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wood trusses installed upside down

wood trusses installed upside down

wood trusses installed upside down

(OP)
What would be structural impact of wood trusses installed upside down to the manufacturers specifications?

RE: wood trusses installed upside down

Tension members go into compression and compression members go into tension.

This could be bad.

RE: wood trusses installed upside down

Yikes!  Most wood trusses are built with camber which means you now have "built in" deflection right off the bat!
Unfortunately, this is the least of your problems...  Most wood trusses are designed and economized to their installed orientation.  In other words, you may have #2 wood for the top plate and dss for the bottom.  Now that it is "upside down", the dss will work, but the #2 may or may not.  (dss = dense select structural)  
Another problem is the orientation of the web members and the connector plates that connect everything together are location specific.

It would be best to get your manufacturer's engineer involved to plan a remedy.

RE: wood trusses installed upside down

(OP)
You are right.  But these are fingerjointed 3x2 no. 2 SPF. I've got a call into the manufacturer to hear their response.

RE: wood trusses installed upside down

Many years ago I saw a design where the Architect wanted to take two "standard" roof trusses and turn them upside down and join them two ends at the center to make one giant scissors truss for a church project. He thought it would save money. As I remember it, the truss company just designed the scissors from scratch - the Architect never new the difference!

RE: wood trusses installed upside down

Thats why he is an architect and not an engineer...

We see all kinds of nutter stuff from architects on almost a weekly basis.

RE: wood trusses installed upside down

Trusses fail! We have had this happen maybe 10 times over the last 15 years, and there has never been a fix. The reversal of forces is simply not covered by the plate sizes.

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