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Old 07-30-2008, 09:35 AM   #1
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Attaching Pre-Fab Trusses


I just ordered Pre-Fab Trusses (6/12) for my 16x32 Cabin (no interior walls). I understand you nail the trusses to the headers of the exterior wall and also mount 2x4's on the underside of the trusses to brace them...my question is do I need to brace the trusses in any other way? Someone mentioned to me that I should brace some 2x4's on an angle (from truss to header) to prevent movement of the roof ????? Do I need to put a piece of 2x4 in between each truss on top of the header for support? Thanks

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Old 07-30-2008, 09:45 AM   #2
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I'm going to give you a very vague answer...And a very accurate one...

It totally depends on the truss. Your supplier/designer will provide you with engineered drawings for each truss you get. If there are 20 trusses and they're all identical, you'll get one diagram. If there are 20 trusses and in that 20 there are 6 different configurations, you'll get 6 diagrams, and so on. The diagrams are usually proprietary, with MiTek and Alpine being the prominent design outfits that support the individual truss manufacturers with their design software.

Each diagram will have detailed bracing requirements that must be followed to get the trusses to perform properly. This is usually accomplished with flat 2x4's attached to the webs, in the specific locations stated. Bracing will usually be required to counteract the anticipated bending in the connective webs or chords when the truss is under load.

Doing extra bracing is not a benefit, and can actually work against the trusses' ability to share loads effectively. I would advise against it.

Blocking at the plateline and ridgeline can be installed between the trusses to aid in installation. Otherwise temporary bracing is the norm. Your roof sheathing will serve to tie the top chord of the trusses together very effectively.

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Old 07-30-2008, 10:10 AM   #3
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Attaching Pre-Fab Trusses


I didn't know that the trusses would actually come with installtion instructions...great!

Thank you!
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Old 07-30-2008, 10:52 AM   #4
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I forgot to ask ... I've heard about these "hurricane brackets" ... are they necassary? Do the trusses sit on top of them like similar to a Joist Hanger except these would be on the header OR are they like L-brackets that you mount to each side of the truss (4/truss)?

Thanks
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Old 07-30-2008, 11:20 AM   #5
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Originally Posted by PaoloM View Post
I didn't know that the trusses would actually come with installtion instructions...great!

Thank you!
"Instructions" would be a stretch. They don't explain much to the layman, but will show your bracing.
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Old 07-30-2008, 11:25 AM   #6
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Attaching Pre-Fab Trusses


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Originally Posted by PaoloM View Post
I forgot to ask ... I've heard about these "hurricane brackets" ... are they necassary? Do the trusses sit on top of them like similar to a Joist Hanger except these would be on the header OR are they like L-brackets that you mount to each side of the truss (4/truss)?

Thanks
Sometimes necessary, sometimes not. It depends on the uplift requirements (shown in pounds on those MiTek or Alpine diagrams that you should get with your trusses). Sometimes 3 or 4 toenails is adequate, sometimes a hurricane clip or something larger is needed. Personally, I'd install them whether needed or not. They're just added (very cheap) insurance in the event of peripheral winds of a tornado or a good gust that happens during a storm.



The Simpson H2.5 is the most common all-purpose hurricane tie. They go on after the trusses are installed, and can be placed on the interior side in many applications (the picture shows exterior). They nail to the face of the top plate and the side of the truss. They're usually in addition to the toenails. One per truss is normal, althoug some circumstances require two per truss or a larger/longer tie, not unlike the one in the picture.
www.strongtie.com

Last edited by Termite; 07-30-2008 at 11:28 AM.
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Old 07-30-2008, 01:01 PM   #7
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Attaching Pre-Fab Trusses


Don't be surprised that with the small size of your trusses, there will be no bracing requirement, or that the roof and ceiling finish will be sufficient as bracing. The engineering spec sheet supplied with the trusses will tell you. If you didn't get one ask the supplier for it. Hurricane straps are a good idea. They will hold the trusses in place far better than just toe nailing. Bracing is sometimes added temporarily to stabilize the trusses until the roof sheathing is applied.
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Old 07-30-2008, 03:01 PM   #8
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Would it be a waste to go with anything thicker than 1/2" sheathing on the roof? I didn't want to go with a higher pitch roof (easier to work on, less worries about wind) but now I have to consider the snow. If I went with something 5/8" would that be ok? Also, when I use the spacer clips (not sure what they are called)...do I use them on all sides of the sheathing? How far apart do I need them?

Thanks!
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Old 07-30-2008, 03:14 PM   #9
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7/16" rated sheathing will span 24" between trusses, although it will show some sags over time, especially with asphalt tab shingles. 19/32" (5/8") rated sheathing would look better in 10 years.

The H clips for plywood are a good idea but not a must. You just have to remember to leave 1/8" between all edges of the panels. They actually increase the span rating 4 more inches on the 5/8" plywood. You use one clip per span...One between each truss on each edge of the plywood. Use a couple on each end. Don't forget to stagger the plywood joints.
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Old 07-31-2008, 06:59 AM   #10
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In my area "H" clips are required for 7/16" OSB on 24" centers. Every inspector makes a point of looking for them.
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Old 07-31-2008, 09:35 AM   #11
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Attaching Pre-Fab Trusses


What we do is stand and level the first gable end and temp brace to the ground with 2 braces about half way up the rake. Stand 3 or 4 more temp bracing to the first one with 2x4s on top in line with the ground braces. Then lay a 2x4 down the center on top of the ceiling joist tieing all trusses together on the right oc spacing. Then run a permenant brace to that board from the top of the gable end keeping close to 45* angle as possible. Finish the rest of trusses and perm. brace the other end the same way. We always use hurricaine ties and H or spacer clips., I dont like spacer clips on the ends of sheets. A 8d nail driven in the truss works better. Start sheeting at bottom of course, and remove the temp braces only when they get in the way not before.

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