat or shallow slope design are at a higher risk of failure, stated Prince William County Building Official Wade Hugh in an e-mail Tuesday.

The hangar at Dulles Aviation at Manassas Regional Airport that collapsed Saturday had a flat roof.

"There is concern that the flat roofs of larger buildings and gathering places could collapse," said Manassas Deputy Planner Robert Halsall in a story in Tuesday's News & Messenger.

"[How much snow buildings can hold] is dependent on the density of the snow. Assuming the actual density of the fallen snow is between light snow, which equals seven pounds per cubic foot, with pounds being divided by cubic feet, and medium snow equaling 10 pounds per cubic feet, a home should be able to withstand between 36 inches and 51 inches of snow," said Prince William County Building Official Eric M. Mays.

City fire officials spent Monday speaking with business owners on Mathis Avenue, some of whom occupy buildings built 40 years ago, asking them to consider closing until the next storm passes. The latest estimates from weather.com show a chance of up to 14 more inches of snow through Wednesday.

According to Hugh, there are several warning signs of an impending roof collapse: If you hear cracking noises in the attic area, observe a deflection in the roof, the windows or door frames seem significantly out of alignment or cracks appear in the exterior or load-bearing walls of the structure.

If you see or hear any of these signs, you should evacuate immediately and call 911, Hugh said.

Staff writer Kipp Hanley can be reached at 703-878-8062.