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Old 08-17-2008, 05:23 PM   #1
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Connecting joists to a beam


I know that joists are generally connected to a beam using joist hangers, which is supposedly better than toe nailing. I am doing a pergola project where the finished product is basically just framing. It's a little difficult to describe but if you are framing a house this way and then flooring is nailed on top of the beam and joists, and wall board is nailed beneath the beam and joists, this gives strength where the rafters can not pull out of the joist hangers. In a pergola, where there is nothing above or below the beam and joists, would there be a different method of attaching joists to beam to achieve pull apart resistance? Because of height problems, I could not run full length rafters over the top of the beam, which would have totally eliminated the problem. Instead, my rafters connect into the side of the beam on both sides so that the beam could be higher off the patio surface.

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Old 08-17-2008, 06:01 PM   #2
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Connecting joists to a beam


Two options that I see here...

1) Joist hangers. That's the strongest, best way. Period. They can be spray painted before installation if you don't want the silver color.

2) Thrust blocks. You can use blocking between the joists, against the beam. The blocks fasten to the beam and the joists are toenailed into the blocks or vice-versa. The blocks will make the beam appear wider, but aren't noticeable if done right. Not as strong as hangers, but fine for most applications in a pergola. If it is being inspected, I'd suggest calling the inspector before using this option.

If all you're worried about is "pull apart" resistance, use Simpson roll straps or something like an MSTA16 over the top of the joist to beam connection. That will add some tensile strength.

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Old 08-17-2008, 07:49 PM   #3
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Connecting joists to a beam


The only reason I am concerned is that the beam is a 28' long 3-1/2" X 16" microlam; setting on 6X6 posts (heavy duty simpson post caps with 6-5/8" diameter bolts in each one. You probably know the ones). So there is some weight there. I'm not really worried about lateral motion of the beam because of those post caps, just outward pressure from the house perpendicular to the beam. There will be 19-2X8's between the ledger and the beam so I may be worrying for nothing.
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Old 08-17-2008, 09:14 PM   #4
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Connecting joists to a beam


... I can't find anything on this.
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Old 08-17-2008, 09:44 PM   #5
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Connecting joists to a beam


Quote:
Originally Posted by JoeP View Post
... I can't find anything on this.
http://www.strongtie.com/products/co...S-HST-LSTA.asp

By the way, are you fully wrapping and properly flashing that microlam? They are not for exterior use in applications if there's a potential of getting wet.
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Old 08-18-2008, 09:52 AM   #6
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Connecting joists to a beam


...according to my lumber supplier, this is one that is rated and guaranteed for exterior use. I have never seen one quite like this (not that I have seen that many). It is not made with plywood strips laminated together vertically and then cut to the 16" dimension (like what I have seen inside some of the new homes with long spans). This appears to be made by laminating a bunch of 2x?s together and then ripping it down in both dimensions to, in my case, the 3 1/2" X 16" dimension beam. So, it actually looks like a stack of 8 or 9 2X4s piled on top of each other glued together on the long side. I am wrapping it with cedar 1x8's so that it doesn't stick out as the only non-cedar component. I wasn't told to flash it. Would you recommend flashing the top anyway? Check out the photo.

Last edited by JoeP; 08-18-2008 at 10:23 AM. Reason: Photo added
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Old 08-18-2008, 10:45 AM   #7
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Connecting joists to a beam


The photo didn't post.

What you're describing is a glulam beam. There are beams that are treated for exterior use, although standard glulams are not. Treatments such as ACQ and pentachlorophenol are used. Glulams are typically made of Fir, Hem-Fir, or Southern Yellow Pine...All of which require treatment if used outside.

I'd suggest calling your supplier and inquiring about the material and the treatment.

If your beams are not treated you absolutely must protect them from water. My suggestion would be to wrap the top and sides in 30# felt before covering them with cedar.
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Old 08-18-2008, 11:18 AM   #8
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Connecting joists to a beam


Sorry for the inaccuracy. The beam is a "Anthony Power Preserved Glulam". The tag says "Treated with Cop-Guard". The tag also says that corosion resistant fasteners are required with cop-guard treated glulams. I will check with the supplier regarding the Simpson joist hangers. I am hoping they are in compliance. Also, I am installing the joist hangers with "Grip-Rite 'Prime Guard Ten' exterior fasteners", instead of Teco nails. Thanks for taking an interest.
P.S. I can see the photo on my end!?!

Last edited by JoeP; 08-18-2008 at 11:45 AM. Reason: typo
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Old 08-18-2008, 12:40 PM   #9
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Connecting joists to a beam


Your beam's good for outdoors. You should be using hot-dipped galvanized nails to fasten the hangers (never use screws unless supplied with the hanger). Any hot-dipped galv nail of the appropriate size for the hanger used will work.

Personally, I wouldn't worry about the hangers. They're galvanized, and will probably never rust. Simpson and USP do make hangers called "triple zinc" that are for use with treated wood, although they do not require their use, nor does the code. They are just galvanized a little thicker than the standard hanger is. I spoke with USP and Simpson reps about this a couple years ago when ACQ replaced CCA and everyone freaked out about rusty nails and hangers. They both indicated that they recommend but do not require the use of special hangers in treated wood applications.
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Old 08-18-2008, 03:17 PM   #10
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Connecting joists to a beam


Just wondering KC, were you able to see my photo? Thanks again for your interest and advice.
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Old 08-18-2008, 06:13 PM   #11
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Connecting joists to a beam


Nope, no photo.

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