Hi all. This may be a simple question but I cannot find the proper way to calculate the scenario I have. I am converting a corn crib into a guest house. In order to open up the side bays I want to remove the walls supporting the 2nd floor and use surplus 3″x12″x12′ (actual dimensions) joists to support the upper floor. The upper floor dimension will be 11’x12′ and the clear span will be 12′. Will a single 12′ long 3×12 on each end adequately support the floor? If not, would two 3×12’s sistered together provide enough support? The upper floor will be a bedroom (no bath) and will actually be larger than 11’x12′ but the rest will be supported by the existing wall (sistered 2″x6″‘s on two foot centers). Thanks.
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Replies
to make this Q more clear - are you asking about using several joists that are each 3x12 over a 11' or 12' span
or
are you asking if a 3x12 rim joist acting as a beam will hold up all the other joists through the middle spanning the open area?
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I hope this helps. The existing upper floor uses 3x12 joists on 2' centers. When I removed the 1st floor walls that support those joists (at each end) I want to replace the walls with 12' long 3x12's that I have as spare. Actually "beam" is probably a more appropriate term. So the beams will support a 12' span for a floor that is 11' wide. Clear as mud?
Upper floor is 11 X 12 = 132 sq ft X 50 lbs/sf (40 live, 10 dead) = total load of 6600 lbs.
Assuming 1/2 of the total load bears on each beam, so 3300 lbs tot load for a 12' span, which equals 275 lbs/running ft of beam w/ a 12' span.
A 3x12 (assuming fiber stress in bending at 1200, and deflection @ L/360) will carry 292 lbs/ft or a total load of 3515 lbs for the 12' span.
This is a little close but appears to work.
however.....
What species and condition is the "salvaged wood"?
Are there loads of knots or cuts along the edges?
The above scenarios can make it necessary to use a doubled-up 3X12.
This is an excellent site for your needs:
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp
Certified boat fetish.
A big thanks for showing me the calculations. This crib has had tin siding for more than half of its life. The wood is all straight grained, clear, and dry. I had been considering some angle bracing (2x10's) in the span for asthetic purposes. I am assuming that this would help structurally but wanted to make sure that the beams could support the load without bracing in case we did not go that way. Thanks again.
I had been considering some angle bracing (2x10's) in the span for asthetic purposes
Just don't make big notches (which will compromise the structural integrity) in the bottom of the beam to accept your "asthetic" braces.
BTW.....the braces should be 3x stock (not 2x10).....same as beam....to have that "timber frame" look.
This is reading like the online version of "Car Talk."
This is reading like the online version of "Car Talk."
Is that a good thing......or not......?
Not familiar w/ "Car Talk".
Hey Gene, I know Car Talk and I know the advice is meant as good natured ribbing, usually about the caller's car. I'm not sure I understand the reference.
I don't get it. You made a comment, addressed it to "All" and then don't bother to respond when we ask what you meant. Did I miss something? Is the intent of the forum to have inexperienced people that don't know all the terminology ask questions and then have others make "witty" remarks to make fun of them? Could you clear this up for me? Thanks.
Didja ever listen to this very entertaining radio program on PBS? Two brothers, Italian mechanics from up near Boston, take calls.
In many of the calls, the callers with their problem cars are required to deal with a large number of followup questions from the brothers, not realizing how much information is needed to diagnose the problem, before one of the guys can get to a solution.
Like pulling teeth, one by one.
I should have referred the OP to the TrusJoist site, to go and get the download for sizing LVL headers. It is all there in pictures and tables, and very easy for the lay person to understand. Such as . . .
What is the wall thickness into which the header is to go?
What is the clear span of your opening over which the header goes?
How much header height can there be?
What is the header supporting that is overhead?
One floor? Two floors? Living space or sleeping space? Special floor coverings? What are the direction of the floor joists that are above?
For the roof above, is the roof shape a gable? A straight eave?
What is the width of the building, i.e., the depth back from the wall requiring the header.
If there is a gable above, is the roof structure one with a structural ridge, thus having a post or posts down with point loads? If this is the case, we need to know much more.
What is the design roof loading? Snow country? Hurricane country? Seismic?
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It all boils down to this. Sizing a header is structural design, and structural design work requires the gathering of a lot of data. Asking "what size header do I need for my six foot patio door," is a silly question, if the asker thinks he or she can get a quick answer to that simple question.
Like I said before I listen to the program and understand the premise. I appreciate your comments and reference to the site, thanks (sincerely). I get that structural design is important. I know the answers to all the questions you listed but did not know the questions that needed to be asked (again a sincere thanks for putting me on track with the TrusJoist site).
I work as a consultant in field that helps customers diagnose smart instrumentation problems. I usually help by providing the information they need to know and not mocking them when they make me pull teeth, one by one. Obviously this thread was not in my area of expertise. I won't bother anyone in the forum anymore with my silly questions (not sincere and rolling my eyes).
Sorry to come on with the "professionals only" BS. I guess I have been spending too much time over at the JLC forum, where they really get nasty when DIYs (as they mockingly refer to everybody but themselves) come on with questions.
The great thing about the guys at Car Talk is how much fun they make the process of extracting the necessary info.
Gene, I want to thank you for your response and to let you know that the website has been a help in a couple of other questions that are forthcoming in my project. I do have to admit that I know a DIY that is a bit of a disaster but only because he never bothers with details like physics and gravity. I agree with your comment on the Car Talk Guys.