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-   -   20' span joist requirement (http://www.diychatroom.com/f19/20-span-joist-requirement-81734/)

johnny331 09-18-2010 05:19 PM

20' span joist requirement
 
I want to add some storage space in the corners of my garage (see pic). I'm not having any luck calculating the required joist size for the span (the "red" in the pic). It will also hold my aluminum garage door/rails.

I have lots of 2x10x10 sitting around, was hoping to maybe sandwich three of those together? Or get some LVLs if I have to. Was hoping to use one joist, maybe two if I have to? It will be for light storage (kids bikes, junk, no human occupation, etc.)

any insight would be appreciated.

http://img801.imageshack.us/img801/3808/garageo.png

Gary in WA 09-18-2010 06:37 PM

1. Weigh the garage door, without the spring assist.


Gary

forresth 09-18-2010 11:56 PM

you'd have to make some complex truss full of diagonal braces to it to do what you'd want I'm guessing.

I had something similar on a previous house of mine, but it had a big I beam instead of a couple patched together 2x10s

Aggie67 09-19-2010 08:56 AM

Avoid the hassle and do it right from the get go: find a local engineer that specializes in this sort of thing. It wouldn't be that expensive.

forresth 09-19-2010 12:09 PM

I've been giving this some thought.

simple span tabless for ceiling joists say a 20' 2x10 would be OK @16" OC,
http://www.wclib.org/pdfs/SimpSpanTbls.pdf
but you want to carry it all in one 1 joist of unknown grade that has been cut in half then patched.

my gut tells me if you take 4 of 10' 2x10s, one spanning the joint of the other 2 evenly, and the last cut in half to even it out you should be in the same ballpark for strength as 1 20', if you join them tightly and properly.

that way you'd need about 6 joists, or 24 2x10s

if you can to make a wooden I beam, you might be able to get away with doing it like you want, but it wouldn't be simple.

you could take 1 joist as I described above, for the web, then take 4 above and below, staggering all of the joints, 8 total to be the flanges, for a total of 12 boards that way.

a truss built out of 3 (or 6)as horizontal elements and some shorter 2x4 or 2x6s as the diagonal elements would probably work too.

basically, I'm saying, it can be done, but just get a beam and do it the right way

eastside 09-19-2010 12:24 PM

I may misunderstand the question. Couldn't you support the cross piece from the rafters above?

luvdairish 09-19-2010 01:16 PM

I misunderstand the pic. Are you talking about storage space at the back of the garage area up in the corners?


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