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katschilling 05-20-2010 02:46 AM

Removing bottom chord from M truss
I have a dropped 7 foot ceiling in my kitchen, above which are scissor trusses. I want to remove the dropped portion and sheet rock the bottom of trusses for a cathedral. Problem: the eating area has a 7 foot 7 inch ceiling with M trusses and one of these is 8 inches into the area I want to cathedral. Can I attach a sister truss in scissor configuration and remove the bottom chord of the M truss? The kitchen and eating area are on the back of the house (under just half of the M and each scissor)

Just Bill 05-20-2010 05:55 AM

I would not recommend changing a truss without an engineer checking things out. Every part of atruss is important, and changing one part can upset the whole truss.

tpolk 05-20-2010 09:15 AM

i would think laminating an EXACT replica of the scissor truss onto the m truss would work

Thurman 05-20-2010 09:52 AM

I'm with Bill on this. Every point on a truss where two boards meet is either a "suspension" point or a "compression" point. It's sort of like making something by stacking up dominoes, or playing the game "Jenga". Once you remove one point that is critical to any other point you have a weak spot. David

katschilling 05-20-2010 10:41 AM

Thanks, all. I have had a few general contractors tell me, "Oh, no problem. We will just sister in a cathedral truss to the regular one." But a structural engineer said, "a truss has to be engineered", which I figure means that the whole truss has to be placed as a unit, not "pieced" in. :( Can that be done from below without removing the roof? Kathleen

Willie T 05-20-2010 11:03 AM

I would NOT "sister", or in any way attach the scissor truss to the existing truss. Doing so might very easily transmit loads and stresses in directions they were not intended to handle thus possibly compromising the structural integrity of both trusses.

Gary in WA 05-20-2010 10:37 PM

" Can that be done from below without removing the roof?" Yes, after engineering. I have done this a half dozen times, using the engineered nailing pattern and length of fasteners required for liability. It will be listed on your papers. Also have sistered trusses next to rafters from inside. Check with your local engineers....

Be safe, Gary

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