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-   -   Max spans of lumber (http://www.diychatroom.com/f19/max-spans-lumber-165596/)

Matthewandbrand 12-04-2012 05:44 PM

Max spans of lumber
 
Ones anyone know of a location online I could find the Max span for different lumber... Ie.. 2x6 2x8... 2x10.. 2x12x
And for beams as well.. 4x10... 4x12 6x10 6x12..


And also , wen I get into the larger dementions is it better to go with a solid beam, build them out of 2 bys , or go with an lvl (to which I have no idea what it is, just read the name somewhere)

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joecaption 12-04-2012 05:58 PM

What are you trying to build?
Just judging by your questions you may be better off having this designed for you then you can build it.

Daniel Holzman 12-04-2012 06:09 PM

Maximum allowable span is controlled by the species and grade of lumber (this determines its maximum allowable bending stress), the span of the element, the dimensions of the element, and the load. There are tables in most code books for common types of elements, for example joists, rafters, and sometimes beams. Allowable span is a function of the specific code enforced in your jurisdiction, so a good place to start would be by having a conversation with your local code enforcement official.

concretemasonry 12-04-2012 07:16 PM

Beyond the simplistic structural tables(psi of stress), deflection or bounce can be a more critical item if you intend to live with what you build. Very often a member meeting the structural requirements will not be adequate from a real functional aspect.

Dick

Matthewandbrand 12-04-2012 07:59 PM

There is no code where I am building. It is going to be far off in the country and on my own land. It will be a small 2 story apartment and I AM doing everything myself. Thank you for all of te information. I found a couple tables online that are species specific and I think I have found the correct one. I do have some pictures up of the flooring system I have started on my other thread. Please feel free to have a look anytime as I will be updating pictures to my profile as it comes together

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Daniel Holzman 12-04-2012 08:09 PM

Since you have no code to follow, you have a lot more flexibility than most people have, who are required to follow code. In your case, you may be able to save costs by designing each major framing element based on principles of mechanics rather than code books, which sometimes require overdesign of the structure.

Generally speaking, long horizontal members such as beams, joists and rafters are designed based on bending strength. Bending is typically controlled by uniform loading on the member (pounds per square foot is typically what is listed in the code book). You size the member based on bending strength, and allowable deflection. Code usually specifies minimum loading for a floor, for example 30 psf for a kitchen, 40 psf for a living room are common loads. You may want to design for lower loads, if you are confident you know what is going in a specific room. Code typically also specifies a minimum stiffness (deflection divided by length), which may also not be applicable to your situation.

The same applies to beams. Stud walls are pretty typically designed 16 inches on center, not because of strength, but generally because of considerations about installation of sheet rock or plywood. In your case, you may want to vary from standard dimensions.

What I am suggesting is that since you are not code driven, you may want to consider working with an architect or a designer, who may be able to save you some money on framing, foundation, and interior fit out, based on actual principles of engineering and intelligent design practices, rather than following a code book for your project.

cleveman 12-04-2012 08:11 PM

Spacing is usually 16" on center. For douglas fir, the allowable span for FLOORS used to be 12' for 2x8's and 16' for 2x10's. I think you can only get 18' out of a 2x12.

I've heard the allowable spans have changed because the lumber is not as good as it used to be.

Yeah, let us know what it is specifically that you wish to do.

jklingel 12-04-2012 10:33 PM

To answer one question, LVL's of the same size will carry a whale of a lot more load and are stiffer than dimensional lumber (from what I have garnered via tables and others). As well as load and stiffness needs, as mentioned above, pay attention to how much bearing there is on the ends (and/or middles) of whatever you load up. Generally, you'll need double trimmers (often need nearly, or a tad over, 2").


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