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2x8 spans


diy99999's Avatar
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DE

08-04-09, 07:21 PM   #1  
2x8 spans

what do contractors think about using select Hem / Fir 2x8 on a span of
12.5 ft ..24 " centers...?? its a about a ft past some charts I saw but only by a foot....

 
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manhattan42's Avatar
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08-04-09, 07:47 PM   #2  
Posted By: diy99999 what do contractors think about using select Hem / Fir 2x8 on a span of
12.5 ft ..24 " centers...?? its a about a ft past some charts I saw but only by a foot....
"Spans" for what?

Ceiling joists?
Floors?
Main floors?
Second story bedroom floors?
Exterior deck floors?
Trellis joists?
What Code?

---------

Hem Fir #SS 24" oc is permitted to span only 11'3" under the 2006 IRC Code for 40psf floors...

For 30psf floors the maximum span is 12'4"...

For ceiling joists, the maximum span for unihabitable attics with a 20psf live load for limited storage 24" oc is only 7'10" for #SS Hem-Fir, and only 9'10" for an attic floor at 10psf designed without any storage at all.

So what are you trying to design and for what purpose?

And to what standard?

In most applications, Hem-Fir #SS cannot be used for 12 foot or greater spans at all.

 
diy99999's Avatar
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08-04-09, 08:04 PM   #3  
roof rafters, for a shed joined to the house wall. If I put in 5 DF evenly spaced thru the 21 hem/fir rafters would that work..?? The pitch is average for snow country....12 6" is close to 12 4" you know what I mean...

 
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08-05-09, 01:47 PM   #4  
What is called for on your permitted plans from the Building Department for this 12 x 40' addition, if you know what I mean? Be safe, G

 
diy99999's Avatar
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08-05-09, 04:56 PM   #5  
its 20x40 and its part of the original plan from 8 years ago , the only part
not completed. The foundation was done well but nothing else.
I am going to double up on the ends and about 4 places across the 40 ft.
And later I will do some additional interior bracing when I see how to do it with minimum space degradation.
It is interesting to wonder what play there is on the span recommends...
they surely have some extra safety built in. From the top of the top plate to 1 inch onto the sturdy D.Fir 3x8 cross beams is 12 ft 4". But the horizontal is 11ft 10" and that is what is considered.
Here is a cool online calculator for spans...

Maximum Span Calculator for Joists & Rafters

But I will add some bracing on the other side of the house at some point because the builder did 24 oc and nothing else. We had some
heavy snow at times here in Idaho/montana and no problems.3x8


Last edited by diy99999; 08-05-09 at 05:21 PM.
 
Jack the Contractor's Avatar
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08-06-09, 05:40 PM   #6  
Joist Span

Its your building, and I guess you can do what you want to. But in all fairness, you asked us the question. You were given correct answers. Now you don't want to take our advice, so I guess you can do as you like. As a builder, I would not do it. Even if its only an inch. These spans are designed for a snow load of 40lbs per sq ft. Have a good day.

 
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