weight bearing problem

trueman

I have a roof. the structure is made of trusses of 2" x 4" , which are 21' long at 2' intervals. The home owner reroofed from COMPOSITION SHINGLE to concrete tiles, and the weight of the tiles is 7.5 pounds per square foot.
Can anybody tell me if the roof is strong enough to bear the concrete tiles?
Thanks.

aussieroofer

i'm not sure about U.S standards but that doesnt sound right to me. 2' centres are quite wide for concrete tiles. trussed house over here have to be latted with a 2x1.5 batton on rafter centres of approx 16 inches. your rafter lenght seems ok for the tiles as long as there are collar ties spanning the upper part of your roof with ceiling joists tieng into the rafter. the rafter intervals would concern me. especially if the batton holding the tile is too thin. i would prefer to see 16 inch intervals. a wide interval on concrete tiles can cause the battons to sag in between the rafters. all the pressure is going to be on the wall plate situated at the bottom of the rafter. as long as you are sufficiently tied in you should be ok.

trueman

Because of the trouble with the house, I didn't get a chance to say thanks. Thank you very much for your information.
I have hired a civil engineer to evaluate the roof. He said the trusses are OK, but he recommend to re-enforce the rafters by doubling them.

Grumpy

Consult an engineer, however I can make a guesstimate that this roof will fail after some years of all that dead weight.

What about the plywood sheathing? What type of sheathing was used? 1/2"? I wouldn't dare put tile on that roof that you described without a release of liability signed by the building owner(s).

__________________
-Grumpy
Chicago Gutters Chicago Roofing

trueman

it is plywood sheathing, it might be 1/2" or thiner. i have the same concern to that roof.
Thank you.

Joe Roofer

An engineer could tell you how to sure it up if it's necessary. Most all of the newer houses here are 15/32 OSB with trusses made of 2x4's, and practically nobody uses shingles on new construction here (they don't take the heat so well.)