How do I calculate stress loads?

Started by matthew q, December 13, 2004, 04:07:18 PM

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matthew q

I am planning on building a 20x30 cabin. I see the term "Stress load" all over the place here.  As I understand it, it is the stress being placed from the roof onto the exterior walls, or am I off base here? How or where can I figure out what my stress loads for my future cabin would be? I would like to go with a 12 in 12 metal roof for a future loft addition. How and what do I need to look at? Thanks in advance. Matt- ;)

John Raabe

#1
Stress is an engineering term. The wooden parts of the structural frame of a house have maximum stress values based on how the member is used (compression, tension or shear) and the type and grade of wood that is used. So this is a factor in determining the span of a floor joist, header, roof rafter, etc. The design of these members involves sizing them so the design loads of floors, roofs, wind, snow and earthquake do not exceed the stress limits of the wood.

Unless you choose to become an engineer you will probably not be too involved with stress values. Most carpenters are involved with the size and grade of lumber, the number and type of fasteners and the way they are put together. The plans will have these spelled out and the engineering will have been done by others prior to the completion of the plans.

If you are willing to spend a few days studying this you can get a good basic home engineering course from the out of print "From the Ground Up" (http://www.amazon.com/gp/product/offer-listing/0316151122//104-2459200-3656713?condition=used), by Charles Wing.

I had a one-year course in this during architecture school. That was a condensation of the 4 year engineering course. Wing distills it down further to about 40 pages. (To tell the truth, Wing taught me more about practical engineering than the architecture professors did.) At any rate, this book is well worth it if you really want to do your own structural design.

Most people don't, however. Especially if the inspector needs the drawings stamped. Then the $300-400 fee of the engineer doesn't look so bad.
None of us are as smart as all of us.


matthew q

John, thanks for the info. At least now I have a working knowledge of what to expect. Thanks again. Matt-