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RE: House Trusses.

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This is a rather dicey retrofit to do. I'm not sure where you are located, but if you have access to the manufacture of the plated trusses (assuming they are metal side plate trusses) you won't know much about them due to the proprietary nature of the truss plates (depth of embedment of teeth, overlap of plate on wood, methods of manufacturing as stipulated by the proprietary plate manufacturer.
In our area there is an engineer I could recommend in Riverside County California who spent many years performing truss design for most all of the major plate manufacturers. He guards his historic documents and can identify the manufacturer of the plates and trusses by visual inspection. He also maintains records of the plate manufacturers information used in the design by various truss companies during his career. He can then model the trusses based on the information provided to see what can be done to reinforce the trusses.
In my opinion, I would not attempt to modify a truss that was not intended to carry a heavy tile roof. I would instead design a secondary, stiffer, roof framing system to take the entire load and consider the old trusses as incidental. The alternative is to have your client remove the heavy tile and replace it with lightweight.
Be very careful if walking in blind to an existing proprietary truss without the plate manufactures design information - which I doubt that you will obtain.
 
I'm interested in finding out how you resolved this. BTW, did he discover his trusses would not take the weight before or after he installed the heavy tiles?
 
If you happen to be in the Southern California area, you might lookup Deadline Engineering in Riverside or San Bernardino. This is the company I mentioned to has a good database of plate manufacturers loads and design specifications.
 
Dennis S. Wish, PE
 
-----Original Message-----
From: Tim Spengler [mailto:timothyps(--nospam--at)cleanpak.com]
Sent: Monday, July 28, 2003 7:57 AM
To: seaint(--nospam--at)seaint.org
Subject: House Trusses.

I’ve got a client who needs his house trusses reinforces due to the “discovery” that his cement tile roof exceeds their design capacity. I’m looking at reinforcing the top chord with 2x10’s and kicking up the tension chord connections to accomadate the added load.  If anyone has any good  references or pointers regarding this type of retro I sure appreciate you passing it along.

 

Tim Spengler PE, SE.