My neighbors fell in. The contractor did a poor job of structural work, not intended for an attic load. I had my builder repair it for him by adding a beam below the ceiling and sheetrocking it in. His garage ceiling was 9 ft so adding a 12 inch beam didn't cause a problem.
My last house a 2 story with basement garage below the main floor, the builder got nervous and added a 3 inch steel colum in the center of the 2 car stalls to support a 22 ft long beam.
It didn't seem like a problem when we bought the house but it screwed up the center isle for walking between vehicles.
Usuall attic junk. It was 3 stalls wide, but a really poor framing job. But typical of residential construction around here. If I had to guess the origional framing plan was modified to make a 3 stall garage out of what was to be a 2 stall.
Mine is 3 stalls wide, no columns, but they used T beams in lieu of joists.
You don't have to worry about snow loading, and you have already tested it I see.
By any chance did you measure the ceiling height before and after you put that much weight up there.
Just look at the bottom chord of the trusses. The way they are loaded with metal and plywood floor stacked on the bottom cord you are putting all the stress on the nailed joints of the bottom cord. Not good. The truss is designed for a load on the roof so that the entire truss is carrying the load.
I would recommend some all thread rod reinforcing of the bottom cord connection, before the nails pull out. You might want to put some temporary colums below untill it's reinforced.
That truss is just not designed to be loaded that way. Remember the Kansas City Motel walkway that gave way killing several people. It failed because of the hanger rods connections not the structure.
Just look at those nailer joints, they are for truss loading from the roof, placing the nailed joint in compression. With weight on the joist they are now in tension.
Last edited by LarryMJones; 10-04-2010 at 05:45 PM.