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Need Angle for Joist Braces


ruauu2's Avatar
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04-20-09, 04:30 PM   #1  
Need Angle for Joist Braces

I tried to teach myself a little trig to figure this out and I got an answer, but I want someone to verify it.

By "braces," I mean those diagonal members criss-crossed between floor joists used to spread the load laterally to adjacent joists. What are those things called?

I need to know what angle to cut the 1x4 braces for 2x6 joists 16" on center. I came up with 17 degrees and 57 minutes (18 degrees). Is that right?

And please don't ask me why I'm using 2x6s for floor joists (because I'm not really - this is just the best way I could describe an unconventional situation).

 
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04-20-09, 05:05 PM   #2  
I'm not one to sidestep a good math question, but in this case I think you should forget the cross bracing and just put in some solid 2x6 blocking that is installed nice and tight.

1x4 cross bracing on 2x6's would be a waste of time, effort, and 1x4's.

But to answer your question, the correct angle is 18.138 degrees, provided the joists are exactly 14.5" apart.

The triangle formed by the cross bracing would actually be 4 3/4" tall, not 5 1/2" tall like the 2x6, due to the thickness of the 1x4 itself.

 
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04-20-09, 05:58 PM   #3  
Just wondering...why not use the metal braces? Do they not work as well?

Math makes my brain hurt late in the afternoon.


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04-20-09, 06:16 PM   #4  
GG, I think I finally got Xsleeper. Let's see. The angle formed will be less than 4 3/4", since the 1x4 is 3/4" when installed at 90 degrees. If installed at an angle, the end relief of the 1x4 will be greater, thus a narrower triangle.

 
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04-20-09, 06:25 PM   #5  
Yeah, if you draw it out it makes sense. The measurements for the triangle formed wouldn't be 5 1/2 and 14 1/2... it would be 4 3/4 and 14 1/2 because it's the distance from the long point of the angle on one end of the 1x4 to the short point of the angle on the other end of the 1x4, and the short point is actually just a little over 3/4" down from the top of the 2x6.

 
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04-20-09, 07:10 PM   #6  
So you were after the angle application of cross bridging or herringbone bridging.

All good carpenters know the correct way to install it: The Importance Of Floor Joist Bridging

Bridging between Joists Be safe, GBR

 
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