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Hardwood timbers vs. Softwood timbers

Started by jeremy86, September 22, 2016, 12:38:15 PM

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jeremy86

Hello, All
I have searched the forum for awhile trying to find an answer to my question and haven't found anything.  I am building a timber framing workshop 26' x 28' on a 10" stem wall foundation, High Cape design.  I will have a loft above the entire floor plan, and will be living up there, like a studio apartment, until I get my house built.  The frame will be all hardwood, mostly red oak expect for the sills white Oak or Locust here.  All plans I have looked at and studied are for softwood, usually doug fir or white pine, both of these are not in my area (Northwestern Missouri); however Oak is all over the place.  This leads me to my question, is there a good rule of thumb or equation for figuring the difference in size of post, beams, girts, etc... from softwood to hardwood, or should I just use the same size and over build it?  Example, I have did the math and a 7" x 10" post will would work for softwood, is this the same as what would work for hardwood?  I know from studying that there is a very complex way to figure this out, but I am really looking for a good rule of thumb. 
Any advice would help thanks!

dukndog

Hard wood sizes should work the same as soft wood. The tool box in the lower left hand corner will verify the sizing with wood type.
In your plans, take the sizes and length of the beam/post and use the tools to make sure. You can adjust the size until you don't get a "pass" on the test.
I'm unsure on a general rule, but Jim would have a better knowledge of this. He helped me with sizing and has taught numbers of us on the forum.

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Jim_Rogers

Lots of designs require the size timbers to be big enough to allow enough wood for joinery more that size of timber for strength, especially in posts. You need to have enough wood so that a tenon will be long enough to have enough peg diameters from the peg hole to the end of tenon.

Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

jeremy86

Thank you for the information, figured it was more of a joinery concern that as strength concern.  I just wanted to make sure. 
Thanks again!

Heartwood

Any species and grade of timber that meets or exceeds the design values (Fb for strength, Modulus of Elasticity for stiffness, Shear, etc.) of the original design can be substituted. Design values can be found on many online sites.
Hardwoods are not necessarily stronger; Doug Fir, for example is stronger in bending than some hardwoods and white pine, but could be weaker in some joinery details.
Yes, there are equations; see the Structural Design section in Jack Sobon's Book Build a Classic Timber Framed House for a good easy-to-read example, or use a spreadsheet as dukndog suggests. You still need to know the species and grade to generate the design values.

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